Browse Topic: Knock

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C919 Trailing Edge Assembly Interchangeable Tooling2019-01-18809/16/2019
Traditional Trailing Edge (TE) assembly that utilise fixtures for accurate positioning of aircraft (a/c) parts do not allow for removal of specific tooling from the fixtures to travel with the TE, post assembly. Instead, the tooling that positions all the primary a/c assembly datums generally utilise precision pins of various sizes that index and clamp the a/c ribs. Often it is difficult to remove the pins post assembly before the spar can be taken out of the fixture. Use of hammers is common place to hit pins out of holes which is less than ideal considering the a/c parts can be fragile and the tooling is precision set. Also, the Main Assembly Fixture (MAJ) that will receive the TE will inevitably need to relocate some if not all the primary a/c ribs and therefore will most likely be subject to some amount of persuasion. Electroimpact have for many years used cup cone locators that allows static tooling to be temporarily ‘loosened’ and therefore made more compliant for pin insertion/removal, this has been successful to reduce the need for hammering, but doesn’t remove the necessity for extensive manual work to reclaim all the datums. The intent of this paper is to highlight how we, on the C919 project, have successfully designed and implemented the use of removable tooling that travels with the TE sub-assemblies into the main TE assembly fixture and similarly the same interchangeable and removable tooling travels with the completed TE and re-engages with identical tooling receivers in the MAJ. Providing a fast, efficient, reduced man-power and accurate means for building a TE and transfer into the MAJ.
Dineley, James
Nominal High-Altitude Electromagnetic Pulse (HEMP) Waveforms19AERP08_088/1/2019
Calculating the characteristics of high-altitude electromagnetic pulses created by the detonation of a nuclear device. Defense Threat Reduction Agency, Fort Belvoir, Virginia Even before the Trinity nuclear test in July of 1945, physicists predicted a transient electromagnetic signal would be caused by high-energy photons released from the detonation interacting with the air around the detonation. Predictions of these signals were difficult to make due to the complexity of the physics unleashed by the detonation. Post-World War II, there was a period of active atmospheric nuclear testing until 1962, during which measurements of these signals were made in order to understand the phenomena that were previously largely viewed as an annoyance and impediment to other instrumentation. The name “electromagnetic pulse” (EMP) began to be used to refer to these signals.
Nominal High-Altitude Electromagnetic Pulse (HEMP) WaveformsTBMG-348708/1/2019
Even before the Trinity nuclear test in July of 1945, physicists predicted a transient electromagnetic signal would be caused by high-energy photons released from the detonation interacting with the air around the detonation. Predictions of these signals were difficult to make due to the complexity of the physics unleashed by the detonation.
Individual Quantum Dots Imaged in 3-D for the First TimeTBMG-338963/1/2019
Researchers have developed an imaging technique that uses a tiny, super sharp needle to nudge a single nanoparticle into different orientations and capture 2-D images to help reconstruct a 3-D picture. The method demonstrates imaging of individual nanoparticles at different orientations while in a laser-induced excited state.
LES Analysis on Cycle-to-Cycle Variation of Combustion Process in a DISI Engine2019-01-00061/15/2019
Combustion cycle-to-cycle variation (CCV) of Spark-Ignition (SI) engines can be influenced by the cyclic variations in charge motion, trapped mass and mixture composition inside the cylinder. A high CCV leads to misfire or knock, limiting the engine’s operating regime. To understand the mechanism of the effect of flow field and mixture compositions on CCV, the present numerical work was performed in a single cylinder Direct Injection Spark-Ignition (DISI) engine. A large eddy simulation (LES) approach coupled with the G-equation combustion model was developed to capture the CCV by accurately resolving the turbulent flow field spatially and temporally. Further, the ignition process was modeled by sourcing energy during the breakdown and arc phases with a line-shape ignition model which could move with the local flow. Detailed chemistry was solved both inside and outside the flame front. A compact 48-species 152-reactions primary reference fuel (PRF) reduced mechanism was used. By implementing an adaptive mesh refinement strategy based on the sub-grid scale reaction progress variable, a good balance between accuracy and efficiency was achieved. Compared with the available experimental data, the simulation results showed a satisfying agreement. Furthermore, a correlation analysis was done based on the combustion phasing, peak pressure and gross indicated mean effective pressure (IMEP). Also, the effect of in-cylinder flow field on the early flame development and the peak pressure was discussed under the considered operating condition.
Chen, Ceyuan, Ameen, Muhsin M, Wei, Haiqiao, Iyer, Claudia, Ting, Foochern, Vanderwege, Brad, Som, Sibendu
Heat of Vaporization and Species Evolution during Gasoline Evaporation Measured by DSC/TGA/MS for Blends of C1 to C4 Alcohols in Commercial Gasoline Blendstocks2019-01-00141/15/2019
Evaporative cooling of the fuel-air charge by fuel evaporation is an important feature of direct-injection spark-ignition engines that improves fuel knock resistance and reduces pumping losses at intermediate load, but in some cases, may increase fine particle emissions. We have reported on experimental approaches for measuring both total heat of vaporization and examination of the evaporative heat effect as a function of fraction evaporated for gasolines and ethanol blends. In this paper, we extend this work to include other low-molecular-weight alcohols and present results on species evolution during fuel evaporation by coupling a mass spectrometer to our differential scanning calorimetry/thermogravimetric analysis instrument. The alcohols examined were methanol, ethanol, 1-propanol, isopropanol, 2-butanol, and isobutanol at 10 volume percent, 20 volume percent, and 30 volume percent. The results show that total heat of vaporization of the alcohol gasoline blends is in line with the decreasing heat of vaporization in kilojoules per kilogram with increasing alcohol carbon number, as expected. Mass spectrometer results show that methanol fully evaporates at significantly lower fraction evaporated relative to other alcohols even though it is present at higher molar concentration at a fixed volumetric concentration. Certain alcohols, especially methanol and ethanol, can suppress the evaporation of aromatic compounds such as cumene during the evaporation process in some samples. While the use of mass spectrometry to analyze the composition of the evolving gas mixture provided useful results for a relatively simple research gasoline (FACE B), additional research is required to practically apply this methodology to more complex commercial gasolines.
Fioroni, Gina M., Christensen, Earl, Fouts, Lisa, McCormick, Robert
Knock Sensor Based Virtual Cylinder Pressure Sensor2019-01-00401/15/2019
Typically the combustion in a direct injected compression ignited internal combustion engine is open-loop controlled. The introduction of a cylinder pressure sensor opens up the possibility of a virtual combustion sensor which could enable closed-loop combustion control and thus the potential to counteract effects such as engine part to part variation, component ageing and fuel quality diversity. Closed-loop combustion control requires precise, robust and preferably cheap sensors. This paper presents a virtual cylinder pressure sensor based on the signal from the inexpensive but well proven knock sensor. The method used to convert the knock sensor signal into a pressure estimate included the stages: Phase correcting the raw signal, Filtering the raw signal, Scaling the signal to known thermodynamic laws and provided engine sensors signals and Reconstructing parts of the signal with other known models and assumptions. The modelled cylinder pressure shows high correlation with the measured pressure trace and it was concluded that it is possible to estimate many important combustion parameters - such as maximum pressure, mass fraction burned and total heat release.
Rugland, Christian, Stenlaas, Ola
Fuel & Lubricant Effects on Stochastic Preignition2019-01-00381/15/2019
In this multi-phase study, fuel and lubricant effects on stochastic preignition (SPI) were examined. First, the behavior of fuels for which SPI data had previously been collected were characterized in terms of their combustion and emissions behavior, and correlations between these characteristics and their SPI behavior were examined. Second, new SPI data was collected for a matrix of fuels that was constructed to test and confirm hypotheses that resulted from interpretation of the earlier data in the study and from data in open literature. Specifically, the extent to which the presence of heavy components in the fuel affected SPI propensity, and the extent to which flame initiation propensity affected SPI propensity, were examined. Finally, the interaction of fuels with lubricants expected to exhibit a range of SPI propensities was examined. Although this final dataset did not yield conclusive results, it suggests that additional factors such as engine condition can have a very significant effect on SPI propensity. The main findings of the study are that lower volatility fuel components appear to affect the propensity of the fuel to create initiation events (which could be fuel-oil droplets or deposit breakoff) that can lead to SPI, and further that the ease by which a flame can be established in the bulk mixture correlates to SPI tendency when the initiation event tendency is fixed. The study also showed that neither soot-forming tendency of a fuel nor the fuel’s antiknock quality necessarily correlate to SPI tendency.
Costanzo, Vincent S., Yu, Xin, Chapman, Elana, Davis, Richard, Haenel, Patrick
Mechanism Analysis on the Effect of Fuel Properties on Knocking Performance at Boosted Conditions2019-01-00351/15/2019
In recent years, boosted and downsized engines have gained much attention as a promising technology to improve fuel economy; however, knocking is a common issue of such engines that requires attention. To understand the knocking phenomenon under downsized and boosted engine conditions deeply, fuels with different Research Octane Number (RON) and Motor Octane Number (MON) were prepared, and the knocking performances of these fuels were evaluated using a single cylinder engine, operated under a variety of conditions. Experimental results showed that the knocking performance at boosted conditions depend on both RON and MON. While higher RON showed better anti-knocking performance, lower MON showed better anti-knocking performance. Furthermore, the tendency for a reduced MON to be beneficial became stronger at lower engine speeds and higher boost pressures, in agreement with previously published modelling work. A new method of interpreting octane appetite is presented which relates the gradient of contour lines of MB50 in RON/MON space to K value. The results can be further interpreted by understanding the relative contribution of low temperature oxidation (LTO) pathways under the prevailing temperature/pressure conditions in the engine.
