A Comparative Study of NO_x Computation Methods Coupled to Quasi-Dimensional Models in SI Engines

Quasi-dimensional models are widely used in the design, development and analyses of automotive engines. Various phenomenological and empirical relations are used in these models to reduce the computational load compared to multi-dimensional models. These quasi-dimensional models have also been used to calculate NO_x, soot and HCs using various reduced chemistry/simplified models. The extended Zeldovich mechanism is widely used for finite-rate NO_x computations in these quasi-dimensional models. However, there are several simplifying assumptions in the rate equation used for the NO_x computations. This paper compares the traditional method of finite-rate NO_x computations with full finite-rate chemistry without the simplifying assumptions used in the former method. NO_x formation in a stationary engine is studied using a single zone and two-zone (burned and unburned zone) using a 6-reaction, 7-species model. A detailed comparison of the two methods of NO computation is presented. Analyses of the temporal variation of NO predicted using these two approaches is also presented.