十六烷值改进剂对甲醇/生物柴油柴油机排放的影响

Experiment of cetane number improver on emissions of diesel engine fueled with methanol/biodiesel

甲醇、生物柴油是柴油机的含氧替代燃料,能有效降低柴油机颗粒物排放。但甲醇的十六烷值低,在柴油机上燃用会出现着火困难的问题,采用添加十六烷值改进剂的方法能有效提高柴油机燃料的着火性能。为了研究不同十六烷值改进剂对柴油机排放污染物的影响,试验选择了烷基硝酸酯、环烷基硝酸酯、醚3种十六烷值改进剂,分别添加到甲醇/生物柴油混合燃料中,考察了十六烷值改进剂对混合燃料理化特性的影响,并在186F柴油机上进行了台架试验,测量了柴油机缸内压力、排气温度、HC、CO、NOX和烟度的变化规律,分析了添加不同十六烷值改进剂时,柴油机排放污染物的变化规律。结果表明:在甲醇/生物柴油中添加十六烷值改进剂,混合燃料的压力峰值升高,滞燃期缩短,燃烧持续期延长,当改进剂的添加量相等时,添加烷基类硝酸酯混合燃料的滞燃期最短;排气温度变化不大,变动范围为-3.24%～3.45%;排放污染物中HC和CO排放升高;NOX和烟度降低,在3 000 r/min,100%负荷时,添加烷基硝酸酯、环烷基硝酸酯、醚分别使NOX降低12.90%、6.45%、3.87%,烟度降低11.76%、17.65%、38.24%。在甲醇/生物柴油混合燃料中添加十六烷值改进剂,不仅可以改善燃料的着火特性,也可以降低NOx和颗粒物排放。

Methanol and biodiesel are the oxygenated alternative fuels of diesel engine,which can effectively reduce particulate emissions of diesel engines.However,due to the low cetane number of methanol,it is difficult for methanol to ignite in diesel engine.The addition of cetane number improver is an effective method to improve the ignition performance of diesel engine fuels.In order to study the effects of different cetane number improvers on diesel engine emission pollutants,three kinds of cetane number improvers,such as alkyl nitrates,naphthyl nitrates and ethers were chosen and added to the methanol/biodiesel blend fuel with the mixing ratios of 0.3%,0.3%,and 3%,respectively.The effects of the cetane number improvers on the physical and chemical properties of methanol/biodiesel blend were investigated.The engine bench test was carried out on the 186F diesel engine without adjusting the structure of the diesel engine during the test.The in-cylinder pressure and exhaust temperature of the diesel engine fueled with methanol/biodiesel blend was measured at 1 800,3 000 r/min,25%,and 100%load,then the ignition delay and combustion duration were calculated.The variation of pollutants such as HC,CO,NOX and smoke emitted from the diesel engine at 1 800 and 3 000 r/min,10%,25%,50%,75%and 100%loads were measured.The effects of cetane number improvers on diesel engine exhaust pollutants were investigated.The results showed that the addition of cetane number improvers had little effects on the density,viscosity and other physical and chemical properties of the methanol/biodiesel blend,but the cetane number of the blend was obviously increased.Because of the low decomposition activation energy of the cetane number improvers,the improvers can help the blend to shorten the chemical delay period.With the addition of cetane number improvers to the methanol/biodiesel blend,the in-cylinder pressure peak was increased,the ignition delay was shortened,and the combustion duration was prolonged.In addition,the corresponding crankshaft angle of in-cylinder pressure peak was advanced.When the amount of improvers was equal,the ignition delay period of alkyl nitrates mixture was the shortest among the three cetane number improvers.When the diesel engine changed from 25%load to 100%load,the exhaust temperature was increased by 194-235 K at the same speed.While the diesel engine speed had smaller effects on the exhaust temperature and the variation range was?3.24%-3.45%.With the addition of cetane number improvers,the HC and CO emission were increased,especially at higher engine load.However,the addition of cetane number improvers can reduce the NOX and the smoke.When the diesel engine was at 3 000 r/min,100%load,NOX was reduced by 12.90%,6.45%,3.87%with the addition of alkyl nitrate,naphthenic nitrates and ethers respectively,and the smoke was reduced by 11.76%,17.65%,38.24%.The addition of cetane number improver in methanol/biodiesel blends not only can improve the ignition characteristics of the fuels,but also reduce NOx and particulate emissions.