Browse Topic: Ignition timing

Items (837)
Find
021 - Development of a 0D Model Starting from Different RANS CFD Tumble Flow Fields in Order to Predict the Turbulence Evolution at Ignition TimingSAE-PP-001501/25/2021
aster combustion and lower cycle-to-cycle variability are mandatory tasks for naturally aspirated engines to reduce emission levels and to increase engine efficiency. The promotion of a stable and coherent tumble structure is considered as one of the best way to promote the in-cylinder turbulence and therefore the combustion velocity. During the compression stroke the tumble vortex is deformed, accelerated and its breakdown in smaller eddies leads to the turbulence enhancement process. The prediction of the final level of turbulence for a particular engine operating point is crucial during the engine design process because it represents a practical comparative means for different engine solutions. The tumble ratio parameter value represents a first step toward the evaluation of the turbulence level at ignition time, but it has an intrinsic limit. The tumble ratio parameter represents the value of the angular velocity of a single macro vortex, while the flow-field is often characterized by multiple vortexes, sometimes some rotating and some counter-rotating. The idea at the basis of the paper is: To develop a quasi-predictive 0D model for defining the final mean level of the turbulence at the ignition time. The model is fed by the curtain intake valve mass flow rate and the intake valve lift trend. In order to validate the 0D model the results were compared versus 3D CFD results. To extract from a 3D CFD flow field at IVC the type and the number of the vortexes. The 3D CFD RANS simulations were performed by AVL Fire code v. 2010. To demonstrate through some 3D CFD results that the flow field structure was a function only of the engine type and the load condition. Finally the flow field structure could be used in the 0D model on varying the engine speeds as a means of improvement of the model prediction capability.
Mutagaana, Festo
Knock, Auto-Ignition and Pre-Ignition Tendency of Fuels for Advanced Combustion Engines (FACE) with Ethanol Blends and Similar RON2020-01-06134/14/2020
Researchers have known about a higher pre-ignition frequency of alcohol fuels for several decades now. Several studies, assessing the effect of ethanol addition on stochastic pre-ignition, have shown contradicting observations. Researchers at FEV observed an increase in pre-ignition frequency with an increase in ethanol concentration, however the pre-ignition events at high ethanol content did not lead to super-knock. Most of the studies have used varying ethanol fraction in a common base-fuel, thereby varying the auto-ignition tendency of the blend. In the current study, the effect of ethanol addition on FACE (Fuels for Advanced Combustion Engines) gasolines is assessed. Five different FACE gasolines (FACE A, C, I, J and G) were used for the study. Ignition delay time of varying ethanol fractions in FACE gasolines was measured in an Ignition Quality Tester (IQT), following ASTM 6890. The measurements showed that 13% ethanol (v/v) is needed for FACE A and C, while 27% ethanol (v/v) is needed for FACE I and J to match the ignition delay time of FACE G fuel. The five blends were tested in a Co-operative Fuel Research (CFR) engine in Homogeneous Charge Compression Ignition (HCCI) and Spark Ignition (SI) combustion mode. The experiments showed similar auto-ignition and knocking tendency for the five blends. After that, the pre-ignition tendency of the blends was assessed in a supercharged AVL engine. In general, increasing ethanol content led to higher pre-ignition frequency. Moreover, the effect of ethanol on increasing pre-ignition frequency was dependent on the base-fuel into which ethanol was added. For the same ethanol fraction added, base-fuels with higher aromatic content showed higher pre-ignition frequency.
Singh, Eshan, Dibble, Robert
Characteristics of Auto-Ignition for Lubricants and Lubricant/Gasoline Based on an Innovative Single Droplet Test System2020-01-14284/14/2020
Due to the advantages of low weight, low emissions and good fuel economy, downsized turbocharged gasoline direct injection (GDI) engines are widely-applied nowadays. However, Low-Speed Pre-Ignition (LSPI) phenomenon observed in these engines restricts their improvement of performance. Some researchers have shown that auto-ignition of lubricant in the combustion chamber has a great effect on the LSPI frequency. To study the auto-ignition characteristics of lubricant, an innovative single droplet auto-ignition test system for lubricant and its mixture is designed and developed, with better accuracy and effectiveness. The experiments are carried out by hanging lubricant droplets on the thermocouple node under active thermo-atmosphere provided by a small “Dibble burner”. The auto-ignition process of lubricant droplets is recorded by a high-speed camera. Influences of different base oil types, viscosities, calcium contents, initial droplet diameters, co-flow speeds, new oil, used oil and blending ratios of lubricant and gasoline on the ignition delay time of droplets are investigated at different droplet temperatures. The background co-flow field temperature varies from 823K to 1323K. Equivalent diameters of droplets, 0.99mm, 1.24mm and 1.63mm, generated by micro-syringes are compared for their characteristics of auto-ignition. The results show that the ignition delay time of all the droplets is significantly shortened with the increase of droplet temperature. When the droplet temperature is lower than 1073K, the ignition delay of droplets from Type III base oil is shorter than that of droplets from Type IV base oil. Besides, lubricant droplets with higher viscosities or larger initial diameters have a longer ignition delay. Furthermore, increasing both the calcium content and co-flow speed can obviously promote the auto-ignition process of droplets. Moreover, there is a critical blending ratio for gasoline to lubricant, whose value is between 20% and 30%. When it is lower than the critical blending ratio, the ignition delay of lubricant droplets increases with the rising of blending ratio. When it is higher than the critical blending ratio, the rule is contrary.
Yu, Yang, Pan, Kaifeng, Deng, Jun, Hu, Zongjie, Xie, Wei, Wu, Zhijun, Li, Liguang
Potential Analysis and Virtual Development of SI Engines Operated with Synthetic Fuel DMC+2020-01-03424/14/2020
On the way to emission-free mobility, future fuels must be CO2 neutral. To achieve this, synthetic fuels are being developed. In order to better assess the effects of the new fuels on the engine process, simulation models are being developed that reproduce the chemical and physical properties of these fuels. In this paper, the fuel DMC+ is examined. DMC+ (a mixture of dimethyl carbonate (DMC) and methyl formate (MeFo) mainly, characterized by the lack of C-C Bonds and high oxygen content) offers advantages with regard to evaporation heat, demand of oxygen and knock resistance. Furthermore, its combustion is almost particle free. With the aid of modern 0D/1D simulation methods, an assessment of the potential of DMC+ can be made. It is shown that the simulative conversion of a state-of-the-art gasoline engine to DMC+ fuel offers advantages in terms of efficiency in many operating points even if the engine design is not altered. This is mainly due to the higher knock resistance and the lower temperatures in the intake stroke resulting from the higher amount of evaporated fuel. For a fixed amount of fuel energy, a lower air mass flow rate is needed, making the fuel particularly interesting for down-sizing concepts. Therefore, the engine design is adapted for the new fuel to take full advantage of the fluid properties. In a first step, the adaptions include the compression ratio, the engine displacement and the turbocharger matching. A considerable efficiency gain in the whole operating range can be demonstrated, making DMC+ a highly promising prospective for future SI engines.
Wagner, Cornelius, Grill, Michael, Keskin, Mahir-Tim, Bargende, Michael, Cai, Liming, Pitsch, Heinz
Effect of Fuel and Lubricant on Engine Vibration2020-01-10154/14/2020
Vibration problems in internal combustion engines produce premature wear on the internal components of the engine, which contributes both to reduce the lifespan of the engine itself as well as cause discomfort to the occupants of the vehicle. Thus, since it is impossible to totally eliminate vibrations from engines, it is important to understand the sources of vibration production and control them to acceptable levels. The general objective of this paper is to measure the vibration in the areas that undergo greater efforts due to the processes of combustion and mechanical forces. These areas are the fixed bearings located to the extremes of the crankshaft. The specified objective of this study is to correlate these levels of crankshaft engine vibration relative to the fuel used, ethanol and gasoline, and assess the influence of lubricant oils on the vibration levels as a function of the viscosity of the lubricant. The results demonstrated that the vibration intensity of the engine increases with increasing engine speed and load. In all operating conditions, the ethanol-run engine has higher vibration intensities than the gasoline-run engine. For the same type of fuel, an oil of higher viscosity attenuates the level of vibration of the engine. Measurements show an average increase of 18% of transverse vibration and 12% of longitudinal vibration in the crankshaft of the engine running on ethanol in relation to gasoline with low viscosity lubricant and 14% and 10% with higher viscosity lubricant.
