The modification of the fuel injection rate in heavy-duty diesel engines: Part 2: Effects on combustion

Abstract

An experimental study has been performed on the effects of injection rate shaping on the combustion process and exhaust emissions of a direct-injection diesel engine. Boot-type injections were generated by means of a modified pump-line-nozzle system, which is able to modulate the instantaneous fuel injection rate. The influence of different values of boot length and boot pressure has been evaluated by analysing the apparent rate of heat release and flame temperatures. Engine operating conditions at different rotating speed and injected fuel mass were considered in order to assess their effect on the injection rate shape. Results show how all the changes in the injection rate agree with changes in the diffusion combustion phase. Medium-load conditions presented larger increases in the dry soot emissions since the boot was longer and it was produced at lower pressure. Changes in engine speed at high load did not show major changes in the combustion evolution. Longer boots produced high soot emissions probably due to less efficient mixing conditions.