Numerical Simulation of Diesel Combustion with a High EGR Rate (A Nitric Oxide Prediction using a PDF Method)

Abstract

A series calculation method from injector nozzle internal flow to in-cylinder combustion in diesel engines has been developed. In this study, the calculation results of in-cylinder pressure, heat release rate, and NO concentration are compared with experimental results for conventional combustion conditions as well as an advanced combustion condition, which combines a high exhaust gas recirculation (EGR) rate, high boost pressure, and high pressure injection. The calculated pressure and heat release rate histories are in reasonable agreement with those of experiments, but the NO concentration is underestimated especially on the higher EGR rate condition. Therefore, the investigation for improving the quantitative accuracy of NO concentration is performed. The probability density function (PDF) method is one way to estimate the accurate mean reaction rate containing the reaction rate fluctuation by turbulence. In this study, the PDF method only applied for NO calculation is developed to balance the calculation accuracy and the computational cost. The result shows that the reaction rate fluctuation, on NO formation, has a small effect on conventional combustion conditions, but increases with decreasing combustion temperature.