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Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels and injection timings sufficiently early or late to extend the ignition delay so that air and fuel mix extensively prior to combustion. This paper investigates the operating region of single injection diesel PPC in a multi cylinder heavy duty engine resembling a standard build production engine. Limits in emissions and fuel consumption are defined and the highest load that fulfills these requirements is determined. Experiments are carried out at different engine speeds and a comparison of open and closed loop combustion control are made as well as evaluation of an extended EGR-cooling system designed to reduce the EGR temperature. In this study the PPC operating range proved to be limited.

A very flexible choice of fuel injection characteristics can be obtained with an advanced electronic unit injector that has been developed with two electronically controlled valves. Single-cylinder engine tests have demonstrated the potential of this advanced EUI system for a heavy-duty diesel engine. Substantial increases in injection pressure can be programmed electronically at individual engine speed/load conditions, compared with a baseline EUI system, to provide much faster rates of air/fuel mixing. Simulated US and European emissions cycle results, with the optimised two-actuator EUI and EGR, show substantially improved soot particulate versus NOx results and lower BSFC compared with a baseline EUI result. A high-pressure post injection has the potential to give further soot reduction.