Browse Topic: Knock

Items (446)
Find
Impact of Ordinal Proximity of Frequency Components on the Auditory Perception of Engine Knocking2024-32-003204/18/2025
This study examines the acoustic properties of engine-knocking sounds in gasoline engines, arising from misfires during spark ignition that negatively affect driving performance. The aim was to understand the frequency characteristics of acceleration sounds and their connection to the proximity of the order components. The study also explores “booming,” where two different frequencies of sounds occur simultaneously, potentially linked to the unpleasant nature of engine knocking. Using a sinusoidal model, we generated engine acceleration sound models with 5th-, 10th-, and 15th-order components, including engine knocking. Two types of sound stimuli were created: one with the original amplitude (OA) and one with a constant amplitude (CA) for each component order, emphasizing the order-component proximity in CA sounds. Aural experiments with 10 participants in an anechoic room using headphones and the MUSHRA method revealed an inverse relationship between OA and CA ratings as the component
Suzuki, Ryuhei, Ishimitsu, Shunsuke, Nitta, Misaki, Sakakibara, Mika, Hakozaki, Tomoyuki, Fujikawa, Satoshi, Iwata, Kiyoaki, Matsumoto, Mitsunori, Kikuchi, Masakazu
Technical Paper
Optimization of HEV Vehicle’s Engine Modulated Noise2025-01-008405/05/2023
One 1.5L Miller-cycle turbocharged four cylinder gasoline hybrid engine is installed on a certain hybrid vehicle. When accelerating at low to medium speeds with a small throttle, there is a "da da" knocking noise inside the car, which seriously affects the overall sound quality of the vehicle. By analyzing the vibration and noise data of the engine, it was found that the frequency of the abnormal knocking sound is 200-1000Hz, which presents a half order characteristic in the time domain, that is, one knocking occurs when the engine crankshaft rotates twice. Through Hilbert demodulation analysis of the vibration data in the problem frequency range, it was found that the knocking noise was modulated in the frequency domain, with a modulation frequency of half of the crankshaft rotation frequency. By building a fully flexible multi-body dynamic model of a hybrid powertrain and inputting the engine's cylinder pressure excitation, the combustion excitation is coupled with mechanical
dan, Kong
Technical Paper
G Index: a novel knock detection method that is simpler and calibration-free2022-01-057703/29/2022
Ever restrictive emissions legislations and fuel efficiency targets have been posing challenges for engine development. Knocking is aloways a limiting factor for spark-ignited engines and has to be tighly controlled during the development phase. There are several methods that address how to detect and measure its occurense. They often require complex calculations with high computational costs that limit them only to laboratorial operation. Moreover, they are often calibrated with subjective factors, for each engine. Thus, this paper offers a novel process that is simpler and does not require previous calibration, called G Index. It is based on the angular position of the peak of maximum pressure rise rate and its relation to the 50% mass fraction burn angular possition. The results showed that there is a locus of knock-free operation with GI between -10 and 0. Higher values lead to a sudden jump towards a locus of knocking operation with GI between 6-10, where the thermodynamic state
Martins, Mario Eduardosantos
Technical Paper
Using multiple ignition sites and pressure sensing devices to determine the effect of air-fuel equivalence ratio on the morphology of knocking combustion 2022-01-052403/29/2022
Knocking combustion inherently presents an interaction between main flame front and end gas autoignition. Conventionally, it generates a high amplitude pressure wave traveling across the chamber, can be responsible for reducing the performance of the engine and can cause heavy damage to engine components. In order to study the phenomenon in a controllable way, experiments were performed on a specialized single-cylinder research engine fitted with a liner equipped with four equi-spaced spark plugs in the side so as to propagate various flames from those locations, and hence achieve more controlled knock events. In addition, six pressure transducers were employed at distinct locations to precisely record details of the autoignition event by monitoring pressure oscillations, and with them combustion characteristics and knock intensity. Four of the six transducers were mounted on the circumference of the liner (each next to one of the spark plugs), one was placed at the center of the
