Intelligent control for air-fuel ratio of compressed natural gas engine

For compressed natural gas (CNG) engine applied on homogeneous combustion way of stoichiometric air-fuel ratio in the entire speed range, in order to furthest purifying CO/HC/NOx by three way catalyst converter(TWC), this paper introduces a air-fuel ratio control method combined with fuzzy feed-forward, intelligent PI feedback and self-learning control. Furthermore the application of the control method to the experiments on Matlab software simulation and the engine bench test applied the control method prove that actual air-fuel ratio(AFR) is better limited to a very narrow band of the desired stoichiometric ratio in the CNG engine stationary and transient conditions, which improves the air-fuel ratio control accuracy required by TWC high purification rate and effectively reduces exhaust emissions. Synchronously the control method is of rapid dynamic response operation in engine dynamic zone and robust to the changes of engine parameters.