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Training / Education
2014-06-11
Fuel composition has had to change with the advent of more stringent emission regulations. Reformulated gasoline (RFG), for example, is vastly different from gasoline of even ten years ago. Tightening regulations on diesel emissions will dramatically change both diesel fuel and engine design. This three-day seminar will review the fundamentals of motor fuels, combustion and motor power generation. The primary content of the course provides a basic introduction to the technology, performance, evaluation, and specifications of current gasoline, diesel, and turbine fuels. The first day of the course begins with a brief review of the evolution of motor fuel through 100 years of performance and specification.
Event
2014-04-08
Papers are invited for this session covering the systems engineering experience required to achieve ultra-low emission levels on light-duty vehicles. Emission system component topics for this session include the development of advanced three-way catalysts, the development of NOX control strategies for gasoline lean burn engines, the application of high cell density substrates to advanced emission systems, and the integration of these components into full vehicle emission systems.
Event
2014-04-08
Advances in automotive gasoline engine technology will continue to play a pivotal role in the reduction of greenhouse gases. A key enabler for improved efficiency is increased power density, but this is restrained by the limits of knock and pre-ignition. Experts will share their experience and thoughts on technologies that can be collectively combined to push beyond the current knock/pre-ignition ceiling. They will also examine how these technologies contribute to greater engine efficiency.
Technical Paper
2014-04-01
Jill M. Spelina, James C. Peyton Jones, Jesse Frey
This paper collates and summarizes recent advances in knock analysis, simulation and control. The statistical properties of knock intensity and knock events are reviewed showing in particular that knock intensity behaves as an independent random process, and that knock events conform to a binomial distribution. These properties have a significant impact on knock control and simulation. Traditional and recently proposed cumulative-summation-based and Likelihood-based knock control strategies are reviewed and illustrated in this context. Efficient tools for simulating both specific instances of the closed loop time response, and the evolution of the distribution of these responses based on a Markov-like approach, are also briefly reviewed. Finally, it is shown how an optimization of the knock threshold and an associated retuning of the controller parameters can result in significantly improved closed loop performance without any other modification of the control algorithm.
Technical Paper
2014-04-01
Kai Morganti, Tien Mun Foong, Michael Brear, Gabriel Da Silva, Yi Yang, Frederick Dryer
This paper presents a combined experimental and numerical study of a modified Cooperative Fuel Research (CFR) engine that allows both the Research and Motor octane numbers (RON and MON) of any arbitrary Liquefied Petroleum Gas (LPG) mixture to be determined. The design of the modified engine incorporates modern hardware that enables accurate metering of different LPG mixtures, together with measurement of the in-cylinder pressure, the air-fuel ratio and the engine-out emissions. The modified CFR engine is first used to measure the octane numbers of different LPG mixtures. The measured octane numbers are shown to be similar to the limited data acquired using the now withdrawn Motor (LP) test method (ASTM D2623). The volumetric efficiency, engine-out emissions and combustion efficiency for twelve alternative LPG mixtures are then compared with equivalent data acquired with the standard CFR engine operating on a liquid fuel. Finally, the modified CFR engine is modelled using GT-Power. The full engine model contains empirical sub-models of the intake and exhaust systems, the gas exchange processes, the flame propagation and the in-cylinder heat transfer.
Technical Paper
2014-04-01
Karthik Nithyanandan, Deyang Hou, Gregory Major, Chia-Fon Lee
This paper focuses on the spray and atomization characteristics of a Dual-Fuel Injector (DFI) which includes a primary and a secondary fuel inlet. Three injectors were analyzed in this study. Apart from the DFI, two conventional diesel injectors were tested as baselines for comparison - a piezo-electric and a solenoid injector. The rail pressures ranged from 200 - 500 bar for the conventional injectors. The DFI was tested first as a single-fuel injector (by sealing the secondary inlet) at pressures ranging from 100 - 300 bar, and then in its dual-fuel mode with the primary inlet pressure ranging from 100 - 300 bar, and the secondary inlet at 25 bar higher than the primary pressure. Injection duration of 0.5 ms was chosen for the experiment. High-speed Mie scattering images were recorded to capture the spray evolution. Phase Doppler Anemometry (PDA) measurements were conducted at different locations in the spray for the acquisition of droplet sizes and velocity distributions. The high-speed images showed that the conventional injectors produced a spray with a wider spray cone angle, relative to the DFI injector which had a narrower spray cone angle leading to equal radial and axial spray penetration, and displaying a fine mist of gasoline droplets surrounding the diesel fuel jets.