Uddeen, Kalim, Shi, Hao, Tang, Qinglong, Turner, James
Technical Paper
Auto-ignition and Anti-Knock Evaluation of Dicyclopentadiene-PRF and TPRF Blends2021-01-116009/21/2021
The increasing demand for high-octane fuels is pushing the combustion research towards investigating new potential fuels and octane boosters. In addition to their high-octane, those additives should be environmentally friendly. In this study, the anti-knock properties of Dicyclopentadiene (DCPD) as an additive to primary reference fuels (PRF) and toluene primary reference fuels (TPRF) have been investigated. The Research octane number (RON) and Motor octane number (MON) were measured using Cooperative Fuels Research (CFR) engine for four different fuel blends; PRF 60 + 10% DCPD, PRF 60 + 20% DCPD, PRF 70 + 10% DCPD and TPRF 70 + 10% DCPD. In addition, homogenous charge compression ignition (HCCI) was also performed using the CFR engine to show the effect of DCPD on suppressing low temperature chemistry of reference fuels. Moreover, the ignition delay times of these mixtures were measured in the rapid compression machine (RCM) at 20 bar and stoichiometric mixtures over a temperature
Al-Khodaier, Mohannad
Technical Paper
Investigations into the Effects of Spark Plug Location on Knock Initiation by using Multiple Pressure Transducers2021-01-115909/21/2021
Despite a long history of development, modern spark-ignition engines are still restricted in obtaining higher thermal efficiency and better performance by knock. Knocking combustion is an unnatural combustion phenomenon caused by the autoignition of unburned air-fuel mixture ahead of the propagating flame front. This work describes investigations into the significance of spark plug location (with respect to inlet and exhaust valve position) on the knock formation mechanism. To facilitate the investigation, four spark plugs were installed in a specialized liner at four equispaced distinct locations to propagate flames from those locations, which provoked a distinct flame travel from each and thus individual autoignition profiles. Six pressure transducers were arranged to precisely record the pressure oscillations, knock intensities, and combustion characteristics. Four of the six transducers were mounted on the circumference of the liner (each next to one of the spark plugs), one was
Uddeen, Kalim, Shi, Hao, Tang, Qinglong, Turner, James
Technical Paper
Comparison of Promising Sustainable C1-Fuels Methanol, Dimethyl Carbonate, and Methyl Formate in a DISI Single Cylinder Light Vehicle Gasoline Engine2021-01-120409/21/2021
On the way to a climate-neutral mobility synthetic fuels with their potential of a CO2-neutral production are currently in the focus of the internal combustion research. In this study the C1-fuels methanol (MeOH), dimethyl carbonate (DMC), and methyl formate (MeFo) are tested as pure C1-fuels mixtures and as blends component for gasoline. The study was performed on a single-cylinder engine in two configurations, thermodynamic and optical. As pure C1-fuels the already investigated DMC/MeFo mixture is compared with a mixture of MeOH/MeFo. DMC is replaced by MeOH, because of its benefits in laminar flame speed, ignition limits and production costs. MeOH/MeFo shows benefits in particle number (PN) emissions at a cooling water temperature of 40°C and in high load operating points. But reversed an increase of 60% in NOx emissions related to DMC/MeFo was observed in hot engine conditions. Both mixtures show no sensitivity in PN emissions for rich combustions. Neither triggered by a global
Blochum, Sebastian, Fellner, Felix, Mühlthaler, Markus, Härtl, Martin, Wachtmeister, Georg, Yoneya, Naoki, Sauerland, Henning
Technical Paper
Novel Engine Sound Quality Evaluation Method in Bench Testing2021-01-102908/31/2021
A lot of engine sound quality issue can be classified as some specific words, such as “Rattle, Knocking, Modulation, Loud, Whistles” and etc. Engineers were trying to quantify this phenomenon with objective data. In this paper, we would like to propose a novel method that separates the engine sound quality into five different objective parameters, which covers engine noise level, whine or whistling, clatter - tick phenomenon and roughness. Based on the new method, the engine sound quality can be mapped into a final sound quality matrix - ESQM (Engine Sound Quality Matrix) to compare by the total number or by the contributors individually.
