In order to eliminate the impact of dynamic effect of fuel film on the accuracy of controlling the transient air to fuel ratio (AFR) of a port fuel injection（PFI） gasoline engine to meet more stringent emissions requirements

a novel applicable fuel film compensation strategy as well as a fuel film model comprising of long term and short term fuel films is proposed to compensate fuel film variation rapidly and precisely under acceleration and deceleration conditions. The initial values of the long term and short term fuel films are calculated by distribution coefficients respectively. The real time values of the long term and short term fuel films as well as their action time are controlled by decay coefficients. The results of engine bench test show that the proposed strategy effectively suppresses the deviation of transient AFR with a maximum error less than 5% and a stable time less than 1 s.