Santana, Claudio Marcio, Mautone, Jose, Gutierrez, Juan, Almeida Junior, Hélder
Experimental Investigation of the Influence of Ignition System Parameters on Combustion in a Rapid Compression-Expansion Machine2020-01-11224/14/2020
Lean burn combustion concepts with high mean effective pressures are being pursued for large gas engines in order to meet future stringent emission limits while maintaining high engine efficiencies. Since severe boundary conditions for the ignition process are encountered with these combustion concepts, the processes of spark ignition and flame initiation are important topics of applied research, which aims to avoid misfiring and to keep cycle-to-cycle combustion variability within reasonable limits. This paper focuses on the fundamental investigation of early flame kernel development using different ignition system settings. The investigations are carried out on a rapid compression-expansion machine in which the spark ignition process can be observed under engine-like pressure and excess air ratio conditions while low flow velocities are maintained. The schlieren setup for high-speed optical investigations of the area of the spark plug electrodes is described and a suitable post-processing routine is introduced. The influence of different spark current durations on early flame kernel formation is investigated using a modulated capacitive discharge ignition (MCDI) system. The outcomes reveal that a short spark current duration results in a slower increase and higher standard deviation of the flame area during the early phase of combustion. Moreover, stable flame initiation appears to require a minimum spark current duration. The methodology introduced in this paper will be applied in detailed investigations of other spark plug geometries and ignition settings in order to shed more light on the ignition of lean mixtures.
Kiesling, Constantin, Pirker, Gerhard, Tilz, Anton, Oppl, Thomas, Nickl, Andreas, Wimmer, Andreas, Meyer, Georg
Optical Diagnostics of Isooctane and n-Heptane Isobaric Combustion2020-01-11264/14/2020
Isobaric combustion has demonstrated a great potential to reach high thermodynamic efficiency in the advanced Double Compression Expansion Engine (DCEE) concept. It appears as one of few viable choices for applications with high-pressure combustion. At these conditions, releasing heat at a constant pressure minimizes the peak in-cylinder pressure and, hence, mitigates excessive mechanical stress on the engine. This study focuses on the effect of fuels on the multiple-injection isobaric combustion. A single-cylinder heavy-duty engine was utilized to test and compare the isobaric combustion with pure isooctane and n-heptane fuels. The engine was equipped with an optical piston to allow a bottom-view of the combustion chamber. The interactions of multiple injections and the combustion behavior were studied using high-speed acquisition of chemiluminescence. The examined isobaric cases have a peak pressure of 70 bar. For cases with high soot luminosity, a short band-pass filter was used to avoid image saturation. Fuels with short ignition delay time such as n-heptane are usually used for isobaric applications as they offer good controllability of injections. However, the study herein demonstrates that isobaric combustion can be achieved even with high octane number fuels such as isooctane. The dwell time between injections is much larger for isooctane, which allows enhanced mixing of the fuel jets with air and thus a partially premixed combustion behavior. The high-speed imaging demonstrated evidence of flame extinguishing during the sequential injection of n-heptane. This contributes to the staging of the heat release rate.
Al Ramadan, Abdullah S., Nyrenstedt, Gustav, Ben Houidi, Moez, Johansson, Bengt
Investigation of the Impacts of Spark Plug Orientation on Combustion Stability under Lean SI Operation2020-01-11214/14/2020
The increasingly stringent restrictions on vehicle emissions and fuel consumption are driving the development of gasoline engines towards lean combustion. Increasing ignition energy has been considered an effective way to achieve lean operation conditions. To further improve the lean limit of engine combustion, the influence of the spark plug orientation on the combustion stability under lean operation should be explored. In this investigation, the original machine spark plug orientation, 90 degrees clockwise rotation, and 180 degrees clockwise rotation are studied to analyze the impact of spark plug orientation. The combustion experiment was carried out under the condition of low excess air ratio of the original machine and high excess air ratio with a 450 mA high energy ignition. It is found that changing the orientation of the spark plug had little effect on combustion at low excess air ratio; however, under high excess air ratio (ultra-lean operation), spark plug orientation had a great influence on combustion stability. The combustion stability can be significantly improved when the spark plug orientation is vertical to the intake direction. What’s more, we found that when the engine speed was low as 1000rpm, the effects of the spark plug orientation were not very clear. However, when the engine speed increased to 2000rpm, the lean operation limit can be improved from an excess air ratio of 1.78 to 1.96 by adjusting the orientation of the spark plug.
Gu, Qifan, Xu, Min, Ye, Chang, Hung, David, Li, Xuesong
A Novel Design of Engine Misfire Detection System Suitable for Small Capacity S.I. Engine for Two Wheeled Vehicle2020-01-02674/14/2020
As per the OBD II regulations, it is essential to detect and monitor the misfire event in an I.C. engine. Misfiring of an I.C. engine affects the quality of combustion and degrades the performance of catalyst convertor which can lead to an increase of emissions. Misfire event can be categorized as partial or complete, based on amount of combustion occurred during that particular engine cycle. Most of the production engine for non-two wheeler vehicle identifies misfire by monitoring angular acceleration of the engine crank-shaft. However, single cylinder engine with lower capacity (less than 300 cubic centimeter) provides challenges to identify misfire due to low mechanical inertia of the I.C. engine using the same approach. The problem of misfire identification for this category of I.C. engine turn out to be more challenging due to presence of various load disturbances on the powertrain. Ion current sensing is one of the alternate method to detect misfire, which received good attention during the last decade of the previous century. When the air-fuel mixture ignites inside the I.C. engine cylinder, air particles get ionize. By applying a suitable high-voltage on spark plug, it is possible to measure the ion current as the amount of ion current reflects the level of ionization of air fuel mixture. The ion current measurement system presented in this paper is implemented in a production vehicle ignition system for two wheeled vehicles. The vehicle ignition system is unique due to the shorted terminals of high & low voltage sides. Due to the shorted primary and secondary connection, it is challenging to implement ion current measurement system using available research work. The proposed novel design of ion current measurement system accommodates the above constraint. The ion current signal is captured during normal combustion event as well as by creating misfire in the combustion. There are significant changes observed in the ion current signal with and without misfire. The information extracted from the ion current signal is utilized to detect the misfire. The proposed design is analyzed with suitable 1D theoretical model of the ignition system.
Bagade, Monika Jayprakash, Das, Himadri Bhushan, Raveendranath Sr, Arjun, Jabez Dhinagar, S
Studying Ignition Delay Time of Lubricant Oil Mixed with Alcohols, Water and Toluene in IQT and CVCC2020-01-14224/14/2020
The auto-ignition of liquid fuel and lubricant oil droplets is considered as one of the possible sources of pre-ignition. Researchers are continually finding new ways to form advanced lubricant oil by changing its composition and varying different oil additives to prevent the occurrence of this event. This study investigates additives for lubricants to suppress its auto-ignition tendency. Three sets of mixtures were prepared. The first set of mixtures were prepared by adding different alcohols namely ethanol, and methanol to the commercial lubricant oil (SAE 15W-40) in ratio of 1 - 5 % by vol The second set of mixtures were prepared by mixing SAE 15W-40 with aforementioned alcohols (1 % vol.) and H2O (1 % vol.). Lastly, the third set of mixtures were prepared by adding toluene to SAE 15W-40 in (1 % - 5% by vol.). Two experimental setups were used in the current work. An Ignition Quality Tester (IQT) was used to investigate the mixtures’ ignition delay time (IDT) following standard ASTM D6890 procedure, and a larger constant volume combustion chamber (CVCC) was used to investigate the combustion characteristics of a suspended single oil droplet. In the CVCC chamber, the droplet was ignited in an atmosphere of air at 300 °C and pressure ranging from 4 bar - 22 bar at 6 bar interval pressures. IDT of lubricant oil was considered as the base IDT, which was compared to those of other mixtures. Addition of alcohols and water in lubricant oil showed a significant increase in IDT compared to toluene addition. On the contrary, the addition of toluene resulted in a decrease in IDT. Among the alcohols, methanol addition showed higher IDT than ethanol addition. Alcohols increased the IDT effectively only beyond the addition of > 4 % by vol.
Maharjan, Sumit, Elbaz, Ayman, Mitsudharmadi, Hatsari, Roberts, William
Ignition System Nomenclature and TerminologyJ139_202002 (Current)2/10/2020
To provide standard terminology and definitions with regard to ignition systems for spark-ignited internal combustion engines.
Ignition Standards Committee
A Study of Ignition Method for Gas Heat Pump Engine Using Low Temperature Plasma2019-32-06221/24/2020
Low temperature plasma ignition has been proposed as a new ignition technique as it has features of good wear resistance, low energy release and combustion enhancement. In the authors’ previous study, lean burn limit could be extended by low temperature plasma ignition while a voltage drop during discharge, leading to the transition to arc discharge, was found. In this study, the structure of plug and power supply’s performance with steep voltage rising with time, dV/dt, are examined to investigate the effects on combustion performance. As a result, comparing three power sources of conventional, IES and steep dV/dt, steep dV/dt showed small cycle-to-cycle variation and shorter combustion period, leading to higher peak value of the rate of heat release and better indicated thermal efficiency by relatively 6% and 4% compared to CIC and IES, respectively.