Tan, Yang, Yang, Jingling
Technical Paper
Analysis of Gasoline Surrogate Combustion Chemistry with a Skeletal Mechanism2020-01-200409/15/2020
Knocking combustion is a major obstacle towards engine downsizing and boosting—popular techniques towards meeting the increasingly stringent emission standards of SI engines. The commercially available gasoline is a mixture of many chemical compounds like paraffins, isoparaffins, olefins and aromatics⁠. Therefore, the modeling of its combustion process is a difficult task. Additionally, the blends of certain compounds exhibit non-linear behavior in comparison to the pure components in terms of knock resistance. These facts require further analysis from the perspective of combustion chemistry. The present work analyses the effects of blending ethanol to FACE-C gasoline. A range of pressures, temperatures, and equivalence ratios has been considered for this purpose. The open source softwares Cantera version 2.4.0 and OpenSMOKE++ Suite have been used for the simulations. Moreover, the present work proposes a skeletal chemical kinetic mechanism for six component gasoline surrogates with
Bhattacharya, Atmadeep, Kaario, Ossi, Vuorinen, Ville, Tripathi, Rupali, Sarjovaara, Teemu
Technical Paper
Experimental Study on Knock Mechanism with Multiple Spark Plugs and Multiple Pressure Sensors2020-01-205509/15/2020
Engine knock is an abnormal phenomenon, which places barriers for modern Spark-Ignition (SI) engines to achieve higher thermal efficiency and better performance. In order to trigger more controllable knock events for study while keeping the knock intensity at restricted range, various spark strategies (e.g. spark timing, spark number, spark location) are applied to investigate on their influences on knock combustion characteristics and pressure oscillations. The experiment is implemented on a modified single cylinder Compression-Ignition (CI) engine operated at SI mode with port fuel injection (PFI). A specialized liner with 4 side spark plugs and 4 pressure sensors is used to generate various flame propagation processes, which leads to different auto-ignition onsets and knock development. Based on multiple channels of pressure signals, a band-pass filter is applied to obtain the pressure oscillations with respect to different spark strategies. Finally, the relationships among in
Shi, Hao, Uddeen, Kalim, An, Yanzhao, Johansson, Bengt
Technical Paper
Experimental evaluation of a custom gasoline-like blend designed to simultaneously improve φ-sensitivity, RON and octane sensitivity.2020-01-113604/14/2020
φ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. However, regular gasoline is only weakly φ–sensitive at naturally aspirated conditions, so intake boosting is required to take advantage of this property. Thus, there is strong motivation for designing gasoline-like blends that improve φ–sensitivity and simultaneously increase RON and octane sensitivity, to improve performance for LTGC and modern SI engines. In a previous study [SAE 2019-01-0961], a 5-component regulation-compliant fuel blend (CB#1) was computationally designed; and simulations showed promising results compared to regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in a LTGC research engine, and the results are compared to RD5-87. For premixed naturally aspirated conditions, the intake heating required to autoignite CB#1 was similar to RD5-87, ensuring that CB#1 can operate under these
Lopez Pintor, Dario, Dec, John, Gentz, Gerald
Journal Article
Detailed Chemistry based Analysis of the Water Effect on Auto-Ignition of different Octane Number Fuels2020-01-055104/14/2020
Water injection can be applied to spark ignited (SI) gasoline engines to increase the Knock Limit Spark Advance (KLSA) and improve the thermal efficiency. The KLSA potential of 6°CA to 11°CA is shown by many research groups for EN228 gasoline fuel using numerical tools and experimental methods. The influence of water is multi-layered since it reduces the in-cylinder temperature by vaporization and higher heat capacity of the fresh gas, it changes the chemical equilibrium in the end gas and prolongs the ignition delay and laminar flame speed. The aim of this work is to extend the investigation of water injection to different octane number fuels (RON0, RON20, RON50, RON80, RON90 and RON100). The investigation is performed for high load operating conditions at three different engine speeds at 1500rpm, 2000rpm and 2500rpm. The numerical toolbox used for the analysis consists of a detailed reaction scheme for gasoline fuels that was previously used to evaluate the water effect on
