The proposed new European emission standards (EURO VI) to be in force by 2013/2014 are considered very severe, having a NO_x-standard of 0.4 g/kWh in the European Transient Cycle (ETC) together with a low particulate limit of 0.01 g/kWh. Above limits require significant in-cylinder reductions of pollutants as well as exhaust gas aftertreatment for both, nitrogen oxides and particulates. Furthermore, due to the much discussed climate change, the emissions of greenhouse gases (GHG) are to be reduced. For EURO VI, the first step will be to reduce engine-out emissions by means of advanced combustion process development using improved fuel injection equipment, supercharging, exhaust gas recirculation, flexible engine systems, extended engine control and by the mechanical development. Then it would appear that exhaust gas aftertreatment systems are needed. Since approximately 30 % of the fuel input is lost in the exhaust gas, an exhaust gas energy recuperation might be a step forward to reduce fuel consumption and GHG-emissions. In a second part an overview of the EU R&D-project GREEN will be given. In this project, European HD engine manufacturers join forces with suppliers, academia and leading engineering institutes. The common goal is to promote future advanced engine technologies to achieve lower emissions, lower fuel consumption and improved sustainability for future fuels. The main objective of GREEN is to perform research, which will lead to innovative sub-systems for heavy duty engines. The project puts emphasis on diesel engines for trucks and rail applications and on natural gas engines for city transport applications.

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Gasoline, diesel, and other alternative transportation fuels contain hundreds to thousands of compounds. It is currently not possible to represent all these compounds in detailed chemical kinetic models. Instead, these fuels are represented by surrogate fuel models which contain a limited number of representative compounds. We have been extending the list of compounds for detailed chemical models that are available for use in fuel surrogate models. Detailed models for components with larger and more complicated fuel molecular structures are now available. These advancements are allowing a more accurate representation of practical and alternative fuels. We have developed detailed chemical kinetic models for fuels with higher molecular weight fuel molecules such as n-hexadecane (C16). Also, we can consider more complicated fuel molecular structures like cyclic alkanes and aromatics that are found in practical fuels. For alternative fuels, the capability to model large biodiesel fuels that have ester structures is becoming available. These newly addressed cyclic and ester structures in fuels profoundly affect the reaction rate of the fuel predicted by the model. Finally, these surrogate fuel models contain large numbers of species and reactions and must be reduced for use in multi-dimensional models for spark-ignition, HCCI and diesel engines.

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Vehicle emissions have dropped dramatically over the past decades, especially with the introduction of ultra low emission vehicles. Emission measuring instruments and systems have kept pace with the challenges, but the changing face of emissions testing has meant that new and more advanced systems have replaced the more familiar, traditional methods. This paper describes the challenges for powertrain emission measurements and the advanced systems that have been developed to meet them.

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For next-generation low-emission vehicles, the Super Clean Diesel (SCD) Engine has been researched and developed. Many devices using the concept of high boost and wide range and high EGR compared with a current system were installed in the six-cylinder engine. Both the low-pressure loop EGR system and the high-pressure one are adopted for reduction of NO_x and PM with the higher EGR rate. In this study, the SCD engine is tuned using a steady state test. Finally, the tuned SCD Engine is tested using the JE05 transient test cycle.

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To evaluate a clean diesel combustion concept, the following technologies were installed on a single cylinder research engine for reducing exhaust emissions: a high boost charging, a high rate and cooled EGR and high injection pressure (Pinj). The Digital Hydraulic Variable Valve Actuation (DHVVA) will also be installed as one of the enabling technologies for the reduction of exhaust emissions utilizing flexible valve lift and timing. The timings of intake valve close (IVC) are significant to increase volumetric efficiency (ηv) and the maximum iv has been obtained at 560 degrees of crank angle. When the maximum iv is realized, the maximum EGR rate is also obtained due to BSNO_x and smoke being at minimum at full load condition. DHVVA can open the exhaust valve in the intake stroke, enabling the introduction of exhaust gas into the cylinder providing internal residual gas difference and reducing pumping losses. DHVVA is effective to increase volumetric while also enabling efficiency and reductions of exhaust emissions and improvement of fuel consumption.

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Research has been conducted on an extended expansion engine, using a multiple linkage system to increase the thermal efficiency of general-purpose engines. A four jointed linkage was used between the connecting rod and the crank pin of a standard piston-crank system. The end of the linkage rotates at half the speed of the crankshaft, resulting in piston strokes unequal length in each revolution. The length of the expansion stroke is greater than that of the compression stroke, thereby providing an extended expansion cycle.

