A phenomenological model of diesel combustion characteristics under CO2/O2 atmosphere

Abstract

In order to investigate the diesel fuel combustion characteristics under CO2/O2 atmosphere, a flame lift-off length (FLOL) mathematical model (HOCD) is developed, which considers the dynamic effect of CO2 concentration change. Firstly, the CO2/O2 densities (ρCO2 and ρO2) and the CO2 volume ratio (x%) are introduced, and the irrelevant substances (N2) is eliminated in the characteristic length scale (X+). Secondly, the platform and optical system of constant volume combustion chamber (CVCC) are established, and six conditions (air atmosphere, 50% CO2 + 50% O2, 47% CO2 + 53% O2, 43% CO2 + 57% O2, 39% CO2 + 61% O2, 35% CO2 + 65% O2) are selected. Finally, the concentration and sensitivity of key components are calculated by chemical reaction kinetics, showing that toluene is very sensitive. Thus, the reaction of toluene with OH radical is refined by quantum chemical calculation. Furthermore, the flame natural luminosity (FNL) taken by a high-speed camera is calculated through python code, and the flame propagation process and temperature map are simulated. The results show that CO2 has a significant effect on diesel combustion characteristics, and the HOCD-model is able to well simulate the FLOL with maximum, minimum and average errors of 8.9%, 0.5% and 1.4%, respectively. Furthermore, the FNL shows a large fluctuation under CO2/O2 atmosphere, while it is smooth and single-peaked under air atmosphere, and CO2 causes unstable flame combustion and turbulence.