Moriyoshi, Yasuo, Matsumoto, Osamu, Kuboyama, Tatsuya, Tsukamoto, Takahiro, Kinuzawa, Yoshiyuki, Maeshima, Hideaki
Analysis of Cycle-to-Cycle Variation in a Port Injection Gasoline Engine by Simultaneous Measurement of Time Resolved PIV and PLIF2019-32-05521/24/2020
Cycle-to-cycle variation (CCV) of combustion in low load operation is a factor that may cause various problems in engine operation. Variable valve timing and variable ignition timing are commonly used as a means to reduce this variation. However, due to mountability and cost constraints, these methods are not feasible for use in motorcycle engines. Therefore, development of an engine with minimal CCV without utilizing complicated mechanisms or electronic control is required. CCV of combustion may be caused by fluctuations in in-cylinder flow, air-fuel mixture, temperature, residual gas and ignition energy. In this study, the relationship between CCV of combustion, in-cylinder flow fluctuation and air-fuel mixture fluctuation was the primary focus. In order to evaluate in-cylinder flow fluctuation, Time Resolved Particle Image Velocimetry (TR-PIV) technique was utilized. In addition, Planar Laser Induced Fluorescence (PLIF) technique was used to measure spatial distribution of the mixture. These two visualization techniques were used together to measure continuous combustion cycles. The fluctuation of net IMEP can be explained by the fluctuation of Turbulence Kinetic Energy (TKE) and fuel concentration. In most cycles, net IMEP was correlated with TKE. In the remaining cycles, net IMEP was correlated with fuel concentration. The contribution of each factor towards net IMEP is to be discussed. It has been also confirmed that TKE fluctuation is caused by fluctuation in the tumble vortex structure, as shown in the authors' previous study [2] [13].
HARAMIISHI, Santa, WATANABE, Takahiro, IIDA, Minoru, HOKIMOTO, Satoshi, KUBOYAMA, Tatsuya, MORIYOSHI, Yasuo
Temperature Calculation Methodology of Pre Chamber With Homogeneous Charge2019-36-02031/13/2020
The methodology for temperature calculations of homogeneous prechamber must be analyzed from a one-dimensional analytical model so that it is possible to determine the temperature profiles during the filling and emptying of the gases, so that it can avoid abnormalities such as increase of Forces, deformation / breaking, performance limitations, increased probability of detonation, increase of NOX and increase in the probability of pre-ignition. The equations of conservation of energy and of the state of gases are used to base the calculations, following the hypothesis that the flow is transient, comprehensible and one-dimensional; The fluid in the control volume is in the gaseous state and the fuel is already injected into the gas phase following the ideal gas equation. A homogeneous mixture is considered to generate a poor mixture in the pre-chamber.
MACHADO, L.F.G, FERREIRA, TIAGO S., RODRIGUES FILHO, F. A., MOREIRA, T. A. A.
Ignition of Individual Droplets in a Reactive Fuel/Air Mixture behind Reflected Shock Waves2019-01-216212/19/2019
Multiphase-induced ignition is frequently discussed as a trigger for early ignition in internal combustion engines. In this context, we investigated the ignition process of single lubricant-oil droplets and their interaction with the bulk air/fuel mixture in a high-pressure shock tube, mimicking oil-fuel interaction in turbocharged internal combustion engines at the end of the compression stroke. A fast micro-dispensing injector released single fuel or lubricant oil droplets with a diameter of 200±50 µm into shock-heated fuel/air mixtures consisting of PRF95 and synthetic air. The injector was flush-mounted in the sidewall of the shock tube. The droplets were released into the gas after the passage of the reflected shock waves at post-shock conditions of 2 MPa and 750-950 K. With a high-frame-rate color camera, the entire evolution of droplet injection and ignition was traced in space and time through a large sapphire window in the endwall of the shock tube. A high-repetition-rate laser at 532 nm was used to illuminate the droplets. The light scattered by the droplets was detected in the green channel of the camera, whereas ignition and soot luminosity were detected in the blue and red channel, respectively. From the camera images the time for the appearance of first detected kernel related to local ignition (originating from either droplet or gaseous ignition) was determined. Additionally, the volume ignition that proceeds after an ignition delay time was determined from the OH* emission time-trace from a photomultiplier tube. It was found that the oil-droplet injection had an influence on the local ignition whereas the ignition delay time was reduced in the low temperature range only.
Niegemann, P., Fikri, M., Kaiser, S. A., Schulz, C.
Using RON Synergistic Effects to Formulate Fuels for Better Fuel Economy and Lower CO2 Emissions2019-01-215512/19/2019
The knock resistance of gasoline is a key factor to decrease the specific fuel consumption and CO2 emissions of modern turbocharged spark ignition engines. For this purpose, high RON and octane sensitivity (S) are needed. This study shows a relevant synergistic effect on RON and S when formulating a fuel with isooctane, cyclopentane and aromatics, the mixtures reaching RON levels well beyond the ones of individual components. The same is observed when measuring their knock resistance on a boosted single cylinder engine. The mixtures were also characterized on a rapid compression machine at 700 K and 850 K, a shock tube at 1000 K, an instrumented and an adapted CFR engine. The components responsible for the synergistic effects are thus identified. Furthermore, the correlations plotted between these experiments results disclose our current understanding on the origin of these synergistic effects. This study concludes that this synergistic effect encourages formulating highly paraffinic fuels for lower specific fuel consumptions and CO2 emissions. Thus, paraffins are still relevant compounds to formulate highly efficient gasolines, despite their low octane sensitivity when individually considered. Furthermore, the CFR engine is still the best known device to anticipate synergistic effects in gasoline's knock resistance, through the Octane Index (OI = RON - K.S). A sensitivity study on the “K value” of the octane index shows that octane sensitivity mainly drives the gasoline performance for the low-sensitivity fuels while RON also drives it for the high-sensitivity ones.
Dauphin, Roland, Obiols, Jerome, Serrano, David, Fenard, Yann, Comandini, Andrea, Starck, Laurie, Vanhove, Guillaume, Chaumeix, Nabiha
Influence of ethanol blending on knocking in a lean burn SI engine2019-01-215212/19/2019
Lean burn is one method for improving thermal efficiency in spark ignition (SI) engines. Suppression of knocking provides higher thermal efficiency, and ethanol blending is considered an effective way to suppress knocking due to its high octane and high latent heat of evaporation. We investigate the effect of ethanol blending on knocking in an SI engine under lean operating conditions. The Livengood-Wu (LW) integral was performed based on ignition delay duration estimated from a zero-dimensional detailed chemical reaction calculation with pressure and temperature histories. Knocking was suppressed and thermal efficiency increased with ethanol-gasoline blending fuel, even at 0.5 equivalence ratio. Decrease in unburned gas temperature by latent heat of evaporation had a comparable influence on knocking suppression, which was supported by LW integral analysis.
Kaneko, Kazuki, Yasutake, Yuki, Yokomori, Takeshi, Iida, Norimasa
SI Combustion Characteristics of Cyclopentane - Detailed Kinetic Mechanism2019-01-230512/19/2019
Cyclopentane (C5H10) has been reported to exhibit large octane sensitivity (RON − MON) = 17. During the course of research for sustainable liquid fuels, fundamental SI combustion characteristics of cyclopentane have been investigated using the kinetic mechanism which has been newly developed based on the quantum chemical calculations for essential chemical species and reactions. It was found that the intramolecular isomerization reaction via six-membered ring transition states are significantly hindered by the cyclic carbon skeleton. As a result, the predicted ignition delay times at low temperature are longer than those for the acyclic hydrocarbons. The effect on the laminar flame propagation speed was found to be small.
Miyoshi, Akira
Numerical Optimization of Compression Ratio for a PPC Engine running on Methanol2019-01-216812/19/2019
Partially premixed combustion (PPC) has shown to produce high gross indicated efficiencies while yielding lower pollutant emissions, such as oxides of nitrogen and soot, than conventional diesel combustion. Gasoline fuels with a research octane number (RON) of 60-70 have been proposed as optimal for PPC as they balance the trade-off between ensuring good combustion stability at low engine loads and avoiding excessive peak pressure rise rates at high loads. However, measures have to be taken when optimizing the engine operating parameters to avoid soot emissions. In contrast, methanol has a much lower propensity for soot formation. However, due to a higher RON of methanol the required intake temperature is higher for the same engine compression ratio to ensure auto-ignition at an appropriate timing. Increasing the compression ratio allows a lower intake temperature and improves combustion stability as well as engine brake efficiency. Nevertheless, a higher compression ratio generally increases in-cylinder heat losses and peak pressure. These effects were investigated in a simulation study, which combined 0-D and 1-D models, of a multi-cylinder heavy-duty Scania D13 engine operated in PPC mode and running on methanol. Engine experiments from a single-cylinder engine at different compression ratios were used to validate the simulation models. The optimal compression ratio from a brake efficiency perspective was found for four operating conditions from the 12 mode non-idle European stationary cycle supplemental emissions test points. This compression ratio was then used for optimizing key engine parameters. The results showed that a 21.6:1 compression ratio was optimal instead of the original 17.3:1 compression ratio. Especially at lower engine loads, a significant increase in brake efficiency was found. The main reason was a lower intake temperature which increased the average ratio of specific heats and allowed for a lower boost pressure.