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Variable engine mechanisms, such as variable compression ratio (VCR) and variable valve actuation (VVA) technologies, are being studied for improving fuel economy. The authors have developed a unique multiple-link VCR mechanism and a variable valve event and lift (VVEL) system as VVA mechanisms. This study examined the potential for improving fuel economy by using a system that combines both the multiple-link VCR and VVEL technologies. The multiple-link VCR mechanism achieves a longer piston stroke characteristic that resembles a simple sine curve. This unique long-stroke configuration suppresses the increase in the surface-to-volume (S/V) ratio of the combustion chamber as the compression ratio is raised, thereby avoiding an increase in the cooling loss. The VVEL system is effective in reducing the pumping loss by using the Miller-cycle under a low-load condition. In addition, the combination with the VCR mechanism expands the EGR limit by maintaining a higher effective compression ratio, resulting in reduced cooling loss. A prototype engine combining the long-stroke multiple-link VCR and VVEL systems was built and evaluated with regard to fuel economy. The results showed that fuel economy was improved by over 20% under a low-load condition through significant reductions of the cooling loss, exhaust loss and pumping loss.

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Diesel particulate and NO_x Reduction system (DPNR) is an effective device for clean diesel aftertreatment system. The NO_x reduction is using NO_x Storage and Reduction (NSR) mechanism. However, NSR catalyst has some issues about deterioration. Therefore, further improvement is hoped for cleaner air in the future. This paper reviews the results of our study to improve the NO_x reduction performance of NSR system. NSR catalyst performance decreases because of thermal stress and sulfur poisoning. In order to improve the thermal resistance of the catalyst, we have studied the suppression of precious metal sintering using Pt-O-Ce bond. As a result, higher catalytic activity after aging especially under lower temperature condition was obtained. On the other hand, improvement for the sulfur tolerance is one of the key technologies to keep the high NO_x conversion efficiency. The temperature uniformity of NSR catalyst on desulfurization control and the catalyst improvement are effective for higher sulfur tolerance. In addition to these suppressions of the deterioration, NO_x reduction method is also important factor. The NO_x reduction method by in-cylinder rich is effective at lower temperature, and by on-catalyst rich using exhaust diesel fuel injection is also effective at higher temperature. Therefore, this combination is a beneficial solution. As a result of these improvements, it is shown that the NSR catalyst has higher NO_x conversion efficiency of over 70% on New European Driving Cycle (NEDC) mode. Moreover, sulfur trap concept has more potential with lower Platinum Group Metal (PGM) loading thanks to improvement of thermal and sulfur tolerance.

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Some manufacturers of heavy-duty commercial vehicles have adopted Urea-SCR system that can significantly reduce NO_x exhaust gas emissions by using a catalyst for the purpose of meeting the Japanese New Long-term Diesel Emissions Regulation. This system can satisfy the demand for excellent fuel economy as well as reduced emissions. With engine modification. combustion efficiency is imnroved. thereby fuel economy is enhanced and engine-out emissions of PM are also reduced simultaneously. Though NO_x emissions increase considerably as a resultant trade-off, a Urea-SCR catalyst is used as an after-treatment technology to reduce the NO_x level. As global exhaust emissions regulations will be further strengthened in the near future, along with newly revised fuel consumption standards, the adoption of DPF together with the enhanced catalytic conversion efficiency for the Urea-SCR system is indispensable. Moreover, miniaturization of the after-treatment system is also an important issue. In order to enhance conversion efficiency of the Urea-SCR system, the improvement of (i) catalyst performance itself, (ii) urea dosing system, and (iii) the exhaust gas flow, etc. are required. At first, we focused on improved catalyst performance itself that could have bigger effect on conversion efficiency. The catalyst materials were improved to increase adsorption capability of the NH_3 as a reducing agent, resulting in increased NO_x and NH_3 reaction rates on the catalyst. Furthermore, capacity of the SCR catalyst was increased and oxidation performance in the oxidation catalyst was optimized, which led to enhanced NO_x conversion efficiency of the system not only in a steady cycle but also in a transient cycle. In addition, the new concept of 'the Urea-SCR system with the DPF function' was proposed for the miniaturization of the system.

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The effect of mixture heterogeneity on PCCI combustion was analyzed using the Large Eddy Simulation model in combination with the reaction kinetics. The aim of this analysis is to find the statistical characteristics of the mixture heterogeneity of the fuel, EGR-gas and temperature distributions in a turbulent flow field for moderating extreme pressure rise and for extending an output limit. The initial velocity field at the beginning of compression was given by a new method, which generated statistically reasonable turbulent velocity fluctuations. The auto-ignition and combustion behaviors were analyzed for several different sets of the rms and the length scale of the spatial fluctuations in the fuel mass fraction, EGR-gas mass fraction and temperature. The analysis shows that the combination of a larger rms value and a longer length scale of the spatially fluctuating fuel mass fraction is effective to slow the combustion in a hot flame reaction phase and to extend a knock limit, and that the heterogeneous distribution of the EGR-gas gives a similar effect. The result shows that non-uniform temperature distribution is not so effective under the conditions tested.

