A Study of the Effects of Biofuel Use on Piston Lubrication During Fuel Post Injection in a Direct Injection Diesel Engine

Abstract

The reduction of both exhaust gases and carbon dioxide emissions is necessaiy to meet future emissions regulations for diesel engines. Exhaust after-treatment devices are gradually being apptied to diesel engines to reduce exhaust gases. Diesel particulate filters (DPF), an after-treatment device for diesel engines, in some cases require fuel post injection for regeneration. Post injection is usually conducted at the midpoint of the expansion stroke, and therefore causes fuel adhesion to the cylinder wall. However, using biofuels in a diesel engine is an effective way of reducing carbon dioxide emissions. It is well known that biofuels are chemically unstable, but the effects of biofuels on piston lubrication condition have not been thoroughly studied. In this study, piston lubrication condition during post injection in a single cylinder DI diesel engine using biofuel was investigated. Piston and ring friction forces were measured under engine operating conditions by means of a floating liner device to investigate the lubrication condition of the piston and rings. Both light fuel oil and biofuel were used in the measurements, with rapeseed methyl ester (RMEj being used as the biofuel. Lubricating oil on the cylinder wall was also sampled under engine operating conditions, and the effect of post injection on fuel adhesion to the cylinder wall was analyzed. It was found that the effect of post injection on fuel adhesion to the cylinder wall was remarkable around the top dead center (TDC), and the fuel dilution rate reached approximately 90%. The results of the measurement of the piston friction forces showed that post injection caused an increase in the friction forces at the compression TDC (CTDC) in the cases of both RME and light fuel oil, and the friction forces at CTDC increased according to the delay of the post injection timing.