Research Of Electronic Controlled Non-road SI Engine With Ultra Low Injection Pressure

The production of Chinese non-road SI engines had accounted for more than 40% of the world’s annual output and the annual export quantity was very huge. Chinese enterprises had recognized the deficiency of carburetor during exporting the engines to the United States and other high-end markets. However, it was hard to transplant the electronic controlled system of vehicle engine because the system was expensive and difficult to be promoted. Therefore, it was imminent and valuable for engineering application to carry out the electronic controlled system research of non-road SI engines.The concept of ultra low injection pressure was proposed in this paper. Taking 168 F gasoline engine as the prototype, the low cost project of electronic controlled system was designed with mechanically driven diaphragm pump and ultra low injection pressure. In order to meet the US EPA phase III emission legislation, the research of electronic controlled fuel injection system of open loop at ultra low pressure(35k Pa and 70 k Pa) was conducted combing test and simulation. Firstly, Ricardo Wave software was used to simulate the working process of gasoline engine influenced by the concentration of the mixed gas and the ignition advanced angle. With low emission as the goal, considering the power, economy and using performance, the ideal excess air coefficient and ignition advanced angle of the high performance non-road SI gasoline engine were got as the basis of designing the initial MAP diagrams. Secondly, the fuel injection pulse width model of 168 F gasoline engine was established using Matlab/Simulink as the tool. The initial fuel injection MAP diagrams of 35 k Pa and 70 k Pa injection pressure were made, which formed the basic dates of calibrating the engine.The electronic controlled fuel injection system at ultra low injection pressure was established. The initial fuel injection MAP and ignition advanced angle MAP were written into ECU and the bench test was carried out. The emission and performance were optimized by optimizing the fuel injection pulse width through analyzing the indicator diagram and the test results. When the injection pressure was 35 k Pa and 70 k Pa, keeping the rated power unchanged, the CO emissions were 259.9 and 258.5 g(k W·h)-1 and HC+NOX emissions were 7.41 and 7.35 g(k W·h)-1, which were lower than the limits of the US EPA emission legislation. Compared with the original engine with carburetor, the specific fuel consumption of electronic controlled gasoline engine at full load speed characteristic decreased and the highest decrease was 3.4%. The starting performance and stability of idle speed and changing load were better than the original engine. The research showed that the non-road SI engine could meet the demand of the US EPA phase III emission legislation with electronic system at ultra low injection pressure and its universal performance was excellent. With the decrease of injection pressure, the combustion time was delayed, the combustion duration increased but the maximum combustion temperature in cylinder, mixing uniformity and the combustion velocity reduced. There was almost no significant difference of CO emission. HC emission increased while NOX emission decreased. Compared with the electronic controlled 168 F using automotive gasoline engine pump at injection pressure of 0.3MPa,the HC emission increased 7.0% to 10.3% while the NOX emission reduced 4.9% to 7.2% at injection pressure of 35 k Pa. The specific emission of HC+NOX was increased by 5.7% and the quantity value was only 0.42 g(k W·h)-1. The electronic controlled fuel injection system of ultra low injection pressure could fully meet the demand of low emission and high performance of small single-cylinder gasoline engines through optimizing the concentration of the mixed gas and the ignition advanced angle.