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Direct numerical simulation (DNS) of ignition/propagation and auto-ignition of turbulent premixed flames has been conducted to investigate turbulent combustion mechanism in PCCI and HCCI engines. DNS are conducted for hydrogen/air, methane/air and n-heptane/air mixtures by considering detailed or reduced kinetic mechanism. From DNS of ignition/propagation of homogeneous and inhomogeneous mixtures, effects of turbulence characteristics, fuel species and pressure on the ignition and propagation processes are clarified. The ignition delay of the premixed mixture is correlated with mean strain rate near the ignition kernel. For high intensity and fine scale turbulent field, multiple-point ignition is observed even for a single initial ignition kernel, which is caused by the local suppression of radical production by turbulence. From DNS of auto-ignition of turbulent premixed flames, effects of turbulence and inhomogeneity of mixture on the auto-ignition process are investigated. Even for the homogeneous mixture, temperature in the auto-ignition process fluctuates in space, while this fluctuation slightly affects on global combustion process of the mixture. As for the hydrogen, inhomogeneity effects are not significant due to molecular diffusion of hydrogen. For hydrocarbons, however, inhomogeneity of the mixture changes auto-ignition process. Form these DNS with different combustion field, turbulent combustion mechanism in PCCI and HCCI engines is discussed.

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This paper studied the potential of HCCI higher load extension by using there types of stratified charge, including temperature (thermal) stratification, concentration (fuel) stratification and species (EGR) stratification. To isolate the influence of three stratifications on HCCI engine performance, HCCI combustion processes with different equivalence ratios, stratification degree, EGR ratios were simulated. The results show that stratification leads to earlier ignition timing, sequential heat release, longer combustion duration, lower rate of pressure rise compared to pure homogeneous cases at same load. However, both fuel stratification and EGR stratification lead to high NO_x. Temperature stratification is most effective one to significantly reduce pressure rise rate during CI combustion process with least negative effect of high NO_x emission or incomplete combustion. With limit of maximum pressure rise rate at 5bar/CA and maximum NO_x emissions at 100ppm, the maximum IMEP of pure HCCI without EGR is 1.86bar, the maximum IMEP can be further extended to 5.4bar using temperature stratification and EGR dilution, under natural aspiration conditions.

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In HCCI engines, high load operation is limited by an excessive pressure rise rate (PRR). Past studies showed that mixing stratification with the fuel that has large heat release in low temperature reaction (LTR), disperses the timing of local ignition and slows the PRR. The purpose of this study was to gain a better understanding of effect of the mixing stratification on HCCI combustion using chemiluminescence imaging. Di-methyl ether (DME) which has large heat release in LTR and n-Butane, smaller heat release in LTR than that of DME, were used. Experiments were conducted on five mixing conditions depending on the combination of the charging methods (homogeneous charge or stratified charge) of DME and n-Butane, using a single-cylinder engine equipped with optical access. Chemiluminescence imaging was used to assess a local combustion phasing. The experimental observation shows that, in the case of fuels stratification, maximum PRR is reduced compared to the case of fuels homogeneity. In the stratified case, the start timing of local chemiluminescence is dispersed and total chemiluminescence duration is longer than that of the homogeneous case.

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The introduction of more stringent standards for engine emissions requires a steady development of engine control strategies in combination with efforts to optimize in-cylinder combustion and exhaust gas aftertreatment. This study presents a simulation approach combining an engine and vehicle model. A well established 1D gas dynamics and engine simulation model is extended by five key features. These are models for (1) general species transport, in-cylinder (2) combustion and (3) pollutant formation, (4) catalytic pollutant conversion and (5) manifold wall wetting. The model is used to investigate the effect of retarded spark timing on engine out and tailpipe emissions during the first 60 seconds of a NEDC. The results lead to the conclusion that the applied simulation approach has the potential to reduce the experimental effort on a roller dynamometer in future.

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One of the major motivators for diesel combustion work is the need for better understanding of the combustion and emission formation processes in diesel engines. This need is driven by pressures from several different directions. One of the most important pressures imposed on transportation systems is the need to be environmentally-friendly. Another pressure is energy efficiency. The requirements of clean environment often clash with those of energy efficiency. Studies of the various stages of the traditional diesel diffusion combustion model are leading to new insights into physical and chemical phenomena that occur during heat release. Research at Southwest Research Institute (SwRI) is capitalizing on these phenomena to benefit in maintaining engine performance as well as low emissions. In this paper the fundamentals of low flame temperature combustion are reviewed with specific emphasis on NO・and soot formation. The understanding gained is applied to a diesel engine designed for off-road applications and the results are demonstrated.

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Because of trade-off relationship between fuel economy and exhaust temperature, the optimization of engine system parameters should be considered not only engine-out emissions but also catalytic conversion efficiency. Therefore, "Total Engine Simulation System (TESS)" with diesel spray combustion model based zero-dimensional phenomenological mode was developed to predict torque and exhaust emissions of diesel engine system equipped aftertreatment devices under JE-05 mode. TESS is useful for the development process both engine and aftertreatment device in the early stages. Moreover, TESS becomes useful for the development of engine control strategy: hence, TESS helps accelerate the engine calibration process. The purpose of this paper is to describe an outline of TESS and the investigation of low emission and fuel consumption diesel engine system by using TESS as an example.

