Engine oil consumption causes particulate matter, poisoning of catalysts, abnormal combustion like pre-ignition in a gasoline engine, and an increase in customer's running cost. Oil consumption, therefore, must be reduced.It is well known that pressure at a piston second land sometimes becomes larger than the cylinder pressure in the latter half of the expansion stroke. Larger pressure at the second land causes an increase in engine oil consumption. For reducing the second land pressure, increasing volume of a piston second land is one of design schemes. Pressure at a piston second land is calculated in piston design stage. In the calculation, pressure at a piston third land is assumed as same as pressure at the crankcase.This study aimed the effect of volume of the third land of a piston on engine oil consumption. The third and the second lands pressure were measured using an optical fiber type pressure sensor. It was found that the third land pressure showed a quite different trend from the crankcase pressure. It was also found that the pressure balance between the second land and the third land affected engine oil consumption. It was suggested that the third land pressure should be considered in the calculation for lands pressure of a piston and further investigation on third land design for reducing engine oil consumption may be required.

Engine oil consumption must be reduced for reducing exhaust gas emissions. It is well known that a cylinder bore shape under engine operating condition affects oil consumption. This study aimed clarifying the conformability of an oil ring against the distorted cylinder bore. Oil film thickness at the sliding surface of oil ring upper and lower rails was successfully measured by LIF method using optical fiber, which was embedded in the oil ring. The piston motion was also measured and compared with measured oil film thickness. It was found that the piston tilting motion affected oil film thickness hence its conformability. It was also found that thicker oil film was found at the following rail than that at former rail, and it was suggested that oil was supplied to the following rail from not only the sliding surface of the former ring but also somewhere, for example, the oil ring groove.

The reduction of both exhaust gases and carbon dioxide emissions is necessary to meet future emissions regulations for diesel engines. Exhaust after-treatment devices are gradually being applied to diesel engines to reduce exhaust gases. Diesel Particulate Filters (DPF), an after-treatment device for diesel engines, in some cases require post injection of fuel for its regeneration. Post injection is usually carried out at the mid point 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 (RME) 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. The increase in the piston friction forces was moderate in the case of RME. It seems that the higher viscosity and the oiliness of RME suppressed the increase in piston friction forces at TDC.The following effects were found in this study. Fuel post injection caused fuel adhesion to the cylinder wall. Such phenomena affected the lubrication condition of the piston. In the case of RME, the increase in the piston friction forces caused by post injection was smaller than that of light fuel oil, but the effects on piston lubrication condition in the case of using other biofuels needs to be investigated.