Research And Development Of A Portable Engine Air-fuel Ratio Meter

This dissertation describes the research and development of a portable engine air-fuel ratio meter, and the operation, theory, construction and characteristics of this instrument, as well as the results of air-fuel ratio of measurements on engines and vehicles using this instrument.In this development, the calculation model of air-fuel ratio is obtained through the calibration experiment to the universal exhaust gas oxygen (UEGO) sensor is established. The output characteristic of the UEGO sensor, which is equipped with controlling unit, is approximately linear. So if the input-output relationship of the UEGO sensor is clear, the air-fuel ratio can be calculated using the model. In this development, we used mathematical software, such as MATLAB and Excel, to dispose with the calibration experiment results. Thereby we constituted the calculation model of air-fuel ratio. And because the measurement of air-fuel ratio is influenced by some factors, such as the fuel component which was used by the engine and the environmental situations, we studied the factor's influencing degree on the measurement of A/F ratio. And by adding correcting factors, we achieved the correcting to the calculation model of the A/F ratio. In this development, PIC16F877 was used as the main chip of the air-fuel ratio meter. And the main program is written by assembly language, the PC interface routine is written by Visual Basic of Microsoft. Main functions of the air-fuel ratio meter as follows:The measurement of air-fuel ratio(A/F), excess air coefficient(λ), and exhaust oxygen concentration(O2%);The measurement of engine rotation speed;Parameter setting, including fuel hydrogen carbon ratio (H/C) and oxygen carbon ratio (O/C);Keyboard input;LED display and light omitting diode indicate the work state of the meter;Communication with the PC, achieved the off-line analysis and solution.In conclusion, the developed A/F ratio meter showed outstanding performanceamong the congener devices. If it can be improved in some details, it must have a good market.