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In a Diesel Oxidation Catalyst (DOC) and Catalyzed Soot Filter (CSF) system, the DOC is used to oxidize additional fuel injected into the cylinder and/or exhaust pipe in order to increase the CSF's inlet temperature during soot regeneration. The catalyst's hydrocarbon (HC) oxidation performance is known to be strongly affected by the HC species present and the catalyst design. However, the engine operating conditions and additive fuel supply parameters also affect the oxidation performance of DOCs, but the effects of these variables have been insufficiently examined. Therefore, in this study, the oxidation performance of a DOC was examined in experiments in which both exhaust gas recirculation (EGR) levels and exhaust pipe injection parameters were varied. The results were then analyzed and optimal conditions were identified using modeFRONTIER.

For diesel emission control systems containing a Diesel Oxidation Catalyst (DOC) and a Catalyzed Soot Filter (CSF) the DOC is used to oxidize the additional fuel injected into the cylinder and/or the exhaust pipe for the purpose of increasing the CSF inlet temperature during the soot regeneration. Hydrocarbon (HC) oxidation performance of the DOC is affected by HC species as well as a catalyst design, i.e., precious metal species, support materials and additives. How engine-out HC species vary as a function of fuel supply conditions is not well understood. In addition, the relationship between catalyst design and oxidation activity of different hydrocarbon species requires further study. In this study, diesel fuel was supplied by in-cylinder, post injection and exhaust HC species were measured by a gas chromatograph-mass spectrometry (GC-MS) and a gas analyzer. The post injection timing was set to either 73°, 88° or 98° ATDC(after top dead center).

Three types of combustion chamber configurations (Types A, B, and C) with compression ratio lower than that of the baseline were tested for improved performance and exhaust gas emissions from an inline-four-cylinder 1.7-liter common-rail diesel engine manufactured for use with passenger cars. First, three combustion chambers were examined numerically using CFD code. Second, engine tests were conducted by using Type B combustion chamber, which is expected to have the best performance and exhaust gas emissions of all. As a result, 80% of NOx emissions at both low and medium loads at 1500 rpm, the engine speed used frequently in the actual city driving, improved with nearly no degradation in smoke emissions and brake thermal efficiency. It was shown that a large amount of cooled EGR enables NOx-free combustion with long ignition delay.

Urea-SCR system has a high NOx reduction potential in the steady-state diesel engine operation. In complicated transient operations, however, there are certain problems with the urea-SCR system in that NOx reduction performance degrades and adsorbed NH3 would be emitted. Here, optimum urea injection methods and exhaust bypass control to overcome these problems are studied. This exhaust bypass control enables NO/NOx ratio at the inlet of SCR catalyst to be decreased widely, which prevents over production of NO2 at the pre-oxidation catalyst. Steady-state and simple transient engine tests were conducted to clarify NOx reduction characteristics when optimum urea injection pattern and exhaust bypass control were applied. In simple transient test, only the engine load was rapidly changed for obtaining the fundamental knowledge concerning the effect of those techniques.

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions in diesel engine. In general, high octane number fuels (gasoline components or gaseous fuels) are used for HCCI operation, because these fuels briefly form lean homogeneous mixture because of long ignition delay and high volatility. However, it is necessary to improve injection systems, when these high octane number fuels are used in diesel engine. In addition, the difficulty of controlling auto-ignition timing must be resolved. On the other hand, HCCI using diesel fuel (diesel HCCI) also needs ignition control, because diesel fuel which has a low octane number causes the early ignition before TDC. The purpose of this study is the ignition and combustion control of diesel HCCI. The effects of parameters (injection timing, injection pressure, internal/external EGR, boost pressure, and variable valve timing (VVT)) on the ignition timing of diesel HCCI were investigated.

A dual fuel natural gas diesel engine suffers from remarkably lower thermal efficiency and higher THC, CO emissions at lower load because of its lower burned mass fraction caused by the lean pre-mixture. To overcome this inevitable disadvantage at lower load, two methods of reducing the number of operating cylinders were examined. One method was to use the two cylinders operation while the second one was to use the quasi-two cylinders operation. As a result, it was found that the unburned hydrocarbons and CO emissions could be favorably reduced with the improvement of thermal efficiency by reducing the number of cylinders to half for a dual fuel natural gas diesel engine. Moreover, it was also found that the quasi-two cylinders operation could improve the torque fluctuation more compared to the two cylinders operation.

A CFD code combined with detailed chemical kinetics has been developed, linking with KIVA-3 and subroutines in CHEMKIN-II directly with some modifications. By using this CFD code, formation processes of combustion and exhaust gas emission for a turbo-charged DI diesel engine with common rail fuel injection system were simulated. As a result, formation processes of pollutant including NOx and soot were also considered according to the calculation results. The results show that NO caused by the extended Zeldvich mechanism accounted for about 88% of all NO, and it was found that there is a possibility to predict where and when soot will be formed by considering a simplified soot formation model.