Kassai, Masaharu, Aksu, Cagdas, Shiraishi, Taisuke, Cracknell, Roger, Shibuya, Masahiko
Influence of Autoignition and Pressure Wave Behavior on Knock Intensity Based on Multipoint Pressure Measurement and In-Cylinder Visualization of the End Gas2018-32-000110/30/2018
In this study, the effect of autoignition behavior in the unburned end-gas region on pressure wave formation and knock intensity was investigated. A single-cylinder gasoline engine capable of high-speed observation of the end gas was used in the experiments. Visualization in the combustion chamber and spectroscopic measurement of light absorption by the end gas were carried out to analyze autoignition behavior in the unburned end-gas portion and the reaction history before autoignition. The process of autoignition and pressure wave growth was investigated by analyzing multipoint pressure histories. As a result, it was found that knocking intensity increases through interaction between autoignition and pressure waves.
Yamashita, Takahiro, Takahata, Shuhei, Kudo, Hiroki, Izako, Takuya, Ishikawa, Takahiro, Saito, Masanori, Tanabe, Mitsuaki, Iijima, Akira
A Study of the Factors Determining Knocking Intensity Based on High-Speed Observation of End-Gas Autoignition Using an Optically Accessible Engine2018-32-000310/30/2018
The purpose of this study was to investigate how autoignition leads to the occurrence of pressure oscillations. That was done on the basis of in-cylinder visualization and analysis of flame images captured with a high-speed camera using an optically accessible engine, in-cylinder pressure measurement and measurement of light emission from formaldehyde (HCHO). The results revealed that knocking intensity tended to be stronger with a faster localized growth speed of autoignition. An investigation was also made of the effect of exhaust gas recirculation (EGR) as a means of reducing knocking intensity. The results showed that the application of EGR advanced the ignition timing, thereby reducing knocking intensity under the conditions where knocking occurred.
Ishikawa, Takahiro, Takahata, Shuhei, Kudo, Hiroki, Izako, Takuya, Yamashita, Takahiro, Koga, Hibiki, Kiura, Toshiro, Iijima, Akira
Mixture Formation and Combustion Evaluation of a Motorcycle Engine Concept Equipped with One Fuel Injector for Each Intake Valve2018-32-000910/30/2018
In light of a more stringent emission legislation and in anticipation of possible future measures to further reduce the real environmental impact of motorcycles, it is necessary to develop engine concepts which are efficient and low on emissions in a wide range of operating points. This poses an important challenge on the development of high performance motorcycles engines as their focus on full load behaviour conflicts sharply with the emission and efficiency demands of the remaining engine load map. The focus of this paper is to evaluate the potential of a port fuel injection (PFI) concept consisting of one individual fuel injector for each intake valve to solve this trade-off. Previous research shows a positive effect of such a setup on mixture formation due to better targeting and atomization, reducing HC emissions and cyclic variations. It also shows improved efficiency, performance and knocking characteristics caused by an enhanced charge cooling effect through open valve injection (OVI). Although the system has been previously investigated, the necessary layout considerations and impacts of the system for a high performance motorcycle engine have not yet been addressed. In this work the mentioned PFI concept was studied using a high performance two-cylinder motorcycle engine. Engine tests were conducted for two injector sets having different static flow values. The results showed improved efficiency and lower HC emissions for higher engine loads, but no performance gain at full load. The reasons for this behaviour were closely analysed by means of CFD simulation and thermodynamic loss analysis of the combustion process. These explanations were further confirmed by additional engine tests using exhaust gas sampling with fast FID. As a final result a set of recommendations for further concept improvement is proposed.
Gaitan, Pedro, Schwarz, Frank, Eibl, Rüdiger
Experimental Study of Spark-Assisted Auto-Ignition Gasoline Engine with Octagonal Colliding Pulsed Supermulti-Jets and Asymmetric Double Piston Unit2018-32-000410/30/2018
Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline. In our previous report (SAE paper 2016-01-2336) using gasoline, there were only some engine cycles indicating high thermal efficiency comparable to that of diesel engines. In the present report, we show that spark-assisted auto-ignition combustion optimized with the hot spot area generated by octagonal pulsed supermulti-jets indicates potential of high thermal efficiency averaged during many cycles, which is about the same level of diesel engines. Mechanical compression ratio is about from 7.8:1 to 11:1 and engine speed is 2,000 rpm under the part load whose exhaust air-fuel ratio is about from 20 to 30. Moreover, experimental data obtained also show the increasing rate of pressure after combustion is less than the knocking limit of reciprocating engines. And we have made a new prototype engine whose asymmetric double piston unit moves non-sinusoidally. We intend to report progress of this new prototype engine.
Isshiki, Yuuki, Naitoh, Ken, Onuma, Yuichi, Ohara, Soichi, Arai, Daisuke, Machida, Yutaka, Ito, Hajime, Kobayashi, Yoshiki, Suzuki, Takahiro, Tada, Yusuke
Study on Knocking Characteristics for High-Efficiency Operation of a Super-Lean Spark Ignition Engine2018-32-000210/30/2018
This study investigated the influence of EGR and spark advance on knocking under high compression ratio, ultra-lean mixture and supercharged condition using premium gasoline as a test fuel. A high-compression ratio, supercharged single cylinder engine was used in this experiment. As a result, the period from ignition to autoignition was prolonged. In addition, knock intensity was drastically reduced. In other words, it is inferred that by combining an appropriate amount of EGR and spark advance, high efficiency operation avoiding knocking can be realized.
Nishiyama, Takeshi, Agui, Keito, Togawa, Masaaki, Saito, Masanori, Tanabe, Mitsuaki, Iijima, Akira
Dual Fuel Injection (DI + PFI) for Knock and EGR Dilution Limit Extension in a Boosted SI Engine2018-01-17359/10/2018
Combined direct and port fuel injection (i.e., dual injection) in spark ignition engines is of increasing interest due to the advantages for fuel flexibility and the individual merits of each system for improving engine performance and reducing engine-out emissions. Greater understanding of the impact of dual injection will enable deriving the maximum benefit from the two injection systems. This study investigates the effects of dual injection on combustion, especially knock propensity and tolerance to exhaust gas recirculation (EGR) dilution at different levels of EGR. A baseline for comparison with dual injection results was made using direct injection fueling only. A splash blended E20 fuel was used for the direct injection only tests. For the dual injection tests, gasoline, representing 80% by volume of the total fuel, was injected using the direct injector, and ethanol, representing 20% by volume of the total fuel, was injected using the port fuel injector. EGR mass fraction was varied from 0% to 21%, under boosted intake air pressure of 1.25 bar for both injection strategies. The results showed dual injection was beneficial to shorten the burn duration and improve combustion stability. Dual injection was more sensitive to knock than direct injection primarily due to increased unburned gas temperature. The overall thermal efficiency for the two injection types was comparable. The particulate matter emissions from dual injection showed slightly lower values, and the gaseous emissions showed lower total hydrocarbons and similar nitrogen oxides compared with only using direct injection of E20.
Han, Taehoon, Lavoie, George, Wooldridge, Margaret, Boehman, André
Distribution of Knock Frequencies in Modern Engines Compared to Historical Data2018-01-16669/10/2018
It is widely known that the rapid autoignition of end-gas will cause an engine cylinder to resonate, creating a knocking sound. These effects were quantified for a simple engine geometry in 1934 in a study where critical resonance frequencies were identified. That analysis, performed by Charles Draper, still forms the basis of most knock studies. However, the resonance frequencies are highly dependent on the engine geometry and the conditions inside the cylinder at autoignition. Since, engines and fuels operate at substantially different conditions than they did in 1934, it is expected that there should be a shift in knock frequencies. Experimental tests were run to collect knock data in an engine, representative of modern geometries, over a range of operating conditions for a number of different fuels. The operating conditions-intake air temperature, intake air pressure, and engine speed-were varied to identify shifts in the critical frequencies. Additionally, fuels were varied in octane number from 80 to 100. The resulting analysis found that the first circumferential mode, at approximately 6 kHz still played a substantial role in knock in modern engines. However, the analysis also found a decreased contribution from radial modes and an increased contribution from the axial modes. The distributions of frequencies did not shift significantly for changes in the intake air temperature or pressure; however, the axial modes became more significant at higher engine speeds. Additionally, the axial modes increase in frequency for higher octane fuels, which have an earlier knock-limited spark advance. These results show the increased importance of the axial modes in knock for modern engines; these modes are typically not audible, though they can still result in engine damage.
Mittal, Vikram
Impact of Engine Age and Engine Hardware on Low-Speed Pre-Ignition2018-01-16639/10/2018
Low-speed pre-ignition (LSPI) is a well-studied phenomenon in boosted, spark ignition engines. The impact of lubricant formulation has received a lot of attention in recent years, yet the impact of engine hardware and engine wear on LSPI is still not fully understood. This paper addresses some of these questions using results from multiple installations of the GM 2.0 L LHU engine platform. In the first part of the study, the effect of engine life on LSPI activity was observed, and it was found that engines were susceptible to variations in LSPI activity during the initial LSPI tests with the activity eventually reaching a “stabilized” level. It was further observed that the LSPI activity generally continued to decline at a steady rate as the engine aged. For engines used in LSPI testing, the life of the engine is often limited as LSPI activity decays with age. This reduction in LSPI activity may correlate to the engine liner wear and it is suggested that the amount of oil transport along the engine liner, which is a function of the liner roughness amongst other factors, is a dominant mechanism for this observed reduction. This observation highlights the importance of baseline testing throughout the life of the engine which is critical for severity adjustments of oils tested at different times. The effect of hardware component replacement on LSPI activity was also investigated. It was determined that the removing, cleaning, and replacing of both pistons and rings had no effect on LSPI activity and did not require re-stabilization of the test engine.
