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A study has been made of an automotive direct injection diesel engine designed to reduce exhaust emissions, particularly NOx and particulates, without performance deterioration. Special emphasis has been placed on air-fuel mixing conditions controlled by the fuel injection rate, the intake swirl ratio, and the intake boost pressure. By means of increasing the injection rate, ignition delay can be shortened enough to improve particulate emissions at retarded injection timings. Enhancing the intake swirl velocity contributes to the reduction of soot emission in spite of the deterioration of NOx emission. Supercharging can favorably enhance diffusion combustion resulting in improved fuel economy for retarded injection timings and reduced emissions. As a result, a good compromise can be achieved between fuel economy and exhaust emissions by increasing the injection rate along with retarding the injection timing. Supercharging was found to be more favorable than swirl enhancement.

An experimental study has been made of a single cylinder, direct-injection diesel engine having a re-entrant combustion chamber designed to enhance combustion so as to reduce exhaust emissions. Special emphasis has been placed on controlling the inert gas concentration in the localized fuel-air mixture to lower combustion gas temperatures, thereby reduce exhaust NOx emission. For this specific purpose, an exhaust gas recirculation (EGR) system, which has been widely used in gasoline engines, was applied to the DI diesel engine to control the intake inert gas concentration. In addition, supercharging and increasing fuel injection pressure prevent the deterioration of smoke and unburned hydrocarbons and improve fuel economy, as well.

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.

Dual-fuel operation of a direct-injection diesel engine with natural gas fuel can yield a high thermal efficiency almost comparable to the diesel operation at higher loads. The dual-fuel operation, however, at lower loads inevitably suffers from lower thermal efficiency and higher unburned fuel. To improve this problem, engine tests were carried out on a variety of engine parameters including diesel fuel injection timing advance, intake throttling and hot and cooled exhaust gas recirculation (EGR). It was found that diesel injection timing advance gave little improvement in thermal efficiency and increased NOx. Intake throttling promoted better combustion and shortened its duration with a consequent improvement in efficiency at higher natural gas fractions. Hot EGR raised thermal efficiency, reduced smoke levels, and maintained low NOx levels. Cooled EGR reduced NOx emissions but lowered thermal efficiency.

An experimental study was conducted to determine combustion and exhaust emissions characteristics in an automotive direct-injection diesel engine dual-fueled with natural gas with the objective of improving exhaust emissions and thermal efficiency. Dual-fuel operation can yield a high thermal efficiency almost comparable to the diesel operation and very low smoke at higher loads. However, NOx cannot be reduced by dual-fueling. On the other hand, at lower loads, a dual-fueled engine inevitably suffers from lower thermal efficiency and higher unburned fuel. To resolve these problems, the effects of exhaust gas recirculation (EGR) were investigated. The results show that in dual-fuel operation, hot EGR can improve thermal efficiency and reduce unburned fuel emission at lower loads, While cooled EGR can considerably reduce NOx at higher loads. A Pt oxidation catalyst can be used for additional reduction in unburned fuel emitted due to dual-fueling.

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.

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 simulation model has been developed to predict the direct injection stratified charge combustion in a constant- volume vessel. Important factors such as local fuel concentration, their fluctuation and turbulent flow characteristics were measured throughout the vessel as function of time. These data were utilized to estimate the buring rate composed of the turbulent fuel-air mixing rate and chemical reaction rate. The model can predict the combustion pressures and heat release rates measured for different ignition timings and spark location.

Vibration has been the most objectable problem that inevitably occurs in high speed multi-cylinder diesel engines. The torsional vibration appearing at the crankshaft of the engine is the major source of the engine vibration. A torsional damper, being attached at the end of the crankshaft, has been widely used to reduce the torsional vibration. For this purpose, various kinds of damper as examplified by a double-mass type and a viscous-rubber type have been subject to many investigations during these twenty years. However, less attention has been paid on dynamic characteristics of a shear-type single mass rubber damper in spite of its potential. Thus, the purpose of this study has been directed to establish the concept for designing a best tuned torsional rubber damper. In this work, rubber geometry is considered as one of the most essential factors influencing on dynamic characteristics of the rubber damper.