Intake oxygen concentration estimation for DI diesel engines

In order to reduce emissions and improve performance of internal combustion engines, it is desirable to know the oxygen concentration of the gas inducted into the engine so that the appropriate amount of fuel can be injected. This is especially true for diesel engines in which up to 50% of the exhaust gas is recirculated back into the engine. This work presents an estimation algorithm for the oxygen concentration in the intake manifold of a turbocharged diesel engine. The only quantities needed for the estimation scheme are boost pressure, fueling rate, engine speed and EGR valve lift, all of which are generally known to the engine control unit. This estimator is a first order linear dynamic model (with time varying coefficients) and asymptotically stable. Due to the unobservability of the oxygen concentration model, the speed of convergence of the estimation scheme is fixed by engine parameters, but is as fast as the phenomenon of mixing of the exhaust gas recirculated with the air in the intake manifold. Simulation studies show the effectiveness of the proposed estimator.