Kalaskar, Vickey B., Swarts, Andre, Alger, Terrence
Detonation Peninsula for TRF-Air Mixtures: Assessment for the Analysis of Auto-Ignition Events in Spark-Ignition Engines2018-01-17219/10/2018
Controlling abnormal auto-ignition processes in spark-ignition engines requires understanding how auto-ignition is triggered and how it propagates inside the combustion chamber. The original Zeldovich theory regarding auto-ignition propagation was further developed by Bradley and coworkers, who highlighted different modes by considering various hot spot characteristics and thermodynamic conditions around them. Dimensionless parameters (ε, ξ) were then proposed to classify these modes and to define a detonation peninsula for H2-CO-air mixtures. This article deals with numerical simulations undertaken to check the relevancy of this original detonation peninsula when considering realistic gasoline fuels. 1D calculations of auto-ignition propagation are performed using the Tabulated Kinetics for Ignition model. Chemical kinetics calculations are first carried out to build the needed look-up table for the auto-ignition delay time τi, and the excitation times τe of E10-air mixtures using a RON 95 TRF surrogate. The dimensionless parameter ε is based on the hot spot radius and on the excitation time τe of the fuel. Previous chemical kinetics calculations confirm the impact of the fuel on this parameter as H2-CO-air mixtures feature much longer excitation times than TRF-air mixtures. Focusing on the parameter ξ, its estimation depends on hot spots characteristics and thermodynamic conditions. The limits of the peninsula therefore vary depending on initial conditions and hot spot characteristics, that is why this paper focuses on several conditions to validate the dependency of the boundaries between the different auto-ignition modes. Hundreds of simulations are performed and due to the large amount of calculations, a specific post-processing methodology is defined to determine the auto-ignition propagation modes by automatically characterizing the coupling conditions between reaction and pressure waves. Several new detonation peninsulas are finally proposed depending on initial conditions in terms of temperature, pressure, fuel-air equivalence ratio and dilution. Limits of the detonation peninsula for TRF-air mixtures are more affected depending on each operating conditions. These new limits can finally be used to better understand abnormal auto-ignition events in spark-ignition engines.
Guerouani, Ahmed, Robert, Anthony, Zaccardi, Jean-Marc
Effect of Mixture Formation and Injection Strategies on Stochastic Pre-Ignition2018-01-16789/10/2018
Stochastic pre-ignition remains one of the major barriers limiting further engine downsizing and down-speeding; two widely used strategies for improving the efficiency of spark-ignited engines. One of the most cited mechanisms thought to be responsible for pre-ignition is the ignition of a rogue droplet composed of lubricant oil and fuel. This originates during mixture formation from interactions between the fuel spray and oil on the cylinder liner. In the present study, this hypothesis is further examined using a single cylinder supercharged engine which employs a range of air-fuel mixture formation strategies. These strategies include port-fuel injection (PFI) along with side and central direct injection (DI) of an E5 gasoline (RON 97.5) using single and multiple injection events. Computational fluid dynamic (CFD) calculations are then used to explain the observed trends. Overall, this study reinforces that interactions between the fuel spray and oil on the cylinder liner can be an important contributor towards stochastic pre-ignition. The occurrence of pre-ignition, as shown by CFD calculations, is successful after completion of two stages. The first stage involves the formation of precursors from interactions between the fuel spray and oil on the cylinder liner. This is shown to be dependent upon the mass of the fuel impinging on the cylinder liner. The second stage involves the ignition of the precursor, which is shown to be dependent upon the temperature of the air-fuel mixture near top dead center.
Singh, Eshan, Mubarak Ali, Mohammed Jaasim, Ichim, Adrian, Morganti, Kai, Dibble, Robert
Combustion Characteristics of PRF and TSF Ethanol Blends with RON 98 in an Instrumented CFR Engine2018-01-16729/10/2018
The CFR F1 engine is the standard testing apparatus used for rating the research octane number (RON) of gasoline fuels. Unlike the motor octane number (MON) method, where the intake port temperature after the carburetor is controlled by an electric heater, the mixture temperature can vary during the RON test due to the heat of vaporization (HoV) of the fuel. Ethanol is receiving increasing attention as a high octane and high HoV fuel component. This work presents an analysis of the combustion characteristics during the RON rating of ethanol fuel blends according to the standard ASTM D2699 method, highlighting the effects of ethanol concentration and base fuel composition. All fuels were blended to a constant RON of 98. Ethanol levels varied from 0 to 50 vol% and the base fuels were surrogate blends composed of primary reference fuels (PRF), toluene standardization fuels (TSF), and a four component gasoline surrogate. These were compared against two full boiling range gasolines, also having a RON of 98. Through the use of detailed cylinder pressure analyses, this paper provides insights into the combustion behavior of various RON 98 fuels which are commonly not captured by the standard RON knock rating method. Ethanol was found to significantly reduce the pressure transducer based knock intensity of PRF fuel blends up to a level of 30 vol%, despite all fuels having the same RON. Meanwhile, the knock intensity of the equivalent TSF fuel blends was found to be relatively insensitive to ethanol concentration. For ethanol concentrations beyond 30 vol%, the pressure transducer based knock intensity behavior did not appear to be affected by the base fuel composition.
Hoth, Alexander, Kolodziej, Christopher P., Rockstroh, Toby, Wallner, Thomas
Simulation of the Effect of Intake Pressure and Split Injection on Lean Combustion Characteristics of a Poppet-Valve Two-Stroke Direct Injection Gasoline Engine at High Loads2018-01-17239/10/2018
Poppet-valve two-stroke gasoline engines can increase the specific power of their four-stroke counterparts with the same displacement and hence decrease fuel consumption. However, knock may occur at high loads. Therefore, the combustion with stratified lean mixture was proposed to decrease knock tendency and improve combustion stability in a poppet-valve two-stroke direct injection gasoline engine. The effect of intake pressure and split injection on fuel distribution, combustion and knock intensity in lean mixture conditions at high loads was simulated with a three-dimensional computational fluid dynamic software. Simulation results show that with the increase of intake pressure, the average fuel-air equivalent ratio in the cylinder decreases when the second injection ratio was fixed at 70% at a given amount of fuel in a cycle. With the increase of intake pressure, ignition timing advances, combustion duration slightly decreases first and then increases while the maximum pressure rise rate first increases and then drops. High intake pressure can prevent the occurrence of knock through decreased fuel-air equivalent ratio around the cylinder. The second injection timing can also influence combustion processes. The improved indicated thermal efficiency occurs when the second injection timing is 90°CA after top dead center. Delayed second injection timing is beneficial for the development of initial flame kernel. But when the second injection timing is 60°CA after top dead center, the fuel is only consumed by flame propagation. When auto-ignition occurs in the end mixture, the heat released by auto-ignition gradually increases with the delay of the second injection timing. Meanwhile, indicated thermal efficiency is increased when little amount of end mixture auto-ignites without knock.
Li, Xiao, He, Bang-Quan, Zhao, Hua, Zhang, Yan, Li, Yufeng, Bai, Honglin
Effectiveness of Fuel Enrichment on Knock Suppression in a Gasoline Spark-Ignited Engine2018-01-16659/10/2018
Knock, and more recently, super-knock, have been limiting factors on improving engine efficiency. As a result, engines often operate rich at high loads to avoid damage resulting from knock and protect the after-treatment system from excessive thermal stress. In this work, port-fuel injection and direct injection of excess fuel is explored as a mechanism to suppress knock and super-knock. Under naturally aspirated conditions, increasing the fuel enrichment initially increases knock intensity. However, further increasing fuel enrichment subsequently decreases knock intensity. The competing mechanism from calorific value and latent heat of vaporization can be used to explain the phenomenon. However, when directly injecting the excess fuel after the spark plug has been fired, knock intensity monotonically decreases with increasing fuel quantity. This decrease is shown to be due to fuel quenching the flame that is propagating from spark location. Under boosted conditions, the amount of fuel injected is of critical importance in avoiding super-knock. A lower fuel quantity leads to knock suppression. But beyond a critical value, higher quantities of fuel result in more interaction with the oil film on the cylinder liner, leading to a greater number of pre-ignition precursors (fuel + oil droplets) and a higher number of pre-ignition events. These spontaneous pre-ignition events arising from fuel enrichment are further advanced and do not lead to super-knock behavior due to high amounts of charge cooling from evaporation of the excess fuel. Furthermore, such spontaneous pre-ignition events are characterized by higher pressure in the intake stroke and dominance of higher frequency oscillations in the cylinder.
Singh, Eshan, Dibble, Robert
New GKI - Gasoline Knock Index for Rating of Fuel’s Knock Resistance on an Upgraded CFR Test Engine2018-01-17439/10/2018
In terms of international efforts for conservation of resources and reducing CO2-emission, the thermal efficiency of SI engines needs to be increased. One key enabler to achieve this goal is the availability of highly knock-resistant fuels: it allows to break up the trade-off between elevated compression ratio demanded for high part-load efficiency and a reduced knock tendency at high engine loads by a minimized requirement for adverse spark retard. In view of the world’s fuel map, which is dominated nowadays by qualities between 91 and 98 RON, there is a beginning transition towards increased knock resistance (above 100 RON) being observed in several countries. The corresponding standards for engine-based fuel quality rating provide a RON scale covering the range from 40 to 120.3, which basically seems to be enough. At a second glance the change in reference material from isooctane/n-heptane mixtures towards isooctane with TEL for RON > 100 changes the rating behavior of the method. Comprehensive research and development has been established considering the test engine operation mode as well as the data processing, conclusively defining an improved test method as a suggestion for future knock resistance rating. In order to increase transferability of the fuel’s quality number to modern engines, especially in view to RDE legislation, the operation mode is basically characterized by a stoichiometric mixture composition in combination with a closed-loop control of the combustion phasing. The CR achievable at predefined knock intensity, statistically assessed by a 95% cumulative frequency of knock pressure amplitudes, defines knock resistance without relevant limitations in scale expressed by the new fuel characteristic GKI - Gasoline Knock Index.
