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Landfill gas (LFG) produced from depletion of biological waste has the potential to become one of the main energy resources in the future. In this study, laminar burning velocity (ul), Markstein length, and flammability limits of different compositions of landfill gas (LFG) are measured using the Schlieren flame front visualization method in an 11 liter constant volume combustion chamber. Three common compositions of LFG with carbon dioxide (CO2) volumetric fraction of fuel ranging from 0.3 to 0.5 are examined. Pressure was changed from atmospheric pressure to 5 bar with an increment of 2 bar. The effects of equivalence ratio, pressure, and CO2 content of fuel on laminar burning velocity are investigated, and rich and lean burn limits of different compositions of fuel are obtained. Numerical investigation is also performed using the CHEMKIN package via GRI3.0 and UBC2.1 chemical kinetic mechanisms. The results indicate that increasing the pressure reduces laminar burning velocity, whereas it increases the adiabatic flame temperature as a result of alternation in the equilibrium point of combustion. Pressure considerably increases the rich burn limit equivalence ratio and expands the flammability range. Markstein length increases by increasing equivalence ratio, and its maximum value occurs at rich conditions. The results also indicate that increasing carbon dioxide content of fuel reduces laminar burning velocity at all pressures and equivalence ratios, mainly due to reduction of the adiabatic flame temperature.

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 l) of three different compositions of biogas fuel containing equimolar H2/CO mixtures and N2 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 l to occur at the equivalence ratio of 1.2. T ad increases by increasing pressure, especially near stoichiometric conditions and for lower N2-containing fuels. The equivalence ratio of the maximum flame temperature changes from the rich state (at φ = 1.05) to the stoichiometric state by increasing the N2 content of fuel from 40 to 60%. H2 plays a dominant role in the combustion of biogas fuel at high H2 concentration conditions. More than 50% of hydrogen burns before the flame front, while CO mainly burns after this position.

The effect of quenching in molten alkaline salt bath medium on the microstructure and surface properties of AISI 1045 steel in comparison with oil was investigated. Salt bath medium used in this research contained 40% NaOH and 60% KOH with addition of 5 wt.% water at 205°C. Hardening of 1045 steel in this medium resulted in an almost uniform microstructure, which consisted of fine martensite and bainite. In comparison, the microstructure of oil quenched sample was martensite, ferrite, widmanestatten ferrite, and pearlite. Quenching in salt bath lead to improved surface properties, i.e., decrease in surface roughness and a good bearing area curve.

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