Kalman filtering for real-time individual cylinder air fuel ratio observer on a diesel engine test bench

We propose an estimator of the individual cylinder air fuel ratios in a turbocharged diesel engine using as only sensor the single air fuel ratio sensor placed downstream the turbine. The observer consists of a time-varying Kalman Filter based on a physics-based model for the engine dynamics. We prove that the reference system converges toward a limit cycle. This limit cycle is used for the design of an extended Kalman filter. Performance is evaluated through test bench experiments on a 4 cylinder Diesel engine. The proposed approach has the advantage over existing methods of providing insight into the cylinders unbalance by considering a higher frequency model of the exhaust manifold. This information could pave the road to efficient closed loop control strategy as demonstrated on an experimental example