Technical Paper
2014-04-01
Susanna Paz, Rosa Delgado, David Riba
Abstract Currently, regulations on vehicle evaporative emissions only focus on the sum of Total Hydrocarbons (THC) without taking into account either the detailed hydrocarbon composition nor other chemicals besides hydrocarbons emitted from gasoline evaporation. As a consequence, this composition, also known as speciation, is not always noted and is even more unknown when biofuels such as ethanol are introduced in the market. Furthermore, these regulations do not differentiate the source of these emissions in the vehicle. The programme described in this paper is designed to investigate the influence of the addition of ethanol to gasoline on evaporative emissions. It has tried to go one step ahead of these directives obtaining more detailed characterization of these evaporative emissions. The programme has enabled a list of compounds (methanol, ethanol, aldehydes, ketones and hydrocarbons) to be determined in evaporative emissions among different ethanol-gasoline fuels (E0, E5-S, E10 and E85), applied to Euro 4 and Flexifuel vehicles by three chromatographic methods based on California Air Resources Board (CARB).
Technical Paper
2014-04-01
Xingyuan Su, Youngchul Ra, Rolf Reitz
Real transportation fuels, such as gasoline and diesel, are mixtures of thousands of different hydrocarbons. For multidimensional engine applications, numerical simulations of combustion of real fuels with all of the hydrocarbon species included exceeds present computational capabilities. Consequently, surrogate fuel models are normally utilized. A good surrogate fuel model should approximate the essential physical and chemical properties of the real fuel. In this work, we present a novel methodology for the formulation of surrogate fuel models based on local optimization and sensitivity analysis technologies. Within the proposed approach, several important fuel properties are considered. Under the physical properties, we focus on volatility, density, lower heating value (LHV), and viscosity, while the chemical properties relate to the chemical composition, hydrogen to carbon (H/C) ratio, and ignition behavior. An error tolerance is assigned to each property for convergence checking. In addition, a weighting factor is given to each property indicating its individual importance among all properties considered; the overall quality of the surrogate fuel model is controlled by a weighted error tolerance.
Technical Paper
2014-04-01
Satheesh Makkapati, Eric Curtis
Abstract Naturally aspirated Homogeneous Charge Compression Ignition (HCCI) operational window is very limited due to inherent issues with combustion harshness. Load range can be extended for HCCI operation using a combination of intake boosting and cooled EGR. Significant range extension, up to 8bar NMEP at 1000RPM, was shown to be possible using these approaches in a single cylinder engine running residual trapping HCCI with 91RON fuel with a 12:1 compression ratio. Experimental results over the feasible speed / load range are presented in this paper for a negative valve overlap HCCI engine. Fuel efficiency advantage of HCCI was found to be around 15% at 2.62bar / 1500RPM over a comparable SI engine operating at the same compression ratio, and the benefit was reduced to about 5% (best scenario) as the load increased to 5bar at the same speed. The primary intention of this paper is to evaluate the compatibility of the presented HCCI concept in a future downsized and boosted engine for improving fuel efficiency over typical drive cycles.
Technical Paper
2014-04-01
Chunsheng Ji, John Dec, Jeremie Dernotte, William Cannella
This study explores the use of two conventional ignition improvers, 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP), to enhance the autoignition of the regular gasoline in an homogeneous charge compression ignition (HCCI) engine at naturally aspirated and moderately boosted conditions (up to 180 kPa absolute) with a constant engine speed of 1200 rpm. The results showed that both EHN and DTBP are very effective for reducing the intake temperature (Tin) required for autoignition and for enhancing stability to allow a higher charge-mass fuel/air equivalence ratio (ϕm). On the other hand, the addition of these additives can also make the gasoline too reactive at some conditions, so significant exhaust gas recirculation (EGR) is required at these conditions to maintain the desired combustion phasing. Thus, there is a trade-off between improving stability and reducing the oxygen available for combustion when using ignition improvers to extend the high-load limit. Because previous works have shown that partial fuel stratification (PFS) can be applied with more reactive fuels to reduce the heat release rate to allow higher loads or more advanced combustion timing without knock, the potential of the ignition improvers to allow effective PFS was also explored over the same range of intake pressures.