Franken, Tim, Seidel, Lars, Matrisciano, Andrea, Mauss, Fabian, Kulzer, André C., Schuerg, Frank
Journal Article
C919 Trailing Edge Assembly Interchangeable Tooling2019-01-188009/16/2019
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
Dineley, James
Technical Paper
Knock and Pre-Ignition Limits on Utilization of Ethanol in Octane-on-Demand Concept2019-24-010809/09/2019
Octane-on-Demand (OoD) is a promising technology for reducing greenhouse emissions from automobiles. The concept utilizes a low-octane fuel for low and mid load operating conditions, and a high-octane additive is added at high load operating conditions. Researchers have focused on the minimum ethanol content required for operating at high load conditions when the low-octane fuel becomes knock limited. However, it is also widely known that ethanol has a high tendency to pre-ignite, which has been linked with its high laminar flame speed and surface ignition tendency. Moreover, ethanol has a lower stoichiometric air-fuel ratio, requiring a larger injected fuel mass per cycle. A larger fuel mass increases the potential for oil dilution by the liquid fuel, creating precursors for pre-ignition. Hence, the limits on ethanol addition owing to pre-ignition also need consideration before the technology can be implemented. In this regard, experiments were performed using light naphtha (RON 68
Singh, Eshan, Morganti, Kai, Dibble, Robert
Technical Paper
Nominal High-Altitude Electromagnetic Pulse (HEMP) WaveformsTBMG-3487008/01/2019
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.
Magazine Article
Nominal High-Altitude Electromagnetic Pulse (HEMP) Waveforms19AERP08_0808/01/2019
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.
Magazine Article
Hewing Out Evacuation Routes for Burning Buses by Linear-Shaped Charge Jet09-07-01-000201/25/2019
In recent years, several buses have ignited in some cities in China, causing numerous deaths and significant property damage. However, few research studies have been conducted to deal with such accidents. Therefore, in this work, a linear-shaped charge jet with rectangular cross sections was used to hew out evacuation routes for burning buses, and the parameter design for the shaped charge jet was improved according to asymmetry limitations and human tolerance. A numerical finite element simulation model of the behavior of a jet penetrating the jambs was established using ANSYS/LS-DYNA software. The asymmetrical characteristics of an arc segment in the structure of a rectangular-shaped charge were analyzed, in addition to the influence on the deviations of the jet penetration capacity and blast injuries to occupants caused by the side effects of detonation. Furthermore, overlooking the risks posed to bystanders by the process of hewing out evacuation routes, the calculation results
Fu, Yanshu, Zhang, Chaoyang
Journal Article
Heat of Vaporization and Species Evolution during Gasoline Evaporation Measured by DSC/TGA/MS for Blends of C1 to C4 Alcohols in Commercial Gasoline Blendstocks2019-01-001401/15/2019
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
Fioroni, Gina M., Christensen, Earl, Fouts, Lisa, McCormick, Robert
Technical Paper
Fuel & Lubricant Effects on Stochastic Preignition2019-01-003801/15/2019
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
Costanzo, Vincent S., Yu, Xin, Chapman, Elana, Davis, Richard, Haenel, Patrick
Journal Article
LES Analysis on Cycle-to-Cycle Variation of Combustion Process in a DISI Engine2019-01-000601/15/2019
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
Chen, Ceyuan, Ameen, Muhsin M, Wei, Haiqiao, Iyer, Claudia, Ting, Foochern, Vanderwege, Brad, Som, Sibendu
Technical Paper
