Heat transfer and combustion characteristics of the radial jet reattachment flames in open and enclosed environments

A detailed experimental investigation on the heat transfer and combustion characteristics of the Radial Jet Reattachment Combustion (RJRC) flames impinging onto a horizontal surface has been carried out. A single RJRC flame is studied in open and enclosed environments. The RJRC flames are also studied in the array configuration in an open environment. A Monte Carlo Method has been used to simulate the radiative heat transfer from the RJRC flame to the impingement surface and the significance of the parameters involved in thermal radiation has been evaluated.; In this study, the local distribution of gas temperature, gas composition (includes CO, CO₂, O₂, and NO_x), impingement surface temperature, surface pressure, radiative and convective heat fluxes on the impingement surface have been measured. The parameters varied in the study include the nozzle exit opening, the separation distance (nozzle-to-surface spacing), firing rate, and fuel/air equivalence ratio. The effect of the nozzle-to-nozzle spacing is studied in an array configuration of RJRC nozzles in an open environment.; The RJRC flame that is in an enclosure is similar to the RJRC flame in an open environment. The richer RJRC flame in an enclosure results in a higher average gas temperature in the recirculation region. It is observed to be a much more stable flame when in an enclosure.; High CO emission is observed in RJRC flame due to the generally low gas temperature, low residence time, and quenching on the cool impingement surface. However, the low gas temperature and residence time produce low NO_x emission. In the recirculation region, low NO_x emission at 8–10 ppm corrected to 15% O₂ has been observed.; The heat transfer to the plate is higher in an enclosure compared to in an open environment. The numerical simulation shows the dominant parameter on the radiative heat flux is the gas temperature. The average radiative heat flux accounts for about 10 to 15% of the total heat flux. However, in the recirculation region, the contribution of the radiative heat flux can be as high as 25% (30% in an enclosure). Convective heat transfer coefficient and Nusselt number are obtained from the measurements. At fixed nozzle-to-plate spacing, the peak Nusselt number is irrelevant to the fuel/equivalence ratio in the range studied and the Nusselt number correlates with Re0.5.