Effects of diesel-aviation kerosene wide distillation blend fuels on combustion process and emission characteristics of diesel engines

Abstract: Limited by the non-uniform fuel-air mixture in the cylinder, there exists "trade-off" relationship between soot and NOX emissions for diesel engines. Studies showed that fuel properties have important impacts on diesel engine performance. Therefore, it is an effective way to improve the combustion process and reduce emissions of diesel engines by changing and designing fuel properties. In order to investigate the effects of diesel-kerosene wide distillation blended fuels on diesel engines, three kinds of wide distillation blended mixed fuels with different physical and chemical properties of diesel and RP3 were prepared，that were D80K20 (80% diesel and 20% aviation kerosene (RP3) by volume), D60K40 (60% diesel and 40% aviation kerosene (RP3) by volume) and D40K60 (40% diesel and 60% aviation kerosene (RP3) by volume) in this research. The engine bench test was carried out in a single-cylinder diesel engine equipped with electronic unit pump. During the test, engine speed was controlled to be constant at 2700 r/min, engine load ratio was 100%, 50% and 10% of the full loads (respectively represented heavy, medium and light load conditions and marked as working conditions A, B, C). Fuel injection tim and injection duration remained unchanged when the test diesel engine was fueled with different fuels at the same load condition. In-cylinder pressure, exhaust emissions, particulate concentration and particulate size for D100(only diesel), D80K20, D60K40 and D40K60 at working conditions A, B, C were experimentally measured. Combustion parameters such as heat release rate, ignition delay, combustion duration and cumulative heat released percentage of premixed combustion phase were calculated based on the in-cylinder pressure data. As RP3 ratios in the diesel-RP3 blends increased from 0 to 60%, the variation of maximum in-cylinder pressure was less than 0.2 MPa, the maximum heat release rate percentage of premixed combustion increased by 4.66%-5.28%. Besides, the ignition delay was prolonged by 2.19-2.53 °CA due to the decreased of cetane number. The cumulative heat released percentage of premixed combustion phase increased by 4.66%-5.28%. The combustion duration decreased by 1.73-1.91°CA. The increasement of maximum in-cylinder temperature was no more than 35 K. The brake thermal efficiency increased slightly by 0.15%-0.46% due to the higher isovolumetric degree. With regard to exhaust gas emissions, soot emissions for the diesel-RP3 wide distillation blended fuels reduced apparently especially at high load conditions. And the higher RP3 ratios in the diesel-RP3 wide distillation blended fuels, the more evident reduction on soot emissions. At working condition A, compared with D100, soot emissions for D80K20, D60K40 and D40K60 respectively decreased from 153.7 to 132.5, 104.9 and 71.4 mg/m3, the reduction range was 13.8%, 31.8% and 53.6% repectively. At working conditions B and C, compared with D100, soot emissions for D40K60 respectively decreased from 25.4 and 1.2 to 14.2 and 0.78 mg/m3, the reduction range was 44.1% and 35% respectively. Due to the similar maximum in-cylinder combustion temperature for D100, D80K20, D60K40 and D40K60, there were no obvious impacts on NOX emissions. At working conditions A, B and C, the growth rate of NOX emissions was no more than 2%. In respect of the particulate size, the curve of particulate size distribution shifted to the smaller size as RP3 ratios increased. At working conditions A, B and C, as RP3 ratios increased from 0 to 60%, the nucleation-mode particulate concentration increased by 12.5%-90.6%, the accumulation-mode particulate concentration, total particulate concentration, surface area concentration and total mass concentration respectively decreased by 20.1%-45.8%, 14.2%-42.1%, 32.5%-41.6%, 28.5%-38.8%. The results showed that diesel-RP3 wide distillation blended fuels have advantages on improving "trade-off" relationship between soot and NOX emissions, as well as reducing particulate concentration of diesel engines. Therefore, it is a potential way to increase the production of diesel fuel, reduce the environmental pollution, decrease the number and mass of particulates accumulated on DPF carrier and extend the regeneration life of DPF by using diesel-RP3 wide distillation blended fuels in diesel engines.