Experimental and numerical studies are conducted on the formation of soot and Polycyclic Aromatic Hydrocarbons (PAHs), regarded as precursors of soot, during the combustion of fuel-rich homogeneous n-heptane mixtures. In-cylinder gases are sampled directly through a high-speed solenoid valve in engine tests, to be analyzed by GC/MS for qualifying PAHs. Smoke concentration is also measured. A numerical study is carried out by using a zero-dimensional model combined with detailed chemical kinetics. The experiments and computations show that PAHs can be predicted qualitatively by means of the present kinetic model.

To improve urban air pollution, stringent emissions regulations for heavy-duty diesel engines have been proposed and will become effective in Japan, the EU, and the United States in a few years. To comply with such future regulations, it is critical to investigate the effects of intake and injection parameters and fuel properties on engine performance, efficiency and emissions characteristics, associated with the use of aftertreatment systems. An experimental study was carried out to identify such effects. In addition, the KIVA-3 code was used to gain insight into cylinder events. The results showed improvements in NOx-Smoke and BSFC trade-offs at high-pressure injection in conjunction with EGR and supercharging.

Natural gas pre-mixture is ignited by a small amount of pilot fuel in the dual fuel engine. In this paper, numerical studies were carried out to investigate the combustion and exhaust gas emissions formation process of this engine type by using a multi dimensional model combined with the detailed chemical kinetics including 57 chemical species and 290 elementary reactions. In calculation, the effect of the pre-mixture concentration on combustion was examined. The result indicated that the increased concentration of natural gas could improve the burning fraction and THC, CO emissions due to the increased pre-mixture consumption rate and the cylinders gas temperature.

It has been recognized that alternative fuels such as liquid petroleum gas (LPG) has less polluting combustion characteristics than diesel fuel. Direct-injection stratified-charge combustion LPG engines with spark-ignition can potentially replace conventional diesel engines by achieving a more efficient combustion with less pollution. However, there are many unknowns regarding LPG spray mixture formation and combustion in the engine cylinder thus making the development of high-efficiency LPG engines difficult. In this study, LPG was injected into a high pressure and temperature atmosphere inside a constant volume chamber to reproduce the stratification processes in the engine cylinder. The spray was made to hit an impingement wall with a similar profile as a piston bowl. Spray images were taken using the Schlieren and laser induced fluorescence (LIF) method to analyze spray penetration and evaporation characteristics.

An experimental ultra lightweight compact vehicle named “the Waseda Future Vehicle” has been designed and developed, aiming at a simultaneous achievement of low exhaust gas emissions, high fuel economy and driving performance. The vehicle is powered by a dual-type hybrid system having a SI engine, electric motor and generator. A high performance lithium-ion battery unit is used for electricity storage. A variety of driving cycles were reproduced using the hybrid vehicle on a chassis dynamometer. By changing the logics and parameters in the electronic control unit (ECU) of the engine, a significant improvement in emissions was possible, achieving a very high fuel economy of 34 km/h at the Japanese 10-15 drive mode. At the same time, a numerical simulation model has been developed to predict fuel economy. This would be very useful in determining design factors and optimizing operating conditions in the hybrid power system.

A numerical study was carried out to investigate combustion characteristics of a dual-fuel gas diesel engine, using a multi-dimensional model combined with detailed chemical kinetics, including 43 chemical species and 173 elementary reactions. In calculations, the effects of initial temperature, EGR ratios on ignition, and combustion were examined. The results indicated EGR combined with intake preheating can favorably reduced NOx and THC emissions simultaneously. This can be explained by the fact that combustion mechanism is changed from flame propagation to HCCl like combustion.

An experimental and numerical study has been conducted on the emission and reduction of HCHO (formaldehyde) and other pollutants formed in the cylinder of a direct-injection diesel engine fueled by methanol. Engine tests were performed under a variety of intake conditions including throttling, heating, and EGR (exhaust gas recirculation) for the purpose of improving these emissions by changing gas compositions and combustion temperatures in the cylinder. Moreover, a detailed kinetics model was developed and applied to methanol combustion to investigate HCHO formation and the reduction mechanism influenced by associated elementary reactions and in-cylinder mixing.

A numerical model has been developed to predict the formation of NOx and formaldehyde in the combustion and post-combustion zones of a methanol DI engine. For this purpose, a methanol-air mixture model combined with a full kinetics model has been introduced, taking into account 39 species with their 157 related elementary reactions. Through these kinetic simulations, a concept is proposed for optimizing methanol combustion and reducing exhaust emissions.

A new type of fuel injection nozzle, called a “slit nozzle,” has been developed to improve poor ignitability and to stabilize combustion under low load conditions in direct-injection methanol diesel engines manufactured for medium-duty trucks. This nozzle has a single oblong vent like a slit. Engine test results indicate that the slit nozzle can improve combustion and thermal efficiency, especially at low loads and no load. This can be explained by the fact that the slit nozzle forms a more highly concentrated methanol spray around the glow-plug than do multi-hole nozzles. As a result, this nozzle improves flame propagation.