Step by Step to a step change

Andre Robert, manager CF34 marketing, said the engine started out for business aviation applications and there are now more than 1,500 in service powering Challenger 601, 604 and 605 aircraft.

The original model was the CF34-1 and it was developed from a military engine (the TF34), entering service in 1983. It is as a regional aircraft engine that it really took off, however, following entry into service on the Bombardier CRJ-100 as the CF34-3A1, the CRJ-100 being a development of the business jet for the airline market. Then the CF34-3B1 helped the CRJ-200 become “the mainstay of the market”, said Robert, with more than 1,000 CRJ aircraft delivered.

By 2001 Bombardier had developed the CRJ-700 and Embraer entered the market segment with the ERJ-170/175, aircraft for which GE developed the CF34-8. The first delivery of the Embraer 170 (as this ‘E Jet’ is now known) was in March 2004, and in the same month Embraer flew its new 190 model powered by two of GE’s new CF34-10E engines.

Between the CF34-3 and -8, GE refined the design for more power with fewer moving parts, going from 14-stage compressor to a ten-stage compressor while achieving an increase in rated thrust from around 9,000lb to some 14,000lb. For the -10 engine there are nine compressor stages plus a three-stage booster after the fan, but GE went from a two-stage to a single-stage high-pressure turbine, keeping to four stages for the low-pressure turbine. It thus borrowed features from the larger CFM56 engine, developed by GE/Snecma joint venture CFM International for Boeing 737s and Airbus A320 family aircraft.

However, various other refinements bumped the overall pressure ratio to 29:1 (slightly higher than the -8 but significantly higher than the 21:1 of the -3) and the engine has a top rating of 20,000lb, significantly higher than the -8. Turbine entry temperature was increased from 900C to 970-990C for the later engines, allowing for better exhaust gas temperature (EGT) margins and longer life.

Another major change, explained Robert, was to synchronise the life-limited part (LLP) deck at 25,000 cycles for the -8 and -10. With the -3, LLP lives varied between 18,000 and 30,000 cycles.

The next step for GE is the NG34, its next generation engine, said Robert. “It is important for us to look to the future so that we’re prepared to support new applications in 2015 and beyond. Our objective with the NG34 technology programme is a 10-15% reduction in operating cost with high reliability – so we will rely on simple, robust designs.”

A key feature is the ‘eCore’, which will take technologies that GE has developed for the GEnx (powering the Boeing 787) a step further. It is aimed at engines in the 10-30,000 thrust range so that they can have a common core architecture, said Robert. “It boils down to taking all the capabilities – aerodynamics, twin annular premixing swirler (TAPS) combustor (which will be eTAPS) etc – to the next level,” he explained. “The fan and low pressure turbine (LPT) will scale well from the GEnx into the NF34 programme but the core will be a generation ahead. We have just completed the first core test and the team is evaluating the results. We plan on testing ‘Core 2’ in the second quarter of 2011, and we aim to bring the engine to test in 2012.”

Meanwhile, the CF34-10A will be the next market application, following the planned entry-into-service of the CRJ-1000 with the CF34-8C5A1 engine at the end 2009. The -10A will power the Chinese ARJ21 – the main difference being that the engine will be rear-mounted. Two aircraft were scheduled to be in flight test as Arabian Aerospace was going to press, with a third due to join them soon and a fourth in 2010, before certification and entry-into-service in late 2010.

The application on the stretched CRJ has seen GE improve the HPT “for durability purposes – because it is a higher base thrust rating”, said Robert. This meant changing the geometry of certain airfoils, software changes and better cooling features. “The most significant change is probably improved nozzles in the turbine, allowing it to go from 48 to 34 vane while holding the same flow function.”

GE believes operators will see up to a 10% reduction in maintenance costs through these various enhancements, which “will become common for the whole -8 programme”, believed Robert.

CF34 engines will not have greater thrust ratings than 20,000lb in the future due to GE’s agreement with Snecma to avoid CFM56 territory – although the eCore will be applied to other engines.

The CF34 engine family is now the dominant engine powering regional aircraft by a huge margin, although the success of P&W in having the its geared turbofan selected for Bombardier’s new CSeries was significant. However, that is larger than the traditional regional jets and Bombardier would have been interested in thrust ratings beyond 20,000lb – whereas the CF34 is at the top of its effective design reach there. That Mitsubishi has also selected the GTF is interesting in that P&W will have a version with a smaller fan diameter and two, rather than three, booster stages behind the geared fan – thus covering the 14-17,000lb thrust range as well as 17-23,000.

Robert said GE looked at geared fan architecture and from all the work it had done felt content with the traditional two-spool design”.

Developing the CF34 has proved a great success but, admitted Robert: “We find that with a given generation of product you can improve up to a certain point but then it is a case of diminishing returns and you have to consider a suite of technologies that will work well together and deliver the improvements expected from the market place.”

He added that the CF34-10 will be further improved in 2010 with a new fan blade and new oil cooler, so it will have improved specific fuel consumption. “It is a another tweak but ultimately we will need the step change,” he said.

The main prize for GE will, perhaps, be the next generation Embraer regional jet. There will be fierce competition between GE and PowerJet, which is yet to prove itself in service and cannot come close to matching the GE support network at present.