Abstract:
Abstract: 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 168F 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 kPa (the minimum injection pressure could satisfy the need of start performance, working conditions and calibration software), 70 kPa (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-7200D 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 kPa, 70 kPa 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 kPa) 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 kPa) can promote the development of non-road spark ignition engine and realize the electric control.