Due to its ease of use in diesel engines, its presumably lower carbon footprint, and its potential as a renewable fuel, biodiesel has attracted considerable attention in technological development and research literature. Much literature is devoted to evaluating the injection and combustion characteristics of biodiesel fuel using unit injectors, where injection pressure and timing are regulated within the same unit. The use of common rail fuel systems, where fuel pressure is now equally governed to each injector (of a multi-cylinder engine), may change the conventionally accepted impact of biodiesel on injection and combustion characteristics. The objectives of this study are to characterize the responses of an electronically-controlled common-rail fuel injector (in terms of timing and duration) when delivering either 100% palm olein biodiesel or 100% petroleum diesel for a diesel engine, and correlate potential changes in injector characteristics to changes in combustion.
The experimental study relies on the analysis of injector command and needle lift measurements to identify major differences (or indifferences) of injection characteristics of biodiesel fuel (relative to petroleum diesel fuel). Further, in-cylinder pressure measurements provide the basis for apparent heat release rate analysis in identifying critical combustion characteristics (i.e., ignition delay and combustion duration). Differing from the typically-observed artificial advance in injection timing with bio-diesel, this study finds that there are no observable differences in the injection timing or needle lift behavior with biodiesel (relative to petroleum diesel) in a common rail diesel engine.
