Effect of injection spray angle and combustion chamber geometry on engine performance and emission characteristics of a large bore diesel engine

摘要

A mismatch of injection parameters and combustion chamber geometry in diesel engines can potentially lead to serious problems such as poor fuel economy, excessive emissions and even oil degradation. During the optimization process of a prototypeengine, it was observed that even though fuel consumption and exhaust emission levels were well within legal and acceptable' limits, the engine had a severe problem of oil degradation.To provide an insight into the causes of this problem, injection parameters and their interaction with the combustion chamber geometry have been studied for a large bore heavy-duty diesel engine using the KIVA code. Two different piston bowl geometriesand three injector spray angles were considered in this study. The experimental emission trends were well reproduced using model parameters optimized on a comparatively small-bore engine. However, some injection and combustion model parameters did need to be re-optimized to improve accuracy when used with the large bore diesel engine. The computational results clearly show that the root cause of the problem of oil degradation was the spray orientation. In this case, the soot formation takes place near thecylinder liner below the top ring turn around position. Soot was then scraped by the ring pack down into the oil sump. The contamination of the lube oil resulted in unacceptable life; 10 percent of the expected life.The results obtained in this simulation study further demonstrate that the CFD model can be used as a design tool with some confidence, particularly for optimizing prototype engines, thereby saving a considerable amount of time and resources.