Detailed chemistry modelling of rotating detonations with dilute n-heptane sprays and preheated air

TL;DR

This study uses detailed simulations to analyze rotating detonation engines with dilute n-heptane sprays and preheated air, revealing how temperature affects combustion dynamics, propagation speed, and performance.

Contribution

It introduces a comprehensive Eulerian-Lagrangian simulation approach with a detailed chemical mechanism to study the effects of temperature and spray dynamics in rotating detonation engines.

Findings

Mixture heterogeneity in the refill zone affects combustion.

Higher air temperature increases detonation speed and specific impulse.

Low-temperature chemistry and droplet evaporation are key to ignition processes.

Abstract

Utilization of liquid fuels is crucial to enabling commercialization of rotating detonation engines in the near future. In this study, Eulerian-Lagrangian simulations are conducted for rotating detonative combustion with dilute n-heptane sprays and preheated air. Two-dimensional flattened configuration is used and a skeletal chemical mechanism with 44 species and 112 elementary reactions for n-heptane combustion is adopted. The flow structure, droplet distribution, and thermochemical parameters in the refill zone are first analyzed. It is shown that the mixture in the refill zone is heterogeneous, including evaporating droplets, vapor, and air. When the total temperature is below 950 K, the average equivalence ratio increases with the total temperature. When it is higher than 950 K, the average equivalence ratio is almost constant. Subsequently, the chemical explosive mode analysis is applied to identify the controlling reactions and dominant combustion modes in the fuel refill zone and reaction fronts. Results demonstrate that the initiation reaction and low-temperature reaction are dominant in the upstream and downstream of the refill zone, respectively. The intermediate species from low-temperature chemistry is found to be important for the chemical explosive mode in the undetonated mixture. The influence of species diffusion and dispersed droplets is further analyzed. Results show that vapor autoignition facilitated by droplet evaporation occurs in the refill zone. Finally, the effects of the air total temperature on the detonation propagation speed and RDE propulsion performance are investigated. It is found that the detonation propagation speed and specific impulse increase with air total temperature.