Experimental And Numerical Investigation On The Effects Of Dilution Gas And Hydrogen Addition On Combustion Of Premixed Methane/Air Flames

With the depletion of crude oil reserves and the tightening of restrictions on emission, the utilization of alternative fuels has captured growing attention in combustion community. Methane, the main component of natural gas, has been regarded as the cleanest and the most promising replacement for conventional fossil fuel and has therefore attracted extensive research interesting. But the flame of methane has low combustion efficiency,remains relatively slow burning velocities and products some pollutants, such as xNO. Therefore, this paper researches combustion dynamics mechanism of premixed laminar methane/air flames enriched by dilution gas and hydrogen in order to establish efficiency and clean combustion approach.Flame thermal characteristics were studied in terms of the maximum flame temperature, peak temperature gradient, flame thickness, average temperature of flame kernel, and heat release rate. Results indicated that carbon dioxide addition shows more significant effects on the flame thermal structures. The kinetic effects of diluent gas were investigated with respect to heat release contribution analyses. Results showed that the heat release contributions of dominant reactions are primarily affected by flame equivalence ratio, while the diluent gas shows weak effect. The reaction rates of dominant reactions are found to be primarily influenced by the concentrations of reactive species, and an exponent expression was proposed to express the correlation between the product of the species concentration and the dilution rate. At the same time, It is revealed that the influence of carbon dioxide on the production of important substances is obvious. Emission indices and combustion efficiency were estimated. Results showed that, the dilution gas can inhibit the production of specific pollutants, but the combustion efficiency was decreased at the same time. On the whole, the profit is generally greater than the loss, but the ratio of the profit to the loss would decrease with the increase of dilution rate.The paper devoted to obtaining the effect of chemical reactivity of hydrogen addition on methane oxidation. The numerical study was conducted for premixed laminar stoichiometric methane/air flames enriched by hydrogen with different activity. The flame thermal properties are computed in terms of flame thickness and global heat release rate. Results suggest that the addition of real hydrogen can lead to a decrease in flame thickness and an increase in the peak rate of heat release, and shift the profile of heat release rate to the upstream side of flame. Flame reactivity is roughly compared by the flame thermal properties. Result shows that the flame enriched by 2R/ 8-H has comparable reactivity with the pure methane/air flame. Chemical kinetic study is conducted by means of the production analyses of active radicals. It is found that 2 2R84(OH ?H ?H ?H O) is the most active reaction routine for methane/air flame with hydrogen addition. Hydrogen exerts its chemical effects primarily through R84. The addition of hydrogen leads to the increased production of H and the increase in OH consumption, and consequently accelerates the global reaction rate. R38 and R84 are the two most important reactions in the formations of H, OH and O. Hydrogen activity is the most important factor for the combustion promotion.