Effects of radiation reabsorption of C1-C6 hydrocarbon flames at normal and elevated pressures

The radiative preheating of the unburned hydrocarbon fuels by the burned combustion products in counterflow diffusion flame at pressures from 1 to 100 atm was investigated. The radiative characteristics of hot H2O, CO2 and cold hydrocarbon gases were calculated from HITEMP 2010, CDSD-4000 and HITRAN 2016 databases respectively. A simplified radiation reabsorption model was given based on the properties of the radiative reabsorption energy at T = 1500–2000 K, P = 1–100 atm. By using this model, the critical strain rate was calculated for eight C1-C6 hydrocarbon species at T = 2000 K, P = 1–100 atm. The results show that radiation reabsorption should be taken into account when the strain rate is less than 2.9 s−1 at P = 100 atm. The comparison results of the radiation time and the residence time in the CH4 counterflow diffusion flame shows that the radiation time scale would dominate at elevated pressures.