Hauber, Johann, Huber, Karl, Nell, Robert
The Fuel Economy Improvement through the Knock Margin Expansion in a Turbocharged Gasoline Direct Injection Engine2018-01-16719/10/2018
Knocking combustion limits the downsized gasoline engines’ potential for improvement with regard to fuel economy. The high in-cylinder pressure and temperature caused by the adaptation of a turbocharger aggravates the tendency of the end-gas to autoignite. Thus, the knocking combustion does not allow for further advancing of the combustion phase. In this research, the effects of the ignition and valve timings on knocking combustion were investigated under steady-state conditions. Moreover, the optimal ignition and valve timings for the transient operations were derived with the aim of a greater fuel economy improvement, based on the steady-state analysis. A 2.0 liter turbocharged gasoline direct injection engine with continuously variable valve timing (CVVT), was utilized for this experiment. 2, 10, and 18 bar brake mean effective pressure (BMEP) load conditions were used to represent the low, medium, and high load operations, respectively. The engine speed was set at 1,500 RPM since the low speed conditions were more vulnerable to knocking combustion than the high speed conditions. Both the intake and the exhaust valve timings were controlled from the reference timings in a step of 10 crank angle degrees (CAD). The ignition timing was also controlled in a similar manner, but only with 1.5 CAD steps. The experimental result showed that reducing the exhaust backpressure by increasing the wastegate opening level was effective in expanding the knock margin. This was mainly owing to the enhanced scavenging driving force created by the increased wastegate opening. During the transient operation, increasing the wastegate opening by maximally advancing the exhaust valve timing was shown to be an effective procedure in this case. With the maximized advance, sufficient exhaust energy was supplied to the turbocharger such that less amount of exhaust flow was required. Thus, the greater wastegate opening could be achieved, which enhanced the scavenging process. As a result, the ignition timings were advanced beyond the previous knock margins. With the use of this procedure, torque output and fuel consumption were improved by a maximum of 3.3% and 2.4%, respectively.
Shin, Ji Yong, Park, Chansoo, Jung, Jinyoung, Bae, Choongsik
On-Road Monitoring of Low Speed Pre-Ignition2018-01-16769/10/2018
To meet increasingly stringent emissions and fuel economy regulations, many Original Equipment Manufacturers (OEMs) have recently developed and deployed small, high power density engines. Turbocharging, coupled with gasoline direct injection (GDI) has enabled a rapid engine downsizing trend. While these turbocharged GDI (TGDI) engines have indeed allowed for better fuel economy in many light duty vehicles, TGDI technology has also led to some unintended consequences. The most notable of these is an abnormal combustion phenomenon known as low speed pre-ignition (LSPI). LSPI is an uncontrolled combustion event that takes place prior to spark ignition, often resulting in knock, and has been known to cause catastrophic engine damage. LSPI propensity depends on a number of factors including engine design, calibration, fuel properties and engine oil formulation. Several engine tests have been developed within the industry to better understand the phenomenon of LSPI. While data from these tests have greatly increased the industry’s knowledge about LSPI, they may not accurately represent LSPI as it occurs while the vehicle is in actual service. This is because the industry tests are conducted on highly controlled engine dynamometers, often using special calibrations. In this work, a vehicle is fully instrumented with a high-speed data acquisition system to monitor LSPI. The vehicle is then operated on public roads with commercially available, pump gasoline for approximately 65,000 miles (104,607 km). Results indicate that LSPI, as it occurs in real world vehicle use, shows some similarities and differences from LSPI that occurs in laboratory engine tests. Additionally, the transient nature of the on-road testing presented a significant departure from the steady-state engine laboratory testing. This difference necessitates the development of a new method for identifying LSPI cycles in real world environments. Finally, results from this work will help the industry develop solutions to LSPI which are effective in the field.
Michlberger, Alexander, Sutton, Mike, Kocsis, Michael, Anderson, Garrett, Van Horn, Adam
Auto-ignition Characteristics of Lubricant Droplets under Hot Co-Flow Atmosphere2018-01-18079/10/2018
It has been revealed by researches that lubricant properties have a great effect on the low-speed pre-ignition (LSPI) frequency in downsizing turbocharged direct-injection engines which are developed for better fuel economy. Droplets of lubricant or lubricant-gasoline mixture are considered to be the potential pre-ignition sources. Those droplets fly into the combustion chamber and ignite the gasoline-air mixture. To study lubricant droplets fundamentally, a novel set of droplet auto-ignition system is designed based on a Dibble Burner for this experiment. Influences of metallic additive contents, viscosities, lubricant diluted with gasoline and waste lubricant on the ignition delay of droplets are investigated by testing 12 groups of lubricants or lubricant-gasoline mixture. The equivalent diameter of each droplet generated by micro-syringes is around 2.1 mm. The co-flow temperature varies from 1123 K to 1223 K, and the experiments are carried out at atmospheric pressure. The auto-ignition process of each lubricant droplet in a dark background is captured and recorded by a high-speed camera. The results show that ignition delays of all groups significantly decrease with the increase of co-flow temperature. Besides, increasing calcium or decreasing zinc dialkyldithiophosphates (ZDDP) in lubricants obviously promotes the trend on auto-ignition of droplets. But magnesium content has little influence on the ignition delay of lubricant droplets. In addition, lubricant with a higher viscosity has a longer ignition delay. Compared with undiluted lubricant droplets, droplets of lubricant-gasoline mixture tend to possess a longer ignition delay at high temperature. Although the ambient pressure in this experiment is much lower than that in an automotive engine, the observed results of effects of lubricant properties on auto-ignition are consistent with the regularities summarized by some engine bench tests. The quantitative results of lubricant droplet auto-ignition may be used as a criterion to evaluate the pre-ignition performance related to lubricants in engines.
Pan, Kaifeng, Deng, Jun, Chen, Yongquan, Zhang, Erbao, Xie, Wei, Qin, Qiushi, Qu, Zongju, Li, Liguang
Effects of EGR Constituents and Fuel Composition on DISI Engine Knock: An Experimental and Modeling Study2018-01-16779/10/2018
The use of exhaust gas recirculation (EGR) in spark ignition engines has been shown to have a number of beneficial effects under specific operating conditions. These include reducing pumping work under part load conditions, reducing NOx emissions and heat losses by lowering peak combustion temperatures, and by reducing the tendency for engine knock (caused by end-gas autoignition) under certain operating regimes. In this study, the effects of EGR addition on knocking combustion are investigated through a combined experimental and modeling approach. The problem is investigated by considering the effects of individual EGR constituents, such as CO2, N2, and H2O, on knock, both individually and combined, and with and without traces species, such as unburned hydrocarbons and NOx. The effects of engine compression ratio and fuel composition on the effectiveness of knock suppression with EGR addition were also investigated. A parametric, experimental matrix of diluents, compression ratio, and fuels was tested to measure knock-limited combustion phasing of each combination. The resulting knock limits were evaluated in the context of thermodynamic effects on the closed cycle, chemical interactions between the EGR constituents and the fuel-oxidizer mixture, and the effect of altered pressure-temperature trajectories on fuel-autoignition behavior. This paper provides an overview of the experimental results, and uses chemical-kinetic modeling to investigate the behavior of a particular fuel - diluent combination which had a strong sensitivity to compression ratio variation. The numerical results shed light on the complex interactions between fuel chemistry, the engine’s thermodynamic cycle, and the effect of residence times on the autoignition chemistry which leads to knock. An important and fuel-dependent role of thermal stratification in the end-gas is also suggested by the chemical-kinetics modeling of the experimentally observed knock limits.
Vuilleumier, David, Kim, Namho, Sjöberg, Magnus, Yokoo, Nozomi, Tomoda, Terutoshi, Nakata, Koichi
Blending Octane Number of 1-Butanol and Iso-Octane with Low Octane Fuels in HCCI Combustion Mode2018-01-16819/10/2018
Due to their physical and chemical properties, alcohols such as ethanol and methanol when blended with gasoline provide high anti-knock quality and hence efficient engines. However, there are few promising properties of 1-butanol similar to conventional gasoline which make it a favorable choice for internal combustion engines. Previously the author showed that by blending ethanol and methanol with low octane fuels, non-linear increase in the HCCI fuel number occurs in HCCI combustion mode. Very few studies have been conducted on the use of 1-butanol in HCCI combustion mode, therefore for this work, 1-butanol with a RON 96 was selected as the high octane fuel. Three low octane fuels with octane number close to 70 were used as a base fuel. Two of the low octane fuels are Fuels for Advanced Combustion Engines (FACE gasolines), more specifically FACE I and FACE J and also primary reference fuel (PRF 70) were selected. In addition, iso-octane, which has a different chemical structure than 1-butanol but an octane number (100) close to 1-butanol, was also selected as high octane fuel. A Cooperative Fuel Research (CFR) engine was used to conduct the experiments in HCCI combustion mode. HCCI fuel number was used for the octane rating similar to RON and MON in SI engine. 1-butanol and iso-octane were added in volume percentage 0, 5, 10, 15 and 20% to each of the base fuels. It was found that the increase of HCCI fuel number of 1-butanol was not linear with percentage added. For most of the operating conditions, non-linear synergistic blending behavior was observed when 1-butanol was blended with the three base fuels. The base fuel composition played a significant role for the blending octane number of 1-butanol. A weaker octane enhancement effect was observed when iso-octane was blended with the three base fuels.
