Effect of a conical nozzle orifice on the combustion and emissions in a direct-injection compression ignition engine under low-load conditions

Abstract

This experimental study investigates the effect of a conical nozzle orifice on the combustion and emissions of an optically accessible single-cylinder diesel engine equipped with a high-pressure common-rail injection system. In-cylinder pressure analysis and emission measurements were conducted to investigate the combustion and emission characteristics. Direct imaging visualization was used to characterize the combustion process. The engine was operated at an indicated mean effective pressure of 0.5 MPa, an engine speed of 1200 r/min and injection pressures of 30 MPa, 80 MPa and 120 MPa. The results showed that overall combustion occurred more quickly when a conical nozzle orifice was used than with a cylindrical nozzle orifice. The ignition delay of the conical nozzle orifice was shorter than that of the cylindrical nozzle orifice. The conical nozzle orifice also showed a lower peak heat release rate and a larger diffusion burn proportion during the combustion process. In terms of emissions, the conical nozzle orifice emitted lower smoke emissions and produced higher nitrogen oxide and hydrocarbon emissions. Direct combustion imaging confirmed that the conical nozzle orifice had a shorter ignition delay and a larger proportion of diffusion combustion. Moreover, its flame intensity was higher than that from the cylindrical nozzle orifice owing to its improved atomization and prolonged diffusion combustion.