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An experimental study on emission formation processes, such as these of nitric oxide, particulate and total hydrocarbon in a small direct injection (D.I.) diesel engine was carried out by using a newly developed total in-cylinder sampling technique. The sampling method consisted of rapidly opening a blowdown valve attached to the bottom of the piston bowl, and quickly transferring most of the in-cylinder contents into a large sampling chamber below the piston. No modification of the intake and exhaust ports in a cylinder head was required for the installation of the blowdown apparatus. The sampling experiment gave a history of spatially-averaged emission concentrations in the cylinder. The effects of several engine variables, such as the length-to-diameter ratio of the nozzle hole, the ratio of the piston bowl diameter to the cylinder bore and the intake swirl ratio, on the emission formation processes were investigated.

A calculative investigation was performed in order to examine the effects of injection rate profile and air entrainment characteristics on exhaust emission using a phenomenological spray combustion model. The calculations were made of an engine with a bore of 114 mm and a stroke of 130 min while changing the injection rate profile and the air entrainment characteristics. As a result of the calculations, effective measures were found for simultaneous reduction of NOx and smoke emissions.

In the previous study of the authors, it was found that some benefits for the mixture preparation of DI gasoline engines can be offered by splitting the fuel injection, such as the phenomenon of high density liquid phase fuel piling up at the leading edge of the spray can be circumvented. In a further analysis, the vapor quantity in the “stable operating” range (equivalence ratio of vapor ϕv in a range of 0.7≤ϕv≤1.3) was significantly increased by the split injection compared to the single injection. In this work, the mechanism of the effect of the split injection on the mixture formation process was studied by combining the laser-sheet imaging, LIF-PIV and the LAS (Laser Absorption Scattering) technique. As a result, it is found that the spray-induced ambient air motion can help the formation of the more combustible mixture of the split injection whereas it played a minus role of diluting the spray by the single injection.

The effects of engine parameters, such as spray characteristics and combustion chamber geometry on performance and exhaust emissions in a small D.I. diesel engine were investigated to find out the optimum way of improving the engine. Diesel spray injected into a high-pressure vessel was photographically analyzed to guess the spray behavior in a firing diesel engine. The ratio of hole length to the diameter of a nozzle (L/D) was varied from 3 to 7 as the main parameter of the nozzle. Piston cavity diameter and intake swirl were chosen as the other parameters. The effect of the above parameters was investigated in terms of brake specific fuel consumption (BSFC), exhaust smoke, nitric oxides (NOx) and total hydrocarbon (THC). The L/D of the nozzle is concluded to be of major importance in terms of BSFC and THC emission. Smaller piston cavity diameters lead to lower exhaust smoke, but to a higher level of NOx emission.