电控低压喷射小型汽油机燃烧与排放特性分析

Analysis of combustion and emission characteristics of electronic controlled low pressure injected small gasoline engine

以168F汽油机为样机,采用自主开发的通用小型汽油机低压电控燃油喷射系统,按照美国EPA排放试验循环工况,对35 k Pa、70 k Pa和0.3 MPa喷射压力下发动机燃烧特性与排放特性进行试验研究。得出小型汽油机采用不同喷射压力喷油,可通过喷油脉宽控制使各工况点过量空气系数无明显差异,能实现以低排放为目标开环控制的电控低压喷射并能优化汽油机的综合性能。降低喷射压力,发动机标定工况缸内最大爆发压力略有降低,最大爆发压力对应曲轴转角推迟。随着喷射压力降低,燃烧持续期略有增加,缸内最高燃烧温度下降,CO排放值几乎保持不变,HC排放值呈上升趋势,NOX排放值则呈下降趋势,有效燃油消耗率略有增加。用喷油压力分别为35 k Pa、70 k Pa和0.3 MPa喷油,CO比排放分别为259.9、258.5和258.3 g/(k W·h);HC+NOX比排放分别为7.41、7.35和6.99 g/(k W·h)。相对于使用化油器供油的原机而言,电控样机整机动力性不变,排放和经济性能明显提高。采用35k Pa的低压电控喷射系统小型汽油机能满足美国EPAⅢ排放法规限值要求,起动性能、运转稳定性明显改善,能降低整机电控系统的成本,可推动整个通用小型汽油机行业电控化发展。

Low fuel consumption and low emissions of internal combustion engines were the subject of the current industry research. The annual production and export of non-road spark ignition engines were very huge but more than 98% of these engines used carburetor to form mixture. Considering the emission regulations of Europe, the United States（US） and China were more and more strict, non-road spark ignition engines using carburetor could not meet the requirement gradually and there were many shortcomings of carburetor compared with the electronic controlled system. Taking 168 F gasoline engine as the sample engine, using the electronic controlled low pressure injection system developed independently, according to the working conditions of the US EPA emission test, the combustion and emission characteristics were researched in this paper under the injection pressure of 35 kP a（the minimum injection pressure could satisfy the need of start performance, working conditions and calibration software）, 70 k Pa（the minimum injection pressure of the early single point injection gasoline engine） and 0.3 MPa（the normal injection pressure of automobile engine using port fuel injection）. The test was performed on CW-9 eddy current dynamometer bench and the emissions were measured by Horiba MEXA-7200 D exhaust analyzer. The KISTLER5117BFD17 spark plug pressure sensor and DEWETRON-800 combustion analyzer were used to judge and analyze the combustion process in the cylinder. Using different injection pressure, the excess air coefficient had no significant difference at the same working condition through controlling the injection pulse width. The open loop control of low pressure injection aiming at low emissions could be achieved and the universal performances of the gasoline engine were optimized. With the decrease of the injection pressure, the maximum cylinder pressure decreased slightly and the crank angle corresponding to the maximum pressure postponed at the rated condition; the combustion duration increased slightly; the maximum combustion temperature in cylinder decreased; the fuel consumption increased slightly. Carbon monoxide（CO） emission remained almost unchanged, and hydrocarbon（HC） emission showed a trend of increase while nitrogen oxide（NOX） emission decreased. Compared to the original machine with carburetor, the power performance remained the same but the emission and economy performances were improved significantly. At the injection pressure of 35 kP a, 70 k Pa and 0.3 MPa, the specific emissions of CO were respectively 259.9, 258.5 and 258.3 g/（kW ·h）, and the specific emissions of HC＋NOX were respectively 7.41, 7.35 and 6.99 g/（kW ·h）. The gasoline engine with the lowest injection pressure（35 kP a） could meet the limit requirements of US EPA III emission regulations, and its starting performance and operating stability were improved significantly compared to the original machine with the carburetor; and it could also reduce the cost of the whole electric controlled system. Therefore the engine with the lowest injection pressure（35 kP a） can promote the development of non-road spark ignition engine and realize the electric control.