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The continuously tightening emission legislations all over the world require more and more complex engine control and exhaust gas after-treatment systems. This confronts current engine development with the need for ever more complex engine systems with a continuously increasing amount of parameters that have to be calibrated and controlled in continuously decreasing time frames. In order to keep the development costs within reasonable limits, the use of model-based approaches is currently widely spreadening. Due to their high potential for calibration, the role of statistical models is also gaining importance. The combination of static statistical models trained by measurement data gained by the classical DoE process has shown great success in recent years and is now state of the art. However, the ability of static models to predict the exhaust gas emissions during the start and the warm-up phase, which are currently coming into the focus of exhaust gas regulations, is still very limited. In this work, we present an approach, which achieves good accuracy for the prediction of the exhaust gases in these crucial operating states, by combining dynamical statistical models with a dynamical DoE for the test bed measurements.

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The characteristics of smokeless low temperature diesel combustion with various fuel-air mixing were systematically studied by engine tests with large quantities of cooled EGR and fuels of various cetane numbers, as well as by CFD simulation of the in-cylinder distributions of mixture concentrations and temperatures. The results show that in addition to combustion temperature, fuel-air mixing is also important for efficient, smokeless, and low-NO_x diesel combustion. Smokeless and low-NO_x diesel combustion can be established even with insufficient fuel-air mixing as long as the combustion temperature is sufficiently low, but at the expenses of very high UHC and CO emissions, and severe deterioration in the combustion efficiency. While smoke is influenced by combustion temperature, it depends strongly upon the premixing time from the end of fuel injection to the onset of ignition. When ignition occurs later than about 4℃A after the end of fuel injection at 1320 rpm, there is smokeless combustion regardless of fuel cetane number and fuel injection timing, and NO_x is suppressed to near zero levels by large quantities of cooled EGR.

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The fuel efficiency of the low temperature combustion (LTC) cycles is commonly compromised by the high levels of hydrocarbon (HC) and carbon monoxide (CO) emissions. More seriously, the scheduling of fuel delivery in HCCI engines has lesser leverage on the exact timing of auto-ignition that may even occur before the compression stroke completes, which may cause excessive efficiency reduction and combustion roughness. New LTC control strategies have been explored experimentally to achieve ultra low emissions under independently controlled EGR, intake boost, exhaust backpressure, and multi-event fuel injection with up to 12 fuel injection pulses per cycle for conventional diesel and neat bio-diesel fuels. Adaptive control strategies based on cylinder pressure characteristics have been implemented to enable and stabilize the LTC when heavy EGR is applied. The impact of heat release phasing, duration, shaping, and splitting on the thermal efficiency has been analyzed with engine cycle simulations. Oxygen sensors at the intake and exhaust of the engine are devised to comprehend the transient impacts of EGR, boost, and load variations.

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The authors have applied flash boiling spray of mixed fuel into premixed charge compression ignition engine to achieve low soot and NO_x emissions while keeping high thermal efficiency because it allows early fuel injection timings without suffering from wall-wetting of fuel or poor mixture preparation. In this case, however, the homogeneous mixture formed causes rapid combustion, leading to combustion noise and knocking issue. To control the heterogeneity of air-fuel mixture and to mitigate the steep heat release, this paper employed a partially premixed charge operation using multiple fuel injections. Through engine tests, better mixture preparation of flashing spray was demonstrated for early injection. Furthermore, the combustion and emissions characteristics of a partially premixed charge operation were evaluated for several combinations of secondary injection timings and the percentages of secondary injection quantity.

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The objective of this study is to find strategies for extending the load range of low-temperature combustion (LTC) while improving thermal efficiency and reducing combustion noise and exhaust emissions. Experiments were performed using a single-cylinder direct-injection diesel engine equipped with a common-rail injection system and a cooled EGR system. First, experiments were carried out with single-stage injection. The results indicated a notable improvement of NO_x and smoke emissions by selecting lower EGR rates and later injection timing according to the increase in injection quantity. However, the problems of high pressure rise rates and unburned species emissions developed. To solve these problems, two-stage injection was applied. Additional experiments started with the injection and EGR conditions based on the results of single-stage injection tests, and modifications were made to mitigate the increased emissions and decreased thermal efficiency. Through the process of optimizing the conditions, a control strategy of two-stage injection was proposed.

