Caliber ratio and caliber-depth ratio as two important structural parameters for the combustion chamber design directly affect the in-cylinder air motion and the fuel-air mixture distribution, which further influence the combustion process. This paper is presented to study the effects of these two important parameters on combustion and emission characteristics of a diesel engine. Results showed that increasing the caliber ratio increased ISFC (Indicate specific fuel consumption) value and soot emissions, while decreased the NOx emissions. A first decrease then increase trends were obtained for both ISFC and soot emissions as the increase of the caliber-depth ratio and the turning points were all located near the ratio of 4.0, which was just opposite to NOx emissions variations. In additions, for both caliber ratio and caliber-depth ratio variations, the proportions of NOx and soot emissions in the near wall region and central region were the greatest, respectively, and mainly contributed to the variations of NOx and soot emissions.
Keywords diesel engine, caliber ratio, caliber-depth ratio, combustion characteristic, emission characteristic