Experimental investigation of neat ethanol combustion via exhaust rebreathing in a heavy-duty diesel engine from low to medium load

The carbon footprint and particulate matter emissions of diesel engines may be reduced by replacing conventional diesel fuel with ethanol. However, ethanol has a poor tendency for autoignition, and is therefore difficult to use with conventional diesel combustion strategies. In this study, exhaust rebreathing is used to increase cylinder temperatures and enable mixing-controlled compression ignition of ethanol in experiments on a heavy-duty diesel engine. The exhaust rebreathing strategy is also implemented with conventional diesel fuel. Results with each fuel are compared to results with conventional diesel fuel using a production-like calibration at a medium torque condition. Finally, the same exhaust rebreathing valve strategy is applied to extremely low load operation with ethanol to investigate the feasible limit of exhaust rebreathing operation. Diesel-like engine performance was achieved with ethanol at medium torque. Analysis of apparent heat release rates revealed that ethanol ignition delay was sensitive to backpressure, whereas diesel fuel ignition delay changed very little across a similar backpressure sweep. As compared to a production-like diesel baseline, the exhaust rebreathing strategy with ethanol penalized thermal efficiency and NOx emissions slightly, but improved particulate and CO emissions. At 1 bar IMEP, coefficient of variation of IMEP as low as 5% was achieved with ethanol, indicating that stable, diesel-like combustion could be achieved at even the lowest loads via exhaust rebreathing. The results of this study demonstrate the feasibility of operating a heavy-duty diesel engine on ethanol, diesel fuel, or any mixture of the two using an exhaust rebreathing strategy.