A Study of Diesel Combustion and Soot Formation as Observed by High-Speed Photography.

Abstract

The processes of combustion and the soot formation in a direct-injection diesel engine were studied experimentally at a low engine speed. Injection was performed by a specially designed injection system relying on the principle of fast hydraulic acceleration of a spool. High-speed photographs at an injection pressure up to 120 MPa show that luminosity fluctuations of flames become less over the combustion space as the injection pressure increases, due partly to the fact that combustion becomes rapid and partly to the leaner mixture formed. Soot clouds taken by using a laser-light sheet method at similar rates of heat release but different injection pressures show that soot clouds do not exist in the later part of combustion processes at a pressurized injection and a smaller nozzle diameter.