Effect of CO2 and its concentration variation on the ignition and combustion of diesel surrogate fuel: Optical experiments and numerical simulations

Abstract

To investigate the influence of CO2 on diesel ignition and combustion, an experimental setup comprising a constant volume combustion chamber with optical channels was constructed. High-speed direct photography was employed to capture flame propagation images during fuel ignition and combustion under different CO2/O2 atmospheres. Additionally, large eddy simulation was conducted to model diesel combustion characterized by CO2/O2 environment. The theoretical calculations were then compared with experimental results, focusing on flame natural luminosity, flame structure, flame field, and heat release analysis. The results indicate that the flame structure in a CO2/O2 atmosphere consists of a diffusion flame surrounding a premixed flame, characterized by elevated levels of CO and a smaller amount of C2 radicals at the flame front. The O2 concentration ranged from 21% to 57%, resulting in a flame morphology with thin strips, intensified flame edge instability, and increased natural luminosity. The inhibitory effect of CO2 concentration within the range of 35%–50% counteracted the promoting effect of O2 concentration within the range of 29%–44%. Consequently, the chemical impact of CO2 plays a crucial role in combustion.