柴油-航空煤油宽馏程混合燃料对柴油机燃烧与排放的影响

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

为了研究柴油-航空煤油宽馏程混合燃料对柴油机燃烧与排放的影响,按照中国3号航空煤油(rocket propellant 3,RP3)的掺混比(体积比)分别为20%、40%与60%与国VI柴油进行混合,配制3种具有不同理化特性的柴油-RP3宽馏程混合燃料(D80K20、D60K40与D40K60),并通过台架试验,研究了最大扭矩转速2700 r/min所对应的100%、50%与10%负荷工况(分别记为A、B、C工况)下,D100、D80K20、D60K40和D40K60对柴油机缸内工作过程、排放、颗粒物浓度与粒径分布的影响规律。结果表明,3种工况下,与D100相比,RP3掺混比增加到60%时,缸内最大压力的变化范围小于0.2 MPa,预混燃烧放热率峰值增大13.21~27.43 J/°CA,滞燃期延长2.19~2.53°CA,燃烧持续期缩短1.73~1.91°CA,预混燃烧累积放热百分比增加4.66%~5.28%,缸内最高温度的上升幅度小于35 K,与放热率峰值和最大燃烧压力相对应的曲轴转角后移1.67~2.23°CA,有效热效率上升0.15%~0.46%。柴油-RP3宽馏程混合燃料能够显著降低柴油机碳烟排放,并且降低效果随着柴油机负荷的增加和RP3掺混比的增大更加明显,但对NOX排放没有明显的影响,与D100相比,柴油机在3种工况下燃用D40K60时的碳烟排放分别降低53.6%、44.1%、35%,NOX排放的上升幅度均小于2%,核态颗粒物数量浓度上升12.5%~90.6%,积聚态颗粒物数量浓度、颗粒物总数量浓度、颗粒物表面积浓度和总质量浓度分别降低20.1%~45.8%、14.2%~42.1%、32.5%~41.6%、28.5%~38.8%,且积聚态颗粒物的粒径朝小粒径方向移动。试验结果表明,柴油-RP3宽馏程混合燃料对柴油机燃烧与排放有重要的影响,能明显改善柴油机碳烟与NOX排放之间的trade-off关系,并且在降低柴油机颗粒物总数量浓度、总质量浓度以及表面积浓度方面具有较为显著的效果,有利于降低柴油机DFP载体上的颗粒物堆积、延长DFP再生周期。

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.