Date of Award
Master of Science (MS)
Koch, Jon D.
Borg, John P.
Federal and global legislation are requiring increasingly stringent emission regulation on household appliances and in particular water heater burners. Emissions like NOx (NO and NO2) are a growing concern due to their adverse health effects and contribution to tropospheric ozone, acid rain, and smog formation. As NOx is more closely controlled, appliance manufacturers are developing low emission burners for use in water heaters.
Flame temperature is strongly correlated to NOx production. Hence, characterizing flame temperatures in new burners is a key part of improving upon burners used today and the development of future burners. Temperature measurements applied to a new, radiant, ultralow-NOx burner are thus the focus of this research. Laser Rayleigh scattering allows us to make near-instantaneous, 2-D measurements using an unobtrusive technique. The application of this technique resulted in flame temperature images in three locations, above and across the burner surface ranging from 800-1600 K in general with an uncertainty of 9.6%. The fluctuation of the flame temperature was also found ranging from 200-800 K, indicating the presence of large scale hot and cold gas mixing.
Other temperature measuring techniques were applied to the burner as well. A type-K thermocouple 5 cm above the center of the burner measured a point gas temperature of 1508 K after an estimated radiative correction was applied. This measurement was within 5.3% of the laser Rayleigh scattering measurement of 1428 K at the same location. An IR camera did not provide quantitative temperature measurements, but the videos indicated similar flame structure and mixing behavior when compared to a series of single-shot laser Rayleigh scattering images.
It was concluded that the large amount of excess air (equivalence ratio of 0.725) was primarily responsible for reducing the flame temperature by 436 K in comparison with the adiabatic flame temperature under stoichiometric conditions. The radiative emission by the burner was estimated from the thermocouple and laser Rayleigh scattering measurements to decrease the temperature further by an average of 420 K relative to the stoichiometric adiabatic flame temperature.