Model development for intake gas composition controller design for commercial vehicle diesel engines with HP-EGR and exhaust throttling

Developers of modern diesel engines have to face rigorous restrictions in emission of nitrogen-oxides and particulate matter. Among several methods (DPF, SCR, improved injection etc) which are used to handle these exhaust gas components precise control of the cylinder charge composition seems to be a cost effective solution. The oxygen concentration of the intake gas has a significant impact on the combustion process hence on the pollutant formation. Moreover the precise adjustment of the cylinder charge oxygen concentration can be used to control low temperature combustion processes. The amount of the backflowing exhaust gases is limited by the pressure difference on the EGR duct. To solve this problem the authors suggest the use of novel exhaust brakes with extended functionality: backpressure adjustment for the precise control of the intake gas composition. This way arbitrary EGR rates can be achieved in any engine operation point. For the implementation of such a function the design of an intake manifold oxygen controller is needed, where the control inputs are the EGR valve and the exhaust throttle. This paper demonstrates the development of a control oriented model of the air path system as the first step of this task. The model considers three balance volumes in the air path and has five state variables. Its performance has been evaluated and validated with engine dyno measurements on a medium duty diesel engine.