Experimental study of the mild combustion of liquid hydrocarbons

A strong exhaust gas recirculation combined with air preheating generates relatively low maximum flame temperatures allowing for a better control of the furnace temperature and a lower pollutant production. While the sustainability of this combustion technology (named mild or flameless combustion) for different gaseous fuels has been extensively studied, much less information are available for liquid fuels. Consequently, this work has focused on the investigation of the sustainability of mild combustion for liquid hydrocarbons using a dual-nozzle laboratory-scale burner. Pure liquid n-octane has been used as a reference fuel, while mixtures involving also other hydrocarbons commonly found in practical fuels have been investigated to start collecting information on surrogate fuels. It has been found that the dual-nozzle configuration allows sustaining mild combustion conditions by directly injecting different liquid hydrocarbons in a mild combustion environment previously attained using a gaseous fuel. Similar results for gaseous alkanes (namely, methane and LPG) have been obtained, while using liquid hydrocarbons (namely, n-octane, n-octane/ i-octane and n-octane/ i-octane/ n-decane) have led to somewhat different results, even if similar to each other. In particular, the mild combustion region in the T avg– K V space enlarges when using liquid hydrocarbons with respect to gaseous ones. However, in this region very low amounts of NO x , CO, as well as negligible PAH and soot precursors have been found, therefore supporting the idea that a dual-nozzle mild combustion burner can create a suitable environment for NO x , PAH and soot depression for a wide range of liquid wastes and low-BTU liquid fuels.