Application of Palm Oil Biodiesel Blends under Idle Operating Conditions in a Common-Rail Direct-Injection Diesel Engine

Abstract

This study describes the effects of palm oil biodiesel blended with diesel on the combustion performance, emission characteristics, and soot morphology in a 4-cylinder common-rail direct-injection (CRDI) diesel engine. The operational condition is idle speed, 750 rpm (the lowest speed of the test engine without any operation by driver), and the load conditions of the engine are 0 Nm and 40 Nm. Five kinds of biodiesel fuels are blended with diesel in 0%, 10%, 20%, 30%, and 100% proportions by volume. A pilot injection was applied at BTDC 15 °CA and 20 °CA. Part of the pilot injection affects the combustion of the main injection due to the deterioration of the spray because of the high viscosity of palm oil biodiesel. Palm oil biodiesel is sufficient to keep the engine stable in an idling state, but the fuel economy deteriorated. The deterioration of the spray due to the high viscosity of palm oil biodiesel is offset by the effect of oxygen content and high cetane number, resulting in a constant nitric oxide (NOx) emission. However, particulate matter (PM) is reduced. When the engine load is increased, the carbon monoxide (CO) emission amount increased because of the insufficient intake air and oxygen content to reduce the fuel-rich areas. However, when the palm oil biodiesel blend ratio was above a certain level, the influence of oxygen content in the palm oil biodiesel increased, resulting in reduced CO emission levels. Hydrocarbon (HC) was reduced by oxygen atoms in palm oil biodiesel. The sizes of particulates emitted from diesel engine using palm oil biodiesel decreased with an increased blend ratio because of oxidization of hydrocarbons absorbed on PM.