A Modeling Study on the Influence of Aromatic Fluorescence Tracers on Compression Ignition Engine Operation 2018-01-1784
Aromatic substances, which are added to the fuel as fluorescing tracers, are in widespread use as a means of investigating mixing and reaction processes in IC engines by laser-based visualization techniques. The fuel/tracer/air mixture may differ from the pure fuel/air mixture in its chemical and its physical properties, and both aspects can be equally relevant for engine operation. They may, furthermore, interact due to the dependence of chemical reaction on physical conditions. In this paper, we study the overall influence of toluene as an exemplary aromatic tracer on engine performance by numerical modeling. The used model features a semi-detailed treatment of chemical reactions for both the fuel and the tracer, as well as their mutual chemical kinetics interactions. The dependence of engine performance parameters like auto-ignition timing and maximum pressures on these parameters is investigated by performing a large set of parametric simulations. To highlight the difference between physical and chemical influence of the tracer, we compare the case of engine operation with pure fuel/air mixture and with a tracer-fuel/air mixture under different aspects: First, a comparison is made based on equal physical conditions, namely equal temperature, pressure and equivalence ratio. In contrast, a second way of comparison is based on equal engine operation parameters. While the first highlights the kinetic aspect of the tracer-fuel interaction, the latter additionally includes the modification of the physical conditions of the mixture by addition of the tracer. The objective of the paper is the theoretical investigation of these aspects based on a widely evaluated chemical kinetic mechanism to improve the understanding and applicability of tracer-LIF diagnostics towards instationary reactive conditions like in compression induced auto-ignition in IC engines.