Svensson, Erik, Verhelst, Sebastian
Development of a Physically/Chemically Based Approach for 2-Stage Ignition Delay Calculation in Medium Speed Dual-Fuel Engines2019-24-00689/9/2019
This paper presents a newly developed 2-stage ignition delay model for pilot ignited medium speed dual-fuel (DF) engines. This provides the first major step towards a new combustion model for the prediction of the DF combustion in the context of 0D/1D simulation. The combustion models known from literature are based on empirical models of a steady jet. Here in most cases the package model of Hiroyasu is used. Because in a DF engine the injection timing of the diesel fuel is very early and the injection ends before ignition, the spray behavior differs from that of a steady jet. Especially the end-of-injection transients lead to stronger entrainment and therefore affect the ignition delay. In addition, the presence of natural gas in the cylinder extends the ignition delay at the chemical level. In this paper the 1D transient spray model of Musculus and Kattke is used to describe the spray behavior. The spray model is extended with a mixing controlled evaporation model to derive the temperature distribution inside the spray. A 2-stage ignition delay model with low temperature heat release is developed based on extensive reaction kinetic simulations with an extended n-heptane mechanism. A comparison with measurements of a single cylinder research engine shows good agreement of the model, whereby no parameter had to be adjusted, but could be taken from the literature. Moreover, a comparison of 1-stage and 2-stage ignition delay calculation shows the benefit of the outlined approach.
Frerichs, Jelto, Eilts, Peter
Computational Chemistry Consortium: Surrogate Fuel Mechanism Development, Pollutants Sub-Mechanisms and Components Library2019-24-00209/9/2019
The Computational Chemistry Consortium (C3) is dedicated to leading the advancement of combustion and emissions modeling. The C3 cluster combines the expertise of different groups involved in combustion research aiming to refine existing chemistry models and to develop more efficient tools for the generation of surrogate and multi-fuel mechanisms, and suitable mechanisms for CFD applications. In addition to the development of more accurate kinetic models for different components of interest in real fuel surrogates and for pollutants formation (NOx, PAH, soot), the core activity of C3 is to develop a tool capable of merging high-fidelity kinetics from different partners, resulting in a high-fidelity model for a specific application. A core mechanism forms the basis of a gasoline surrogate model containing larger components including n-heptane, iso-octane, n-dodecane, toluene and other larger hydrocarbons. Moreover, poly-aromatic hydrocarbon modules are developed in addition to a NOx formation module. This work describes the challenges and approach for merging the different modules, discussing and analyzing the results from the model, obtained by comparing with experimental targets typically used for model validation (i.e. ignition delay times, laminar flame speed, species measurements in ideal reactors and flames). The case study here focuses on a gasoline TPRF surrogate, obtained by merging the kinetic modules of the disparate chemistry including hydrocarbon (alkene, alkane, aromatic and PAH species) and NOx chemistry. In addition, this work also describes the effort towards using these mechanisms for practical CFD simulations.
Pelucchi, Matteo, Cai, Liming, Pejpichestakul, Warumporn, Tripathi, Rupali, Wagnon, Scott, Zhang, Kuiwen, Raju, Mandhapati, Mehl, Marco, Faravelli, Tiziano, Pitz, William, Pitsch, Heinz, Curran, Henry, Senecal, Peter Kelly
Evaluation of Water and EGR Effects on Combustion Characteristics of GDI Engines Using a Chemical Kinetics Approach2019-24-00199/9/2019
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently improved with the use of water vapor obtained via direct or indirect injection. The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions. The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor. To overcome the limitations of the experimentation is possible to predict the value of the ignition delay using numerical models based on chemical kinetics theory. The increased performance of computing systems makes possible the use of mechanism with a high number of species and reactions without an excessive temporal cost. In this work a methodology, based on a non-reduced kinetic scheme and an open-source solver (Cantera), is applied to the determination of the laminar flame speed and the ignition delay for a commercial gasoline surrogate, under the typical conditions of GDI engines with the addition of the effects of dilution with water and EGR.
Cazzoli, Giulio, Bianchi, Gian Marco, Falfari, Stefania, Ricci, Matteo, Forte, Claudio
Effects of In-Cylinder Flow Structures on Soot Formation and Oxidation in a Swirl-Supported Light-Duty Diesel Engine2019-24-00099/9/2019
In this paper, computation fluid dynamics (CFD) simulations are performed to describe the effect of in-cylinder flow structures on the formation and oxidation of soot in a swirl-supported light-duty diesel engine. The focus of the paper is on the effect of swirl motion and injection pressure on late cycle soot oxidation. The structure of the flow at different swirl numbers is studied to investigate the effect of varying swirl number on the coherent flow structures. These coherent flow structures are studied to understand the mechanism that leads to efficient soot oxidation in late cycle. Effect of varying injection pressure at different swirl numbers and the interaction between spray and swirl motions are discussed. The complexity of diesel combustion, especially when soot and other emissions are of interest, requires using a detailed chemical mechanism to have a correct estimation of temperature and species distribution. In this work, Representative Interactive Flamelets (RIF) method is employed to describe the chemical reactions, ignition, flame propagation and emissions in the engine. The CFD simulations are validated using experimental measurement of light-duty diesel engine at two different loads. A good agreement is achieved between the model results and the pressure, heat release rates and emissions from the experiment. These cases are considered as the base-line for the parameter study cases.
Fatehi, Hesameddin, Persson, Håkan, Lucchini, Tommaso, Ljungqvist, Mattias, Andersson, Oivind
Piston Bowl Geometry Effects on Combustion Development in a High-Speed Light-Duty Diesel Engine2019-24-01679/9/2019
In this work we studied the effects of piston bowl design on combustion in a small-bore direct-injection diesel engine. Two bowl designs were compared: a conventional, omega-shaped bowl and a stepped-lip piston bowl. Experiments were carried out in the Sandia single-cylinder optical engine facility, with a medium-load, mild-boosted operating condition featuring a pilot+main injection strategy. CFD simulations were carried out with the FRESCO platform featuring full-geometric body-fitted mesh modeling of the engine and were validated against measured in-cylinder performance as well as soot natural luminosity images. Differences in combustion development were studied using the simulation results, and sensitivities to in-cylinder flow field (swirl ratio) and injection rate parameters were also analyzed. In-cylinder mixture formation analysis showed that ignition of the pilot injection mixture develops nearly as it would in a homogeneous adiabatic reactor, being mostly advected, not mixed, by the bowl’s swirling motion, while its timing is influenced by the local flow field. Details of the local in-cylinder flow are also more crucial than injection parameters in igniting the main injection’s premixed fuel, as it determines the relative overlap with the high-temperature pilot ignited mixture. Bowl geometry effects drive diffusive and late-cycle combustion, as structural differences of the main injection spray flames appear due to the different impact geometries at the piston bowl rim. However, these do not affect wall heat transfer significantly: it is dominated by the piston surface area. Better air utilization with the stepped-lip geometry, thanks to greater azimuthal spreading at the rim, a strong recirculating vortex in the squish region, and better mixing in the bowl, is responsible for better late-cycle combustion efficiency and lower soot emissions.
Perini, Federico, Busch, Stephen, Zha, Kan, Reitz, Rolf, Kurtz, Eric
Large Eddy Simulation of an Ignition Front in a Heavy Duty Partially Premixed Combustion Engine2019-24-00109/9/2019
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane). Two injection timings are investigated; start of injection at -17 CAD aTDC and -30 CAD aTDC. One-equation transported turbulence sub-grid closure is used for the unresolved momentum and scalar fluxes and the fuel spray is modelled using a Lagrangian particle tracking (LPT) approach. Initial flow conditions (prior to intake valve closing) are generated using a scale forcing method with a prescribed large-scale swirl mean flow motion. Fuel reactivity is modeled using finite rate chemistry based on a skeletal chemical kinetic mechanism (44 species, 140 reactions). The results are compared with optical engine experimental data and satisfactory agreement with the experiments is obtained in terms of the liquid spray length, cylinder pressure trace and ignition location. A majority of the fuel consumption is found to be in ignition fronts where small variations in temperature at low fuel concentrations are observed to cause large stratification in ignition delay time.
Ibron, Christian, Fatehi, Hesameddin, Jangi, Mehdi, Bai, Xue-Song
Compression Ratio and Intake Air Temperature Effect on the Fuel Flexibility of Compression Ignition Engine2019-24-01109/9/2019
The effect of compression ratio (CR) and intake air temperature on the combustion characteristics of fuels with different octane ratings were investigated on a single-cylinder heavy duty engine. The study focused on Primary Reference Fuels (PRFs) and commercial grade diesel with octane numbers ranging from 0 to 100. The engine was configured at a CR of 11.5:1, which is lower than typical heavy-duty compression ignition CI engines. This aims to compare the fuels’ burning regime with recently reported measurements at CR17:1. Experiments were performed at different intake air temperatures of 20 to 80 °C and net indicated mean effective pressure (IMEPNet) of 5 to 20 bar. The injection rates have been characterized to determine the hydraulic delay of the injector and thus define the actual ignition delay time. At low loads, diesel-like fuels were found to burn in partially premixed combustion (PPC) mode whereas high octane fuels did not ignite. At high loads, fuels combustion becomes diffusion driven regardless of their RON or MON values. The effect of intake air temperature on the combustion characteristics depended on the combination of the octane ratings and the engine load. At high loads, fuels with low octane numbers were insensitive to the change of the intake air temperature. The ignition delay time was short enough to maintain a diffusion driven combustion. At lower loads, it is more challenging to reach conditions where the combustion characteristics are invariant regardless of the fuel’s RON and MON values (Fuel Flexible). At the low tested compression ratio of 11.5:1, the extent of fuel flexibility is limited to only high loads (IMEPNet = 20 bar) whereas it is extended to intermediate loads (IMEPNet = 10 and 15 bar) at CR17:1.
