D'Ambrosio, S. and Ferrari, A., "Potentialities of Boot Injection Combined with After Shot for the Optimization of Pollutant Emissions, Fuel Consumption and Combustion Noise in Passenger Car Diesel Engines," SAE Int. J. Engines 10(2):2017.
The present paper illustrates a preliminary investigation about the potentialities of injection rate shaping coupled with an after shot injection. A pilot shot can be either absent or present before the rate-shaped boot injection. The experimental tests have been performed on a partial PCCI Euro 5 diesel engine endowed with direct-acting piezoelectric injectors. Starting from optimized triple pilot-main-after injection strategies, boot injection was implemented by maintaining the needle of the direct-acting piezo injector open at part lift. The results at two steady state working conditions have been presented in terms of engine-out emissions, combustion noise and brake specific fuel consumption. In addition, in-cylinder analyses of the pressure, heat-release rate, temperature and emissions have been considered. Considering the in-cylinder pressure traces and curves of heat release rate, the injection rate shaping proved to highly influence combustion in the absence of a pilot injection. A pilot shot added before the boot injection determined a mitigation of the influence of rate shaping. Simultaneous reduction of NOx and soot can be achieved for small quantities of fuel injected during the boot injection compared to the optimized triple injection strategies. However, a trade-off exists between emissions and combustion noise. On the other hand, the variations of bsfc were only minor. The advantages of the application of the boot injection are higher at the low to medium loads than at medium to high loads. However, it was not possible to find a working condition in which the boot injection provided simultaneous advantages on emissions, noise and consumption compared to the optimized triple injection.