Technical Paper
2014-04-01
Amir Maria, Wai Cheng, William Cannella, Kenneth Kar
Abstract Factors affecting the pressure rise rate, and consequently the high-load limit, in the sequential ignition of a homogeneous charge in a temperature gradient have been identified. The pressure rise rate decreases with an increase in the magnitude of the temperature gradient and an increase in the sensitivity of the constant volume ignition delay time to temperature. It increases with an increase in the intrinsic reaction rate (i.e., the reaction rate for a charge of uniform composition and temperature). Since the ignition delay time and the intrinsic reaction rate are directly related to fuel properties, the high-load limit is sensitive to fuel selection. The above three factors are used to explain the high-load limit obtained from a knock limited Controlled Auto-Ignition (CAI) engine with a homogeneous charge operating with three different fuels. The fuel comparisons are made with the engine operating at the same combustion phasing. The fuel ignition delay time and intrinsic heat release rate have been characterized in a Rapid Compression Machine (RCM).
Technical Paper
2014-04-01
Christopher P. Kolodziej, Stephen Ciatti, David Vuilleumier, Bishwadipa Das Adhikary, Rolf Reitz
Abstract Previous work has demonstrated the capabilities of gasoline compression ignition to achieve engine loads as high as 19.5 bar BMEP with a production multi-cylinder diesel engine using gasoline with an anti-knock index (AKI) of 87. In the current study, the low load limit of the engine was investigated using the same engine hardware configurations and 87 AKI fuel that was used to achieve 19.5 bar BMEP. Single injection, “minimum fueling” style injection timing and injection pressure sweeps (where fuel injection quantity was reduced at each engine operating condition until the coefficient of variance of indicated mean effective pressure rose to 3%) found that the 87 AKI test fuel could run under stable combustion conditions down to a load of 1.5 bar BMEP at an injection timing of −30 degrees after top dead center (°aTDC) with reduced injection pressure, but still without the use of intake air heating or uncooled EGR. A 0.4% concentration (by volume) of 2-Ethylhexyl Nitrate (EHN) was added to the 87 AKI test fuel to test the effects of increased reactivity on the minimum load attainable and injection timing at which it would occur, while maintaining similar physical mixing properties.
Technical Paper
2014-04-01
Mark Sellnau, Matthew Foster, Kevin Hoyer, Wayne Moore, James Sinnamon, Harry Husted
In previous work, Gasoline Direct Injection Compression Ignition (GDCI) has demonstrated good potential for high fuel efficiency, low NOx, and low PM over the speed-load range using RON91 gasoline. In the current work, a four-cylinder, 1.8L engine was designed and built based on extensive simulations and single-cylinder engine tests. The engine features a pent roof combustion chamber, central-mounted injector, 15:1 compression ratio, and zero swirl and squish. A new piston was developed and matched with the injection system. The fuel injection, valvetrain, and boost systems were key technology enablers. Engine dynamometer tests were conducted at idle, part-load, and full-load operating conditions. For all operating conditions, the engine was operated with partially premixed compression ignition without mode switching or diffusion controlled combustion. At idle and low load, rebreathing of hot exhaust gases provided stable combustion with NOx and PM emissions below targets of 0.2g/kWh and FSN 0.1, respectively.
Technical Paper
2014-04-01
Meixia Rong, Xu He, Hai Liu, Yong Shang, Weilin Zeng, Xiangrong Li, Fushui Liu
Abstract The combustion characteristics of gasoline-diesel dual-fuel in an electronic-controlled high pressure common rail optical engine were investigated under different diesel injection timings and gasoline/diesel ratios by a high-speed photography method. The experimental results show that the dual-fuel combustion process is influenced by diesel combustion and gasoline homogenous combustion, respectively, with bright yellow flames and blue flames observed in the combustion chamber. At a gasoline/diesel ratio of 0.91, the injection timing affects the ignition timing and combustion modes significantly. When the diesel injection timing is before −25° after top dead center (ATDC), advancing the injection timing tends to prolong the ignition delay and the gasoline-diesel dual-fuel combustion is similar to the pre-mixed charge compression ignition (PCCI) combustion with a rapid single-stage heat release. When the diesel injection timing is after −25° ATDC, as the injection timing is advanced, the ignition timing is also advanced and the dual-fuel combustion takes place in two stages.
