Pratt & Whitney is testing a new combustor design for the JT8D-200-series engine. The new design is expected to reduce nitrous oxide (NOx) emissions by 20% as part of a drive to keep the engine compatible with imminent emissions legislation.
The revised combustor is aimed at new-build -200s and for potential retrofit into engines powering Boeing MD-80s. "We still intend to be building JT8D-200s in 2000," says P&W, which is optimistic that it may even have to step up production for an intended Boeing 707-300 re-engineing programme.
The current -200 series meets other requirements of the new International Civil Aviation Organisation (ICAO) emissions rules which come into effect by the end of 1999, but falls down on NOx. "We have come up with a new combustor that will cut NOx by 20%, and reduce hydrocarbons from the current 55% level to 80% below the ICAO ruling. It should reduce overall emissions by around 10%," says P&W, although it admits that the design will produce a "modest" rise in carbon monoxide.
The new design changes the scheduling of the airflow and fuel nozzles to alter the mixing of the air/fuel vapour and reduce residence time in the combustor. This cuts the volume of mixture at peak temperature, and thus the production of NOx, while still maintaining an optimum combustion temperature of around 2,200íC. The inner and outer swirlers, primary pressure atomiser and secondary fuel filmer have all been redesigned and repackaged within the same volume, allowing the combustor to be retrofitted.
Verification tests of the design will be completed in the third quarter of this year, with entry into production due to start in the first quarter of 1999. "We could also theoretically put it into some of the 'straight eights' [JT8D-15/-17 powering 727s], but we don't see a great demand," says P&W.
Source: Flight International
