The crank angle locations for the first occurrences of several main combustion events in a Diesel engine were investigated for varied fuel parameters. The events studied include preflame reactions premixed flame propagation, start of pressure rise, maximum rate of pressure rise (dp/dt), and peak cylinder pressure. The fuels employed in the study were in two groups (1) Base fuel-1 and derivatives prepared by mixing it with small doses of a cetane number (CN) enhancing additive and (2) Base fuel-2 and those made by adding different amounts of bio-Diesel fuel.
The experiment was performed by using a single-cylinder direct-injection (DI) Diesel engine equipped with an electronically controlled high-pressure fuel injection unit. The in-cylinder processes during the periods of ignition delay and combustion reaction were measured by using a high-speed multispectral infrared (IR) imaging system developed at Rutgers University. The other events were found from the pressure-time history.
The purpose of using these fuels was to investigate additive effects on the (invisible) preflame reaction and visible premixed flame development flame behaviors of bio-Diesel fuels CN effects on in-cylinder reactions, and others There is some evidence that the formation of the visible flame kernels may not be directly related to the preflame reactions when the addictive is used to increase CN. The reactions during the ignition delay of bio-Diesel fuels were rather unpredictable, therefore requiring additional investigation. Among the most indicative timelines for determining a fuels CN were those of the maximum dp/dt the start of pressure rise, the first premixed flame and the peak pressure. In particular the timeline of maximum dp/dt seems to be most insensitive to the variation of injection timing. Some new findings are also reported in the paper.