Technical Paper
2014-04-01
Wei Luo, Bo Chen, Jeffrey Naber, Chris Glugla
Abstract The ability to operate a spark-ignition (SI) engine near the knock limit provides a net reduction of engine fuel consumption. This work presents a real-time knock control system based on stochastic knock detection (SKD) algorithm. The real-time stochastic knock control (SKC) system is developed in MATLAB Simulink, and the SKC software is integrated with the production engine control strategy through ATI's No-Hooks. The SKC system collects the stochastic knock information and estimates the knock level based on the distribution of knock intensities fitting to a log-normal (LN) distribution. A desired knock level reference table is created under various engine speeds and loads, which allows the SKC to adapt to changing engine operating conditions. In SKC system, knock factor (KF) is an indicator of the knock intensity level. The KF is estimated by a weighted discrete FIR filter in real-time. Both offline simulation and engine dynamometer test results show that stochastic knock control with fixed length of finite impulse response (FIR) filter has slow and excessive retard issue when a significant knock event happens.
Technical Paper
2014-04-01
Huayin Tang, Richard Burke, Sam Akehurst, Chris Brace, Les Smith
Abstract Vehicle start-stop systems are becoming increasingly prevalent on internal combustion engine (ICE) because of the capability to reduce emissions and fuel consumption in a cost effective manner. Thus, the ICE undergoes far more starting events, therefore, the behaviour of ICE during start-up becomes critical. In order to simulate and optimise the engine start, Model in the Loop (MiL) simulation approach was selected. A proceduralised cranking test has been carried out on a 2.0-liter turbocharged, gasoline direct injection (GDI) engine to collect data. The engine behaviour in the first 15 seconds was split into eight different phases and studied. The engine controller and the combustion system were highly transient and interactive. Thus, a controller model that can set accurate boundary conditions is needed. The relevant control functions of throttle opening and spark timing have been implemented in Matlab/Simulink to simulate the behaviours of the controller. Good agreements were found between the measured and predicted control parameters.
Technical Paper
2014-04-01
Francesco Catapano, Silvana Di Iorio, Paolo Sementa, Bianca Maria Vaglieco
Abstract The objective of this paper is the evaluation of the effect of the fuel properties and the comparison of a PFI and GDI injection system on the performances and on particle emission in a Spark Ignition engine. Experimental investigation was carried out in a small single cylinder engine for two wheel vehicles. The engine displacement was 250 cc. It was equipped with a prototype GDI head and also with an injector in the intake manifold. This makes it possible to run the engine both in GDI and PFI configurations. The engine was fuelled with neat gasoline and ethanol, and ethanol/gasoline blends at 10% v/v, 50% v/v and 85% v/v. The engine was equipped of a quartz pressure transducer that was flush-mounted in the region between intake and exhaust valves. Tests were carried out at 3000 rpm and 4000 rpm full load and two different lambda conditions. These engine points were chosen as representative of urban driving conditions. The gaseous emissions and particle concentration were measured at the exhaust by means of conventional instruments.
Technical Paper
2014-04-01
Xin Wang, Yunshan Ge
Abstract Compressed natural gas (CNG) is widely used as an alternative option in spark ignition engines because of its better fuel economy and in part cleaner emissions. To cope with the haze weather in Beijing, about 2000 gasoline/CNG dual-fuel taxis are servicing on-road. According to the government's plan, the volume of alternative fuel and pure electric vehicle will be further increased in the future. Thus, it is necessary to conduct an evaluation on the effectiveness of alternative fuel on curbing vehicular emissions. This research examined the regulated emissions and particulate matter of gasoline/CNG dual-fuel taxi over New European Driving Cycle (NEDC). Emission tests in gasoline- and CNG-fuelled, cold- and warm-start modes were done for all five taxies. Test vehicles, Hyundai Elantra, are powered by 1.6L spark-ignited engines incorporated with 5-gear manual gearboxes. The taxis were registered in May and June, 2013, and their millage was within 3500 and 10000 km on odometer when the emission tests were performed.
