Effects of carbon dioxide addition on diesel spray flame characteristics in oxygen-carbon dioxide atmospheres

In order to study the diesel flame combustion characteristics in the different OCD atmospheres, a DCER model is proposed, which considers the air entrainment rates and the influences of OCD atmospheres. Firstly, FLOL and X⁺ calculation formulas are obtained. Furthermore, the chemical model of primary reference fuel (n-heptane) and the geometric structure of CVCC are established. Secondly, to verify the model, the experiment is carried out in a visualized CVCC and processes of flame combustion are captured by a high-speed camera. Furthermore, results of flame structure, temperature maps, FLOL and FNL are discussed at 3 MPa and 850 K in air, 50%O₂/50%CO₂(50 CDC), 43 CDC and 35 CDC, respectively. Through comparison between the DCER model simulation and the experiment, the conclusions are as follows: combustion characteristics are quite different in several atmospheres. Comparing the temperature maps, there is an obvious distinction in the upper part of the flame upstream region in 50 CDC and 43 CDC. The DCER model can predict the diesel FLOL in 50 CDC, 43 CDC and 35 CDC with errors of 5.35%, 6.47% and 3.65%, respectively. The changes of OCD have a great influence on FLOL and FNL. With CDC decreasing, FLOL and FNL decline stably and the maximum of FNL appears earlier.