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.

Updated Kinetic Mechanism for High-Pressure Hydrogen Combustion

A chemical kinetic model for high pressure combustion of H2/O2 mixtures has been developed. Some of the rate constants important in high pressure conditions were updated. Particular attention has been paid to different channels of the H+HO2 reaction, and to the third body efficiency in the H+O2+M and H+OH+M reactions. An analysis of the performance of an updated model is presented by comparing with various experimental data. Although the present model could reproduce most of shock tube data of ignition delay with variety of bath gases, there is still some discrepancy in the pressure dependence of flame speed between model predictions and recent experimental data. These models were validated against a wide range of experimental conditions and, in general, were found to be in good agreement with various experimental data including shock tube ignition delay, flow reactors, and laminar flame speed measurements. Basic characteristics of hydrogen combustion are now well understood because of those excellent modeling works and related experimental studies. Most recent kinetic model of Konnov 3 is probably the most extensively validated. The modeling range covers ignition delay measurements by shock tubes from 950 to 2700 K and from the atmospheric pressure up to 87 atm, and flow tube experiments at around 900 K with pressures from 0.3 to 15.7 atm. The mechanism is also validated against laminar flame burning velocities up to 4 atm. However, as pointed by Konnov, there is still some discrepancy between the model prediction and the measured flame velocities of hydrogen-oxygen-inert gas mixtures at higher pressures. The pressure dependences of mass burning rates for hydrogen mixtures have recently been studied experimentally and numerically by Burke et al. 4 . Flame speeds and mass burning rates were measured for equivalence ratios from 0.85 to 2.5, pressures from 1 to 25 atm. They found that the mass burning rate is increasing with pressure at low pressures, while at grater pressures, the mass burning rate is found to decrease with pressure. At lower pressures, predictions using recently published chemical kinetic models agree well with experimental data. However, the predicted mass burning rates differ significantly from model to model. Burk et al. suggested that

A Noble Kinetic Model of H2/O2 System Applicable to Liquid Rocket Engine Combustion

Two-dimensional simulation on atomization in a rocket engine coaxial injector flow

Numerical simulation code for rocket engine injector flow has been developed in order to investigate atomization and mixing of oxygen with hydrogen, and clarify the combusting flow in a liquid rocket engine combustor. In the simulation code, equation of state for the real fluid can be strictly considered and incompressible and compressible flow can be solved at the same time. Simulation results on the vibration of a single liquid drop agree well with theoretical ones. The simulation results also successfully show the breakup of liquid jet with inlet fluctuation. It is confirmed from these facts that numerical method used in this study is correct and can be applied to simulation on atomization and mixing in a liquid rocket engine injector.

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Paper ID ICLASS06-182 TWO-DIMENSIONAL SIMULATION ON ATOMIZATION IN A ROCKET ENGINE COAXIAL INJECTOR FLOW

The numerical method for combustion flow in the super critical pressure condition has been developed in non conservative form. The method can treat the steep gradient of density, incompressible and compressible flow together and equation of state for real fluid. Numerical results about droplet vaporization show the separation at the wake of the droplet for the high Reynolds number. In the coaxial combustion flow analysis, the thin flame and the recirculation region in the mixing layer are shown. The validity of numerical method and the possibility of applying it to the injector flow analysis in a liquid rocket engine are confirmed from these test problems.

Kazuya Shimizu

Papers

Updated Kinetic Mechanism for High-Pressure Hydrogen Combustion

A Noble Kinetic Model of H2/O2 System Applicable to Liquid Rocket Engine Combustion

Two-dimensional simulation on atomization in a rocket engine coaxial injector flow

Paper ID ICLASS06-182 TWO-DIMENSIONAL SIMULATION ON ATOMIZATION IN A ROCKET ENGINE COAXIAL INJECTOR FLOW

Study on Development of Unified Simulation Method for Atomization and Combustion in a Coaxial Injector Flow