Premixed MILD Combustion of Propane in a Cylindrical Furnace with a Single Jet Burner: Combustion and Emission Characteristics

Abstract

This paper reports the combustion and emission characteristics of the premixed MILD combustion of propane established by a single jet burner in a laboratory-scale cylindrical furnace. Measurements are made of spatial distributions of the furnace temperature and species concentrations (O2, CO2, CO, and NO) and also exhaust emissions of CO and NO. Experiments are conducted for different values of thermal input, injection diameter, and global equivalence ratio (Φ). Results are analyzed with the aids of computational fluid dynamics (CFD) simulations and chemical kinetic calculations, which use a simplified perfectly stirred reactor (PSR) system with exhaust gas recirculation (EGR). It is observed that the premixed MILD combustion of propane in the present furnace can be established once the injection momentum rate is sufficiently high to enable the flue gas recirculation rate Kv > 2.5 (critical value) for Φ = 1.0. The critical Kv increases as Φ falls. Inlet conditions of the transition regime should be avoided to prevent the occurrence of instability and flashback for this regime. The present premixed MILD combustion of propane generates low CO and NO emissions. At a sufficient residence time, an increased speed injection reduces NO emission mainly by growing Kv and thus reducing the local peak temperature. In the present premixed MILD combustion, the prompt and reburning routes of NO formation are important. The effects of temperature, equivalence ratio, recirculation rate, and residence time should be systematically considered when optimizing the combustion system for ultralow NO emission.