Rolls-Royce is completing certification work on a new low-emissions combustor for the RB211-535E4 engine to be introduced into service on Condor's first Boeing 757-300 in January 1999.
The Phase Five combustor is based on the low-emissions design of the larger Trent powerplant, and scaled to fit the -535, says RB211 and Trent 700 project director Mike Terrett. "The major reason we did it was to meet legislation for 2000 and beyond. We have seen a 40% reduction in NOx [nitrous oxides] relative to the current design," he explains.
The amount of turbofan-produced NOx is governed by the residence time of burning gases at high temperature in the combustor. "If you can reduce residence time, then you lower NOx. That's achieved by reducing the volume of the combustor by 30%," says Terrett.
To overcome the resulting problem of optimising the fuel/air mix in the smaller space, R-R has increased the number of fuel injectors from 18 to 24. The injector design promotes "-more vigorous mixing, and increases richness in the primary zone", says R-R vice-president, Seattle operations, Chris Hornblower.
Flight tests of the Phase Five combustor are expected to begin within three months on the prototype 757-300, which was due to make its first flight about 2 August. The combustor should be certificated on the -300 in December.