Abstract
Lean premixed pre-vaporized (LPP) combustion is a dominant low emission combustion technology. In a center-staged LPP combustor, diffusion combustion in pilot stage and premixed combustion in main stage are combined to fulfill combustion performances and emission requirements under various operating conditions. Different from traditional combustor, since more air flows into flame tube through the dome, the airflow used for adjusting outlet temperature is very limited. Three-dimensional numerical simulations are carried out in the present investigation to analyze the influence of dilution holes on combustor outlet temperature distribution and NOx emissions. Five cases of dilution holes are simulated and analyzed. Realizable k-ε model, partially premixed combustion model and discrete phase model are employed in present work. The simulation results show that there are high temperature regions between two adjacent domes under take off mode. Cases with dilution holes in position C achieve better OTDF. The more airflow issued from these dilution holes, the lower OTDF obtained. At the same time, the radial height of outlet circumferentially averaged temperature will be increased. Under idle mode, dilution holes in position D and E are both very useful to decrease OTDF, thus it would be beneficial to increase the size of dilution holes D and E to issue more dilution air while decreasing the size of hole C. Nevertheless this modification will deteriorate OTDF under take off mode. However, under take off and idle modes, most high temperature regions appears in upper side of outlet. Hence, increasing the percentage of dilution air flowing into the upper side of flame tube will decrease the RTDF and reduce the radial height of outlet maximum circumferentially averaged temperature. It is also found that the dilution air has little effect on NOx emission in all five cases, because the dilution holes are axially located in the downstream of the primary combustion area where most of NOx is produced.
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