Recent advances in understanding of flammability characteristics of hydrogen

The effect of temperature on the adiabatic burning velocities of diluted hydrogen flames: A kinetic study using an updated mechanism

The numerical simulations of 2D and 3D rotating detonation engines for a hydrogen–oxygen mixture are performed using a detailed chemistry model. The comparison of 2D/3D flow fields for the same injection conditions indicates that the overall flow structures are in agreement for the two simulations and that both rotating velocities are approximately 96% of the CJ value. However, I sp for the 2D RDE is approximately 10 s larger than I sp for the 3D RDE. The grid resolution study indicates that the higher grid resolution produces detonation cellular structure; however, its effects on I sp are approximately a few seconds. Although I sp in the 2D smallest scale for higher mass flow is approximately 10 s larger than that of the other large scales, I sp for low mass flow is not affected by the scale. However, 3D scale effects are important because the radius of curvature along the circumferential direction changes, which affects the propagation of the rotating detonation. Because I sp and thrust are governed by the stagnation pressure and the micro-nozzle area ratio, the mass flow rate from the injector also depends on these parameters. I sp and thrust for RDE are found to be correlated with the mass flow rate, similar to the case of a conventional rocket engine. This result indicates that the two important parameters, A ∗ / A and p 0 , can be replaced by one parameter, i.e., the mass flow rate.

Numerical estimation of the thrust performance on a rotating detonation engine for a hydrogen–oxygen mixture

The propulsive performance for an H2/O2 and H2/Air rotating detonation engine (RDE) with conic aerospike nozzle has been estimated using three-dimensional numerical simulation with detailed chemical reaction model. The present paper provides the evaluation of the specific impulse (Isp), pressure gain and the thrust coefficient for different micro-nozzle stagnation pressures and for two configurations of conic aerospike nozzle, open and choked aerospike. The simulations show that regardless of the nozzle, increase the micro-nozzles stagnation pressure increases the mass flow rate, the pre-detonation gases pressure and consequently the post-detonation pressure. This gain of pressure in the combustion chamber leads to a higher pressure thrust through the nozzle, improving the Isp. It was also found that the choked nozzle increases the chamber time-averaged static pressure by 50–60% compared with the open nozzle, inducing higher performance for the same reason explained before.

Three-dimensional numerical thrust performance analysis of hydrogen fuel mixture rotating detonation engine with aerospike nozzle

A numerical simulation of the spontaneous ignition of high-pressure hydrogen in a duct with two obstacles on the walls is conducted to explore the spontaneous ignition mechanisms. Two-dimensional rectangular ducts are adopted, and the Navier–Stokes equations with a detailed chemical kinetic mechanism are solved by using direct numerical simulations. In this study, we focus on the effects of the initial pressure of hydrogen and the position of the obstacles on the ignition mechanisms. Our results demonstrate that the presence of obstacles significantly changes the spontaneous ignition mechanisms producing three distinct ignition mechanisms. In addition, the position of the obstacles drastically changes the interaction of shock waves with the contact surface, and spontaneous ignition may take place at a relatively low pressure in some obstacle positions, which is attributed to the propagation direction and interaction timing of two reflected shock waves.

Numerical study of the effect of obstacles on the spontaneous ignition of high-pressure hydrogen

A chemical kinetic model for high-pressure combustion ofH2=O2 mixtures has been developed by updating some of the rate constants important under high-pressure conditions without any diluent. The revised mechanism is validated against experimental shock-tube ignition delay times and laminar flame speeds. Predictions of the present modelarealsocomparedwiththosebyseveralotherkineticmodelsproposedrecently.Althoughpredictionsofthose models (including the present model) agree quite well with each other and with the experimental data of ignition delay times and flame speeds at pressures lower than 10 atm, substantial differences are observed between recent experimental data of high-pressure mass burning rates and model predictions, as well as among the model predictions themselves. Different pressure dependencies of mass burning rates above 10 atm in different kinetic models result from using different rate constants in these models for HO2 reactions, especially for H HO2 and OH HO2 reactions.TherateconstantsforthereactionH HO2 involvingdifferentproductchannelswerefound to be very important for the prediction of high-pressure combustion characteristics. An updated choice of rate constants for those reactions is presented on the basis of recent experimental and theoretical studies. The role of O 1 D, which can be produced by the H HO2 reaction, in the high-pressure combustion of H2 is discussed.

Mituso Koshi

Papers

Updated Kinetic Mechanism for High-Pressure Hydrogen Combustion