农用拖拉机燃用生物柴油排放特性研究

Emission characteristics of biodiesel fueled in agricultural tractors

农业机械已日益成为中国大气污染的重要来源,其排放问题需要更深入的研究。为探究在高海拔条件下农用拖拉机燃用不同比例生物柴油对实际作业条件下的CO(carbon monoxide)、HC(hydrocarbon)、NOX(nitrogen oxides)和PN(particulate number)排放特性的影响,该研究对比分析了一台国III排放标准的农用拖拉机在海拔2 200 m下掺烧B10(10%体积大豆甲酯生物柴油+90%体积柴油)、B20、B30与柴油(B0)在旋耕时(发动机转速处于1 500~1 700 r/min,发动机功率在20~30 kW)的相关污染物排放的情况。分别使用OBD(on board diagnostics)和PEMS(portable emission measurement system)进行拖拉机工况和污染物的数据采集。试验结果表明:生物柴油的使用会略微降低燃油的经济性,增加有效燃油消耗率(brake specific fuel consumption, BSFC),B10、B20和B30相较于B0的BSFC分别增加了2.31%、2.71%和2.04%。该研究基于发动机功率方面来表征农用拖拉机CO、HC、NOX和PN的排放因子。生物柴油有助于降低农用拖拉机的CO、HC和PN排放因子,B10、B20和B30相较于B0基于发动机功率的CO排放因子分别下降了10.15%、12.73%和32.10%;相较于B0基于功率的HC排放因子分别降低了13.22%、26.45%和30.58%;相较于B0基于功率的PN排放因子分别降低了8.22%、10.91%和14.17%。随着生物柴油比例的增加,CO、HC和PN排放因子降低幅度增大。生物柴油会略微增加农用拖拉机的NOX排放,随着生物柴油比例的增加,NOX排放因子也相应增加,B10、B20和B30相较于B0基于发动机功率的NOX排放因子分别增加了1.60%、2.78%和4.20%。该研究中所有测试燃料基于功率的NOX排放因子较《指南》推荐值高3倍多,可见《指南》推荐值对高原环境下的NOX排放因子不适用,高原环境会影响拖拉机在实际作业过程中的污染物排放。为减少高海拔条件下农用拖拉机在实际作业过程中的污染物排放,考虑到燃油的经济性和生物柴油对NOX排放的影响,将小比例掺混生物柴油作为农用拖拉机替代燃料来使用,不仅可以减少CO、HC和PN的排放,还可以减少化石燃料的使用。研究结果可为高海拔环境下农用拖拉机燃用生物柴油的实际污染物排放控制优化提供参考,可以补充在高海拔地区农业机械的排放数据库,以辅助环境污染研究和政策制定。

Agricultural machinery has been one of the most important sources of air pollution in China.It is very necessary to do more research on its emissions.This study aims to investigate the effects of burning different proportions of biodiesel in agricultural tractors at high altitudes on the emission characteristics of CO(carbon monoxide),HC(hydrocarbon),NOX(nitrogen oxides),and PN(particulate number)under the actual operating conditions.A series of tests were carried out on the blending B10(10%by volume of soya bean methyl ester biodiesel+90%by volume of diesel fuel),B20,B30,and diesel fuel(B0)in a National III emission standard agricultural tractor at an altitude of 2200 m during rotary plowing(with the engine speed at 1500 to 1700 r/min and the engine power at 20 to 30 kW).OBD(board diagnostics)and PEMS(portable emission measurement system)were used to collect data on the tractor operating conditions and pollutants,respectively.The results showed that the biodiesel slightly reduced the fuel economy for the brake-specific fuel consumption(BSFC),which increased by 2.31%,2.71%,and 2.04%for B10,B20,and B30,respectively,compared with B0.The emission factors were also obtained for the CO,HC,NOX,and PN of agricultural tractors using engine power.Specifically,the CO,HC,and PN emission factors of agricultural tractors were reduced by 10.15%,12.73%,and 32.10%for B10,B20,and B30,respectively,compared with B0 using biodiesel engine power;13.22%,26.45%and 30.58%for B0-based power and 8.22%,10.91%and 14.17%for B30-based PN emission.The CO,HC,and PN emission factors increased with the increase in the percentage of biodiesel.Biodiesel slightly increased the NOX emissions from agricultural tractors.The NOX emission factor increased,as the proportion of biodiesel increased.The NOX emission factors for B10,B20,and B30 increased by 1.60%,2.78%,and 4.20%,respectively,compared with B0-based engine power.The power-based NOX emission factors of all tested fuels in the plateau environment were more than three times higher than the recommended values of the Guideline.There was a great variation in the pollutant emission of the tractor during actual operation.A tradeoff was made on the fuel economy and the effect of biodiesel on NOX emissions,in order to reduce the pollutant emissions from agricultural tractors during actual operation at high altitudes.Biodiesel can be expected to serve as an alternative fuel in small proportions for agricultural tractors.The CO,HC,and PN emissions can be reduced to avoid the use of fossil fuels.The finding can provide a strong reference to optimize the actual control of the pollutant emission of biodiesel combustion in agricultural tractors under high-altitude environments.The emission database of agricultural machinery can also be supplemented to reduce environmental pollution in high-altitude areas.