Investigation into Effect of Adding Coal Suspension on Combustion Stability and Methane Lower Flammability Limit in Methane–Air Mixtures

This paper presents a study on the possibility of combustion waves in α CH_4 /air gas mixtures and heterogeneous dual-fuel mixtures (HDMs) α CH_4 /air/coal suspension with methane bulk concentration α = 5- 8 % in a closed vertical shock tube and in a horizontal quartz tube open at one end. It has been shown that the value of the methane lower flammability limit (LFL) α * and the flame stability depend on the channel location relative to the gravity vector and on the coal suspension concentration. In a vertical closed channel, combustion waves propagated from top to bottom in gas mixtures and HDMs at α 6 %, whereas mixtures did not ignite at α 5.5 %. In a horizontal tube, flame propagated at α 6 % in gas mixtures and at α 5.5 % in HDMs. Adding coal suspension to methane–air mixtures has little effect on the flame velocity, increases the flame brightness, and lowers the LFL.