Date of Award

Fall 2012

Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

First Advisor

Koch, Jon

Second Advisor

Bowman, Anthony

Third Advisor

Borg, John


The NOx emissions of a 40,000 BTU/hr (11.7kW) natural gas water heater are studied at different primary equivalence ratios (Φ). CO emission, O2 content in the flue gas and other related parameters are measured to assess the potential for NOx emission reductions with relatively modest changes in current burner and combustion chamber designs. In addition, N2 is introduced into the primary fuel and air flow to simulate flue gas recirculation (FGR) in order to estimate what benefit such a strategy might provide. NOx concentration in the exhaust decreases from 84 ppm to 34 ppm (at 3% dry O2) when the primary equivalence ratio is decreased from 4.8 to 1.3. The flame structure also varies with primary equivalence ratio. When Φ is lower than 2.1, the flame starts to show a highly unsteady structure, and NOx emissions fluctuate at this range of Φ. However, the observed NOx emissions decrease with a decreasing Φ indicates a potential method of significant NOx reduction in natural gas water heaters if the flame could be stabilized. Introducing 10 standard liters per minute (SLPM) N2 (15% of the primary air at Φ=3) into the primary fuel and air flow further decreases NOx emission levels by 20% to 29%, which indicates that flue gas recirculation (FGR) may be a viable method of reducing NOx of natural gas water heaters using on pancake burners.