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Low-temperature diesel combustion in conjunction with high levels of EGR is being paid much attention and investigated due to its ultra-low NO_x and soot emissions. The compound combustion as a new low temperature combustion technology has been proposed previously by authors, which combined Premixed Charge Compression Ignition (PCCI) and Lean Diffusion Combustion (LDC), where fuel and air are premixed to a lean equivalence ratio less than 2 before the onset of high-temperature heat release. The compound combustion is mainly dominated by the oxygen concentration and mixing. In order to have an insight into the effects of mixing on low temperature diesel combustion, a quantitative "φ(equivalence ratio)-T(temperature)" map for CO formation has been created by performing the zero dimensional calculations using a detailed chemistry of n-heptane in this study. Then a two-zone combustion model accounting for both heat loss and mass transferred between the two zones is developed to explore the lean diffusion combustion process for different EGR levels as well as mixing rates on the CO-φ-T map. The results show that at lean diffusion combustion phase, when the mixing rate is too high, NO_x emissions increase, and when the mixing rate is too low, CO emissions increase. As the EGR rate increases, mixing rate at the phase must properly increase so as to reduce CO emissions, achieving high efficiency and low NO_x emissions simultaneously.

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A technique for in-cylinder stratification of external EGR gas for Direct Injection (DI) diesel engines was developed in order to reduce toxic exhaust emissions. EGR gas is supplied from one of the two intake ports which make upper swirl flow and lower swirl flow during the intake stroke. After the intake stroke, the vertical stratification of EGR gas is formed. In the final stage of compression stroke, a squish flow brings the vertically stratified gas into the piston cavity, and EGR gas is radially stratified in the piston cavity at the end of the compression stroke. This technique for stratification was developed by using unsteady computational fluid dynamics (CFD) simulation. Prior to exhaust emission tests, the accuracy of the simulation was evaluated by in-cylinder visualization using Laser Induced Fluorescence (LIF) imaging. Exhaust emission tests showed smoke reduction effect under medium load condition, when the EGR gas delivered to the inner part of the piston cavity. This smoke reduction effect was investigated by CFD simulation using a series calculation methodology from the injector nozzle internal flow to the in-cylinder fuel spray, mixture formation and combustion. At the beginning of the combustion, the higher concentration of EGR gas in the inner part of the cavity lowered combustion temperature and reduced the soot formation rate. The fresh air, which existed in the outer part of the cavity at the injection timing, accelerated the oxidization of the soot cloud at the latter period of the combustion.

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In 2002 the European Commission adopted a European Union strategy to reduce atmospheric emissions from seagoing ships. The strategy reports on the magnitude and impact of ship emissions in the EU, and sets out a number of actions to reduce the contribution of shipping to health and climate change. One possible approach for the reduction of NO_x and soot emissions of marine diesel engines is the use of multiple injection strategies, similar to the ones used in automotive diesel engines. In this way, diesel combustion could be optimized with respect to pollutant emissions, without compromising fuel efficiency. Our interest is in investigating the potential for emissions reduction and overall optimization of combustion in large two-stroke marine diesel engines, using numerical simulation. In this context, we study the effects of advanced injection strategies by utilizing Computational Fluid Dynamics (CFD) tools. We use the KIVA-3 code as the modeling platform, with improved models for spray breakup, autoignition and combustion. Here, we report first results, corresponding to pilot injections, which are visualized for the fuel injection and combustion processes, and are also mapped on temperature - equivalence ratio charts (T φ maps). This analysis reveals important information on pollutant formation mechanisms in large marine diesel engines, and suggests that fuel savings with simultaneous reduction of soot emissions may be feasible.

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Exhaust gas recirculation (EGR) is widely used for reduction of NO_x emission from diesel engines. However, particulate matter emission and thermal efficiency tend to be worse at the high EGR ratios. EGR induces the heterogeneous distributions of oxygen and temperature in a combustion chamber and these heterogeneities affect the emissions and combustion characteristics of diesel engine. If the heterogeneities of oxygen and temperature distributions can be controlled, it is expected that the simultaneous reduction of NO_x and PM from diesel engine will be achieved by active control of internal and external EGR devices. In this study, the NO_x and PM emissions and combustion characteristics of diesel combustion achieved in various distributions of oxygen concentration and temperature are investigated in order to clarify the effect of these heterogeneities of surroundings on the diesel combustion. The experiment was conducted with the rapid compression expansion machine (RCEM) and the combustion chamber in which various distributions of intake gas can be formed. The enthalpy and the amount of oxygen entrained into the spray upstream the ignition region are selected as the parameters in order to clarify the effect of heterogeneities of surrounding conditions on the diesel spray combustion. The results indicated that the NO_x and soot emissions from diesel combustion are governed mainly by the amount of enthalpy entrained into the spray upstream the ignition region, when the temperature distribution in a chamber is changed with keeping the oxygen fraction at constant.

