The effect of pressure increase on droplet evaporation in two-phase combustion environment

Abstract

The effects of pressure increase on combustion quality due to the droplet evaporation in dropletladen mixtures have been analyzed with the emphasis on the importance of detailed chemistry. A one-dimensional (1D) code with detailed chemistry and transport has been utilized in order to investigate the evaporation process of fuel droplets of different diameters at a high ambient pressure. Steady-state parametric analyses are performed using n-heptane fuel droplets. It has been found that the initial droplet diameter and the stoichiometry have significant effects on droplet evaporation, thus on flame propagation and combustion quality under high-pressure conditions. The findings regarding the effects of droplet diameter on combustion indicate that evaporation rate of the droplets is directly related to the gaseous fuel mass fraction. Small droplets evaporate before the flame front, but larger droplets cannot complete their evaporation before they reach the flame front, causing a lower gaseous fuel mass fraction. Findings regarding the stoichiometry effects are that the gaseous fuel mass fraction reaches its highest value after the flame front under rich mixture conditions. While the droplets in the lean mixture evaporate completely before the flame front, the droplets in the rich mixture can penetrate towards the flame. Increase in the equivalence ratio and decrease in the droplet diameter increase the evaporation rate and flame spread. It should be noted that this is only a theoretical study on combustion phenomena using detailed chemistry. However, pressure levels used in the analyses are similar to operating pressure of various combustors. For this reason, findings are believed to give researchers insight into the design of many combustors with spray combustion.