Observation of local heat release rate with changing combustor pressure in the CH4/air flame (wrinkled laminar regime)

The influence of combustor pressure on the local heat release rate of methane/air flames (wrinkled laminar regime) was investigated by measurements of local chemiluminescence intensity. Induced flow is often applied to the industrial boiler systems to improve heat transfer and prevent leakage of combustor. To investigate the combustion characteristics in the induced flow pattern, the pressure index (P*) was controlled in the range of 0.7–1.3 for various equivalence ratio conditions for the present combustion system, where P* is defined as the ratio of absolute pressure to atmospheric pressure. Relationships between local heat release rate and pressure index have been investigated by simultaneous measurements of C2*, CH* and OH* chemiluminescence intensities. Flame length became longer with decreasing P*. The mean value of C2* and CH*, which indicated the reaction intensity in the hydrocarbon flames, decreased with decreasing pressure index for Φ ≤ 1, but increased with decreasing pressure index for Φ > 1. The C2/CH value, which has a strong relationship with the local equivalence ratio, was almost the same for Φ ≤ 1, regardless of the change of the pressure index, but showed a large level for lower pressure index and Φ > 1 conditions. For rich combustion conditions, a combustor pressure lower than the atmospheric pressure enhanced the combustion reaction by increasing the diffusion velocity of unburned fuel.