Mechanism Analysis on the Effect of Fuel Properties on Knocking Performance at Boosted Conditions2019-01-003501/15/2019
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
Kassai, Masaharu, Aksu, Cagdas, Shiraishi, Taisuke, Cracknell, Roger, Shibuya, Masahiko
Technical Paper
Knock Sensor Based Virtual Cylinder Pressure Sensor2019-01-004001/15/2019
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
Rugland, Christian, Stenlaas, Ola
Technical Paper
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
Technical Paper
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
Li, Tie, Yin, Tao, Wang, Bin
Technical Paper
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
Gaitan, Pedro, Schwarz, Frank, Eibl, Rüdiger
Technical Paper
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
Technical Paper
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
Isshiki, Yuuki, Naitoh, Ken, Onuma, Yuichi, Ohara, Soichi, Arai, Daisuke, Machida, Yutaka, Ito, Hajime, Kobayashi, Yoshiki, Suzuki, Takahiro, Tada, Yusuke
Technical Paper
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
Technical Paper
The Fuel Economy Improvement through the Knock Margin Expansion in a Turbocharged Gasoline Direct Injection Engine2018-01-167109/10/2018
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
Shin, Ji Yong, Park, Chansoo, Jung, Jinyoung, Bae, Choongsik
Technical Paper
Development of a Standardized Test to Evaluate the Effect of Gasoline Engine Oil on the Occurrence of Low Speed Pre-Ignition - The Sequence IX Test2018-01-180809/10/2018
The study described in this paper covers the development of the Sequence IX Low Speed Pre-Ignition (LSPI) test for the new engine oil category, ILSAC GF-6. The purpose of the Sequence IX test is to evaluate a lubricant’s ability to protect against LSPI events which are prevalent when operating a highly boosted/downsized gasoline direct-injected engine. LSPI is characterized as a combustion event that starts before ignition spark, typically followed by excessive in-cylinder pressures and heavy knock, which can cause severe engine damage and failure. Industry research has shown that oil formulation can contribute to the frequency of LSPI activity. The Sequence IX test was developed using a turbocharged gasoline direct-injected 2.0 liter Ford Ecoboost engine with dual independent variable cam timing. The engine was modified with in-cylinder pressure sensors and a high-resolution crank angle encoder to characterize individual engine combustion cycles and identify potential LSPI events
Mounce, Felt
Technical Paper
Distribution of Knock Frequencies in Modern Engines Compared to Historical Data2018-01-166609/10/2018
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
Mittal, Vikram
Technical Paper
Blending Octane Number of 1-Butanol and Iso-Octane with Low Octane Fuels in HCCI Combustion Mode2018-01-168109/10/2018
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
Waqas, Muhammad Umer, Mohammed, Abdulrahman, Masurier, Jean-Baptiste, Johansson, Bengt
Technical Paper
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 Loads2018-01-172309/10/2018
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
Li, Xiao, He, Bang-Quan, Zhao, Hua, Zhang, Yan, Li, Yufeng, Bai, Honglin
Technical Paper
Combined Fuel and Lubricant Effects on Low Speed Pre-Ignition2018-01-166909/10/2018
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
Kocsis, Michael Clifford, Briggs, Thomas, Anderson, Garrett
Technical Paper
Combustion Characteristics of PRF and TSF Ethanol Blends with RON 98 in an Instrumented CFR Engine2018-01-167209/10/2018
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
Hoth, Alexander, Kolodziej, Christopher P., Rockstroh, Toby, Wallner, Thomas
Technical Paper
A Comparative Study on Knock Occurrence for Different Fuel Octane Number2018-01-167409/10/2018
