小功率非道路用柴油机动力、经济及排放特性

Power, economy and emission characteristics of low power non-road diesel

为提高小功率非道路用柴油机的动力性、经济性、降低有害物排放,开展了柴油机缸内燃烧过程的试验研究。该文以非道路用N490直喷柴油机为样机,通过对燃料喷射系统参数优化,提高喷油压力和优化喷油特性;通过对配气定时调整,提高柴油机常用转速下的充量系数;通过对燃烧室结构的优化设计,改善缸内油气混合。柴油机经优化后,性能得到大幅提升,柴油机在标定工况、最大扭矩工况燃油消耗率分别下降了3.0%、2.43%,不透光烟度分别减少了14.6%、10%;整机的CO、NO_x+HC、颗粒(PM)与原机相比分别下降了34.7%、21.5%、34.9%,排放达到了非道路国三排放标准限值要求。通过对燃料喷射系统、进气系统与燃烧室的优化匹配,完全可以在降低有害物排放的同时,提高柴油机的经济性。试验研究可为提升非道路用柴油机性能并满足国三排放法规提供技术参考。

As society and economy developing, the problem caused by non-road diesel engine emission has been widely drawing people＆#39;s attention. Increasingly serious environmental problems have forced people to use advanced technology to reduce engine emissions and lots of countries have established non-road diesel engine emission regulations. Developed countries, represented by the United States of America and the European Union, have formulated stringent emission regulations to limit emissions from non-road diesel engines. China issued the limits and measurement methods for exhaust pollutants from diesel engines of non-road mobile machinery in 2014. By using the vehicle emission control technology, the high power （＞37 kW） diesel engine could meet the emission standards. Because of the structure, production costs and application limit, electronic control system, common rail system, turbocharger, exhaust gas recirculation and selective catalytic reduction can＆#39;t be applied in low power （＜37 kW） non-road diesel engine. So there are a lot of technical difficulties for the upgrade of low power non-road diesel engine emissions. In addition, the strict regulations on the brake specific fuel consumption （BSFC） of diesel engines were made, which further increases the difficulty of such diesel engine emissions meeting the requirements. The emission standards implementation and requirements of the low power non-road diesel engine are constantly tightened. The electronically controlled VE pump-line-nozzle fuel injection system has the advantages of low cost, simple structure, convenient arrangement on the engine, and also has the potential to meet Level III or even Level IV emission regulation requirements in China. Therefore, it＆#39;s necessary to research and develop a low power non-road diesel engine with high performances and low emissions. In this article, the non-road N490 direct injection diesel engine was taken as the prototype, By using a combination of theoretical analysis and experimental research, technology strategy of low non-road diesel engines was explored to meet the requirements of high performance and low emissions. By increasing the pump cam lift, reducing the inner diameter of the high-pressure fuel pipe, and improving nozzle geometry of the injector, the maximum nozzle side pressures at the rated condition and the maximum torque condition increased by 32.7% and 50%, respectively. Re-entrant dumbbell-shaped chamber was designed to strengthen the central bulge of the combustion chamber bottom, which improved the air movement in the combustion chamber. By adjusting the valve timing, the volumetric efficiency of the diesel engine was improved. The combustion was optimized by reducing the fuel injection quantity during ignition delay period. After optimizing the parameters of the fuel injection system, the valve timing and combustion chamber, the diesel engine performance was greatly improved. Compared with the original engine, both at the rated condition and at the maximum torque condition, the specific fuel consumption was decreased by 3.0% and 2.43%, respectively, and the light-proof smoke was also decreased by 14.6% and 10%, respectively. The experimental results showed that the exhaust emissions of carbon monoxide （CO）, nitrogen oxide （NOx） ＋ hydrocarbon （HC）, and particulate matter （PM） were 1.109, 6.23 and 0.522 g/（kW＆#183;h）, respectively, which were lower than Level Ⅲ emission standards in China. Compared with the results of the prototype, the measured values of CO, NOx＋HC and PM were reduced by 34.7%, 21.5% and 34.9%, respectively. At the same time, both the maximum cylinder pressure and the heat release rate were greatly reduced. At the rated and the maximum torque conditions, the maximum cylinder pressures were decreased by 15.8% and 9.6%, respectively; the maximum heat release rates were decreased by 9% and 8.8%, respectively. Through the analysis of experimental data, the research shows that optimization matching of fuel injection, in-cylinder air movement and combustion chamber can not only decrease the exhaust emissions obviously but improve the fuel economy of the engine.