Effect of combustion chamber geometry on emissions from a single cylinder diesel engine

Many of the stationary power generation and agricultural pumping applications in India utilize diesel engines. Recently, as per Government regulations, these engines are required to satisfy stringent emissions norms. This forms the motivation for the present study on a stationary, direct-injection, single cylinder, 10 HP diesel engine. The selected engine was not satisfying the norms. The engine has a hemi- spherical piston bowl and an injector with a finite sac volume. The combustion chamber was made re-entrant and the injector was replaced with a sac-less injector. After these modifications, there is a significant change in emission levels. To understand clearly the effect of the combustion chamber geometry on the emission levels, three-dimensional computational fluid dynamics (CFD) simulations have been performed for the complete suction and closed-valve part of the cycle. Comparisons of turbulent kinetic energy and swirl levels of old and new geometries were systematically conducted. In contrary to the expected, that the swirl and turbulence levels are consistently less in the modified geometry than that of original geometry. A third combustion chamber was proposed and tested computationally. It was found that the in the proposed combustion chamber swirl and turbulence levels are much higher than the baseline engine. Thus, the proposed combustion chamber geometry shows significant potential for the engine to meet the prescribed norms.