Sensitivity of a DI Diesel NOx Model to Changes in Common Rail Pressure, Injection Patterns and EGR

This paper describes some capabilities and limitations of a simplified semi-empirical method of estimating NOx quantities produced during each cycle of diesel engine combustion. This scheme accepts measured cylinder pressure-volume data as an input and uses this to compute NOx pollutant quantities formed during each engine cycle. The methodology employs basic thermodynamic principles but assumes very simplified chemistry of pollutant formation.

The approach taken has relied on the availability of an extensive bank of experimental data obtained from two different light duty common-rail diesel engines. Steady-state tests were carried out over a range of those engine parameters known to affect NOx emissions. Parameters varied included engine speed, equivalence ratio, exhaust gas re-circulation quantity, common rail pressure and start and duration of fuel injection. This paper focuses on assessment of the ability of the model to reflect the measured effects of individual variables, with a view to assessing its suitability for use in real-time onboard emissions control systems.