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Thermal ignition of fuel-air mixtures due to hot particles can pose security risks and be hazardous under various circumstances, leading to their auto-ignition. The ignition characteristics of hydrogen-air mixtures with hot particles were investigated by performing 2-D numerical simulations using a detailed H2-air kinetic model. The simulations were performed with hot particles of various sizes and shapes with hydraulic diameters of 2, 4, and 6 mm. The effect of particle surface temperature on the ignition characteristics was studied by performing simulations at various particle surface temperatures ranging from 1000 to 1200 K. The results showed that for different particle shapes and sizes, the ignition delay depends strongly on the particle temperature. The location of the ignition point depends on the particle shape and temperature. A particle with a temperature of 1200 K ignites at the front stagnation point. The behavior significantly differs at 1000 K as the ignition location is shifted to a different point due to a competition between reaction kinetics and flow around the hot particles. Spherical particle showed the highest heat release rate compared to other particle shapes.

Two-dimensional numerical simulations are performed to study the flame dynamics of DME/H2/air mixtures in a microchannel with a controlled wall temperature profile. The characteristics of premixed stoichiometric DME/H2/air flames at various H2 compositions (% by volume) are analyzed in a 1 mm diameter tube of 120 mm length for a mixture inlet velocity of 0.15 m/s at 300 K temperature and 1 bar pressure. For every mixture composition under investigation, flame repetitive extinction and ignition (FREI) instability is noted. When the hydrogen percentage in the mixture rises, the frequency of FREI considerably decreases. The effect of hydrogen addition is nonlinear when the H2 composition in the mixture is above 40 %. Throughout the FREI cycle, a stable, weak flame is observed at the upstream side of the combustor. When the H2 composition in the mixture is increased to 80 %, the hot flame interacts with the weak flame, resulting in an increased rate of weak flame reactions. The weak flame shifts further upstream in this condition. The CH2O and H2O2 produced at the weak flame region are being consumed downstream, resulting in another peak in heat release rate between the cool flame and hot flame regions. This intermediate peak disappears during the propagation phase.

Characteristics of microjet hydrogen diffusion flames stabilized near extinction are investigated numerically. Two-dimensional simulations are carried out using a detailed reaction mechanism. The effect of burner wall material, thickness, and thermal radiation on flame characteristics such as flame height and maximum flame temperature are studied. Results show that the flame stabilizes at lower fuel jet velocities for quartz burner than steel or aluminum. Higher flame temperatures are observed for low conductive burners, whereas the flame length increases with an increase in thermal conductivity of the burner. Even though thermal radiation has a minor effect on flame characteristics like flame temperature and flame height, it significantly influences the flame structure for low conductive burner materials. The burner tip and its vicinity are substantially heated for low conductive burners. The effect of burner wall thickness on flame height is significant, whereas it has a more negligible effect on maximum flame temperature. Variation in wall thickness also affects the distribution of H and HO2 radicals in the flame region. Although the variation in wall thickness has the least effect on the overall flame shape and temperature distribution, the structure near the burner port differs.