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 $$\alpha {\text{C}}{{{\text{H}}}_{{\text{4}}}}$$ /air gas mixtures and heterogeneous dual-fuel mixtures (HDMs) $$\alpha {\text{C}}{{{\text{H}}}_{{\text{4}}}}$$ /air/coal suspension with methane bulk concentration $$\alpha = 5{-} 8$$ % 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) $$\alpha \text{*}$$ 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 $$\alpha \geqslant 6$$ %, whereas mixtures did not ignite at $$\alpha \leqslant 5.5$$ %. In a horizontal tube, flame propagated at $$\alpha \geqslant 6$$ % in gas mixtures and at $$\alpha \geqslant 5.5$$ % in HDMs. Adding coal suspension to methane–air mixtures has little effect on the flame velocity, increases the flame brightness, and lowers the LFL.