On the effects of fuel inlet configurations and equivalence ratio to the pre-heating stage of a liquid fuelled flameless swirl combustor

Flameless combustion has once again managed to attract the attention of various researchers in trying to find an alternative solution in the energy crisis that we are facing today. Thus, to join in into the parade, a lab-scale liquid fuelled Flameless Swirl Combustor (FSC) was fabricated in the High Speed Reacting Flow Lab (HiREF) to study the flameless combustion using liquid fuel. The combustion process in this combustor has two stages: preheating stage (using gas fuel) and flameless mode (using liquid fuel). This paper will be focusing on the pre-heating stage of the overall flameless combustion process using Liquefied Petroleum Gas (LPG). Gas fuel is injected axially while air at room temperature is injected tangentially from 12 inlet ports. 18 gas fuel inlets were arranged in a hexagon shaped array on the inlet flank. 6 inlet configurations with different equivalence ratios ranged from 0.3 to 1.2 were tested to preheat the combustion chamber. The results shows that regardless of different inlet configurations, flameless mode was successfully achieved using gas fuel at equivalence ratios around 0.6 and the peak temperature inside the chamber never exceeds 900°C which is well below the temperature of thermal NO_x formation. It can also be observed that for equivalence ratios lower than 0.65, the temperature profile inside the chamber has less fluctuation compared to the higher ends of the equivalence ratios. The results also showed that the maximum peak temperature (T_max) was almost always achieved just above the equivalence ratio of 0.7 and Swirl Number (S_g) of 350.