AlRamadan, Abdullah S., Ben Houidi, Moez, Aljohani, Bassam S. E., Eid, Hassan, Johansson, Bengt
Fuel-Lubricant Interactions on the Propensity for Stochastic Pre-Ignition2019-24-01039/9/2019
This work explores the impact of the interaction of lubricant and fuel properties on the propensity for stochastic pre-ignition (SPI). Findings are based on statistically significant changes in SPI tendency and magnitude, as determined by measurements of cylinder pressure. Specifically, lubricant detergents, lubricant volatility, fuel volatility, fuel chemical composition, fuel-wall impingement, and engine load were varied to study the physical and chemical effects of fuel-lubricant interactions on SPI tendency. The work illustrates that at low loads, with fuels susceptible to SPI events, lubricant detergent package effects on SPI were non-significant. However, with changes to fuel distillation, fuel-wall impingement, and most importantly engine load, lubricant detergent effects could be observed even at reduced loads This suggests that there is a thermal effect associated with the higher load operation. It was hypothesized that the thermal effect was associated with lube oil nitrogenation. To test this theory, nitromethane (CH3NO2) was blended at 6.5% by volume CH3NO2 resulted in significant sensitivity to lubricant additive package effect on SPI, even at reduced loads where no lubricant sensitivity was observed without the addition of CH3NO2. The combined results highlight the interplay of fuel-lubricant interaction on SPI events, but more importantly suggest that there is the potential of a chemical interaction unique to high-load engine operation that results in reactive chemical processes, such as nitration, where lubricant chemistry becomes an active pathway for SPI activity.
Splitter, Derek, Kaul, Brian, Szybist, James, Speed, Lake, Zigler, Bradley, Luecke, Jon
Machine Learning Algorithm for the Prediction of Idle Combustion Uniformity2019-01-15516/5/2019
Combustion stability is a key contributor to engine shake at idle speed and can impact the overall perception of vehicle quality. The sub-firing harmonics of the combustion torque are used as a metric to assess idle shake and are, typically, measured at different levels of engine break mean effective pressure (BMEP). Due to the nature of the combustion phenomena at idle, it is clear that predicting the cycle-to-cycle and cylinder-to-cylinder combustion pressure variations, required to assess the combustion uniformity, cannot be achieved with the state of the art simulation technology. Inspired by the advancement in the field of machine learning and artificial intelligence and by the availability of a large amount of measured combustion test data, this paper explores the performance of various machine learning algorithms in predicting the idle combustion uniformity. The algorithms that are explored include Neural Network (NN), Support Vector Machine (SVM), Ensembles of Trees (EOT) and Gaussian Process (GP). The variables selected as inputs to these algorithms include BMEP, indicated mean effective pressure (IMEP), pumping mean effective pressure (PMEP), spark timing, crank angle at 10% fuel burn (Burn0010), crank angle at 90% fuel burn (Burn1090), and crankshaft timing at 50% fuel burn (CA50). The algorithms output the amplitude of 0.5 order, 1.0 order and the 1.5 order harmonics of the combustion torque. The results presented in this paper show the superiority of the Gaussian Process algorithm in predicting the combustion torque harmonics. Using this algorithm, this paper further investigates the sensitivity of the engine torque harmonics to the parameters, used as inputs to the algorithm, in order to establish potential design guidelines for upfront combustion system development.
Li, Xiaoqi, Zouani, Abdelkrim
Comparison of Kinetic Mechanisms for Numerical Simulation of Methanol Combustion in DICI Heavy-Duty Engine2019-01-02084/2/2019
The combustion process in a homogeneous charge compression ignition (HCCI) engine is mainly governed by ignition wave propagation. The in-cylinder pressure, heat release rate, and the emission characteristics are thus largely driven by the chemical kinetics of the fuel. As a result, CFD simulation of such combustion process is very sensitive to the employed reaction mechanism, which model the real chemical kinetics of the fuel. In order to perform engine simulation with a range of operating conditions and cylinder-piston geometry for the design and optimization purpose, it is essential to have a chemical kinetic mechanism that is both accurate and computational inexpensive. In this paper, we report on the evaluation of several chemical kinetic mechanisms for methanol combustion, including large mechanisms and skeletal/reduced mechanisms. These mechanisms are evaluated in terms of homogeneous ignition delay time, laminar flame speed, and multi-phase simulations of HCCI heavy-duty engine. The results are compared with experimental data and evaluated in terms of the accuracy and computational cost. It was found that scattering of ignition delay time predicted from different chemical kinetic mechanisms reported in the literature under homogeneous mixture ignition conditions give rise to a high sensitivity of the engine in-cylinder pressure prediction to the selected mechanism.
Pucilowski, Mateusz, Li, Rui, Xu, Shijie, Li, Changle, Qin, Fei, Tuner, Martin, Bai, Xue-Song, Konnov, Alexander A.
An Experimental Study on the Factors Affecting Ethanol Ignition Delay Times in a Rapid Compression Machine2019-01-05764/2/2019
Ignition delay, using a rapid compression machine (RCM), is defined as the time period between the end of compression and the maximum rate of pressure rise due to combustion, at a given compressed condition of temperature and pressure. The same compressed conditions can be reached by a variety of combinations of compression ratio, initial temperature, initial pressure, diluent gas composition, etc. It has been assumed that the value of ignition delay, for a given fuel and at a given set of compressed conditions, would be the same, irrespective of the variety of the above-mentioned combinations that were used to achieve the compressed conditions. In this study, a range of initial conditions and compression ratios are studied to determine their effect on ignition delay time and to show how ignition delay time can differ even at the same compressed conditions. Experiments were carried out at two compression ratio conditions (11.7 and 17.1) for stoichiometric ethanol-air mixtures over a temperature range of 800 K - 875 K at 20 bar pressure. With the help of optical images, in addition to the pressure traces, the combustion characteristics for the abovementioned conditions were analyzed and compared. Another factor that was determined to be important in consistent ignition delay measurements was the cleanliness of the combustion chamber and some discussion on the suggested protocol is included.
Wadkar, Chaitanya, Chinnathambi, Prasanna, Toulson, Elisa
Optical Experiments on Strong Knocking Combustion in Rapid Compression Machines with Different Fuels2019-01-11424/2/2019
Nowadays the strong knocking combustion involving destructive pressure wave or shock wave has become the main bottleneck for highly boosted engines when pursuing high thermal efficiency. However, its fundamental mechanism is still not fully understood. In this study, synchronization measurements through simultaneous pressure acquisition and high-speed direct photography were performed to comparatively investigate the strong knocking combustion of iso-octane and propane in a rapid compression machine with flat piston design. The pressure characteristics and visualized images of autoignition and reaction wave propagation were compared, and the correlations between thermodynamic trajectories and mixture reactivity progress were analyzed. The results show that iso-octane behaves a greater propensity to strong knocking combustion than propane at similar target pressures. Visualized images show that strong knocking combustion results from secondary autoignition and subsequent supersonic reaction wave propagation. Further analysis on thermodynamic trajectories shows that the secondary autoignition may closely correlate with the negative temperature coefficient behavior controlled by low-temperature chemistry.
Hu, Zhen, Pan, Jaying, Wei, Haiqiao, Ma, Guobin, Li, Tao, Liu, Changwen
Analysis of the Impact of Production Lubricant Composition and Fuel Dilution on Stochastic Pre-Ignition in Turbocharged, Direct-Injection Gasoline Engines2019-01-02564/2/2019
The occurrence of abnormal combustion events leading to high peak pressures and severe knock can be considered to be one of the main challenges for modern turbocharged, direct-injected gasoline engines. These abnormal combustion events have been referred to as Stochastic Pre-Ignition (SPI) or Low-Speed Pre-Ignition (LSPI). The events are characterized by an undesired, early start of combustion of the cylinder charge which occurs before or in parallel to the intended flame kernel development from the spark plug. Early SPI events can subsequently lead to violent auto-ignitions that are often referred to as Mega- or Super-Knock. These heavy knock events lead to strong pressure oscillations which can destroy production engines within a few occurrences. SPI occurs mainly at low engine speed and high engine load, thus limiting the engine operating area that is in particular important to achieve good drivability in downsized engines. Recent experimental SPI studies have linked this phenomenon strongly to engine oils. While numerous studies have been published using target blended oils, the presented study focuses on the impact of lubricants with production level formulations on SPI event occurrence. The utilized test engine is a production, turbocharged, direct-injection gasoline (GTDI) engine with a homogeneous common rail high pressure injection system and side mounted multi-hole injectors. All experiments were conducted on a steady state engine test bench with intake air, coolant, oil and fuel conditioning. The engine was equipped with a prototype engine controller that allowed negating the influence of vehicle, knock mitigation or balancing algorithms on combustion properties. 11 market relevant production engine oils for sale in the US in 2017 were analyzed regarding their composition using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). All 11 oils were then tested for their impact on SPI occurrence, severity and characteristics. The experimental results were subsequently correlated to the oil analysis results. In addition, one oil was analyzed regarding the impact of fuel dilution and ageing on SPI occurrence using the same test setup.
