Studies on Low Compression Ratio Diesel Engine : 2nd Report, Effects of Combustion Chamber Configuration in Direct Injection Type Diesel Engine

Abstract

In a diesel engine, the form of combustion chamber is considered to be important in designing a low compression ratio engine. In this paper, the optimum form of combustion chamber for the performances was found out and by using this chamber the reduction of the compression ratio approximately to 12 was attained without deterioration of performances, for example the maximum output and the specific fuel consumption. This seems to depend mainly on the increase of the degree of constant volume owing to shortened duration of combustion as the compression ratio decreases. To determine the form of combustion chamber, the air velocity into the combustion chamber with varied diameters of combustion chamber entrance was controlled and the relation between the aspect of combustion and the performances was obtained. As the air velocity increased, the degree of constant volume increased because of increased maximum rate of heat release and shortened duration of combustion and this worked effectively on the thermal efficiency, but in contrast, the cooling loss increased. Thus, this resulted in the optimum diameter of combustion chamber entrance especially at heavier load range. Besides, even when the diameter of combustion chamber entrance decreased, the throttling loss was considered to be negligible in the direct injection type engine.