Numerical Simulation of Air Inlet Conditions Influence on the Establishment of MILD Combustion in Stagnation Point Reverse Flow Combustor

CATEGORY: COMBUSTION
Mathematical Problems in EngineeringVolume 2013 (2013), Article ID 593601, 9 pages, http://dx.doi.org/10.1155/2013/593601
Numerical Simulation of Air Inlet Conditions Influence on the Establishment of MILD Combustion in Stagnation Point Reverse Flow Combustor
Xiao Liu and Hongtao Zheng
College of Power and Energy Engineering, Harbin Engineering University, Harbin, Heilongjiang 150001, China
Introduction
With theworld’s increasing care for purifying and sustainability of environment, moderate or intense low-oxygen dilution combustion (MILD)  is becoming a credible candidate to simultaneously meet themitigation of combustion-generated pollutants (NO𝑥 ) andgreenhouse gases (CO2)whilstmeeting combustion efficiency needs. When the MILD combustion occurs, particularly firing gas and light oil, the entire furnace is bright and transparent and no flame is visible, so that it is often called “flameless combustion (FLOX) ” or “colorless combustion.” This combustion is also named “high temperature air combustion” (HiTAC)  because the combustion air is usually preheated to beyond 1200 K for industrial regenerative combustor systems.
The air preheating requirements of the high temperature air combustion system limits the application of the MILD combustion technology. Because the reversed flow combustion configuration can avoid this procedure, more and more attention was focused here. Yang and Blasiak  showed that flameless oxidation can only be reached if the inlet velocities of the reactants are high enough to establish recirculation zones in the reversed flow combustion chamber. Unfortunately, high velocity of air inlet will lead to combustion instabilities, insufficient residence time, and high CO emission.
These issues may be overcome by a combustor design where both the burner and the exhaust port were mounted at the same end of the combustion chamber.
The present study is aimed at accurately capturing the characteristics of MILD combustion in this reversed flow small-scale combustor, using the modified Eddy Dissipation Concept (EDC) model with detailed mechanism. According to the test conditions of M. Castela , there are two variables from conventional lean combustion to flameless combustion: the total content of oxygen and the momentum (mass and velocity) of the air inlet; therefore, the main objective of the simulations is to investigate and explain the air inlet conditions impact on the establishment of MILD combustion.
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