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Numerical simulations and experiments have been carried out to meet the next IMO(International Maritime Organization) Tier2 NO_x regulations, which would be determined to reduce about 19-21% of the current limit for medium-speed diesel engine. The selected parameters in this study are piston bowl shape, fuel injection nozzle configuration and fuel injection rate. The behavior of spray and combustion phenomena in diesel engine was examined by the three-dimensional FIRE code. As a droplet breakup model, the wave breakup model was used. In order to predict spray characteristics accurately in the wide range of ambient gas density, the model constant B_1 with respect to breakup time was set as a function of ambient gas density ρ, B_1=1.4239×ρ+0.2093. The spray visualization experiment was performed in the constant-volume high-pressure chamber to clarify the numerical results on the spray characteristics of the spray angle and penetration. The fuel injection rig test was performed to know the fuel injection rate profile as an input data for the numerical analysis by using Bosch-tube injection rate metes. The computational results for the two different nozzle configurations were verified with the experimental data on the cylinder pressure, fuel consumption and NO_x formation through adjustment of some model constants at 50% load. The effects of fuel injection nozzle, piston bowl and fuel injection rate on the engine performance were investigated to find the optimum parameters on NO_x control. Finally, 23.7% NO_x reduction could be achieved with 0.71% deterioration in fuel consumption to meet the next IMO Tier2 regulations.

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To develop an understanding of the combustion produced by two different valve strategies the techniques of combustion imaging, for flame front propagation, and laser Doppler anemometry, LDA, for the air flow and turbulence characteristics in the vicinity of the spark plug were applied in the optical engine configured to replicate the 2000 rpm 2.7 bar IMEP load point of a conventional thermodynamic engine for both valve strategies. A sequence of combustion images were taken at 4^0 CA intervals to span the entire combustion event with fifty images taken at each crankangle to produce a mean image for each crankangle in the sequence. A Matlab code, utilising the "jet" colormap, identified the minimum and maximum visible flame intensity levels and the intensity contour corresponding to the flame front overlaid with the combustion chamber outline. A radial coordinate system was applied which allowed the flame front propagation and velocity to be quantified in both the vertical and horizontal planes. Laser Doppler anemometry was applied to quantify the time resolved mean and fluctuating flow characteristics of the axial and cross flow components directly below the spark plug in the pent roof. The engine was motored, without fuel injection, to establish the flow field likely to exist at the time of spark and the appearance of the flame kernel.

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The purpose of this research has been to investigate the influence of turbulence on charge consumption and flame front propagation. There are two aspects of this work: Firstly, engine based research has been carried out in order to ascertain the turbulent structures that affect combustion. Secondly, a technique for quantifying the interaction between flame propagation and specific flow structures has been developed within a twin chamber combustion bomb. The levels of turbulence that exist within each cycle of a single cylinder DISI engine have been measured using high speed particle image velocimetry (HSPIV), then compared to engine output in terms of IMEP and the rate of charge consumption. In order to determine the range of spatial and temporal scales of turbulence that affect the burn rate and IMEP, frequency analysis was carried out upon the velocity field data. This analysis was achieved by FFT filtering the HSPIV data captured in the vicinity of the spark plug, separating the velocity fields into low frequency bulk motion and high frequency turbulence components. The data demonstrates that removing fluctuating components with a frequency below 240Hz successfully removes the variation in bulk motion from the calculation of turbulence intensity, revealing the relationship between high frequency turbulence and charge consumption. Moreover, FFT filtering of fluctuating components above 600Hz reduced the correlation between high frequency turbulence and IMEP, demonstrating the influence of these high frequency/small scale turbulent structures on flame propagation rate, and thereby rate of charge consumption and engine performance. In conjunction with the engine based analysis, research has also been carried out on the fundamental interaction between flame and flow within a twin-chamber combustion bomb. The study of the stable and repeatable flow structures produced within the bomb, which replicate known engine turbulence length scales, holds distinct advantages over the complex three-dimensional turbulent fields of the SI engine. The purpose of this data is to develop further understanding of the physical and chemical processes of turbulent flame propagation. As part of this work a new algorithm for the calculation of local burning velocity has been developed. Applying this new approach, through the use of multiple camera asynchronous PIV, has enabled the measurement of local burning velocity of a flame front as it interacts with a rotational flow.

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Many studies have already been conducted in order to improve knowledge on impacts of tumble motion on combustion processes. Furthermore, many studies have also been performed to study the links between flame kernel behaviour and combustion stability. But only a few experimental studies have concentrated on the links between local conditions during the ignition, including the spark itself, and flame kernel. With this study we aim at specifying the occurrence of combustion instabilities, as well as their key factors connected to air flow motion. Thus the current paper presents a study led on 4-valve spark ignition optical single cylinder engine. Different operating conditions were characterized using several optical and non optical diagnostics. The diagnostics used were PIV measurement in the combustion chamber, direct visualizations of the spark and flame visualizations. Additionally, recordings of the intensity and the voltage of the secondary side of the ignition coil, as well as in-cylinder pressure were acquired. The provided analysis confirmed the importance of the link existing between air flow motion prior to spark and combustion stability. Regarding the impact of tumble motion on combustion, it has been showed that the more velocity is obtained at the vicinity of the spark plug, the more cyclic fluctuation of air flow motion occurs. Nevertheless, analyses confirmed that stronger tumble motion is favourable to decrease in the ignition delay by convection of the spark and consecutive flame kernels further from spark plug electrodes, which is directly linked to the resulting ignition duration. Thus the air flow needed at the ignition timing has to be optimized for higher flow velocity, rather than higher flow reproducibility with lower flow velocity.

