This paper describes about the effects of air swirl on the exhaust smoke, the nitrogen oxides emissions and the combustion efficiency of a direct-injection diesel engine. Using a 1.35 ltr singlecylinder engine with a disc-type combustion chamber, the investigations were made, by means of the exhaust gas analysis, into the influences of the swirl ratio (swirl speed/engine speed), S_R, the numbers of holes of fuel injection nozzle, N_h, and the oxygen concentration in intake air on the concentration of soot and nitrogen oxides and the combustion efficiency.
The results of experiments are as follows:
(1) The effects of the swirl on the diesel combustion varies with the numbers of the holes of fuel injection nozzle. The sooting ratio, the nitrogen oxides concentration and the combustion efficiency are able to be put in order of S_R N_h values.
(2) In the condition of small value of the excess air ratio, the over swirl phenomenon clealy occurs at S_R N_h>about 15.
(3) The effect of swirl on the exhaust smoke and combustion efficiency becomes remarkable with the decreases in the excess air ratio and the oxygen concentration in intake air.
(4) The effects of oxygen concentration in intake air, ν_S (O₂), on the soot concentration, S_WV, and the combustion efficiency, η_u, are expressed as follows:
S_WV=S_WV(0.21){ν_S(O₂)/0.21}^-α,
η_u=1-{1-η_u(0.21)}{ν_S(O₂)/0.21}^-β,
where the values of α and β vary with S_R and N_h.

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This paper presents some experimental results of the characteristics of the diesel fuel spray injected into a chamber charged with the high pressure and room temperature air, impinging upon a flat plate.
The results show that the apparent spray volume decreases slightly after the impingement upon the plate verticaly, and then increases remarkably up to twice as much as the volume without impingement.

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