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The influence of different multiple injection strategies on the emissions, combustion noise and BSFC (brake specific fuel consumption) of a small non-road diesel engine prototype equipped with a Common Rail (CR) fuel injection system has been analysed. The two most critical operating points according to the ISO 8178 - C1 test cycle as far as the exhaust emissions are concerned (Intermediate Speed/Full Load; Rated Speed/Full Load) were considered. Different injection strategies, each with a fixed number of consecutive injections (up to 4), were tested for the selected operating points. It was found that multiple injection strategies can be very effective also for small displacement non-road diesel engines in reducing particulate matter (PM), NOx and noise levels without increasing fuel consumption.

High pressure common-rail injection systems nowadays allow a very high degree of flexibility in the timing and quantity control of multiple injections, which can be used to obtain significant reductions in engine noise and emissions. The aim of this study is to develop a better understanding of the relationship between injection strategies and the combustion and emission formation process. Some multiple injection strategies (pilot-pilot-main and pilot-main-after) have therefore been analyzed to highlight their influence on soot, NOx, combustion noise and bsfc (brake specific fuel consumption) on a passenger car DI Diesel engine prototype. One operating point (2000×2 rpm/bar) was analyzed for the pilot-pilot-main injection strategy while two operating points (1500×5 and 2500×8 rpm/bar) were tested for the pilot-main-after injection strategy.

The effect of variations of compression ratio (CR) and injection pressure (IP) on the emissions and performance of a small displacement common rail off-road diesel engine was evaluated. The operating point corresponding to the 5th mode of the ISO 8178 - C1 test cycle (intermediate speed / full load) was considered, since it represents one of the most critical operating conditions as far as exhaust emissions are concerned. The main effect of a reduction of the compression ratio, for a fixed injection timing, was found to be, as expected, an increase in NOx emissions along with a decrease of PM emissions, with a substantial redefinition of the PM-NOx trade-off curve; the choice of a proper value for the start of injection can therefore lead to a better compromise among pollutant emissions, although remarkable variations in BSFC and combustion noise must be taken into account.