Haenel, Patrick, de Bruijn, Rob, Tomazic, Dean, Kleeberg, Henning
Study of Flash Boiling Spray Combustion in a Spark Ignition Direct Injection Optical Engine Using Digital Image Processing Diagnostics2019-01-02524/2/2019
Flash boiling spray has been proven to be a useful method in providing finer fuel droplet and stronger evaporation in favor of creating a homogeneous fuel-air mixture. Combustion characteristics of flash boiling spray are thus valuable to be investigated systematically for aiding the development of efficient internal combustion system. An experimental study of flash boiling spray combustion in a SIDI optical engine under early injection has been conducted. The fuel, Iso-octane, was used across all tests. Three fuel spray conditions experimented in the study: normal liquid, transitional flash boiling and flare flash boiling sprays, within each case that Pa/Ps ratio was set in (>1), (0.3~1), and (<0.3) respectively. A small quartz insert on the piston enables optical access for observing combustion process; non-intrusive measurements on flame radicals has been carried out using a high-speed color camera. With the use of digital image processing and color analysis, the imaging system was turned into an abstract multi-spectral system to determine the characteristics of flame emission. In addition, the near infrared region was capable of being discriminated from the rest regions of the flame using HSV color model. The near infrared flame area and diffusion flame region as well as pool fire were found to be reduced, when implementing flash boiling spray under early injection condition. It is found that flash boiling spray contributes the reduction of particulate number (PN) emissions in exhaust gas and makes the improvement of indicated mean effective pressure (IMEP) and cyclic variation, which lead to more efficient combustion in SIDI engine under early injection.
Sun, Zhe, Ma, Zhen, Li, Xuesong, Xu, Min
Impact of CO 2 Dilution on Ignition Delay Times of Iso-Octane at 15% and 30% Dilution Levels in a Rapid Compression Machine2019-01-05694/2/2019
Iso-Octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF) surrogate. Auto ignition of iso-octane was examined using a rapid compression machine (RCM) with iso-octane, air and carbon dioxide (CO2) mixtures. Experiments were conducted over a temperature range of 650K-900K at 20bar and 10 bar compressed conditions for equivalence ratios (Φ =) 0.6, 0.8, 1.0 and 1.3. CO2 dilution by mass was introduced at 0%, 15% and 30% levels with the O2:N2 mole ratio fixed at 1:3.76 emulating the exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines. In this study the direct test chamber (DTC) approach is used for introducing iso-octane directly into the RCM test chamber via a direct injector. The results using this approach are compared with other RCM data available in the literature at undiluted Φ = 1.0 and 20 bar compressed pressure and show good agreement. For a given equivalence ratio, the negative temperature coefficient (NTC) region was fixed irrespective of the dilution levels confirming the fact that CO2 does not participate in the chemistry of the base fuel but rather reduces the reactivity leading to increased ignition delay times. At 30% dilution levels the increase in ignition delay times is more than twice that of the 15% dilution levels for the same compressed conditions and stoichiometry.
Chinnathambi, Prasanna, Wadkar, Chaitanya, Toulson, Elisa
Water Injection Benefits in a 3-Cylinder Downsized SI-Engine2019-01-00341/15/2019
With progressing electrification of automotive powertrains and demands to meet increasingly stringent emission regulations, a combination of an electric motor and downsized turbocharged spark-ignited engine has been recognized as a viable solution. The SI engine must be optimized, and preferentially downsized, to reduce tailpipe CO2 and other emissions. However, drives to increase BMEP (Brake Mean Effective Pressure) and compression ratio/thermal efficiency increase propensities of knocking (auto-ignition of residual unburnt charge before the propagating flame reaches it) in downsized engines. Currently, knock is mitigated by retarding the ignition timing, but this has several limitations. Another option identified in the last decade (following trials of similar technology in aircraft combustion engines) is water injection, which suppresses knocking largely by reducing local in-cylinder mixture temperatures due to its latent heat of vaporization. Addition of adequate water can lead to stoichiometric air/fuel ratio engine operation, and hence both reduction in fuel consumption and full utilization of a three-way catalytic converter (TWC). Further information about effects of various water injection parameters is required. Thus, in this study, a 4-stroke, 1.5 liter, 3-cylinder turbocharged engine with direct fuel injection and port water injection was operated on 91, 95 and 98 RON gasoline fuel to assess effects of water injection on knock mitigation, combustion phasing, required air:fuel ratios and exhaust gas temperature control. Full- and part-load curves obtained with different fuels and water injection strategies are presented and discussed.
Khatri, Jayesh, Denbratt, Ingemar, Dahlander, Petter, Koopmans, Lucien
Reduction of Cyclic Variations by Using Advanced Ignition Systems in a Lean-Burn Stationary Natural Gas Engine Operating at 10 Bar BMEP and 1800 rpm03-12-01-000512/14/2018
In stationary natural gas engines, lean-burn combustion offers higher engine efficiencies with simultaneous compliance with emission regulations. A prominent problem that one encounters with lean operation is cyclic variations. Advanced ignition systems offer a potential solution as they suppress cyclic variations in addition to extending the lean ignition limit. In this article, the performance of three ignition systems-conventional spark ignition (SI), single-point laser ignition (LI), and prechamber equipped laser ignition (PCLI)-in a single-cylinder natural gas engine is presented. First, a thorough discussion regarding the efficacy of several metrics, besides coefficient of variation of indicated mean effective pressure (COV_IMEP), in representing combustion instability is presented. This is followed by a discussion about the performance of the three ignition systems at a single operational condition, that is, same excess air ratio (λ) and ignition timing (IT). Next, these metrics are compared at the most optimal operational points for each ignition system, that is, at points where λ and IT are optimized to achieve highest efficiency. From these observations, it is noted that PCLI achieves the highest increase in engine efficiency, Δη = 2.1% points, and outperforms the other two methods of ignition. A closer look reveals that the coefficient of variation in ignition delay (COV_ID) was negligible, whereas that in coefficient of variation in combustion duration (COV_CD) was significantly lower by 2.2% points. However, the metrics COV_ID and COV_CD are not well correlated with COV_IMEP.
Almansour, Bader, Vasu, Subith, Gupta, Sreenath
Combustion Analysis with Residual Gas as a Design Parameter for Two-Stroke Engines2018-32-004510/30/2018
In a variety of applications, two-stroke engines assert their usage as a propulsion unit, for examples in off-road vehicles, scooters, hand-held power tools and others. The outstanding power to weight ratio is the key advantage for two-stroke engines. Furthermore, two-stroke engines convince with high durability and low maintenance demand. However, an increasing environmental awareness, the protection of health and the shortage of fossil resources are the driving factors to further enhance the internal combustion process of two-stroke engines. The reduction of emissions and fuel consumption with a constant power level is focused on. Developments deal with the optimization of the combustion process itself or the enhancement of the exhaust gas aftertreatment. Especially in very small two-stroke engines an exhaust gas aftertreatment system is rarely applied, due to disadvantages regarding component temperatures and product costs. Beside different parameters, the exhaust gas back pressure mainly influences the residual gas content as well as the gas exchange in two stroke engines. Both are essential for the combustion process quality, which can be determined by values of 50% MFB, COV, glow ignition and knock behavior. Additionally, scavenging losses and the volumetric efficiency vary in dependency of exhaust gas back pressure. The emission level is significantly affected by these values. To gain deeper insights into these engine specific connections, a wide operation range concerning equivalence ratio (rich and lean) as well as ignition timing of a two-stroke engine is analyzed. The aim of research is to declare the limits of the combustion and gas exchange process with respect to the residual gas content. From this, possible optimizations can be derived. To gain knowledge about the combustion specific relations with the focus on residual gas, an approach is presented, which gives an opportunity to estimate the residual gas content inside the combustion chamber for two-stroke engines.
