Coupling Micro-Mixing Combustion With a Pre-Reactor Operating Under Ultra-Rich Conditions for Low-NOx Combustion of Hydrocarbons

Abstract Micro-mixing combustion is promising because of its non-premix like combustion stability while having the potential to achieve NOx emissions near premix levels. However, based on our previous work, the heavier the hydrocarbons, the higher the thermal NOx because of the increase of the mixing timescale. Consequently, there is a need to achieve faster mixing with heavy hydrocarbons to allow their pairing with micro-mixing combustion. This paper presents an experimental proof-of-concept of a combustor architecture composed of a micro-mixing injector coupled with a pre-reactor operating under ultra-rich conditions. Air is introduced in the fuel at high equivalence ratio, between 15 and 25, and the reaction is activated with the heat of the main combustion. The thermally coupled reactor forms lighter species from heavy hydrocarbons through partial oxidation of the fuel, balancing the effects of heavier fuels and decreasing mixing timescale. Experimental tests with propane at atmospheric pressure, and at adiabatic flame temperatures between ∼1500 K and ∼2000 K, were performed to demonstrate the concept. NOx emissions were reduced by a factor up to 3 with this combustion architecture compared to baseline tests, achieving near premix NOx emissions. Increasing the air injected in the reactor decreased further the NOx emissions. Additionally, tuning of the combustion stability was possible by adjusting the reactor parameters.