Abstract
In this study, combustion field with intermittent fuel jet has been investigated. A combustor consists of inner central fuel nozzle and surrounding air nozzle. To reveal an effect of fuel injection, ratio of fuel injection time to total period (R) is changed. When fuel supply rate is kept constant, fuel injection velocity is increased at larger R. In experiments, NO_x concentration was measured. The fuel is propane. To discuss flame structure and flame characteristics in detail, numerical simulation was conducted. The fuel injection time and velocity were changed to in the range of R=0.14, 0.20, 0.33, and 1.0. A flame index was obtained to examine premixed and non-premixed combustion regions. The so-called jet diffusion flame is formed at R=1.0. Experimental results show that, the combustion area is very fluctuating by intermittent fuel injection. As R is decreased, EINO_x is reduced. Based on numerical simulation, by decreasing R, the flame region is detached at the burner port. In this case, some of the fuel is re-ignited in burned gas area of high temperature. At this condition, it is found that fuel and air are mixed to form premixed combustion zone, with lower flame temperature. Hence, the low level of NO_x emission by intermittent fuel injection is explained by this partial premixing effect of fuel and air.
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