Abstract
This paper provides an insight into the design of a compound combustion chamber, with square and circular cavities, for use in a direct injection diesel engine. Automotive diesel engines using square combustion chamber design have shown improvement in oxides of nitrogen and particulate exhaust emissions. An experimental study, based on liquid injection technique (LIT), was conducted to evaluate mixture formation in compound combustion chambers of different designs. These chambers have square geometry of depth h at the top and a circular cavity at the bottom, with the total chamber depth being H. The influence of the quadrangle corner part on mixture formation was evaluated by LIT technique and validated through experimental work on a single cylinder, DI diesel engine. The quality of mixture formation was evaluated by analyzing optical transmissivity of the fuel spray emulsion in the liquid chamber. The combustion chamber cavity with h/H = 0.65 showed lower optical transmissivity indicating better fuel spray dispersion in the chamber. These results were verified through engine experiments that showed lower fuel consumption and lower exhaust emissions at this depth ratio. The combustion chamber with h/H = 0.65 produced a peculiar turbulence to aid in mixture formation in the upper square corners of the chamber. These characteristics of the compound chamber of cavity ratio h/H = 0.65 are believed to be responsible for improved performance of the DI diesel engine.