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Both NOx and unburned HC were reduced by changing the direction of the flame propagation. It is generally said that the optimum ignition position of spark ignition engine is in the center of combustion chamber. However by igniting arround the chamber and propagating the flame toward the center, a smooth heat release pattern due to the decrease in the flame area and a decrease in the unburned gas entering the ring crevise can be anticipated. These effects of this combustion process, which was named the surrounding combustion process (SCP), were experimntally confirmed using the constant volume combustion vessels and the spark ignition engine equipped with six spark plugs per cylinder. Next, the steps for decreasing the number of ignitions TCre considered, and additional three spark plugs for SCP were installed in the four valve pentroof combustion chamber. With this engine, the NOx reduction and the capability of SCP to further improve the lean burn engine fuel economy were confirmed.

In order to investigate effects of the multi-hole nozzle with micro orifices on mixture formation processes in Direct-Injection Diesel engines, mixture characteristics were examined via an ultraviolet-visible laser absorption scattering (LAS) technique under various injectors. The injection quantity per orifice per cycle was reduced by nozzle hole sizes. The LAS technique can provide the quantitative and simultaneous measurements of liquid and vapor phases concentration distributions inside of the fuel spray. Mass of ambient gas entrained into the spray, liquid/ vapor mass and mean equivalence ratio of total fuel were obtained based on Lambert Beer's law. As a result, the leaner and more homogeneous fuel-gas mixture can be achieved by reducing the nozzle hole diameter, in the meanwhile more ambient gas were entrained into the spray. Moreover, relationships between mixture formation and D.I.

The concept of two closely spaced micro-orifices (group hole nozzle) has been studied as a promising technology for the reduction of soot emission from direct injection (DI) diesel engines by improving the fuel atomization and evaporation. One of the main issues on group hole nozzle is the arrangement of orifices with various distances and angles. In this study, the ignition and combustion characteristics of wall-impinging diesel sprays from group-hole nozzles were investigated with various angles between two micro-orifices (included angles). A laser absorption scattering (LAS) technique for non-axisymmetric sprays, developed based on a LAS technique for axisymmetric spray, was applied to investigate the liquid/vapor mass distribution of wall-impinging sprays. The direct flame images and OH radical images inside a high pressure constant volume vessel were captured to analyze the effect of included angle on spray ignition and combustion characteristics.

The group-hole (GH) nozzle concept that uses two closely spaced micro-orifices to substitute the conventional single orifice has the potential to facilitate better fuel atomization and evaporation, consequently attenuate the soot emission formed in direct-injection (D.I.) diesel engines. Studies of quantitative mixture properties of the transient fuel spray injected by the group-hole nozzles were conducted in a constant volume chamber via the laser absorption-scattering (LAS) technique, in comparison with conventional single-hole nozzles. Specific areas investigated involved: the non-evaporating and the evaporating ambient conditions, the free spray and the spray impinging on a flat wall conditions. The particular emphasis was on the effect of one of key parameters, the interval between orifices, of the group-hole (SH) nozzle structure.

In this study, air entrainment, fuel evaporation and mixing process of diesel sprays injected by micro-orifices for direct-injection diesel engines were investigated at the end of injection transient and after the end of injection. The mixture formation process was analyzed using a laser absorption scattering (LAS) technique, providing the information of quantified liquid and vapor mass concentration, entrained air concentration and equivalence ratio. The data was obtained at the timings of quasi-steady state, sudden velocity decrease, the end of injection and after the end of injection. Two micro-orifices, which have different orifice diameters, were selected as test nozzles to investigate the end-of-injection characteristics at different nozzle geometries. In case of smaller orifice diameter, the liquid phase regression was observed around the end of injection, while it was not observed at larger orifice diameter due to denser liquid concentration near the nozzle tip.

The group-hole nozzle concept is regarded as a promising approach to facilitate better fuel atomization and evaporation for direct injection diesel engine applications. In the present work, the spray and mixture properties of group-hole nozzle with close, parallel or a small included angle orifices were investigated experimentally by means of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique, in comparison with the conventional single-hole nozzle. Three series of group-hole nozzles were designed to investigate the effect of group-hole nozzle specification while varying the included angle and interval between the orifices. The results suggested that: 1) Group-hole nozzle with very close, parallel orifices presents the similar spray characteristics with those of the single-hole nozzle.

An all-ceramic swirl chamber has been developed which meets the 1987 U.S. particulate emission standard for LDV. The all ceramic construction raises combustion temperature to reduce particulate emission to the necessary level. But particulate reduction led to two-fold increase in NOx. This problem was coped with by applying EGR and fuel injection timing control. As a result NOx has been cut to the same level as with a base engine and particulate has been further reduced.

The combustion processes in the prechamber and the main chamber of a small indirect injection (I.D.I.) diesel engine were observed simultaneously by high-speed photography. These observations made it possible to characterize the behavior of flames in both chambers, that is, ignition of fuel, developing and rotating flames in the prechamber, and a flame jet spouting into the main chamber. The effect of engine variables, such as fuel injection timing, cross-sectional area of a throat, fuel injector location, and a recess in a piston top, on the combustion process as well as the engine performance were considered. A flame jet spouting into the main chamber separated into two directions and induced two vortexes. Brown sooty flames appeared along the prechamber wall and inside the flame jet which struck on the piston top. The higher-velocity flame jet and the two Intense vortexes induced by the flame jet realized superior fuel consumption and lower smoke emission.

The objective of the paper is to characterize the diesel spray under the ambient conditions relevant for direct injection (D.I.) diesel engines. The particular emphasis is on the comparisons between laser measurements and predictions by empirical correlations and theoretical analyses. The ultraviolet-visible laser absorption-scattering (LAS) imaging technique is employed to quantitively determine the spray/mixture properties of the diesel spray injected by a hole-type injector, in terms of spray tip penetration and spatial concentration distributions of liquid and vapor phase. The structure of evaporating spray is obtained and analyzed. Based on the penetration correlations in the literature, a non-dimensional analysis of the spray tip penetration data is carried out. The results indicate that a self-similar state of the evaporating fuel spray is achieved.

In the present study, a challenge has been made to quantitatively determine the vapor phase concentration distributions in an evaporating multicomponent fuel spray using the LAS imaging technique. The theoretical considerations were particularly given when applying the LAS imaging technique to the multicomponent fuel spray and reconstructing the vapor concentration distributions from the spray images.