PULSE COMBUSTION - THE MECHANISMS OF NOX PRODUCTION

A study has been performed to elucidate the fundamental mechanisms controlling the production of NO in a Helmholtz-type pulse combustor. Cycle-resolved measurements of velocity and temperature in the combustion chamber were made. These measurements were combined with the Zeldovich NO formation mechanism to explain the mechanism responsible for the low NO formation found in pulse combustors. The mechanism responsible for low NO formation found in pulsating flow as compared to nonpulsating flow was found to be a short residence time at high temperature. Three different possible mechanisms for this short residence time were investigated: (1) hot products from combustion are cooled by mixing with the cooler exhaust gases entering the combustion chamber from the tail pipe, thus quenching the NO formation reaction ("Automatic Exhaust Gas Recirculation"), (2) hot combustion products are quickly cooled by mixing with the incoming cold reactants, and (3) residual products with a lower overall temperature (due to an increased rate of heat transfer in the combustion chamber) readily mix with hot products producing a short residence time at high temperature. It is shown that the mechanism responsible for the low NO emission in pulse combustors is a result of item 3. A short residence time at high temperature is caused by rapid mixing with cooler residual gases that are lower in temperature due to increased rates of heat transfer in the combustion chamber. © 1990.