Control oriented air path model for compressed air boosted Diesel engines
In this paper an air path model of a diesel engine is presented for control system design. The model was developed for common-rail, direct injected, turbocharged and intercooled commercial vehicle diesel engines which are equipped with compressed air booster system (PBS® – Pneumatic Booster System), high pressure exhaust gas recirculation loop (EGR) with EGR-cooler and exhaust brake (EB). In current and next generation emission standards and legislation introduced significant limitations for NOx and soot. It is really challenging to handle these components, especially at transient engine operations. Additionally the fuel economy and driveability requirements also have to be fulfilled. It is widely known that the nitric oxide formation can be limited with an appropriate amount of exhaust gas recirculation. It can be achieved even in transient modes with precisely controlled EGR-valve operation and with a suitable backpressure generation by the exhaust brake. The soot formation is influenced mainly by the air-fuel ratio of the mixture which can be affected by the intake manifold pressure in case of a desired engine load and EGR rate. With the compressed air booster system the intake manifold pressure can be controlled in transients arbitrarily. Therefore with a suitable air path controller the modeled engine setup is able to handle both the NOx and soot formation in transient cases. To solve the presented control problem a model based controller design is targeted. The reported model is the first step of this work.