Combustion with knock is an abnormal phenomenon which constrains the engine performance, thermal efficiency and longevity. The advance timing of the ignition system requires it to be updated with respect to fuel octane number variation. The production series engines are calibrated by the manufacturer to run with a special fuel octane number. In the experiment, the engine was operated at different speeds, loads, spark advance timings and consumed commercial gasoline with research octane numbers (RON) 95, 97 and 100. A 1-dimensional validated engine combustion model was run in the GT-Power software to simulate the engine conditions required to define the knock envelope at the same engine operation conditions as experiment. The knock intensity investigation due to spark advance sweep shows that combustion with noise was started after a specific advance ignition timing and the audible knock occur by increasing the advance timing. Therefore, the engine operation was divided into three
Ghanaati, Ali, Muhamad Said, Mohd Farid, Mat Darus, Intan Zaurah
Technical Paper
Detonation Peninsula for TRF-Air Mixtures: Assessment for the Analysis of Auto-Ignition Events in Spark-Ignition Engines2018-01-172109/10/2018
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
Guerouani, Ahmed, Robert, Anthony, Zaccardi, Jean-Marc
Technical Paper
Impact of Engine Age and Engine Hardware on Low-Speed Pre-Ignition2018-01-166309/10/2018
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
Kalaskar, Vickey B., Swarts, Andre, Alger, Terrence
Technical Paper
Effectiveness of Fuel Enrichment on Knock Suppression in a Gasoline Spark-Ignited Engine2018-01-166509/10/2018
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
Singh, Eshan, Dibble, Robert
Technical Paper
On-Road Monitoring of Low Speed Pre-Ignition2018-01-167609/10/2018
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
Michlberger, Alexander, Sutton, Mike, Kocsis, Michael, Anderson, Garrett, Van Horn, Adam
Technical Paper
Effects of EGR Constituents and Fuel Composition on DISI Engine Knock: An Experimental and Modeling Study2018-01-167709/10/2018
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
Vuilleumier, David, Kim, Namho, Sjöberg, Magnus, Yokoo, Nozomi, Tomoda, Terutoshi, Nakata, Koichi
Technical Paper
Auto-ignition Characteristics of Lubricant Droplets under Hot Co-Flow Atmosphere2018-01-180709/10/2018
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
Pan, Kaifeng, Deng, Jun, Chen, Yongquan, Zhang, Erbao, Xie, Wei, Qin, Qiushi, Qu, Zongju, Li, Liguang
Technical Paper
New GKI - Gasoline Knock Index for Rating of Fuel’s Knock Resistance on an Upgraded CFR Test Engine2018-01-174309/10/2018
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
Hauber, Johann, Huber, Karl, Nell, Robert
Technical Paper
Effect of Mixture Formation and Injection Strategies on Stochastic Pre-Ignition2018-01-167809/10/2018
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
Singh, Eshan, Mubarak Ali, Mohammed Jaasim, Ichim, Adrian, Morganti, Kai, Dibble, Robert
Technical Paper
Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines2018-01-172209/10/2018
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
Mubarak Ali, Mohammed Jaasim, Luong, Minh Bau, Sow, Aliou, Hernandez Perez, Francisco, Im, Hong
Technical Paper
Dual Fuel Injection (DI + PFI) for Knock and EGR Dilution Limit Extension in a Boosted SI Engine2018-01-173509/10/2018
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
Han, Taehoon, Lavoie, George, Wooldridge, Margaret, Boehman, André
Technical Paper
Method for Establishing Cool Flames and Flameless Fuel Oxidation with Zero Emissions Using Non-Equilibrium Plasma ActivationTBMG-2905206/01/2018
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
Magazine Article
Numerical Analysis of the Impact of Water Injection on Combustion and Thermodynamics in a Gasoline Engine Using Detailed Chemistry2018-01-020004/03/2018
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
Netzer, Corinna, Franken, Tim, Seidel, Lars, Lehtiniemi, Harry, Mauss, Fabian
Journal Article
Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine2018-01-021004/03/2018
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
Rockstroh, Toby, Kolodziej, Christopher P., Jespersen, Mads C., Goldsborough, S. Scott, Wallner, Thomas
Journal Article
A Computational Study of Abnormal Combustion Characteristics in Spark Ignition Engines2018-01-017904/03/2018
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
Mubarak Ali, Mohammed Jaasim, Hernandez Perez, Francisco, Sow, Aliou, Im, Hong
Journal Article
Items per page:
1 – 50 of 446