Development of New and High Performance Combustor with Low CO_2 Emission

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Theoretical and experimental investigations were conducted for development of new and high performance combustor with low CO_2 emission. The effect of an addition of CO_2, which absorbed the emission of flame to the unburned gas, on flammability limit and burning velocity was mainly investigated as a model of lean burning technology by using the re-circulation of burnt gas. In the numerical analysis, the reabsorption of radiation emitted from a flame resulted in broader flammability limit and larger burning velocity than those of the adiabatic flame. The burning velocity of the mixture including 10% CO_2 became larger than that of the mixture with no CO_2. Moreover, it was revealed in the analysis that the effect of radiation reabsorption more strongly appeared under high pressure condition than atmospheric pressure because of decrease in the optical thickness at high pressure.Extinction limit of counterflow premixed flame with CO_2 addition was experimentally measured in a high pressure vessel to verify the above theoretical results. Stretch rates at extinction monotonically decreased with the pressure and the concentration of CO_2, and the ratio of decrease was almost same for any condition. Therefore, the effect of radiation reabsorption was small under conditions of the experiment(0.5MPa(pressure), 15mm(diameter of burner)). On the other hand, strong instability of the flame surface due to a hydrodynamic instability at high pressure appeared in the experiment. Therefore, a consideration to such instability is important for a design of combustor used under high pressure condition.