Technical Paper
2014-04-01
Richard R. Steeper, M. Lee Davisson
Negative valve overlap (NVO) is an operating mode that enables efficient, low-temperature gasoline combustion in automotive engines. In addition to retaining a large fraction of residuals, NVO operation also enables partial fuel injection during the recompression period as a means of enhancing and controlling main combustion. Thermal effects of NVO fueling on main combustion are well understood, but chemical effects of the products of NVO reactions remain uncertain. To address this topic, we have fabricated a dump valve that extracts a large fraction of cylinder charge at intake valve closing (IVC), yielding a representative sample of NVO products mixed with intake air. Sample composition is determined by gas chromatography. Results from a sweep of NVO start-of-injection (SOI) timings show that concentrations of the reactive species acetylene and hydrogen rise to several hundred parts-per-million as NVO SOI is retarded toward top center of NVO. Since experiments have previously demonstrated that low concentrations of acetylene seeded into the intake flow advance combustion phasing, the current results support the conclusion that NVO fueling can chemically enhance main combustion.
Technical Paper
2014-04-01
Vickey B. Kalaskar, Derek A. Splitter, James P. Szybist
In recent years a number of studies have demonstrated that boosted operation combined with external EGR is a path forward for expanding the high load limit of homogeneous charge compression ignition (HCCI) operation with the negative valve overlap (NVO) valve strategy. However, the effects of fuel composition with this strategy have not been fully explored. In this study boosted HCCI combustion is investigated in a single-cylinder research engine equipped with direct injection (DI) fueling, cooled external exhaust gas recirculation (EGR), laboratory pressurized intake air, and a fully-variable hydraulic valve actuation (HVA) valve train. Three fuels with significant compositional differences are investigated: regular grade gasoline (RON = 90.2), 30% ethanol-gasoline blend (E30, RON = 100.3), and 24% iso-butanol-gasoline blend (IB24, RON = 96.6). Results include engine loads from 350 to 800 kPa IMEPg for all fuels at three engine speeds 1600, 2000, and 2500 rpm. All operating conditions achieved thermal efficiency (gross indicated efficiency) between 38 and 47%, low NOx emissions (≤ 0.1 g/kWh), and high combustion efficiency (≥96.5%).
Technical Paper
2014-04-01
Thomas G. Leone, Edward D. Olin, James E. Anderson, Hosuk H. Jung, Michael H. Shelby, Robert A. Stein
Engine dynamometer testing was performed comparing fuels having different octane ratings and ethanol content in a Ford 3.5L direct injection turbocharged (EcoBoost) engine at three compression ratios (CRs). The fuels included midlevel ethanol “splash blend” and “octane-matched blend” fuels, E10-98RON (U.S. premium), and E85-108RON. For the splash blends, denatured ethanol was added to E10-91RON, which resulted in E20-96RON and E30-101 RON. For the octane-matched blends, gasoline blendstocks were formulated to maintain constant RON and MON for E10, E20, and E30. The match blend E20-91RON and E30-91RON showed no knock benefit compared to the baseline E10-91RON fuel. However, the splash blend E20-96RON and E10-98RON enabled 11.9:1 CR with similar knock performance to E10-91RON at 10:1 CR. The splash blend E30-101RON enabled 13:1 CR with better knock performance than E10-91RON at 10:1 CR. As expected, E85-108RON exhibited dramatically better knock performance than E30-101RON. The data were used in a vehicle simulation of a 3.5L EcoBoost F150, which showed that E20-96 RON at 11.9:1 CR offers 5% improvement in tailpipe CO2 emissions and 1% improvement in miles per gallon (MPG) fuel economy relative to E10-91RON at 10:1 CR.