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A new gasoline combustion engine system with high compression ratio was studied and proposed in order to achieve higher thermal efficiency than that of a conventional SI engine. A special cranking mechanism was adopted which allowed the piston to move rapidly near TDC. Some mechanisms were proposed and two of them were designed and built for the testing. The experimental results showed that knocking was avoided and better indicated thermal efficiency was obtained. An inconstant speed gear mechanism with compression ratio of 14 could be operated up to 2500 r/min and thermal efficiency was improved by 18% compared to a conventional engine with compression ration of 10. Also, a cam mechanism driven by a planetary gear was tested to achieve higher engine speed up to 4000 r/min, but the improvement of thermal efficiency was not so large as much as of the inconstant speed gear mechanism.

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In the automotive industry, today's major objectives concern the reduction of pollutant emissions and fuel consumption while improving performance and driveability. For this purpose, during the last decade, the classical engine has evolved towards a very complex system combining many hi-tech components with advanced control strategies. Optimising the whole engine system and controlling its behaviour has then become a real challenge for car manufacturers. In this context, powertrain simulation tools have been shown to provide an undisputable support during all stages of engine development from concept design to control strategies development and calibration. However these tools require sophisticated models to be efficient, especially in the combustion chamber where combustion and pollutant formation processes take place. This paper presents a 0D physical combustion model devoted to the prediction of heat release and pollutants in SI engines. The originality of this model derives from the fact it is based on the reduction of the 3D CFD E-CFM (Extended Coherent Flame Model) model developed at IFP [1]. The CFM formalism distinguishes two zones : the fresh and the burnt gases, which are separated by a flame front and are both described by their temperature, mass and composition. The proposed model is an important evolution of the CFM-1D model previously published in [2]. It computes the rate of consumption of the fresh gases and is based on the calculation of the flame front surface using the real engine geometry and a 0D derivation of the flame surface density approach. Pollutants (CO and NO_x) are computed both through the flame front and within the burnt gases using a reduced kinetic scheme and a classical extended Zel'dovitch mechanism. The whole model is validated against experimental data at several steady state operating points for two engine configurations. A good agreement with experiments is observed for both configurations, showing the interest of reducing 3D CFD models to build predictive 0D models for engine system simulations.

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A new combustion model has been introduced for the prediction of turbulent propagating combustion in SI engines. The model assumes that the flamelets consist of a turbulent dissipation part and a laminar part and is called Hybrid Fractal Flame Model (HFFM). A CFD code integrated the model and separately a pure laminar flamelet model, which was tested for comparison. Computational results were compared with measured pressures and heat release rates for several different engine speeds. It is shown that the HFFM agrees well with the measurements for 1000, 1500 and 1800 rpm, while the pure laminar flamelet model overestimates at lower engine speed and underestimates at higher engine speed. The analysis of the computed results indicates that the turbulent dissipation heat release rate contributes more to the total heat release rate as engine speed increases; from around 27% at 1000 rpm to 52% at 1800 rpm.

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Ethanol could play an important role to reduce the use of fossil fuels in the automotive industry together with a substantial increase in the efficiency of direct injection gasoline engines. As suggested by Cohn, Bromberg, and Heywood, the concept of ethanol DI boosted gasoline engine can facilitate the high compression ratio engine operation by reducing the knock constraint. In this concept, the direct injection of ethanol was proposed as an effective knock suppressant. As described, a small amount of ethanol could be used to reach the engine efficiency corresponding to injection of larger (by 30 %) amount of gasoline. Gasoline consumption and out emissions would be reduced by 25%. The concept has been validated for the small bore model engine using the KIVA3V code supplemented by the detailed chemistry approach. The chemical mechanism for gasoline surrogate/ethanol blend was constructed consisting of 129 species participating in 700 reactions. The gasoline surrogate model was constructed using sub-mechanisms for constituent components (iso-octane, toluene, and n-heptane in a selected proportion) from classes of hydrocarbons typical for gasoline. The mechanism was validated using shock-tube auto-ignition data taken from Sakai (University of Tokyo) and Gauthier (Stanford University) data compilations. The sub-mechanism of ethanol combustion is described by the reduced mechanism of Marinov (LLNL). The KIVA3V code was modified to treat the chemical mechanism developed and allowing injections of different fuels. The numerical results illustrate the possible efficiency gain for the model DI gasoline engine with conventional compression ratio within the range of 10-20% by ethanol injection in 10-20% of the total amount of fuel.

