In this investigation highly diluted engine tests have been conducted to study effects of dilution, heat release rate and combustion phasing on both efficiency and emissions in the Partially Premixed Combustion regime. It has been reported that over the complete phasing range an increase of more than two percent points in indicated efficiency at high load could be expected, with an astonishing 4 to 5 percent points for the low load case. The origins of these increases were sought and found to be caused by improved heat release shapes, combustion efficiencies or heat losses or a combination of these. On the other hand, soot emissions are greatly reduced due to the excess oxygen available, but nitrogen oxide emissions are found to increase: both in concentration and power specific units
