Numerical solution on the effects of bluff body with slit in micro-channel combustor

Small-scale electronic devices required long hours operation and fast charging time. Potential technology to support requirement of small-scale electronic device is micro scale combustor. Production of heat in micro level from progression of exothermic chemical reaction between reactants is known as micro combustion and may be utilized to generate electricity for small-scale electronic devices. Unfortunately, micro scale combustion is prone to combustion instability. This research is to study micro scale combustion with slit. Therefore, objective of this study is to investigate the combustion characteristics, mechanism that stabilize the flame and combustor performance of the 2-D microchannel combustor with bluff body having various slit percentages gap using ANSYS Fluent 15.7. Effects of the bluff body with slit in the micro-channel combustor have been studied numerically. Two-dimensional computational domain with the height and length of the channel H = 1 mm and L = 16 mm is used respectively. The height of the bluff body is 0.5 mm and located at 2 mm from the inlet. The slit gap percentage varied in this study is 0% to 70%. The percentage of the slit size is the ratio between slit gap height and the bluff body height. The one-step reaction mechanism of CH4/air mixture is utilized. Equivalence ratios of 0.8 to 1.0 with inlet velocities 1.0 m/s to 5.0 m/s were used. The results show that the combustion characteristic such as stable flame, wavy flame, blow-off and flame split into two parts is significantly influenced by the slit gap percentage. Flame is moving downstream and blow-off at the slit percentage of 10% to 25%. At the slit percentage of 30%, the flame zone moves towards the upstream result in stable flame. From the observation is suggested due to the secondary vortex exist behind the bluff body as slit gap increases and pull or push the flame to the upstream or downstream. The reaction zone is split into two parts at 60% and 70% slit gap percentage. It is due to the incoming fresh mixture of CH4/air mixture flows through the slit and cut the flame zone. It is also found that by increasing inlet velocity beyond 2.0 m/s, the flame become unstable and lead to blow-off as increase in equivalence ratio up to 1.0. Lastly, the highest emitter efficiency is found for the case of 40% slit which is 25 W/m.