الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 135 |  |  |
| | | from | 135 | | |
Abstract
Due to strict regulations on harmful emissions such as NOx and CO, many novel combustion techniques have been investigated in order to decrease emissions from gas turbines. One of these novel techniques is colorless distributed combustion (CDC) or flameless combustion (FC). CDC has been examined under non-reacting conditions for swirl and non-swirl combustors using ANSYS 18.1 Fluent at different operating cases. This research aims to develop a design equation and a 3D flameless combustion map that includes the effect of air diameter, confinement size and excess air ratio on recirculation ratio to allocate flameless combustion regions. Flameless combustion maps were developed for swirl and non-swirl investigated combustor and 4 regions where identified A,B,C and D where region ”D” indicate that the combustor will not be able to operate at flameless mode. Furthermore, design equations were obtained to predict the most appropriate air diameter that if combined with the available combustor diameter achieves a minimum recirculation ratio suitable to sustain flameless combustion. For the non-swirl model, as the diameter decrease 40% there is an increase in the recirculation ratio with about the same percentage (43%) and as the air diameter increases the recirculation ratio decreases, taking into consideration that the percentage of decrease is more significant at smaller confinements than at larger ones where, reducing the diameter by 40% in the non-swirl model at combustor diameter( D=150mm) result in about 40.24% decrease in the recirculation ratio , however reducing it in D=50mm result in about 56% reduction in the recirculation ratio. The energy contained in the recirculation zone eddies (turbulence kinetic energy) depends on the change in the air jet diameter but doesn’t depend on the confinement size and that observation was seen in both swirl and non-swirl model. In addition , it was found that air jet diameter should be at most 10% of the combustor diameter in order to Sustain flameless combustion and the design equation can be applied at a large scales. For the swirl model , 40% increase in the recirculation ratio was observed when changing the combustor form non-swirl to swirl. Moreover, reducing the air jet diameter by half of its value in a swirl type combustor results in about 57% decrease in the recirculated mass inside the combustor. It was also found that the optimum exit position was the base design configuration with a central axial exit location ”CA” since it gives the highest recirculation ratio as well as an effective use of the combustor volume where other configurations result in (7-23%) reduction in the recirculation ratio. Bundling of the air flow into one air jet results in a deeper penetration and high recirculation ratio since 40% reduction in the recirculation ratio was observed when separating the air jet into 2 air jets each of which has half the mass flow rate but same jet diameter, however, 30% increase in the recirculation ratio was observed when each jet had half the diameter and injected oppositely. The near exit ”NE” configuration showed an improvement in the recirculation ratio than the base investigated design; however that improvement was insignificant since it results in less than 1% increase in the recirculation ratio. Furthermore, the air jet diameter should be at most 20% of the combustor diameter in order to achieve flameless combustion and thus sustaining flameless combustion in swirl based models is much easier that sustaining it in a non-swirl combustor.