Waqas, Muhammad Umer, Mohammed, Abdulrahman, Masurier, Jean-Baptiste, Johansson, Bengt
Combined Fuel and Lubricant Effects on Low Speed Pre-Ignition2018-01-16699/10/2018
Many studies on low speed pre-ignition have been published to investigate the impact of fuel properties and of lubricant properties. Fuels with high aromatic content or higher distillation temperatures have been shown to increase LSPI activity. The results have also shown that oil additives such as calcium sulfonate tend to increase the occurrence of LSPI while others such as magnesium sulfonate tend to decrease the occurrence. Very few studies have varied the fuel and oil properties at the same time. This approach is useful in isolating only the impact of the oil or the fuel, but both fluids impact the LSPI behavior of the engine simultaneously. To understand how the lubricant and fuel impacts on LSPI interact, a series of LSPI tests were performed with a matrix which combined fuels and lubricants with a range of LSPI activity. This study was intended to determine if a low activity lubricant could suppress the increased LSPI from a high activity fuel, and vice versa. The results showed that a low activity fuel was insensitive to the lubricant used in the test, while a high activity fuel could be moderated by a low activity lubricant. The combination of a high activity fuel and high activity lubricant, as expected, yielded a large number of LSPI events. These results help to understand how formulation changes to the lubricant or to the fuel may impact the other fluid, particularly with respect to regional variations in fuel specification and in lubricant additive standards.
Kocsis, Michael Clifford, Briggs, Thomas, Anderson, Garrett
Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines2018-01-17229/10/2018
This study presents a computational framework to predict the outcome of combustion process based on a given RANS initial condition by performing statistical analysis of Sankaran number, Sa, and ignition regime theory proposed by Im et al. [1]. A criterion to predict strong auto-ignition/detonation a priori is used in this study, which is based on Sankaran-Zeldovich criterion. In the context of detonation, Sa is normalized by a sound speed, and is spatially calculated for the bulk mixture with temperature and equivalence ratio stratifications. The initial conditions from previous pre-ignition simulations were used to compute the spatial Sa distribution followed by the statistics of Sa including the mean Sa, the probability density function (PDF) of Sa, and the detonation probability, PD. Sa is found to be decreased and detonation probability increased significantly with increase of temperature. The statistic mean Sa calculated for the entire computational domain and the predicted Sa from the theory were found to be nearly identical. The predictions based on the adapted Sankaran-Zel’dovich criterion and detonation probability agree well with the results of the previous high fidelity pre-ignition simulations.
Mubarak Ali, Mohammed Jaasim, Luong, Minh Bau, Sow, Aliou, Hernandez Perez, Francisco, Im, Hong
Method for Establishing Cool Flames and Flameless Fuel Oxidation with Zero Emissions Using Non-Equilibrium Plasma ActivationTBMG-290526/1/2018
Current engines and combustors run at high temperature, which leads to problems of engine knocking, soot and NOx emissions, and difficulty in combustion control. On the other hand, low-temperature combustion and fuel oxidation below 1000 K is typically too inaccessible or unstable to be used for engines and fuel processing. The novelty of the present invention is that by using oxygen-rich oxidizer stream and non-equilibrium plasma — which creates new chemical species such as singlet oxygen, ozone, ions, and intermediate radicals — stable, low-temperature cool flames and flameless combustion can be established to enable fast, low-temperature fuel oxidation in a broad range of pressures (0.1 to 50 atm). Due to the low flame temperature (500 K to 900 K), no soot emissions and no NOx emissions are formed in the cool flames and flameless combustion region. Moreover, the new cool flame regime allows rapid fuel (gasoline, diesel, and jet fuel) decomposition and partial oxidation to form clean and valuable small-molecule fuels such as C2H4, CH2O, CH3HCO, and CH4 at low cost and high efficiency.
Fuel Effects on PM Emissions from Different Vehicle/Engine Configurations: A Literature Review2018-01-03494/3/2018
Particulate matter (PM) emitted from gasoline combustion continues to be a subject of research and regulatory interest. This is particularly true as new technology gasoline direct injection (GDI) engines can produce significantly higher levels of PM compared to older technology port fuel injection (PFI) engines. The goal of this study was to conduct a comprehensive literature search and subsequent statistical analysis related to the effects of gasoline properties, such as aromatics, octane indices, and fuel volatility, on PM (mass and number) emissions from PFI and GDI vehicles/engines. The statistical analyses showed a range of positive and negative correlations between different fuel properties and PM mass, total particle number (PN) and solid particle number (SPN) for different engine types (GDI, PFI, and for subdivisions of these engine types), numbers of engine cylinders and driving cycles. For GDI vehicles, total aromatic content, T70, T90 (the temperature when 70% and 90% of a fuel by volume boils away during a distillation test), and distillation end point (EP) [(the highest temperature achieved during a distillation test)] were positively correlated with PM mass emissions, PN emissions, or both. Anti-Knock index (AKI), research octane number (RON), and motor octane number (MON), and T10 (the temperature when 10% of a fuel by volume boils away during a distillation test) were negatively correlated with PM mass emissions, PN emissions, or both. For PFI vehicles for the Federal Test Procedure (FTP), LA92 and US06 cycles, T50, T70, T90, AKI and MON showed more mixed results, with both positive and negative correlations, while distillation EP and RON showed a negative correlation with PM mass emissions. Many of these analyses also showed statistically significant interactions, which indicates that the magnitude and direction of the regression coefficient (slope) estimated between the fuel property and PM emissions component varied as of function of at least one of the categorical variables (i.e., vehicle engine technology or model year, number of cylinders, and/or drive cycle). The presence of such statistical interactions demonstrates the underlying complexity in the data set. The details related to the interactions can provide valuable information to researchers for interpreting data sets that include combinations of different vehicle technologies. The information can also be used in the design of test programs, where a better understanding of how the effects of different fuel properties can vary as a function of different vehicle technologies and drive cycles can aid in study planning.
Karavalakis, George, Durbin, Thomas D., Yang, Jiacheng, Ventura, Luciana, Xu, Karen
Enhanced Two-stage Ignition Delay Model Based on Molar Fraction of Fuel Components for SI Engine Simulation2018-01-08494/3/2018
Simulation based design and control optimization is widely used to assist the development of highly complex modern downsized turbocharged gasoline direct injection (GDI) engines. In such engines, knock phenomenon is a major constraint that limits performance and fuel economy enhancements. Thus, an accurate knock prediction model is critically important for virtual engine development process. In this paper, an enhanced ignition delay model is proposed for spark ignition (S)I combustion model based on previously developed empirical two-stage ignition delay model using fuel blends [1]. The ignition delay model provides a capability of predicting ignition delay of the end-gas zone for different fuel blends without additional calibration when fuel blending ratio changes. To adapt the ignition delay model to the SI combustion environment, the model is modified to have the sensitivity to the dilution effect by residual gas. Shock tube experimental data from the literature were collected and used to validate the dilution effect model. The ignition delay model developed in this study is implemented into a commercial simulation code (GT-Power®) as a user subroutine for a versatile simulation capability. Experimental data are taken from a 4-cylinder turbocharged GDI engine at various engine operating conditions. The experimental data are processed to extract the auto-ignition timings for the operation conditions in which knock is clearly observed. The ignition delay model integrated with the engine simulation is calibrated at reference cases and validated with various knocking and non-knocking cases.
Kwak, Kyoung Hyun, Jung, Dewey, Park, Hyunil, Paeng, Jeonghwan, Hwang, Kyumin
Investigations on the Influence of Fuel Oil Film Interaction on Pre-ignition Events in Highly Boosted DI Gasoline Engines2018-01-14544/3/2018
Premature and uncontrolled flame initiation, called pre-ignition (PI), is a prominent issue in the development of spark-ignited engines. It is commonly assumed that this abnormal combustion mode hinders progress in engine downsizing, thus inhibiting development of more efficient engines. The phenomenon is primarily observed in highly turbocharged spark ignited (SI) engines in the full load regime at low engine speeds. Subsequent engine knock induces extremely high peak pressures, potentially causing severe engine damage. The mechanisms leading to this phenomenon are not completely understood; however, it is quite plausible that a multiphase process is responsible for the pre-ignition. One effect could be the interaction between injected fuel drops and the oil film on the cylinder liner. Under certain conditions, droplets of oil or oil/fuel mixture can detach or splash from the film, leading to pre-ignition at the droplet surface towards the end of the compression phase. To gain further understanding of the possible mechanisms leading to pre-ignition events it is important to know under which conditions splash effects on the film can cause droplet detachment. In this paper pre-ignition events in a 2.0 liter 4-cylinder production engine are analyzed regarding the different operating conditions of their occurrence. Parameters effecting splash conditions are injection timing and pressure (fuel impingement on liner), liner temperature, boiling curves of the fuel and lubricating oil viscosity. Conditions leading to increased pre-ignition rates are compared to a generic drop/wall film interaction experiment to evaluate whether splash events are a likely cause or not. The impact of a single drop onto a wetted wall using different liquids is investigated. A large parameter range is obtained by varying drop diameter, impact velocity, film thickness and fluid combinations of drop and wall film. Finally, a dimensionless number K * is defined in order to describe the splashing threshold. Typical K * numbers for various operating conditions of the engine are then computed and compared with results from generic drop impact experiments.
