Experimental study on the flame propagation and laminar combustion characteristics of landfill gas

Biogas is the least expensive renewable energy source with an almost neutral balance of CO2 emissions. As a type of biogas, landfill gas could potentially be used in the internal combustion engines, gas turbines, and industrial furnaces. However, the combustion characteristics of landfill gas, which are the foundations of further use of the landfill gas, are not clear. In this paper, the flame propagation characteristics of landfill gas were measured in a constant volume combustion chamber using a schlieren system. The experiments were conducted over the equivalence ratio range of 0.7-1.4, the pressure range of 0.1-0.5 MPa, the temperature range of 290-380 K, and the methane contents of 47%, 55.5% and 59%. The main influencing factors of the combustion stability and laminar combustion velocity of landfill gas in laminar combustion were also investigated. The results showed that the preferential diffusion or buoyancy instability appeared during the flame propagation process, and flame front exhibited irregular cellular structure and protuberances or the flame core moved upward under the condition that the Markstein number was small or the laminar burning velocity was lower than 0.15 m/s. At the same time, the Markstein number and the stability of the flame front decreased with a lower equivalence ratio and methane content or higher initial pressure. However, the effect of the initial temperature on the Markstein number was not obvious. The unstretched flame velocity and the laminar combustion velocity initially increased and then gradually decreased with the increase of the equivalence ratio, and the maximum values were measured under the condition that the equivalence ratio was 1.1. Furthermore, the laminar combustion velocity of landfill gas decreased with a higher initial pressure or lower initial temperature and methane content.