Cooling characteristics of dilution holes in can-type combustor of micro gas turbine

Abstract

For the purpose of studying the effect of structural changes in the dilution zone on the main performance evaluation parameters of the combustor, a can-type combustor of a micro gas turbine containing 16 dilution holes was used as the original structure. Seven optimization cases were designed by adjusting the number of dilution holes and the area of single hole in the range of hole numbers from 8 to 28 while keeping the total area of dilution holes. The main conclusions obtained by the numerical simulation study are as follows. The total flow of the dilution zone decreases with the number of holes reduce but due to the increase of single hole flow with the area, the airflow rigidity is significantly enhanced, so the entire airflow is disturbed more strongly and the dilution effect is strengthened. In general, the total pressure loss of the combustor presented an increasing trend with the decrease in the number of holes, and the pressure loss reaches a minimum value of 3400 Pa when the number of holes is 14. The combustion efficiency decreased as the number of holes increased, when the hole numbers increased to 20, the combustion efficiency dropped abruptly below 95%. The variation tendency of outlet temperature distribution factor (OTDF) is generally consistent with the combustion efficiency, and the minimum OTDF is 0.29 for the number of holes of 28. In summary, compared with the original structure with 16 holes, the OTDF decreases by 7.69%, the NOx concentration decreases by 16.67%, and the combustion efficiency increases by 3.1% when the number of holes is 8. Although the total pressure loss is increased by 8%, it is still within a reasonable range. Therefore the combustor with 8 holes can be considered a better optimized case.