BMW Rolls-Royce has completed initial tests of a staged combustion chamber for its BR700 turbofan as part of the German Government-backed Engine 3E (environment, economy and efficiency) technology programme.

The Dahlewitz-based company says that six weeks of testing have shown that significant reductions in emissions of oxides of nitrogen (NOx), carbon monoxide and unburned hydrocarbons (UHC) can be achieved with the staged combustor.

BMW R-R's director of engineering, Gunter Kappler, says: "The test demonstrates how new technologies can be introduced into existing modern aero engines like the BR700 family to further reduce the pollutants."

The manufacturer claims the new combustor cut NOx emissions to 50% below the regulatory requirement, while carbon monoxide (CO) was down to 20% of the limit. UHC emissions were measured at 3% - unchanged from those produced by the conventional combustor used in the BR715 for the Boeing 717.

"We are encouraged by the results, since the reduction of NOx was achieved without resulting in higher CO, UHC and smoke emissions," says Kappler. "With this we can offer our customers the latest low-emissions technology when the market asks for it."

The staged combustion chamber uses two rows of fuel atomisers, offset in the direction of the gas flow. The first is the pilot stage and the second the main stage. Depending on the thrust level, either the pilot only is activated, or the pilot and the main stages together.

Because the two "burning zones" are each optimised in terms of the fuel-air ratio, flame temperature and gas "residence time", a significant reduction in NOx can be achieved without compromising CO or UHC emissions, says BMW R-R.

The company is carrying out the research in partnership with the German DLR aerospace research centre in Cologne and the technical universities of Chemnitz, Darmstadt, Dresden, Karlsruhe and Munich. The staged combustor project is one of seven involving BMWR-R under Engine 3E, which has a budget of DM100 million ($60 million). It is 50%-funded by the Government.

Source: Flight International