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Controlled autoignition in gasoline engines is a promising concept to simultaneously reduce both emissions and fuel consumption of internal combustion engines. To describe the spatial progress of the chemical reactions in three-dimensional simulations of CAI engine cycles an efficient combustion chemistry model was developed. To analyze the effects of mixture homogeneity on the progress of the reactions, thermodynamic analyses and numerical simulations of engine operation in HCCI mode have been performed based on experimental investigations with an optically-accessible single-cylinder engine. The numerical simulations were used to interpret the experimental observations in terms of mixing and reaction progress. Both experimental investigations and simulations show that injection timing is a feasible control parameter for the optimization of operating points because autoignition is influenced by the start of injection and the therewith connected temperature and mixture distribution. Furthermore spark assisted HCCI combustion at high load was investigated by thermodynamic analyses and com-bustion visualization. The results of the combustion visualization and heat release analyses suggest a superposition of flame front propagation and autoignition. Therefore the kinetic model to describe autoignition was coupled with a model to describe the turbulent flame propagation and three averaged cycles at different load were simulated. In all cases a good accordance between simulation and experiment can be stated. Like the results of the combustion visualiza-tion the simulations show a propagating flame front near the spark plug followed by sequential autoignition in the outer regions of the combustion chamber.

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The CAI engine, a kind of HCCI engine, as a new type of gasoline engine is one of the eco-friendly engines. The main merits of CAI engines are low NO_x emission and fuel economy. Combustion of CAI engine is purely dominated by fuel chemical reactions. In order to simulate the combustion of CAI engine, a reduced chemical kinetic mechanism of gasoline surrogate and multi-zone method is proposed in this paper. A reduced chemical kinetic mechanism for a gasoline surrogate was validated in this study for a CAI combustion. This gasoline surrogate was modeled as a blend of iso-octane, n-heptane, and toluene. This reduced mechanism consists of 49 species and 67 reactions and it includes main reaction paths of iso-octane, n-heptane, and toluene. A RCM was used for the validation of this reduced mechanism and matched with the modeling of the RCM using STAR-CD. The results of the experiment and the simulation showed good agreement. For the analysis of CAI combustion, a multi-zone method was developed and incorporated into the computational fluid dynamics code, STAR-CD. This coupled multi-zone model can calculate 3 dimensional computational fluid dynamics and multi-zoned chemical reaction simultaneously in one time step. In other words, every computational cell interacts with the adjacent cells during the chemical reaction process. The effect of the EGR gas uniformity and equivalence ratio were studied. In the same EGR gas quantity, EGR distribution could affect on engine performance. EGR leaned to cylinder wall could lower the pressure rise rate, so it can be adopted to solve the noise and vibration problem of CAI engines. Equivalence ratio has very sensitive influence in bulk temperature.

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Basic investigation aiming to develop a gasoline engine of high thermal efficiency is presented in this paper. The high efficiency is established by increasing the compression ratio while the engine is operated in SI mode. In order to suppress knocking, fuel is thermally processed to raise the octane number by partially cracking the hydrocarbon molecule prior to supply fuel to the engine. The primary reference fuel 90 (PRF90), which shows that 10% n-heptane is blended with 90% iso-octane, was applied to the test fuel. And the regular gasoline, which octane number was approximately 90, was also used as the test fuel in order to show the practical rise of thermal efficiency. The fuel reformer was constructed in this study and the fuel component was measured with gas chromatography and mass spectroscopy (GC - MS). It was found that the fuel was partially cracked into small size hydrocarbons including methane, ethylene, propene, and so on. Under the high temperature condition over 973 K, benzene and toluene were also formed in the reformed fuel, which would suppress knocking. Both gas and liquid components of the reformed fuel was supplied to a test engine. The test engine is a 4-cylinder, 2-litter, turbo gasoline engine and the compression ratio was modified to be 12. The thermal efficiency was investigated for operating conditions set as IMEP 236 kPa, 437 kPa and 623 kPa at 1600 rpm, and IMEP 700 kPa at 1200 rpm. The thermal efficiency increased by 4.2% using PRF90 and by 0.8% using regular gasoline. Knock was suppression by 1.5% using PRF90 and by 1.2% using regular gasoline.

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The purpose of this study is to investigate the potential use of in-cylinder thermal and mixing stratification for reducing the pressure-rise rates in HCCI engines by going through numerical analysis with multi-zones modeling. The computations are conducted using both a standard single-zone and the custom multi-zone version of the Senkin application of the CHEMKIN II kinetics rate code, and kinetic mechanisms for Di-Methyl Ether (DME). The objective of calculation with the multi-zones model is to examine the mechanism of thermal and mixing stratified charge to reduce an excessive pressure-rise rates. The mechanism of reducing the pressure-rise rates in the thermal and mixing stratified charge is proved with 2-zones and 5-zones model. It is found that thermal and mixing stratification have the effect of reducing the pressure-rise rates (extended combustion duration) and have potential for extending the upper load limit in HCCI engines.

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