NOx Formation in Diesel Engines for Various Fuels and Intake Gases

The NO formation is essentially determined by the flame temperature. In an engine the latter depends on the composition of the fuel and the intake gas. In this study the efficiency of various NO reducing measures is analysed by means of a comparison of measurements and computations for the Most frequent operation point of a 1.9 1 DI Diesel engine.

The O₂ concentration, which is shown to be the dominant source of influence on the flame temperature and NO formation, is varied using synthetic gas mixtures or by EGR. The molar heat capacity of CO₂ and H₂O in the recirculated exhaust gas, the intake temperature and the H/C ratio in the fuel are less important for the formation of NO. Measures which reduce the NO formation increase the ignition delay and thereby the fraction of the premixed combustion. The impact of EGR on the combustion process is illustrated by high speed filming.