Technical Paper
2014-04-01
Randall D. Partridge, Walter Weissman, Takanori Ueda, Yoshihiro Iwashita, Paul Johnson, George Kellogg
ExxonMobil, Corning and Toyota have collaborated on an Onboard Separation System (OBS) to improve gasoline engine efficiency and performance. OBS is a membrane based process that separates gasoline into higher and lower octane fractions, allowing optimal use of fuel components based on engine requirements. The novel polymer-ceramic composite monolith membrane has been demonstrated to be stable to E10 gasoline, while typically providing 20% yield of ∼100 RON product when using RUL 92 RON gasoline. The OBS system makes use of wasted exhaust energy to effect the fuel separation and provides a simple and reliable means for managing the separated fuels that has been demonstrated using several generations of dual fuel test vehicles. Potential applications include downsizing to increase fuel economy by ∼10% while maintaining performance, and with turbocharging to improve knock resistance.
Technical Paper
2014-04-01
Caroline Nicola Orlebar, Arndt Joedicke, William Studzinski
Abstract This study investigates the effects of octane quality on the performance, i.e., acceleration and power, and fuel economy (FE) of one late model US vehicle, which is powered by a small displacement, turbocharged, gasoline direct injection (GDI) engine. The relative importance of the gasoline parameters Research and Motor Octane Number (RON and MON) in meeting the octane requirement of this engine to run at an optimum spark timing for the given demand was considered by evaluating the octane index (OI), where OI = (1-K) RON + K MON and K is a constant depending on engine design and operating conditions. Over wide open throttle (WOT) accelerations, the average K of this Pontiac Solstice was determined as −0.75, whereby a lower MON would give a higher OI, a higher knock resistance and better performance. Over a part load cycle, a positive average K value was identified, whereby higher MON would give a (generally desirable) higher octane index, however, because lower load operation tends to be less constrained by knock, the impact of MON (high or low) on FE and efficiency under such conditions is smaller.
Technical Paper
2014-04-01
Stefano Fontanesi, Giuseppe Cicalese, Giuseppe Cantore, Alessandro D'Adamo
Abstract In order to improve fuel conversion efficiency, currently made spark-ignited engines are characterized by the adoption of gasoline direct injection, supercharging and/or turbocharging, complex variable valve actuation strategies. The resulting increase in power/size ratios is responsible for substantially higher average thermal loads on the engine components, which in turn result in increased risks of both thermo-mechanical failures and abnormal combustion events such as surface ignition or knock. The paper presents a comprehensive numerical methodology for the accurate estimation of knock tendency of SI engines, based on the integration of different modeling frameworks and tools. Full-cycle in-cylinder analyses are used to estimate the point-wise heat flux acting on the engine components facing the combustion chamber. The resulting cycle-averaged heat fluxes are then used in a conjugate heat transfer model of the whole engine in order to reconstruct the actual point-wise temperature distribution of the combustion chamber walls.
Technical Paper
2014-04-01
Young Suk Jo, Raymond Lewis, Leslie Bromberg, John Heywood
Abstract 1 Downsizing and turbocharging a spark-ignited engine is becoming an important strategy in the engine industry for improving the efficiency of gasoline engines. Through boosting the air flow, the torque is increased, the engine can thus be downsized, engine friction is reduced in both absolute and relative terms, and engine efficiency is increased. However knock onset with a given octane rating fuel limits both compression ratio and boost levels. This paper explores the operating limits of a turbocharged engine, with various gasoline-ethanol blends, and the interaction between compression ratio, boost levels, and spark retard, to achieve significant increases in maximum engine mean effective pressure and efficiency.
Technical Paper
2014-04-01
Zhi Wang, Hui Liu, Tao Song, Yaqi Xu, Jian-Xin Wang, Dong-Sheng Li, Tao Chen
Abstract High boost and direct injection hold the potential of enhanced power density and fuel consumption in the development of gasoline engines. However, super-knock with strong destructiveness was widely reported at low-speed and high-load operating regime in turbocharged GDI engines. The objective of this study is to clarify the characteristics of super-knock and to try to find some feasible solutions to suppress super-knock. To fast evaluate super-knock at low-speed and high-load regime, a rapid test procedure including three super-knock test sections of 5000 cycles with 3 idle operations, was proposed. The experimental data indicate that pre-ignition is not the sufficient condition for super-knock. Pre-ignition may lead to super-knock, heavy knock, slight knock, and non-knock. Compared with conventional knock, knock intensity of super-knock is much higher and the maximum amplitude of pressure rise at start of knock is more than one order of magnitude higher. This paper also clarifies that the injection strategies highly influence the frequency of super-knock occurrence in the turbocharged GDI engine.
