Study On Method Of Controlling The Air-Fuel For LPG Engine

In order to meet higher and higher demands for strict emission regulations, it is essential to precisely control the air-fuel ratio (A/F) of engine while developing the clean and economical gaseous fuel. This paper presents an A/F control system for LPG engine. The system adopts the method of combining the open and closed loop control, applies the Fuzzy control, and makes the parameters of PID change online. So it can control the LPG engine steadily and quickly.Firstly, during the period of open loop control, system traces the change of LPG injection of engine quickly by checking the pre-set two-dimension MAP if conditions of engine are changed suddenly.Then, during the period of closed loop control, by the method of Fuzzy control, system acquires three reasonable parameters (K_p,K_i and K_d) of PID control according to the signal of the oxygen sensor. After getting them, system finally acquires the suitable LPG injection unit by putting these parameters into incremental PID control.In addition, a monitoring system has been designed in this research. When engine runs, computer can display and store the data sent by ECU. Computer also can control the engine if it is needed. So it is clear that the monitoring system offers great help for this research.The experiments prove that the control system can finish the adjustment in two seconds when the engine changes suddenly. Compared with control system of the literature [20], the time of adjustment is shortened by about three seconds, and performance is steady almost as same as hers. Compared with the control system of the British Leyangd CFI Engine, though the time of adjustment is increased by about 1 second, the performance is improved by 500%. So the control system reaches satisfied result, improves the LPG engine.