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In an effort to protect the earth''s environment emission regulations in the diesel engine field are becoming increasingly strict. Especially, free acceleration smoke is one of the major concerns because it not only affects the perception for the clearance of diesel engines, but also is regulated by emission legislations. In this report, we will describe how various engine parameters effect the free acceleration smoke and also describe how we can optimize a startability of vehicle simultaneously with the reduction of smoke.

Numerical analysis of the flow field and fuel spray in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A simple valve treatment technique is employed to handle multiple moving valves without difficulties in generation of a body-fitted grid. The swirl motion of a hollow-cone spray is simulated by injecting droplets with initial angular momentum around the nozzle periphery. The model for spray-wall impingement is based on single droplet experiments with the droplet behaviors after impingement determined by experimental correlations. Different behaviors of an impinging droplet depend on the wall temperature and the critical temperature of fuel with the fuel film taken into account. The test engine is a 4-stroke 4-valve gasoline engine with a pent-roof head and vertical ports to form a reverse tumble flow during the intake stroke. A hollow-cone spray by a high-pressure swirl injector is employed to enhance mixture preparation and mixing.

Three-dimensional computation of the flow field and fuel spray in a DISC engine is performed using a modified version of KIVA-II. A special valve treatment technique is employed to simulate multiple moving valves without excessive efforts for body-fitted grid generation. The test engine is a 4-valve 4-stroke gasoline engine with a pent-roof head and a hollow-cone spray by a high-pressure swirl injector. The injection strategy is divided into two categories, ‘early’ and ‘late’ injection to optimize the combustion process. A spray-wall impingement model based on a single droplet experiment is implemented to consider both ‘early’ and ‘late’ injection case. Parametric studies are performed with respect to the load, injection timing, duration and position, spark-plug position, and the combustion chamber geometry. Results show that the current numerical analysis is capable of representing the spray motion and mixture formation in an operating engine qualitatively.

In order to realize lean burn engine by improving the ignitability of ignition system, the possibility about the adaptability of the Multi Spark Capacitor Discharge Igniter (MSCDI) was analyzed. The MSCDI had an effect on the increase of the ignition energy and discharge period, and it was excellent in high speed without noise. The result of engine test with the MSCDI shown about 10% extension of lean limit, and 5% increase of brake thermal efficiency than the ignition system with single spark ignition apparatus. And the coefficient of cycle variation in the IMEP was remarkably decreased.

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.