The LPP concept has the likely potential of reaching the lowest levels of NO x . This approach results in a low flame temperature with enough residence time to complete combustion and produce low NO x . In practice, premixing is achieved with large numbers of small-diameter premixers. The RBQQ concept is a derivative of an axially staged combustor and presents the more stable combustion configuration. In a second stage, air is quickly introduced to mix with the partially reacted fuel.
Combustion is completed in a final stage at lean conditions.
Most of the NO x is produced in the second stage and is a function of the uniformity and time it takes to dilute the reacting mixture. Design challenges with this concept include indirect cooling of the primary combustion zone which may require high-temperature ceramic materials currently under development and an advanced second stage that produces nearly instantaneous, uniform mixing of reacting gas and air. The intrinsic outputs from combustion of conventional fuels are more difficult to alleviate. With kerosene as a fuel, for every ton of fuel burned, 3.2 tons of CO 2 and 1.2 tons of water are produced.