Effect of fuel injection strategy on combustion performance and NOx/smoke trade-off under a range of operating conditions for a heavy-duty DI diesel engine

Abstract

The combustion process and exhaust emissions of a conventional diesel engine can be improved by manipulating the injection strategy (timing and pressure) without modification of the design. In this work, the influence of the injection strategy on the NOx emissions and smoke level was investigated experimentally for a heavy-duty diesel engine operated using diesel fuel. Different injection timings and pressures were applied to produce a variety of engine-out emission levels over different engine operating conditions. The experimental results revealed that retarding the fuel injection timing enhanced the fuel economy by reducing the brake-specific fuel consumption (BSFC). In addition, the NOx emissions were also reduced by retarding the injection timing at different engine speeds and loads. For the tested operating conditions, the NOx emissions and BSFC were lower at low engine speed and high engine load, in particular at 1200 rpm and full load (100%), respectively. The results of the experimental work indicated that the brake thermal efficiency (BTE) increased with retarded injection timings at various engine speeds. Also, the BTE was higher at low engine speed (1800 rpm) and for different injection timings. Besides, the smoke level was improved for retarded injection timing and low engine speed. Lower exhaust smoke opacity was obtained at high injection pressure compared with low injection pressure for different engine test conditions. Use of the control engine operating conditions and high injection pressure enhanced the exhaust gas temperature and BSFC, but slightly increased the NOx emissions.