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Many excellent papers have been written about the subject of estimating engine-out NOx on diesel engines based on real-time available data. The claimed accuracy of these models is typically around 6-10% on validation data sets with known inputs. This reported accuracy typically ignores input uncertainties, thus arriving at an optimistic estimate of the model accuracy in a real-time application. In our paper we analyze the effect of input uncertainty on the accuracy of engine-out NOx estimates via a numerical Monte Carlo simulation and show that this effect can be significant. Even though our model is based on an in-cylinder pressure sensor, this sensor is limited in its capability to reduce the effect of other measured inputs on the model.

This paper describes the test of a direct injection diesel engine, operating electronically controlled diesel fuel unit injectors with variable injection timing. Diesel fuel injection was electronically controlled to retard or advance initiation of the injection event. Advancing or retarding injection timing of a direct injection diesel engine has a significant effect upon performance and emissions. Injection timing was varied to determine effects on exhaust emissions, performance, and fuel efficiency.