Effects of furnace chamber shape on the MILD combustion of natural gas

The objective of this work is to assess the effects of furnace chamber shape (by changing the angle α between the furnace roof and sidewall) on the MILD (moderate or intense low-oxygen dilution) combustion characteristics for natural gas using high temperature air (1573 K) with the aid of CFD simulations. The present simulations agree well with the previous experimental results, and some new findings are revealed. For instance, when increasing angle α under the present furnace-burner conditions, stronger recirculation, smaller temperature gradient as well as larger reaction zone are obtained, indicating the easier establishment of MILD combustion. In contrast, the combustion regime transforms from MILD combustion towards flame combustion in the stability limits of diffusion combustion provided by Wünning et al. (Prog. Energy Combust. Sci. 23 (1997) 81–94) when reducing angle α. It is also suggested that there is a critical value for angle α below which MILD combustion cannot be established under the present conditions.