Investigations on reduction of NOx emission in DI diesel engines through CFD simulation

Abstract

Direct Injection (DI) diesel engines have taken a prominent place in public and private transport. Emissions of the diesel engine emissions Carbon monoxide (CO), Hydro Carbon (HC) have been effectively controlled with improvement in engine deign. However Nitrogen Oxides (NOx) and soot are still a matter of concern for the engineers. The main objective of the present work is to study the ways and means to reduce NOx emission in DI diesel engines. A significant portion of the combustion process in DI diesel engines takes place in diffusion flames. Under these conditions, rates of chemical reaction and heat release are therefore controlled by rates of fuel-air mixing. The physical effects, which drive the fuel-air mixing in these engines, appear to be related to the air motion effects, combustion chamber geometry and fuel injection process. An understanding of relative influences of these individual effects is necessary. With the experimental techniques available today, it is possible to make reasonably accurate measurements to study the in-cylinder fluid characteristics. But they are very expensive and time consuming. Over the past two decades, simulation of fluid dynamic based multi-dimensional models for studying in-cylinder fluid dynamics has become popular in the Internal Combustion (IC) engines field. The main advantages of such models are that they reduce the cost and time consuming experimental research. ii In this work, an attempt is made to study the influence of engine operating parameters on Nitric Oxide (NO) emissions using a Computational Fluid Dynamic (CFD) code. STAR-CD a 3-dimensional (3-D) CFD code based on finite volume method has been used for this purpose, which is capable of solving 3-D unsteady turbulent flows, sprays and combustion of IC engines. As a first step, a four-stroke single cylinder Compression Ignition (CI) engine fitted with hemi-spherical bowl-in-piston for which experimental results are available is considered to carryout the CFD analysis.