Nonlinear Transient Fuel Film Compensation (NTFC)

A very important component of an accurate steady state and transient air/fuel (A/F) ratio control strategy is the transient fuel compensation (TFC) substrategy. This is the part of an engine control algorithm which cancels the fuel film dynamics and makes it possible to place injected fuel into the intake manifold (or close to the intake ports or valves) of a spark ignition (SI) engine at the correct time and location.

This paper presents the results of a very large series of experiments conducted with the same engine with either a throttle body (TBI) (or central fuel injection (CFI)) manifold or with a multi-point port injection (MPI) (or electronic fuel injection (EFI)) manifold. These experiments have shown that in some practical applications it may be necessary to model the intake manifold as a two time constant dynamic system rather than as a single differential equation system.

A solution for the problem of correctly compensating for the nonlinear two time constant model is presented in the paper and tested on both TBI and MPI equipped engine mentioned above with excellent results. The experimental behavior of the engine (and its two different injection manifolds) has also been mapped in an extended temperature range using a deterministic compensation technique developed earlier. A “tuning” procedure is described which is simple and can easily be mechanized on a personal computer (PC) or a small computer. The results are thus immediately applicable to automatic production calibration applications.