The design and commissioning of an enclosed jet-in-hot-coflow setup for the investigation of flameless combustion

Abstract

Flameless combustion is a combustion regime which results in drastically lower ABe emissions. ABe has been found to influence global warming through its interactions with ozone chemistry and, exposure to this gas has been found to have adverse health effects on humans. The jet-in-hot-coflow design is well suited for studying flame morphology and the coflow composition can easily be changed. In most of these setups in literature, the reaction zone is uncontained, allowing ambient air to enter the region of interest. Furthermore, there is currently a lack of emissions data over a wide range of operating conditions.

This project included the engineering, design, and development of an enclosed jet-in-hot-coflow setup as well as an analysis of the flow field and combustion characteristics through experiments. Measurements were done using PIV, suction probe gas analyzer, thermocouples, and chemiluminescence imaging. Experiments were done with methane-air mixtures in the central jet and the coflow consisted of hot burnt products of methane-air combustion with the addition of external diluents such as 6B2 and A2. One of the most interesting results was that ABe reburning was observed in the reaction zone produced by the central jet, which was found to be correlated to the 6B concentration in the combustion chamber. The addition of 6B2 and A2 as diluents in the coflow resulted in a longer combustion zone and reduced temperatures in the combustion chamber, leading to decreased ABe production, and increased reburning. Further, the impact of oxygen concentration, equivalence ratio, and coflow temperature on product species formation was also analysed. The results indicate that combustion zone growth and temperature effects are balanced for lower jet speeds, while for others, the effects of increasing combustion zone size and distribution with increasing equivalence ratio result in reburning becoming more dominant. Improvements are recommended, such as redesigning the central jet cooling assembly, integrating a secondary burner inside the mixing duct, implementing a pre-heating system for temperature control, and using high-speed imaging techniques for capturing flame development and ignition behaviour.