Experimental and Numerical Investigation of the Laminar Burning Velocity and Combustion Characteristics of Biogas at High Pressures

摘要

Continuous variation in the composition of gaseous fuels derived from biomass is a challenge in designing efficient combustors for using them. In this study, experimental measurement of the laminar burning velocity (u(1)) of three different compositions of biogas fuel containing equimolar H-2/CO mixtures and N-2 ranging from 40 to 60% by volume is conducted. Numerical calculations of the flame structure, adiabatic flame temperature (T-ad), species concentrations, and sensitivity analysis are also performed. Investigations are conducted over a practical range of equivalence ratios (ranging from 0.4 to 1.2) and at high pressures up to 4 bar. The experimental method of schlieren in a high-pressure combustion chamber is used for flame speed measurement. Numerical calculations are performed using the premixed code of CHEMKIN using four well-known reaction mechanisms. Laminar burning velocities calculated using the USC Mech Version II mechanism showed the best agreement with the experiments. The results indicated that the mole fraction of the H radical increases by equivalence ratio at the whole range considered in this study, while the OH radical declares its maximum concentration at stoichiometric conditions. This causes the maximum value of u(1) to occur at the equivalence ratio of 1.2. T-ad increases by increasing pressure, especially near stoichiometric conditions and for lower N-2-containing fuels. The equivalence ratio of the maximum flame temperature changes from the rich state (at phi = 1.05) to the stoichiometric state by increasing the N-2 content of fuel from 40 to 60%. H-2 plays a dominant role in the combustion of biogas fuel at-high H-2 concentration conditions. More than 50% of hydrogen bums before the flame front, while CO mainly burns after this position.