Modeling Production and Abatement of Nitrogen Oxide Pollutants in Direct Injection Diesel Engines

Bedford, F. C. Modeling Production and Abatement of Nitrogen Oxide Pollutants in Direct Injection Diesel Engines. University of Wisconsin-Madison, 2001.

This is a computational study of pollutant formation and reduction in direct injection diesel engines. The first portion of this study explores the use of water injection as a practical method for reducing emissions without incurring a fuel economy penalty. Comparisons to experimental data are done for both bomb and engine cases to validate the methodology and the emissions models. An optimization algorithm is used to find the most effective means of inducing water into a fuel/water spray to minimize engine emissions and fuel consumption. It is shown that water injection is very effective at reducing engine out NOx, however the predicted engine out NOx levels are lower than experimentally obtained values by up to twenty percent, which initiated an investigation of a means of using detailed chemistry for a more accurate representation of pollutant formation.

Three mathematically based methods for the reduction of detailed chemical mechanisms are explored?the Intrinsic Low Dimensional Manifold (ILDM) method, the Adaptive (quasi-Steady State Approximation (AQSSA) method and the Trajectory Generated Low Dimensional Manifold (TGLDM). The methods were compared in an effort to find the most accurate and robust means to reduce available detailed mechanisms. The methods differ in the amount of insight gained about the chemistry, the computational cost associated with the scheme and the robustness of the reduction. It is shown that the TGLDM is the most robust scheme for the calculation of low dimensional manifolds of large systems and is the least expensive mathematically based scheme to calculate. The mathematically reduced schemes are applied to zero and one dimensional combustion problems with good results compared to full chemistry. The TGLDM method is extended for rich chemistry by constructing a progress variable which is single valued over the course of the reaction. The manifold method is used to create a NOx model based on a detailed methane mechanism of 325 reactions and 53 species. The NOx model is applied to two dimensional spray calculations with reasonable qualitative results, however stiffness of the NO species with respect to progress variable causes numerical oscillations as chemical equilibrium is approached.