Relationship Between Visible Spray Observations and DI Diesel Engine Performance

This investigation was conducted to enhance understanding of combustion in a direct injection (DI) diesel engine with square combustion chamber. The investigation included a bench study of spray and its interaction with the chamber and correlation with engine performance. The bench study was conducted by using a liquid injection technique (LIT). The technique relies on the use of instantaneous photo images of emulsified fuel spray patterns to deduce spray behavior. It captures spray images in forced swirling flow on a positive film, which was used to deduce fuel-air mixing by scattering radiation technique. Three different chamber configurations, with different ratios of arc radius (r) to inscribed circle radius (R), and several spray deflecting angles were used in the study. The best parameters were found to be a deflecting angle of about 30 deg and a ratio of $r/R$ of about 0.65. The results of the bench test were used to compare engine performance at similar design parameters. The engine performance was found to be superior at the above values of $r/R$ and the deflecting angle. Engine exhaust of NOx and exhaust smoke were found to be lower at these design parameters. The experimental technique of using emulsified spray with LIT can be used qualitatively to evaluate effects of combustion chamber and fuel system design variables on engine performance. [S0742-4795(00)00104-6]