Analysis of NO x reduction in diesel engines by air injection using stochastic

Abstract

Combustion phenomena have been found to be dependent on the turbulence of the air/gas and fuel in the cylinder. By enhancing turbulent mixing of fuel in the combustion chamber it is possible to improve combustion process. Based on the stochastic nature of turbulence of combustion processes as occurring in an IDI internal combustion engine, a model was developed based on these principles when compressed air was injected into the engine. The air injection was carried out in order to control the emission of NOx and soot simultaneously. In the present model, the mechanism of NOx formation is modeled using the thermal NOx principles while the soot emission is modeled using the global combustion model, which considered combustion as heat addition. Obtained results show close agreement with the experimental ones. The Zeldovich model used has been found model closely IDI engine processes also for the case of air injection as is case of a normal engine. This is due to the microscopic treatment of the mixing process, which involved over-simplification of HC combustion chemistry. It is shown that although there is no substantial temperature drop when compressed air was injected into the chamber, at microscopic scales, the mixing process that occur lead to local temperature drop. It is these local areas of temperature quenching that enhance the suppression of the formation of NOx. At high loads, however, particulate and HC are increased due to the enrichment of fuel in the local areas where the temperatures have substantially been reduced.