The Effect of Cooled EGR on Emissions and Performance of a Turbocharged HCCI Engine

This paper discusses the effects of cooled EGR on a turbo charged multi cylinder HCCI engine. A six cylinder, 12 liter, Scania D12 truck engine is modified for HCCI operation. It is fitted with port fuel injection of ethanol and n-heptane and cylinder pressure sensors for closed loop combustion control. The effects of EGR are studied in different operating regimes of the engine. During idle, low speed and no load, the focus is on the effects on combustion efficiency, emissions of unburned hydrocarbons and CO. At intermediate load, run without turbocharging to achieve a well defined experiment, combustion efficiency and emissions from incomplete combustion are still of interest. However the effect on NO_x and the thermodynamic effect on thermal efficiency, from a different gas composition, are studied as well. At high load and boost pressure the main focus is NO_x emissions and the ability to run high mean effective pressure without exceeding the physical constraints of the engine. In this case the effects of EGR on boost and combustion duration and phasing are of primary interest. It is shown that CO, HC and NO_x emissions in most cases all improve with EGR compared to lean burn. Combustion efficiency, which is computed based on exhaust gas analysis, increases with EGR due to lower emissions of CO and HC.