Numerical study of inhibition mechanism of high-pressure hydrogen leakage self-ignition with the addition of ammonia

Hydrogen and ammonia have attracted increasing attention as carbon-free fuels.Ammonia is considered to be an effective energy storage and hydrogen storage medium.However,a small amount of unremoved NH3 is still present in the product during the decomposition of ammonia to produce hydrogen.Therefore,it is very essential to investigate the self-ignition of hydrogen-ammonia mixtures in order to accommodate the various scenarios of hydrogen energy applications.In this paper,the effect of NH3 addition on the self-ignition of high-pressure hydrogen release is numerically investigated.The RNG k-εturbulence model,EDC combustion model,and 213-step detailed NH_(3)/H_(2) combustion mechanism are used.CHEMKIN-Pro programs for zero-dimensional homogeneous and constant volume adiabatic reactor models are used for sensitivity analysis and ignition delay time of the chemical reaction mechanism.The results showed that the minimum burst pressure required for self-ignition increased significantly after the addition of ammonia.The maximum temperature and shock wave intensity inside the tube decreases with increasing ammonia concentration.The ignition delay time and H,HO2,and OH radicals reduce with increasing ammonia concentration.H and HO2 radicals are suggested as indicators for tracking the second and third flame branches,respectively.

Self-ignition characteristics of the high-speed ramjet kinetic energy projectile in the launch process

To research the self-ignition characteristics of high-speed ramjet kinetic energy projectile in the launch process, the self-ignition process based on the solid fuel of polyethylene was numerically simulated by using the dynamic grid technology. The effect of different muzzle velocity on the self-ignition performance, and the effect of opening the blockage at different times on the flow field stability of the combustion chamber and the flow field characteristics after the solid fuel ramjet stabilized were analyzed. The results show that the occurrence of self-ignition is not only related to the pressure, temperature in the combustion chamber, and the muzzle velocity, but also to the content of C_2H_4 and its degree of mixing with air in the combustion chamber. After the kinetic energy projectile gets out of the muzzle and before the blockage opens, there is oscillation occurring in the combustion chamber. The higher the muzzle velocity of the kinetic energy projectile, the more prone to the occurrence of the self-ignition and the negative effects can be avoided due to the pressure oscillation in the combustion chamber. The effect of opening the blockage at different times on the flow field stability after the self-ignition occurs in a period of time is weak. After the blockage opens, the solid fuel ramjet can reach a stable working condition quickly.

Statistical analysis to establish an ignition scenario based on extrinsic and intrinsic variables of coal seams that affect spontaneous combustion

Spontaneous combustion of coal seams in open pit mines is a problem that occurs in coal mines around the world.Theories have been developed that express several factors which generate self-heating in the coal and favor combustion.The synergy of these factors contributes to the increase in the temperature of oxidation reactions,facilitating the culmination of the activation energy of the system,in which the ignition develops and the reaction is spontaneous.Currently,the incidence of each variable’s susceptibility to coal combustion is unknown,so in this work a methodology was developed to determine statistically which of the variables has the greatest contribution in the phenomenon.Descriptive statistics,atypical values detection,principal component determination,cluster analysis,and logistic regression were used to determine how many indicator variables are necessary to describe susceptibility to coal combustion.For the analysis,21,000 data from different seams of two open-pit coal mines in endwalls and abandoned pits were processed with consideration given to extrinsic and intrinsic factors.Seam temperature,atmospheric pressure,wind speed,oxygen,methane,height,ash,volatile matter,heat power,vitrinite,liptinite and the Hardgrove Index are the most influential variables in the phenomenon.

Research progress on solid-fueled Scramjet

The solid-fueled Scramjet is an interesting option for supersonic combustion ramjet.It shows significant advantages such as simple fuel supply and compactness,avoiding the complex system of tanks and pipelines that encountered in liquid-fueled Scramjets.The solid-fueled Scramjet could be the simplest air-breathing engine for the hypersonic flight regime.This paper presents a comprehensive and systematic review of the research progress on solid-fueled Scramjet in various institutes and universities.It summarizes a progress overview of three types of the solid-fueled Scramjet,which covers a wealth of landmark numerical and experimental results.Based on this,several relevant key technologies are proposed.Several inherent scientific issues are refined,such as the mixing mechanism of multi-phase flow and supersonic airflow,ignition and combustion mechanism of the condensed phase in a supersonic airflow,and coupling mechanism of gas and solid phase in a supersonic flow.Finally,the historical development trend is clarified,and some recommendations are provided for future solid-fueled Scramjet.

Design and simulation of gas burner ejectors

Ignition within gas burner ejectors can lead to off design conditions and has significant influence on the burner behavior.Thus ignition in the ejector should be prevented.In the present study the influence of combustion reactions on the performance of gas burner injectors is investigated.To investigate if ignition is possible,simulated ignition delay times,using a detailed reaction mechanism,are compared to predicted mean residence times of the gas in the ejector.Gas burner ejectors are designed using one dimensional analytic equations,based on energy and momentum conservation equations and conventional isentropic equations.1D results are compared to 2D computational fluid dynamics(CFD)simulations,to take into account non-ideal mixing effects along the ejector.Results are validated with experiments with air at room temperature.1D results show very good agreement not only with CFD simulations for the case of non-reactive flows,but also with performed experiments.It is shown that the assumption of ideal mixing along the ejector and thus the comparison of the ignition delay time to the gas mean residence time,to predict ignition in the ejector,is not valid.Ignition in the ejector is possible,even if the ignition delay time is more than thirty times higher than the mean residence time.In addition to that,it is shown,that ignition and the choice of reaction mechanism have significant influence on the predicted gas burner ejector performance.Thus,the accurate prediction of ignition delay time and the use of a detailed reaction kinetic are mandatory to correctly predict the burner ejector behavior.