Modeling of nitrogen oxides emission in the cylinder of tractor gas-diesel engine

Abstract

The article is devoted to the modeling of process of nitrogen oxides formation in the cylinder of diesel engine operating on compressed natural gas. The combustion of methane-air mixture, ignited by atomized pilot oil that is injected through multijet nozzle, in the cylinder of gas-diesel engine increases the rate of turbulent fluctuations, which leads to intensification of heat and mass exchange in the plume, and significantly increases the rate of formation and decomposition of nitrogen oxides. The calculation of expected emissions of nitrogen oxides in the cylinder of diesel engine and their content in the exhaust gases is carried out. It is done on the basis of the results of kinetic systems modeling for calculation of the kinetics of nitrogen oxides formation during combustion of natural gas and diesel fuel, taking into account the influence of turbocharging, intermediate cooling of charged air and exhaust gas recirculation. In the mathematical modeling of nitrogen oxide formation in the cylinder of diesel engine, the combustion process is divided into two zones, namely the zone of fresh mixture and the zone of combustion products. First zone is a mixture of fresh air with recycled gases (if there is a process of recycling) and residual gases. Before combustion starts, this zone occupies the whole cylinder. During combustion, the volume of zone of combustion products increases. Theoretical researches are carried out on the basis of developed mathematical model for calculation of nitrogen oxides in the cylinders of 4Ch 11.0/12.5 and 4ChN 11.0/12.5 diesel engines. The high precision of theoretical calculations of volumetric content and mass concentration of nitrogen oxides is confirmed, compared to the results of experimental researches (the difference does not exceed 5%).