Experimental study on combustion and thermoacoustic instability characteristics of ethanol/methane Co-firing flames

This paper investigates the combustion and thermoacoustic instability characteristics of ethanol/methane co-firing flames. Methane was introduced into the combustion chamber in three different mixing methods: the premixing method, single-tube injection, and dual-tube injection. The effects of mixing ratio, equivalence ratio, jet pipe diameter and position on combustion performance are also considered. The results show that under the premixed combustion mode, as the methane ratio increases, combustion instability shows a trend of first enhancement and then weakening, reaching a maximum pressure pulsation of 228.8 Pa at a 30 % mixing ratio. When methane is injected transversely into the combustion chamber using a single-tube or dual-tube, the inner diameter of the injection tube, injection height, and injection distance are essential factors affecting combustion instability, all of which will change the inhibitory effect of the transverse jet on instability. In addition, when the methane mixing ratio reaches 50 %, the co-firing flames will be in a relatively stable combustion state under all conditions. But at this time, the increase in flame temperature and the oxygen-deficient environment in the combustion chamber will cause simultaneous increases in CO and NOx emissions, which are not conducive to clean and efficient fuel combustion.