Effect Of Fuel Type On The Reaction Zone Structure Of Moderate And Intense Low Oxygen Dilution (MILD) Combustion

Abstract

This paper reports on the systematic variation of fuel type for turbulent nonpremixed flames issuing into a heated and diluted coflow. The combustion of fuel in a low O2 and high temperature oxidant stream creates a unique combustion regime referred to as Moderate or Intense Low oxygen Dilution (MILD) combustion. MILD combustion leads to a distributed reaction zone, a reduction in pollutant emissions (notably NOx) and an increase in nett radiation flux. The influence of combustion chemistry on the flame behaviour and reaction zone structure is examined using a combination of experimental and laminar flame calculations. Temperature, the hydroxyl radical and formaldehyde are measured instantaneously and simultaneously using planar laser imaging techniques to reveal the structure of the reaction zone. A range of hydrocarbon fuels are used to provide an assessment of the sensitivity of the MILD combustion regime to fuel type. The role of hydrogen addition to the primary fuel is also considered, and it was found necessary to stabilise the flame in the experimental burner and has implications for the potential use of hydrogen as a supplemental fuel additive. The comparison between the various fuels reveals that the fuel type does not have a significant effect on the reaction zone structure. The insensitivity to fuel type suggests that a wide variety of fuels may be useable for achieving MILD combustion. This independence of the reaction zone structure is potentially a significant advantage for the implementation and application of MILD combustion to practical systems.