Technical Paper
2014-04-01
Karel Steurs, Christopher Kim Blomberg, Konstantinos Boulouchos
Abstract Knock is studied in a single cylinder direct injection spark ignition engine with variable intake temperatures at wide open throttle and stoichiometric premixed ethanol-air mixtures. At different speeds and intake temperatures spark angle sweeps have been performed at non-knocking conditions and varying knock intensities. Heat release rates and two zone temperatures are computed for both the mean and single cycle data. The in-cylinder pressure traces are analyzed during knocking combustion and have led to a definition of knocking conditions both for every single cycle as well as the mean engine cycle of a single operating point. The timing for the onset of knock as a function of degree crank angle and the mass fraction burned is determined using the “knocking” heat release and the pressure oscillations typical for knocking combustion. A detailed chemical kinetic model for ethanol combustion is used to compute ignition delay times (IDT) for stoichiometric ethanol-air mixtures at pressures and temperatures relevant to the conditions measured on the engine test bench.
Technical Paper
2014-04-01
Namho Kim, Seokwon Cho, Hoimyung Choi, Han Ho Song, Kyoungdoug Min
Abstract Ethanol, one of the most widely used biofuels, has the potential to increase the knock resistance of gasoline and decrease harmful emissions when blended with gasoline. However, due to the characteristics of ethanol, a trade-off relationship between knock tolerance and BSFC exists which is balanced by the blending ratio of gasoline and ethanol. Furthermore, in a spark-ignited engine, it is reported that the blending ratio that maximizes thermal efficiency varies based on the engine operating conditions. Therefore, an injection system that can deliver gasoline and ethanol separately is needed to fully exploit the benefit of ethanol. In this study, PFI injectors and a DI injector are used to deliver ethanol and gasoline, respectively. Using the dual fuel injection system, the compression ratio was increased from 9.5 to 13.3, and the knock mitigation characteristics at the full load condition were examined. Changes in thermal efficiency and emission characteristics were also investigated at full load and part load conditions.
Technical Paper
2014-04-01
Yunliang Qi, Yaqi Xu, Zhi Wang, Jianxin Wang
Super knock which occurs in highly boosted spark ignition engines in low speed pre-ignition regime can lead to severe engine damage. However, super knock occurs occasionally, it is difficult to clearly identify the causes. The widely accepted assumption for the cause of this phenomenon is oil intrusion. Most of oils have been proved to have higher cetane number than n-heptane dose, indicating that the intruded oil is very liable to auto-ignition in a boosted engine. Although there have been reported the type of base oil and additive has significant effect on pre-ignition frequency, the oil induced super knock is still so far not supported by any direct evidence. This paper presents the effect of direct oil intrusion into cylinder on super knock. The experiment was carried out in a single cylinder engine. The diluted oil by gasoline with different ratio was directly injected into cylinder using a modified single-hole injector with 4MPa injection pressure. The results showed that oil intrusion before TDC could indeed induce pre-ignition then cause knock.
Technical Paper
2014-04-01
Claudio Forte, Enrico Corti, Gian Marco Bianchi, Stefania Falfari, Stefano Fantoni
Abstract Knocking combustions heavily limits the efficiency of Spark Ignition engines. The compression ratio is limited in the design stage of the engine development, letting to Spark Advance control the task of reducing the odds of abnormal combustions. A detailed analysis of knocking events can help improving engine performance and diagnosis strategies. An effective way is to use advanced 3D CFD (Computational Fluid Dynamics) simulation for the analysis and prediction of combustion performance. Standard 3D CFD approach is based on RANS (Reynolds Averaged Navier Stokes) equations and allows the analysis of the mean engine cycle. However knocking phenomenon is not deterministic and it is heavily affected by the cycle to cycle variation of engine combustions. A methodology for the evaluation of the effects of CCV (Cycle by Cycle Variability) on knocking combustions is here presented, based on both the use of Computation Fluid Dynamics (CFD) tools and experimental information. The focus of the numerical methodology is the statistical evaluation of the local air-to-fuel and turbulence distribution at the spark plugs and their correlation with the variability of the initial stages of combustion.
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