Emissions and Soot in Partially Premixed Combustion

Abstract

Practical combustion systems typically undergo non-premixed mode of combustion, in which the fuel is injected directly into the combustion chamber, which already has compressed air. The emissions tend to be high in this diffusion mode of combustion as compared to premixing mode. But a switch to premixing is not desirable for practical systems as the premixed air-fuel mixtures are more accident-prone. Partial premixing implies that the flame is only partially premixed and in parts, it is also a diffusion flame. This refers to the condition when a small amount of air or oxygen is mixed with the fuel (rich mixture), before it enters the reaction zone and then further at the reaction zone, more quantities of oxidizer are added, so as to make the overall mixture lean and to complete the combustion. Experimental study of partially premixed, co-flow, LPG-air flames are reported in this chapter, which show substantial improvement in emission and soot characteristics in comparison to a pure diffusion flame for a swirl stabilized combustor when the premixing equivalent ratio was kept between 1.5 to 2.0.