Rolls-Royce has completed testing of the latest build of a research two-shaft engine core, known as “Core 3/2d,” as part of the E3E (efficiency, environment, economy) program. The core evaluation campaign ends without a previously planned endurance test, however. E3E technology forms the basis of Rolls-Royce’s Advance2 future two-shaft engine program, which targets entry into service in 2018.
The 40 hours of tests took place at Stuttgart University’s altitude test facility. This last series of trials focused on the operation of a lean-burn combustor in simulated bad weather. Core 3/2d thus performed windmill re-lights in a tropical hailstorm. “The combustor exceeded all expectations in terms of NOx reduction and engine stability under adverse operational conditions,” said Holger Klinger, Rolls-Royce chief project engineer for technology programs. “Core 3/2d’s emissions were up to 60 percent lower than current CAEP6 regulations,”
The experiment was the last in a sequence that began in 2008. By 2010 Rolls-Royce still planned on fitting “Core 3/3” with minimal instrumentation, allowing it to perform 1,200 cycles in an endurance test. But the program ultimately fell short of trying Core 3/3.
In addition to the combustor, Core 3/2d consists of a two-stage high-pressure (HP) turbine. For the blades, design engineers found new 3-D aerodynamic shapes that allowed them to reduce the number of blades. However, the larger distance between the blades would render the shrouds at their tips too large to withstand stress and temperature. That, in turn, calls for finding another way to manage tip clearance. Rolls-Royce designed an abradable ceramic liner for the inner case. Blade tips receive a coating to make them abrasive. Rolls calls the design a rub-in tip clearance control system.
In E3E, a nine-stage HP compressor with six blisk (blade-integrated disk) stages has demonstrated a 22:1 pressure ratio. An in-service V2500 needs another stage of HP compressor and an additional four-stage low-pressure compressor (booster) to reach a comparable pressure ratio.
The Advance2 program stands distinct from any technology platform on which Rolls and Pratt & Whitney might cooperate under a new partnership agreement announced in 2011, a Rolls-Royce spokesperson said. The new joint venture will focus on geared turbofan technology. While Advance2 brochures refer to regional jets in the 70- to 130-seat category, Rolls and Pratt would work on 120- to 230-seaters. Advance2 aims at burning 15 percent less fuel than current engines in the 13,000- to 25,000-pound-thrust range.