Kubach, Heiko, Weidenlener, Alex, Pfeil, Juergen, Koch, Thomas, Kittel, Hannah, Roisman, Ilia V., Tropea, Cameron
A Two-Stage Knock Model for the Development of Future SI Engine Concepts2018-01-08554/3/2018
At specific operating conditions, the auto-ignition in the unburnt mixture that precedes the occurrence of knock in conventional SI engines happens in two stages. In a previous publication, the authors demonstrated that the low-temperature heat release significantly influences the auto-ignition behavior of the mixture, thus severely impairing the prediction capabilities of the Livengood-Wu integral that the majority of the commonly used 0D/1D knock models are based on. Consequently, a new two-stage auto-ignition prediction approach for modeling the progress of the chemical reactions was introduced. It was demonstrated that the proposed auto-ignition model predicts the occurrence of two-stage ignition and accurately considers the significant influence of low-temperature heat release on the mixture’s auto-ignition behavior at various operating conditions. However, the correct prediction of local auto-ignition is not sufficient for the reliable calculation of the knock boundary, as the occurrence of this phenomenon does not necessarily result in knock. Based on the proposed two-stage auto-ignition prediction approach, this paper presents a new knock model for the development of future SI engine concepts in a 0D/1D simulation environment. In addition to not considering low-temperature ignition, the commonly used knock models based on the Livengood-Wu integral assume that no knock can occur after a pre-defined, constant MFB-point. The evaluation of measured knocking single cycles however has revealed that the latest possible MFB-point where knock can occur changes significantly with parameters such as engine speed and EGR rate. Hence, a cycle-individual criterion for the occurrence of knock accounting for the current operating conditions is needed. To this end, an approach based on the unburnt mass fraction in the cool thermal boundary layer at the time of auto-ignition is proposed. Besides the operating conditions, this knock occurrence criterion also considers the flame propagation and the cylinder geometry. Additionally, the already published submodels integrated into the two-stage auto-ignition prediction approach are expanded by the influence of injected water. Thus, as the new knock model also accounts for EGR, fuel composition and properties as well as air-fuel equivalence ratio effects, it fulfills all requirements for the simulation of future engine concepts. The approach contains no empirical measurement data fits and has just one calibration parameter that does not change with the operating conditions. Finally, model validation against measurement data on a handful of different engines at various operating conditions is performed. It is demonstrated that the new model can estimate the knock boundary very accurately with errors in the predicted center of combustion below 2°CA and thus contributes to the cost-effective development of future SI engine concepts in a 0D/1D simulation environment.
Fandakov, Alexander, Grill, Michael, Bargende, Michael, Kulzer, Andre Casal
Experimental Study on Combustion Characteristics of Methane/Gasoline Dual-Fuel in a SI Engine at Different Load Conditions2018-01-11404/3/2018
Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions. Under large load conditions, methane addition showed good knocking resistance and the potential of knocking limit extension. Through advancing spark-ignition timing, methane/gasoline dual-fuel combustion was able to provide sufficient torque output with optimized combustion phasing. Current research results shall give insights into combustion optimization of methane (or natural gas) and gasoline dual-fuel engines.
Pan, Jiaying, Wei, Haiqiao, Shu, Ge-Qun, Feng, Dengquan
Performance Assessment of Extended Stroke Spark Ignition Engine2018-01-08934/3/2018
The performance of an extended stroke spark ignition engine has been assessed by cycle simulation. The base engine is a modern turbo-charged 4-stroke passenger car spark-ignition engine with 10:1 compression ratio. A complex crank mechanism is used so that the intake stroke remains the same while the expansion-to-intake stroke ratio (SR) is varied by changing the crank geometry. The study is limited to the thermodynamic aspect of the extended stroke; the changes in friction, combustion characteristic, and other factors are not included. When the combustion is not knock limited, an efficiency gain of more than 10 percent is obtained for SR = 1.5. At low load, however, there is an efficiency lost due to over-expansion. At the same NIMEP, the extended stroke renders the engine more resistant to knock. At SR of 1.8, the engine is free from knock up to 14 bar NIMEP at 2000 rpm. Under knocking condition, the required spark retard to prevent knocking is less with the extended stroke. Then the operating point is closer to that of most efficient timing and the efficiency penalty due to knock constraint is reduced. With the extended stroke, since less exhaust energy is delivered to the turbine, the engine air throughput and thus the output power is reduced. At low speeds, the increase in efficiency overpowers the decrease in air flow so that the maximum NIMEP at a fixed speed increases with SR. At high speed, however, the reverse is true and the maximum NIMEP decreases with SR. For the engine/turbocharger combination used in this study, the transition point is at approximately 1500 rpm.
Anandhan, Muthu, Cheng, Wai K.
Modeling the Evolution of Fuel and Lubricant Interactions on the Liner in Internal Combustion Engines2018-01-02794/3/2018
In internal combustion engines, a portion of liquid fuel spray may directly land on the liner and mix with oil (lubricant), forming a fuel-oil film (~10μm) that is much thicker than the original oil film (~0.1μm). When the piston retracts in the compression stroke, the fuel-oil mixture may have not been fully vaporized and can be scraped by the top ring into the 1st land crevice and eventually enter the combustion chamber in the format of droplets. Studies have shown that this mechanism is possibly a leading cause for low-speed pre-ignition (LSPI) as the droplets contain oil that has a much lower self-ignition temperature than pure fuel. In this interest, this work aims to study the oil-fuel interactions on the liner during an engine cycle, addressing molecular diffusion (in the liquid film) and vaporization (at the liquid-gas interface) to quantify the amount of fuel and oil that are subject to scraping by the top ring, thereby exploring their implications on LSPI and friction. An analytical model is developed by coupling multi-component heat and mass transfer using an implicit, adaptive-time and fixed-space numerical scheme. The results of this model suggest that a substantial fraction of the fuel-oil mixture still remains on the liner when the piston retracts if the initial fuel film thickness is on the order of 20 μm; this fuel-oil mixing also results in a local oil dilution that can lead to a significant increase in the ring-liner contact force.
Zhang, Qin, Kalva, Vinayak Teja, Tian, Tian
Investigation of Combustion Knock Distribution in a Boosted Methane-Gasoline Blended Fueled SI Engine2018-01-02154/3/2018
The characteristics of combustion knock metrics over a number of engine cycles can be an essential reference for knock detection and control in internal combustion engines. In a Spark-Ignition (SI) engine, the stochastic nature of combustion knock has been shown to follow a log-normal distribution. However, this has been derived from experiments done with gasoline only and applicability of log-normal distribution to dual-fuel combustion knock has not been explored. To evaluate the effectiveness and accuracy of log-normal distributed knock model for methane-gasoline blended fuel, a sweep of methane-gasoline blend ratio was conducted at two different engine speeds. Experimental investigation was conducted on a single cylinder prototype SI engine equipped with two fuel systems: a direct injection (DI) system for gasoline and a port fuel injection (PFI) system for methane. The experiments were conducted at 1500 rpm and 2000 rpm, 12.0 bar net indicated mean effective pressure wherein the engine was boosted using compressed air. E10 gasoline and methane were used in this study. The results from blending two fuels show that the log-normal distribution provides a good fit to the measured distribution and captures the knock characteristics. The independency of log-normal distribution to the knock distribution at different spark timings was examined. The distribution parameters (log normal mean (μ) and standard deviation (σ)) show a linear correlation with the spark timing from knock borderline (BD) to 1.75° crank angle retarded. A μ and σ fit based log-normal (calculation-based log-normal) distribution model was proposed. The coefficients of multiple determination (CoMD) for the calculation-based log-normal model are all above 0.8 over the tested conditions. The validation of calculation-based log-normal was also conducted for all blending ratios and speeds.
Yang, Zhuyong, Rao, Sandesh, Wang, Yanyu, Harsulkar, Jaideep, Ansari, Ehsan, Miganakallu Narasimhamurthy, Niranjan, Dice, Paul, Naber, Jeffrey, Lonari, Yashodeep, Szwaja, Stanislaw
An Experimental Study on the Knock Mitigation Effect of Coolant and Thermal Boundary Temperatures in Spark Ignited Engines2018-01-02134/3/2018
Increasing compression ratio is essential for developing future high-efficiency engines due to the intrinsic characteristics of spark-ignited engines. However, it also causes the unfavorable, abnormal knocking phenomena which is the auto-ignition in the unburned end-gas region. To cope with regulations, many researchers have been experimenting with various methods to suppress knock occurrence. In this paper, it is shown that cooling the combustion chamber using coolants, which is one of the most practical methods, has a strong effect on knock mitigation. Furthermore, the relationship between thermal boundary and coolant temperatures is shown. In the beginning of this paper, knock metrics using an in-cylinder pressure sensor are explained for readers, even though entire research studies cannot be listed due to the innumerableness. The coolant passages for the cylinder head and the liner were separated to examine independent cooling strategies. In addition, piston surface temperature was changed through the oil supply to the piston oil gallery. To investigate the effects on the thermal boundary temperature under knocking conditions, temperatures were measured. Knock mitigation effects were quantified while the coolant temperatures were varied. Quantification in this study consists of two methods: The advancement of the crank angle ignition timing and the expansion of the borderline knock (detonation border line). The different impacts of cooling between PFI (port fuel injection) and GDI (gasoline direct injection) engines and the differences under various S/B (stroke-to-bore) ratios are also shown in this study. After implementation, it was shown that decreasing the coolant temperature in the cylinder head has a greater effect than that of the liner. Furthermore, 4.2 CA and 5 CA of ignition timing advance and 10% and 6.8% of knock load limit expansion were achieved while the coolant temperature was decreased from 85 °C to 60 °C under 1500 rpm and 2000 rpm, respectively. GDI engine also showed knock mitigation effects by the coolant temperature decrease. Higher stroke-to-bore ratio led to expanded load limit due to increased knock suppression. However, there was no significant difference in the effect of coolant temperature decrease for various stroke-to-bore ratios.
