On Transient Temperature vs. Equivalence Ratio Emission Maps in Conjunction with 3D CFD Free Piston Engine Modeling
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2007
In order to acquire knowledge about temperature vs. equivalence ratio, conditions in which species are formed and destroyed during the combustion of diesel fuel, parametric maps were constructed for CO2, CO, OH, soot and soot precursors (C2H2) as well as for nitrogen oxides (NO and NO2). Each map was obtained by plotting data from a large number of simulations for various temperature vs. equivalence ratio combinations in a zero-dimensional, 0D, closed Perfectly Stirred Reactor, PSR. Since both the elapsed time and pressure change in an engine cycle, the maps were constructed according to engine pressure traces obtained from the Computational Fluid Dynamics, CFD, simulations. Since the pressure is changing in elapsed time intervals, the maps are called transient. Correlations between the maps and the 3D engine simulation results were then examined by plotting the temperature vs. equivalence ratio conditions in all computational cells of the CFD simulation on the maps. The map approach is a useful tool for visualizing the links between in-cylinder temperature vs. equivalence ratio conditions and emission levels, and to identify conditions that promote efficient, low-emission engine operation. All engine simulations were made for a free piston engine, but conclusions can be valid for conventional engines as well. The effect of varying spray model parameters such as the initial sauter mean radius, droplet size distribution and the constants in the break-up model was studied.