Cylinder to Cylinder Deviations in Combustion and Emission at Idling in DI Diesel Engines with Pilot Injection

Abstract

Pilot injection in DI Diesel Engines is a very effective method reducing nitrogen oxides and noise. However the injection behavior of small quantities of pilot fuel is unstable, and the cylinder-to-cylinder deviations in injection mass and spray development occur in multi-cylinder direct injection diesel engines. This study investigates the correlation between cylinder-to-cylinder deviations in spray development and combustion and emissions when the pilot injection was applied at idling. It was found that the cylinder-to-cylinder deviations in spray behavior are not the sole reason for the deviations in combustion and emission, but that peculiar conditions to a cylinder such as air movement and in-cylinder carbon deposits also play a role. In this study the HC components in the exhaust gas with and without pilot injection was investigated, and it is shown that deviations in combustion with pilot injection result in deviations in low carbon component emissions and in the rate of pressure rise which is responsible for exhaust odor and engine noise.