Cho, Seokwon, Song, Chiheon, Oh, Sechul, Min, Kyoungdoug, Ha, Kyoung-Pyo, Kim, Back-Sik
Combined Effects of Valve Strategies, Compression Ratio, Water Injection, and Cooled EGR on the Fuel Consumption of a Small Turbocharged VVA Spark-Ignition Engine2018-01-08544/3/2018
In this work, various techniques are numerically investigated to assess and quantify their relative effectiveness in reducing the Brake Specific Fuel Consumption (BSFC) of a downsized turbocharged spark-ignition Variable Valve Actuation (VVA) engine. The analyzed solutions include the Variable Compression Ratio (VCR), the port Water Injection (WI), and the external cooled Exhaust Gas Recirculation (EGR). The numerical analysis is developed in a 1D modeling framework. The engine is schematized in GT-Power™ environment, employing refined sub-models of the in-cylinder processes, such as the turbulence, combustion, knock, and heat transfer. The combustion and knock models have been extensively validated in previous papers, at different speed/load points and intake valve strategies, including operations with a relevant internal EGR rate and with liquid WI. The 1D model is coupled to an automatic optimizer, to explore the potential BSFC benefits arising from the adoption of the above-listed solutions. The base engine architecture, only including the VVA device, is preliminarily optimized to define reference BSFC levels. Then, single and combined solutions are analyzed to outline the maximum achievable BSFC gains. Operating conditions typical of a Worldwide harmonized Light vehicles Test Procedure (WLTP) driving cycle are considered. More than proposing an advanced, very complex, engine architecture, the aim of the activity is to clearly outline isolated and mutual effects of each technique at various operating points. In this way, some guidelines are offered to engine developers to select the preferred solution and to have information on the expected improvements. The optimization outcomes show that the WI proves a higher effectiveness at medium-high load, mainly thanks to its knock suppression capability. Cooled EGR is preferable at low load, to reduce the pumping work. If coupled to the WI, a high Compression Ratio (CR) is always beneficial. The combination of the above techniques provides BSFC reductions of 6.9%, 5.2%, and 9.0% at low, medium, and high loads, respectively.
Teodosio, Luigi, De Bellis, Vincenzo, Bozza, Fabio
A Computational Study of Abnormal Combustion Characteristics in Spark Ignition Engines2018-01-01794/3/2018
Super-knock that occurs in spark ignition (SI) engines is investigated using two-dimensional (2D) numerical simulations. The temperature, pressure, velocity, and mixture distributions are obtained and mapped from a top dead center (TDC) slice of full-cycle three-dimensional (3D) engine simulations. Ignition is triggered at one end of the cylinder and a hot spot of known temperature was used to initiate a pre-ignition front to study super-knock. The computational fluid dynamics code CONVERGE was used for the simulations. A minimum grid size of 25 μm was employed to capture the shock wave and detonation inside the domain. The Reynolds-averaged Navier-Stokes (RANS) method was employed to represent the turbulent flow and gas-phase combustion chemistry was represented using a reduced chemical kinetic mechanism for primary reference fuels. A multi-zone model, based on a well-stirred reactor assumption, was used to solve the reaction terms. Hot spots introduced inside the domain at various initial temperatures initiated a pre-ignition front, which resulted in super-knock due to detonation of the end gas. The detonation was induced for temperatures greater than 1000 K during the start of pre-ignition flame propagation. The detonation speed was around 2000 m/s, at temperatures higher than 1000 K. For temperatures between 800 K and 1000 K, detonation was observed near the end of combustion. The laminar pre-ignition flame front speed calculated from the simulations was an order of magnitude higher than the one-dimensional laminar flame speed, which is characteristic of sequential auto-ignition. Multiple auto-ignition sites in the end-gas region were observed at higher temperatures. The auto-ignition location initiated an auto-ignition front of higher velocity that later transitioned into detonation. Interaction between the detonating fronts generated local pressure peaks inside the domain. End-gas reactivity was characterized by the formation of formaldehyde (CH2O) and was an indicator for occurrence of auto-ignition/detonation. Negative temperature coefficient regimes (750 K-850 K) exhibited higher mass fraction of CH2O indicating enhanced reactivity of end gas, leading to highest peak pressures during detonation onset. The low-temperature case, 700 K, exhibited a deflagration mode of flame propagation without detonation development. The results were analyzed and reported by comparison with Bradley diagram, which predicted a deflagration mode of combustion for the lowest temperature case, and developing a detonation mode for all other cases considered in this study.
Mubarak Ali, Mohammed Jaasim, Hernandez Perez, Francisco, Sow, Aliou, Im, Hong
Understanding the Effect of Inhomogeneous Mixing on Knocking Characteristics of Iso-Octane by Using Rapid Compression Machine2018-01-02124/3/2018
As fuel injection strategies in spark-ignition (SI) engines have been diversified, inhomogeneous mixing of the fuel-air mixture can occur to varying extents during mixture preparation. In this study, we analyzed the effect of inhomogeneous mixing on the knocking characteristics of iso-octane and air mixture under a standardized fuel testing condition for research octane number (RON), based on ASTM D2699. For this purpose, we assumed that both lean spots and rich spots existed in unburned gas during compression stroke and flame propagation and calculated the thermodynamic state of the spots by using an in-house multi-zone, zero-dimensional SI engine model. Then, the ignition delay was measured over the derived thermodynamic profiles by using rapid compression machine (RCM), and we calculated ξ, the ratio of sound speed to auto-ignition propagation speed, based on Zel’dovich and Bradley’s ξ − ε theory to estimate knock intensity. As a result, we discovered that lean spots would have higher reactivity than stoichiometric mixture (ξ > 0), while rich spots would not (ξ < 0); thus, knocking has more tendency to be initiated from a lean spot. For further analysis, ξ was divided into two terms, ξT for temperature gradient and ξϕ for equivalence ratio gradient, and each term was evaluated separately. At a lean spot, ξT is generally positive because temperature is higher than that of stoichiometric mixture due to smaller fuel charge cooling and higher specific heat ratio of the mixture. On the other hand, ξϕ is negative but rapidly converges to zero as flame propagates; thus, ξ is determined dominantly by ξT. In addition, ξ from various spot radii and steepness of gradient were compared to analyze the effect of spot structure on knock intensity. As a result, we found that a steeper gradient of equivalence ratio leads to a weaker knock intensity, while the effect of radius change is negligible.
Cho, Jaeyoung, Song, Han Ho
Development of a Virtual CFR Engine Model for Knocking Combustion Analysis2018-01-01874/3/2018
Knock is a major bottleneck to achieving higher thermal efficiency in spark ignition (SI) engines. The overall tendency to knock is highly dependent on fuel anti-knock quality as well as engine operating conditions. It is, therefore, critical to gain a better understanding of fuel-engine interactions in order to develop robust knock mitigation strategies. In the present work, a numerical model based on three-dimensional (3-D) computational fluid dynamics (CFD) was developed to capture knock in a Cooperative Fuel Research (CFR) engine. For combustion modeling, a hybrid approach incorporating the G-equation model to track turbulent flame propagation, and a homogeneous reactor multi-zone model to predict end-gas auto-ignition ahead of the flame front and post-flame oxidation in the burned zone, was employed. In addition, a hybrid methodology was implemented wherein a laminar flame speed lookup table generated a priori from a chemical kinetic mechanism could be used to provide flame speed as an input to the G-equation model, instead of using conventional empirical correlations. Multi-cycle Reynolds-averaged Navier-Stokes (RANS) simulations were performed for two different spark timings (STs) corresponding to non-knocking and knocking conditions, with other operating conditions kept the same as those of a standard research octane number (RON) test. Isooctane was considered as the fuel for the numerical study. Two different reduced kinetic mechanisms were employed to describe end-gas auto-ignition chemistry and to generate the flame speed lookup table. Experimental data, including intake/exhaust boundary conditions, was provided by an isooctane ST sweep study conducted in an in-house CFR engine. Moreover, cylinder wall/valve/port surface temperatures and residual gas fraction (RGF) were estimated using a well-calibrated one-dimensional (1-D) model. On the other hand, a novel methodology was also developed to analyze experimental data for the knocking case and identify the most representative cycle. For the non-knocking case, a good agreement was found between experiment and CFD simulation, with respect to cycle-averaged values of 10% burn point (CA10), 50% burn point (CA50), and peak pressure magnitude/location. The virtual CFR engine model was also demonstrated to be capable of predicting average knock characteristics for the knocking case, such as knock point, knock intensity, and energy of resonance, with good accuracy.
Pal, Pinaki, Kolodziej, Christopher P., Choi, Seungmok, Som, Sibendu, Broatch, Alberto, Gomez-Soriano, Josep, Wu, Yunchao, Lu, Tianfeng, See, Yee Chee
Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine2018-01-02104/3/2018
Of late there has been a resurgence in studies investigating parameters that quantify combustion knock in both standardized platforms and modern spark-ignition engines. However, it is still unclear how metrics such as knock (octane) rating, knock onset, and knock intensity are related and how fuels behave according to these metrics across a range of conditions. As part of an ongoing study, the air supply system of a standard Cooperative Fuel Research (CFR) F1/F2 engine was modified to allow mild levels of intake air boosting while staying true to its intended purpose of being the standard device for American Society for Testing and Materials (ASTM)-specified knock rating or octane number tests. For instance, the carburation system and intake air heating manifold are not altered, but the engine was equipped with cylinder pressure transducers to enable both logging of the standard knockmeter readout and state-of-the-art indicated data. For this study, the engine was operated using primary reference fuel 90 (PRF90) at 600 rpm, first following the procedures of the ASTM D2699 research octane number test protocol in order to define the geometric compression ratio set point for standard knock number. Thereafter, compression ratio sweeps were conducted at intake temperatures ranging from 30 to 150°C and intake air boost extending from 0 to 0.3 bar above ambient. The resulting operating map provided a broad envelope of compressed in-cylinder conditions relevant to modern spark-ignition engines. Detailed analysis of the indicated data highlighted a poor correlation between established knock intensity metrics and the knockmeter reading, which is used to characterize a fuel’s octane number. It was further found that the auto-ignition characteristics of PRF90 could be perturbed by means of intake air boosting and heating without being captured by the knockmeter reading.
