Oxygen Enriched Air Effects on Combustion, Emission, and Distributed Reaction

A novel combustion technology which combines colorless distributed combustion (CDC) and oxygen enriched combustion (OEC) air is examined to achieve optimum benefits of both technologies and to foster novel technologies for cleaner environment. The influence of oxygen enriched air–methane flames under nonpremixed and premixed fuel-lean combustion conditions is examined with focus on emission of NO and CO, combustor exit temperature (T_exit), and distribution of reaction zone in the combustor using OH^* chemiluminescence intensity distribution. A cylindrical combustor was used at combustion intensity of 36 MW/m³·atm and heat load of 6.25 kW. Results are also reported with normal air (21% oxygen). Oxygen enrichment provided stable combustion operation at lower equivalence ratios than normal air and also reduced CO emission. Increase in oxygen concentration from 21% to 25% or 30% increased the NO and decreased CO emissions at all the equivalence ratios examined. Using 30% O₂ enriched air in premixed case showed NO emissions of 11.4 ppm and 4.6 ppm at equivalence ratios of 0.5 and 0.4, respectively. Oxygen enrichment also reduced CO emission to 38 ppm at equivalence ratio of 0.5. Operating the combustor with normal air at these equivalence ratios resulted in unstable combustion. OH^* chemiluminescence revealed increased intensity with the reaction zone to shift upstream at increased oxygen concentration. The exhaust temperature of the combustor increased with oxygen enrichment leading to lower CO concentration and increased combustion efficiency. The oxidizer injected at higher velocities moved the reaction zone to upstream location with simultaneous reduction of both NO and CO, specifically under nonpremixed combustion.