A Study on the Effects of the Chamber Walls on the Diesel Combustion Phenomena

The combustion chamber plays an important role in the fuel-air mixing process and resultant fuel spray pattern which have a large influence in a diesel engine. Furthermore, the chamber wall cools off the gas in the combustion chamber and quenches the combustion zone, thus the thermal efficiency and the combustion efficiency of an engine would be lower.In order to investigate the effect of the combustion chamber shape on the engine performance, the authors conducted some experiments using a single cylinder 4-cycle test engine and a test equipment. Piston crown shape, combustion chamber height, number of fuel nozzle holes, direction of fuel nozzle hole and charge air pressure were chosen as the experimental factors.From the results, it is confirmed that the fuel mixing process with surrounding gas is mainly done by the mobility of the fuel spray. Therefore, it was concluded that the interference of the chamber wall in the motion of the fuel spray must be avoided especially on the early stage of the spray travel.Based on the results, then the authors redesigned the piston crown of their 4-cycle medium-speed diesel commercial engine, and confirmed the improvement of the combustion performance.