Multi Cylinder Partially Premixed Combustion Performance Using Commercial Light-Duty Engine Hardware 2014-01-2680
This work investigates the performance potential of an engine running with partially premixed combustion (PPC) using commercial diesel engine hardware. The engine was a 2.01 SAAB (GM) VGT turbocharged diesel engine and three different fuels were run - RON 70 gasoline, RON 95 Gasoline and MK1 diesel. With the standard hardware an operating range for PPC from idle at 1000 rpm up to a peak load of 1000 kPa IMEPnet at 3000 rpm while maintaining a peak pressure rise rate (PPRR) below 7 bar/CAD was possible with either RON 70 gasoline and MK1 diesel. Relaxing the PPRR requirements, a peak load of 1800 kPa was possible, limited by the standard boosting system. With RON 95 gasoline it was not possible to operate the engine below 400 kPa. Low pressure EGR routing was beneficial for efficiency and combined with a split injection strategy using the maximum possible injection pressure of 1450 bar a peak gross indicated efficiency of above 51% was recorded. The split injection strategy showed in general higher efficiency and did lead to noticeable smoother engine operation with a reduction of combustion noise. However, soot emissions did increase strongly when the time between injections was reduced.
Compared to conventional diesel combustion, CDC, higher efficiency combined with low NOx and soot operation could be realized with gasoline PPC. Typically, soot levels were two orders of magnitude lower than for CDC. The injection pressure showed an unexpectedly strong correlation with efficiency. Idle operation was realized by closing the VGT and thus increasing the amount of trapped residual gases. Increasing swirl did not lead to any improvements but rather the opposite in terms of fuel consumption and NOx.
The standard VGT was a limiting factor and pumping losses typically meant that the net indicated efficiency was limited to slightly above 45%. The results indicate, however, that a simple PPC engine using standard diesel hardware with the addition of LP-EGR and using RON 70 gasoline could be an interesting option trading off some efficiency for complexity and hardware cost.