Piecha, Pascal Richard, Jandl, Stephan, Sturm, Stefan, Schmidt, Stephan, Kirchberger, Roland, Schumann, Florian
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
Application of the Newly Developed KLSA Model into Optimizing the Compression Ratio of a Turbocharged SI Engine with Cooled EGR2018-32-003710/30/2018
Owing to the stochastic nature of engine knock, determination of the knock limited spark angle (KLSA) is difficult in engine cycle simulation. Therefore, the state-of-the-art knock modeling is mostly limited to either merely predicting knock onset (i.e. auto-ignition of end gas) or combining a simple unburned mass fraction (UMF) model representative of knock intensity (KI). In this study, a newly developed KLSA model, which takes both predictions of knock onset and intensity into account, is firstly introduced. Multiple variables including the excess air ratio, EGR ratio, cylinder pressure and the end gas temperature are included in the knock onset model. Based on the auto-ignition theory of hot spots in end gas, both the energy density and heat release rate in hot spots are taken into consideration in the KI model. Assuming the lognormal distribution of KI in consecutive cycles, the knock factor based on the likelihood ratio is employed as the criterion for definition of knocking cycles. After validation of the KLSA model with the experimental data, the geometric compression ratio of a boosted port fuel injection spark ignition (SI) engine modified with cooled EGR is optimized by using a strategy combining the artificial neural networks (ANNs) and genetic algorithm (GA) with the one-dimensional engine cycle simulation. The results reveal that the newly developed model predicts the KLSA better than the existing other models in the engine cycle simulations. With combined optimization of the geometric compression ratio and the operative control variables including the spark timing, intake valve closure, EGR ratio and so on, the engine thermal efficiency is improved by 2-8% at the most frequently operated points.
Li, Tie, Yin, Tao, Wang, Bin
Modeling of Quasi-Steady State Heat Transfer Phenomena with the Consideration of Backflow Gas Effect at Intake Manifold of IC Engines and Its Numerical Analyses on 1-D Engine Simulation2018-32-002910/30/2018
An empirical equation was developed for modeling the heat transfer phenomena taking place in an intake manifold which included the backflow gas effect. In literature, heat transfer phenomenon at intake system is modeled based on steady flow assumptions by Colburn analogy. Previously, authors developed an equation with the introduction of Graetz and Strouhal numbers, using a port model experimental setup. In this study, to further improve the empirical equation, real engine experiments were conducted where pressure ratio between the intake manifold and engine cylinder were added along with Reynolds number to characterize the backflow gas effect on intake air temperature. Compared to the experimental data, maximum and average errors of intake air temperature estimated from the new empirical equation were found to be 2.9% and 0.9%, respectively. Furthermore, Colburn analogy and suggested empirical equation were consecutively implemented to 1-D engine simulation software on gasoline and diesel engine setups. Naturally aspirated gasoline engine simulations revealed the importance of the backflow gas effect in line with the real engine experiments. Maximum and average temperature differences between the Colburn analogy and suggested equation showed 36.0 K and 28.7 K, respectively. In turbocharged diesel engine simulations, intake air temperature’s effect on auto ignition timing was analyzed. At engine speed of 2250 rpm, in-cylinder air temperature difference at IVC was found to be 5.8 K. This difference corresponded to an advanced auto-ignition timing by 1.15 deg. CA, which could be interpreted an estimated reduction of CO2 gas by 0.28%.
Yilmaz, Emir, Ichiyanagi, Mitsuhisa, Suzuki, Takashi
Influence of Ethanol and 2-Butanol Blended Fuels on Combustion and Emissions in a Small Displacement Two Stroke Engine2018-32-004410/30/2018
Small displacement two-stroke engines are cheap and low-maintenance propulsion systems and commonly used in scooters, recreation vehicles and handheld power-tools. The restriction by emission legislation and the increasing environmental awareness of end users as well as decreasing energy resources cause a rethinking in the development of propulsion systems and fuels in these fields. Despite recent improvements of electric powertrains, two stroke engines are the challenged propulsion system in high performance handheld power tools at the moment. The reasons are the extraordinary high power to weight ratio of two-stroke engines, the high energy density of liquid fuels and the reliability of the product with respect to extreme ambient conditions. Nevertheless, further improvements on emissions and fuel consumption of small displacement two-stroke engines can be realized. This research is focused on the use of alternative renewable fuels, so called biofuels, like ethanol and 2-butanol in small displacement two-stroke engines. The different physical and chemical properties of ethanol and 2-butanol can have a positive impact on the combustion process and emission composition and are a possibility to contribute future engine requirements. Beside advantages in combustion and emission behavior, liquid biofuels can have an advantageous CO2 lifecycle in comparison to conventional gasoline. To point out the characteristics of different alcohol gasoline blends, the ignition timing and the air to fuel equivalence ratio have been modified in a wide range. The results are focused on power, efficiency, knock, combustion stability and emissions under rich and lean operation. On this basis, it is possible to determine the boundary conditions for an alcohol fuel use in small displacement two-stroke engines serving as basis for future combustion process developments with respect to decreasing emissions and fuel consumption.
Jandl, Stephan, Schmidt, Stephan, Piecha, Pascal, Schacht, Hans-Juergen, Seidel, Tilman
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
Diesel CAI Combustion in Uniflow Scavenging 2-Stroke Engine Provided with Port Fuel Injection Device2018-32-001510/30/2018
We studied a simple and cost effective controlled auto ignition (CAI) combustion engine in order to achieve simultaneous reduction of NOx and soot, which are issues in diffusion combustion. The engine type was a uniflow scavenging 2-stroke engine, and the fuel used was diesel, as is common in diesel engines. We examined the position of the injector that effectively forms the premixture and realized stable operation with diesel fuel by the low pressure fuel injection device for port fuel injection (PFI), and it was found that the CAI combustion ignition timing can be controlled through setting the air/fuel ratio that obtains the optimal ignition timing per operation conditions. As a result of verifying the potential of this engine, it was confirmed that the regulation emissions level required for joint use of common rail fuel injection system (CRS), exhaust gas recirculation (EGR), diesel particulate filter (DPF), diesel oxidation catalyst (DOC), etc. in nonroad compression ignition (NRCI) engines can be achieved only by exhaust aftertreatment with a DOC. Furthermore, it was confirmed that break mean effective pressure (BMEP) equivalent to 4-stroke is about the same level as naturally aspirated NRCI engines and specific fuel consumption (SFC) has the potential to be about the same level or lower than NRCI engines with displacement of less than 2000 cm3.
Kurata, Mashu, Yamada, Yoshikazu
Study of Turbulent Entrainment Quasi-Dimensional Combustion Model for HCNG Engines with Variable Ignition Timings2018-01-16879/10/2018
Presently, urban transportation highly depends on the fossil fuels, but its rapid fluctuating economic issues and environmental consequences impose the variegation of energy sources. Hydrogen enriched compressed natural gas (HCNG) engines offer the potential of higher brake thermal efficiency with low emissions, which also satisfies the strict pollutant emission standards. The two-zone turbulent entrainment quasi-dimensional combustion model is developed to predict the combustion process of spark-ignited hydrogen enriched compressed natural gas-fueled engines. The fundamentals of thermodynamic process, turbulent flame propagation model and other sub-models like laminar burning velocity, adiabatic temperature and ignition lag model are introduced for the better accuracy. The experiments have been conducted for three different fuels; pure CNG, 20% HCNG, and 40% HCNG blends under MAP of 105 kPa for various excess air ratios (λ) and ignition timing (θi). The three calibration coefficient of the model; Turbulent intensity coefficient C2, the Taylor length scale coefficient C3, and Ignition lag coefficient Cig are tuned to generate the pressure traces which closely resembled to experimental results. After comparing the numerical simulation results with the experiment’s outcomes it is found that the predictive accuracy of the presented model is quite impressive, and it is well accepted for the extremely fuel lean conditions where issues of bad combustion become serious.
Mehra, Roopesh Kumar, Ma, Fanhua, Hao, Duan, Juknelevičius, Romualdas
Holistic Evaluation of CO 2 Saving Potentials for New Degrees of Freedom in SI Engine Process Control Based on Physical Simulations2018-01-16549/10/2018
Specific shifting of load points is an important approach in order to reduce the fuel consumption of gasoline engines. A potential measure is cylinder deactivation, which is used as a study example. Currently CO2 savings of new concepts are evaluated by dynamic cycles simulations. The fuel consumption during driving cycles is calculated based on consumption-optimized steady-state engine maps. Discrete load point shifts occur as shifts within maps. For reasons of comfort shifts require neutral torque. The work of deactivated cylinders must be compensated by active cylinders within one working cycle. Due to the larger time constant of the air path the air charge must be increased or decreased in order to deactivate or activate cylinders without affecting the torque. A working-cycle-resolved, continuously variable parameter is prerequisite for process control. Manipulation of ignition timing enables a reduction of efficiency and gained work. So far dynamic cycle simulation does not take into account additional fuel consumption due to shifts of operating points. A new method is developed to investigate the influence of these highly dynamic operating events on total CO2 savings. Relevant operating point shifts are determined by dynamic cycle simulations. Additional fuel consumption is calculated by use of a one-dimensional model of air path and a predictive zero-dimensional model of the combustion chamber. A wheel-neutral discrete shift of operating points is controlled by automatically generated setpoint trajectories of process parameters. Applying cost functions enables the evaluation of different degrees of freedom in process control independently from the controller’s quality. After calculating setpoint trajectories for an engine configuration the results are applicable to further driving cycles and vehicle configurations without additional effort. This method is examined on various driving cycles. Taking into account the consumption by shift operations the advantages of cylinder deactivation in cycle simulation decrease with increasing operating dynamics.
