Numerical investigation on effect of air/fuel ratio on ramjet dump combustor performance

Ramjets are the preferred air-breathing engines at high supersonic speeds. The combustion phenomenon in ramjet combustors is very complex. The complexities arise due to liquid - gas phase coupling, high temperature variation and intricate flame chemistry. Numerical simulation of flow environment in ramjet combustors is formidably challenging because the flow process comprises simultaneous momentum, heat and mass transport processes. Flow simulation software FLUENT is used to simulate the flow environment in a ramjet dump combustor with two side inlets 90° apart by solving the governing equations with appropriate boundary conditions. The turbulent flow features are predicted by employing standard k - ε equations based on generalized Boussinesq eddy viscosity concept. Eulerian approach is used to model the gas phase heat and mass transfer. Fuel particles are tracked using Lagrangian formulation. In liquid phase modelling, the momentum, energy and species balances are carried out by treating the droplet as a lumped system. Probability Density Function (PDF) approach is employed to describe the turbulent fluctuations in the mixture fraction. Predictions of temperature inside a ramjet combustor were compared with the limited experimental data available and reasonable matching was observed. A detailed study has been carried out on the baseline combustor geometry under consideration for air/fuel ratios of 10, 15 and 30 and the results are discussed in this paper.