Optimization of the Combustion System in a Marine Engine based on Orthogonal Design Method

In order to improve the performance of a four stroke marine engine, a new marine diesel engine has been developed based on the baseline engine. The crank speed of the new developed engine is higher than the baseline engine and the stroke is shortened. However, the compression ratio is unchanged. The shortened stroke of the new developed engine enhances the tendency of spray-wall impingement and combustion deteriorated which results from the reduction of the squish height. To solve this problem, four factors in combustion system: nozzle protrusion height, the upper nozzle angle, the lower nozzle angle and the injection timing, are optimized based on orthogonal design method. Under the restriction of in-cylinder pressure 20MPa, -9 degrees CA is the optimal injection timing. When the nozzle protrusion height is 7mm, the upper nozzle and lower nozzle angle are 170 degrees and 160 degrees respectively, the spray and flame relatively evenly distribute in the combustion chamber, further strengthens the utilization of fresh air and then enhance the output of engine.