Simulations of hydrogen-air detonations using Direct Simulation Monte Carlo

Abstract

In this paper, the Direct Simulation Monte Carlo (DSMC) method is used to perform molecular level simulations of one-dimensional (1-D) hydrogen-air detonations. Since DSMC emulates the motion of real molecules, it is well suited for rarefied flow problems and is capable of treating rigorously processes in which measurable departures from molecular and chemical equilibrium exist, such as for molecular transport, internal energy relaxation, and chemical reactions. DSMC has been demonstrated to be a robust and more appropriate tool for fundamental studies of reacting flows at higher densities where regions of thermal and chemical non-equilibrium exist. Two cases of stoichiometric hydrogen-air mixtures are considered. First, a preheated case is simulated with reactants at an initial temperature of 900 K and an initial pressure of 0.3 atm. The second example is a detonation wave at a standard initial condition of 300 K and 1 atm. The results are compared with the Zel’dovich–von Neumann–Döring (ZND) solution obtained using the Shock and Detonation (SDT) toolbox. The temperature, pressure, flow velocity, density and species mass fractions are compared. It is found that for the preheated case, using DSMC results in a robust and steady detonation structure and shows excellent agreement with the ZND solution. The second example of the detonation wave at standard conditions is expected to fluctuate, and DSMC captures this effectively. However, the 1-D profiles differ slightly from the ZND solution. DSMC shows strong promise to carry out molecular-level simulations of detonations but requires ab initio data for robust non-equilibrium reacting flow simulations.

Novelty and significance statement

Combustion studies using the Direct Simulation Monte Carlo (DSMC) method have been few and far between. Although it is usually thought of as a method for computing rarefied flows, it is well-suited for flows with thermal and chemical non-equilibrium since it can incorporate information directly from ab-initio calculations, which can be used to estimate reaction rates for challenging elementary reactions. Such conditions can be encountered in scramjets and rotating detonation engines. The novelty of this paper lies in assessing the ability of DSMC to simulate hydrogen-air detonation for which aspects of molecular non-equilibrium may be present. This is a proof-of-principle study utilizing the current models, with the aim of extending this approach to other combustion problems with higher levels of non-equilibrium. This will particularly require improvements in reaction rate modeling in DSMC.