Wandschneider, Tim, Wiege, Katharina, Gottschalk, Wolfram
Investigation of Flame Propagation Description in Quasi-Dimensional Spark Ignition Engine Modeling2018-01-16559/10/2018
The engine development process has been enhanced significantly by virtual engineering methods during the last decades. In terms of in-cylinder flow field, charge flow and combustion modelling, 3D-CFD (three dimensional) simulations enable detailed analysis and extended investigations in order to gain additional knowledge about design parameters. However, the computational time of the 3D-CFD is an obvious drawback that prevents a reasonable application for extensive analysis with varying speed, load and transient conditions. State-of-the-art 0D (zero dimensional) approaches close the gap between the demand of high computational efficiency and a satisfying accordance with experimental data. Recent improvements of phenomenological combustion approaches for gasoline spark ignition engines deal with the consideration of detailed flow parameters, the accuracy of the laminar flame speed calculation and the prediction of the knock limit. Little attention has been given to the influence of different combustion chamber designs on the prediction capability so far. This leads to an often used simplification consisting of a combustion chamber modeled as a disk and an acceptable inaccuracy of combustion modelling. With an increasing deviation of the surrogate combustion chamber from the investigated real chamber, the prediction capability becomes insufficient. This effect is intensified by the shift of the combustion process to a fast combustion nearby the top dead center (TDC), typical for high performance engines with advanced ignition timing for maximum brake torque. In order to improve the model accuracy, this examination highlights the effect of different descriptions of the flame propagation in 0D combustion modeling. Two calculation paths are introduced. On the one hand the flame propagation description is determined by the combustion chamber geometry prior to the model calibration process, and on the other hand the flame data is derived from measured data after the model calibration. The forward path considers exemplary combustion chamber designs, e.g. through different piston cavities, their effect on the flame front as well as on the 0D model results. A deep analysis via 3D-CFD of the flame propagation reveals characteristic points, which are related to different geometrical aspects. Despite the consideration of the flame maps, the related changes of the charge motion are calculated through 3D-CFD and transferred to 0D. The improvement of the predictive capability through the flame data and flow parameters is investigated by experimental data of two different high performance engines. The backward path deals with the calculation of flame propagation from measured cylinder pressure data. On the one hand this gives the opportunity to analyze the combustion process with the knowledge gained by the previous introduced characteristic aspects, on the other hand it creates flame maps that are simple to use. Latter improve the 0D combustion model accuracy even without knowing the exact geometry.
Malcher, Simon, Bargende, Michael, Grill, Michael, Baretzky, Ulrich, Diel, Hartmut, Wohlgemuth, Sebastian, Röttger, Gordon
The Effect of Pressure, Temperature and Additives on Droplet Ignition of Lubricant Oil and Its Surrogate2018-01-16739/10/2018
Numerous studies have attributed pre-ignition events in turbocharged spark ignited engines to the auto-ignition of lubricant oil-fuel mixture droplets. These droplets result from the interaction of the directly injected fuel spray on the lubricant oil film on the cylinder walls, causing fuel splashing to pull oil off the walls, forming droplets. The dilution of the oil by the fuel also changes lubricant oil droplet properties. Therefore, it is important to understand lubricating oils, with and without fuel dilution, as a possible ignition source in pre-ignition and super knock events. In this work, a constant volume (4 L) combustion chamber (CVCC) that allows the introduction of a single droplet of lubricating oil has been built. It is capable of operation at elevated pressures and temperatures. To simulate the droplet-induced pre-ignition event, a droplet injection system was incorporated into the vessel. The oil droplet was suspended on the junction of a thermocouple where the instantaneous internal droplet temperature was measured throughout the oil droplet lifetime. The experiments were carried out in an air atmosphere heated to 300 °C. The ambient pressure was varied from 2-15 bar. In the present work, the effect of pressure on droplet ignition of conventional engine oil (SAE 15 W-40), its surrogate hexadecane (C16H34), and hexadecane mixed with lubricant oil additives has been investigated to understand the fundamental physics of droplet-induced ignition. The objective of this study is to determine the probability that an oil droplet will ignite at temperatures and pressures relevant to modern turbocharged GDI engines.
Maharjan, Sumit, Qahtani, Yasser, Roberts, William, Elbaz, Ayman
Effect of Temperature-Pressure Time History on Auto-Ignition Delay of Air-Fuel Mixture2018-01-17999/10/2018
When the compression ratio of the spark ignition engine is set high as a method of improving the fuel efficiency of passenger cars, it is often combined with the direct fuel injection system for knock mitigation. In port injection, there are also situations where the fuel is guided into the cylinder while the vaporization is insufficient, especially at the cold start. If the fuel is introduced into the cylinder in a liquid state, the temperature in the cylinder will change due to sensible heat and latent heat of the fuel during vaporization. Further, if the fuel is unevenly distributed in the cylinder, the effect of the specific heat is added, and the local temperature difference is expanded through the compression process. In this research, an experiment was conducted using a rapid compression machine for the purpose of discussing the effect of the temperature-pressure time history of fuel on ignition delay time. From the results, it was confirmed that the ignition timing can be advance and retard depending on the temperature-pressure history regardless of the time for the fuel to stay in the cylinder. This indicates that ignition delay can be controlled arbitrarily according to the purpose by manipulating the temperature-pressure history. In addition, zero-dimensional detailed chemical reaction calculation was carried out in order to discuss the effect of the spatial heterogeneity of fuel mixture concentration and temperature on the ignition delay. The results showed that the heterogeneity of the air-fuel mixture essentially shortens the ignition delay time.
Matsuura, Katsuya, Iida, Norimasa
Modeling the Pilot Injection and the Ignition Process of a Dual Fuel Injector with Experimental Data from a Combustion Chamber Using Detailed Reaction Kinetics2018-01-17249/10/2018
The introduction of the so called Emission Controlled Areas within the IMO Tier III legislation forces manufacturers of maritime propulsion systems to adherence to stringent emission thresholds. Dual fuel combustion, which is characterized by the injection of a small amount of fuel oil to ignite a premixed natural gas air mixture, constitutes an option to meet this target. At high diesel substitution rates and very short pilot injection events, the injector is operated in the ballistic regime. This influences spray penetration, mixture formation and ignition behavior. In the present work, a seven-hole dual fuel injector was measured in a combustion chamber to provide data for the generation of a CFD model using the commercial code AVL FIRE®. The liquid and the vapor phase of the fuel spray were quantified by Mie-scattering and Schlieren-imaging technique for different chamber conditions. Based on the measured spray characteristics, a methodology was developed to imprint a velocity profile to the initial droplets in the CFD model, to depict the spray penetration for small injection durations. To characterize the ignition process and the flame propagation, measurements of the OH* emission and the natural luminosity of the flame were carried out. A detailed reaction mechanism, which is able to predict both diesel and dual fuel combustion, was integrated in the CFD model. The ignition delay was fitted to the experimental data by adapting the reaction mechanism for different chamber temperatures. The influence of the presence of natural gas on the ignition behavior was validated using data from a rapid compression machine. Even for low temperatures and high pressures, similar to the start of injection under engine operating conditions, a good correlation could be achieved. The developed knowledge will be transferred to an engine model to investigate the limits of dual fuel combustion processes.
Frühhaber, Jens, Peter, Andreas, Schuh, Sebastian, Lauer, Thomas, Wensing, Michael, Winter, Franz, Priesching, Peter, Pachler, Klaus
Strategies to Define Surrogate Fuels for the Description of the Multicomponent Evaporation Behavior of Hydrocarbon Fuels2018-01-16929/10/2018
The scope of this work is to propose a methodology to define multicomponent surrogate mixtures which describe the main evaporation characteristics of real gasoline fuels. Since real fuels are commonly complex mixtures with hundreds or thousands of hydrocarbons, their exact composition is generally not known. Only global characteristics are standardized. An accurate modeling of such complex mixtures in 3D-CFD requires the definition of a suitable surrogate. So far, surrogate mixtures have mostly been defined based on their combustion properties, such as ignition delay or burning velocity, irrespective of their evaporation characteristics. For this reason, in this work, a systematic study is carried out to develop a methodology to define mixtures of representative components that mimic the evaporation behavior of real fuels. Specifically, the following aspects are analyzed: the necessary number and type of the surrogate components, the definition of optimization targets representing the real fuel properties of interest (i.e. the vapor pressure and the distillation curve), the formulation of an appropriate numerical model to evaluate these quantities and the choice of a suitable optimization algorithm to obtain the optimal surrogate composition. It is shown that these different aspects can influence the surrogate definition, potentially leading to a non-optimal representation of the real fuel target properties. This investigation is carried out for four representative real fuels, for which experimental data on their vapor pressure and distillation curve are available. Finally, suitable surrogates are proposed for all fuels.
Pati, Andrea, Gierth, Sandro, Haspel, Philip, Hasse, Christian, Munier, Jerome
Items per page:
1 – 50 of 837