Rockstroh, Toby, Kolodziej, Christopher P., Jespersen, Mads C., Goldsborough, S. Scott, Wallner, Thomas
Numerical Analysis of the Impact of Water Injection on Combustion and Thermodynamics in a Gasoline Engine Using Detailed Chemistry2018-01-02004/3/2018
Water injection is a promising technology to improve the fuel efficiency of turbocharged gasoline engines due to the possibility to suppress engine knock. Additionally, this technology is believed to enable the efficient operation of the three-way catalyst also at high-load conditions, through limiting the exhaust temperature. In this numerical study, we investigate the effect of water on the chemical and thermodynamic processes using 3D computational fluid dynamics (CFD) Reynolds-averaged Navier–Stokes (RANS) with detailed chemistry. In the first step, the influence of different amounts of water vapor on ignition delay time, laminar flame speed, and heat capacity is investigated. In the second step, the impact of water vaporization is analyzed for port and direct injection. For this purpose, the water mass flow and the injection pressure are varied. A steady-state, medium-speed, high-load engine operating point is investigated with focus on the effect of water injection on knock tendency and exhaust temperature. The impact of water injection on oxidation chemistry and auto-ignition is investigated using a detailed ethanol toluene reference fuel (ETRF) (ethanol, iso-octane, n-heptane, and toluene) reaction scheme. The combustion is predicted using the level-set method for flame propagation and a well-stirred reactor model in the unburned zone to predict auto-ignition. The laminar flame speed is retrieved from precompiled look-up tables calculated for each specific composition (surrogate, diluents, and oxidizer). Engine knock is evaluated using Bradley’s detonation diagram (Bradley et al. 2002, Gu et al. 2003). With numerical models, we are able to separate the influence of chemical and thermodynamic properties by using different flame speed tables, thermodynamic properties, and third body efficiencies for pressure-dependent reactions. This allows to quantify and rank the impact of the investigated properties. The impact on the knock limit spark advance in descending order of importance is found to be laminar flame speed, heat of vaporization, chemical equilibrium, water vapor heat capacity, third body efficiency, and ignition delay time.
Netzer, Corinna, Franken, Tim, Seidel, Lars, Lehtiniemi, Harry, Mauss, Fabian
Effect of Fuel-Air Mixture Dilution on Knock Intensity in an SI Engine2018-01-02114/3/2018
Occurrence of knock in spark ignition (SI) engines is usually suppressed by inhibiting auto-ignition of the fuel-air mixture. A steep increase in pressure by auto-ignition of the local mixture is thought to initiate the pressure oscillation, which results in knock. Therefore, in order to prevent knock, the strength of the pressure oscillation would be decreased by reducing the local heat release of the end gas. In this study, the oxidation reaction rate of the auto-ignition was attempted to be reduced by dilution of the mixture. The effect of mixture dilution on the strength of pressure oscillation, that is knock intensity, was examined using a rapid compression machine (RCM) and a single cylinder SI engine. The test result of compression ignition of homogeneous mixture using RCM showed that increase in dilution ratio could decrease the knock intensity even if the input heat increased and the auto-ignition timing advanced. The maximum load without knock as well as without end gas auto-ignition at MBT spark timing was explored for various dilution ratios with inert gas or air in the SI engine. It was cleared that the knock-limited load was higher than the auto-ignition-limited one under high dilution conditions, while both were equal under low dilution conditions. That is to say, knock intensity with auto-ignition of the end gas was also reduced by mixture dilution regardless of dilution gas composition. The knock intensity was well arranged in accordance with the maximum temperature and pressure of the cycle, which are the representative values in the auto-ignition process.
Ohtomo, Mitsuaki, Suzuoki, Tetsunori, Yamamoto, Seiji, Miyagawa, Hiroshi
Effects of Heat of Vaporization and Octane Sensitivity on Knock-Limited Spark Ignition Engine Performance2018-01-02184/3/2018
Knock-limited loads for a set of surrogate gasolines all having nominal 100 research octane number (RON), approximately 11 octane sensitivity (S), and a heat of vaporization (HOV) range of 390 to 595 kJ/kg at 25°C were investigated. A single-cylinder spark-ignition engine derived from a General Motors Ecotec direct injection (DI) engine was used to perform load sweeps at a fixed intake air temperature (IAT) of 50 °C, as well as knock-limited load measurements across a range of IATs up to 90 °C. Both DI and pre-vaporized fuel (supplied by a fuel injector mounted far upstream of the intake valves and heated intake runner walls) experiments were performed to separate the chemical and thermal effects of the fuels’ knock resistance. The DI load sweeps at 50°C intake air temperature showed no effect of HOV on the knock-limited performance. The data suggest that HOV acts as a thermal contributor to S under the conditions studied. Measurement of knock-limited loads from the IAT sweeps for DI at late combustion phasing showed that a 40 vol% ethanol (E40) blend provided additional knock resistance at the highest temperatures, compared to a 20 vol% ethanol blend and hydrocarbon fuel with similar RON and S. Using the pre-vaporized fuel system, all the high S fuels produced nearly identical knock-limited loads at each temperature across the range of IATs studied. For these fuels RON ranged from 99.2 to 101.1 and S ranged from 9.4 to 12.2, with E40 having the lowest RON and highest S. The higher knock-limited loads for E40 at the highest IATs examined were consistent with the slightly higher S for this fuel, and the lower engine operating condition K values arising from use of this fuel. The study highlights how fuel HOV can affect the temperature at intake valve closing, and consequently the pressure-temperature history of the end gas leading to more negative values of K, thereby enhancing the effect of S on knock resistance.
Ratcliff, Matthew A., Burton, Jonathan, Sindler, Petr, Christensen, Earl, Fouts, Lisa, McCormick, Robert L.
Testing and Implementation of a Turbocharged Formula SAE Vehicle2018-01-09674/3/2018
Research on turbocharging for FSAE at the University of Malta, has been ongoing for a number of years. 1D simulations were done to determine best design configuration and determine a lowered compression ratio. A decompression plate was installed on the Kawasaki 600 cc engine. Calibration of the engine was performed on the engine dynamometer. A hot-gas test stand for testing of the turbocharger was developed. The turbocharger speed was measured by a custom built hall-effect sensing setup that is compact enough to be implemented also in the FSAE vehicle. Bespoke camshafts with optimized valve timing determined through WAVE 1D simulations and designed with Valdyn® were machined. The turbocharged setup was used on the University of Malta FSAE vehicle in the FSAE Italy 2017 competition. Knock was investigated through in-cylinder pressure measurements and use of commercial knock sensor on the 600 cc engine. Benchmarking in-cylinder pressure measurement tests were carried out on a 1.4 liter naturally aspirated Ford engine for both ‘masked’ and ‘unmasked’ in-cylinder pressure sensors to assess the possibility and effect of cavity resonance in such experimental tests. High speed data acquisition was performed at 200 kHz per channel and was post-processed using LabVIEW®. Calibration of the knock detection feature on the programmable ECU required the determination of the relevant parameters namely: knock frequency, reference and knock windows and knock to reference window amplitude ratio. Calibration of the ECU knock parameters was aided by playing back recorded engine sensor data to minimize the time of engine knocking.
Azzopardi, Jean Paul, Farrugia, Jean-Paul, Caruana, Carl, Grech, Nicholas, Farrugia, Nicholas, Chircop, Marlon, Farrugia, Mario, Farrugia, Michael
Real World Performance of an Onboard Gasoline/Ethanol Separation System to Enable Knock Suppression Using an Octane-On-Demand Fuel System2018-01-08794/3/2018
Higher compression ratio and turbocharging, with engine downsizing can enable significant gains in fuel economy but require engine operating conditions that cause engine knock under high load. Engine knock can be avoided by supplying higher-octane fuel under such high load conditions. This study builds on previous MIT papers investigating Octane-On-Demand (OOD) to enable a higher efficiency, higher-boost higher compression-ratio engine. The high-octane fuel for OOD can be obtained through On-Board-Separation (OBS) of alcohol blended gasoline. Fuel from the primary fuel tank filled with commercially available gasoline that contains 10% by volume ethanol (E10) is separated by an organic membrane pervaporation process that produces a 30 to 90% ethanol fuel blend for use when high octane is needed. In addition to previous work, this paper combines modeling of the OBS system with passenger car and medium-duty truck fuel consumption and octane requirements for various driving cycles. Medium duty driving cycles were included; HHDDT cruise mode for long-haul heavy truck cruising and HTUF 4 for delivery truck duty. Commercial vehicle modeling was done under unloaded, half and fully loaded conditions. Additionally, for the first time, transient separator performance and effective separation limits were included in the evaluation. Separator start-up, and membrane selectivity decrease achievable real-world fuel economy from what can be achieved with two separate tanks: one with gasoline, the other with ethanol. However, using the fuel separation system, the reduction in fuel economy is modest compared to a two tank system with pure ethanol while the need to fill a second tank is removed. Fuel efficiency gains compared to equivalent-performance current engines, including real world limitations ranged from 17.5-30% with commercial gasoline that includes 10% ethanol as base fuel.
Kasseris, Emmanuel, Heywood, John B., Seitz, Scott, Kolakaluri, Ravi
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