HomeWorld RegionsAsiaTurbocharged efficiency: Advanced engine technology

Turbocharged efficiency: Advanced engine technology

The J920 engine features a distinctive two-stage turbocharger design to enable an electrical efficiency of 48.7 per cent Source: GE Jenbacher

Tim Probert reports from the global headquarters of GE Jenbacher, which has entered a new league in gas engine technology with the launch of the J920, the most powerful and most efficient engine the Austrian company has developed to-date.

Tim Probert, Deputy Editor

Eighty per cent of the cost of operating a gas fired power plant is made up of fuel. With this in mind, GE Jenbacher has launched the J920 gas engine, a 9.5 MW unit with an electrical efficiency of 48.7 per cent, which the Austrian-based firm claims is the most efficient in its class.

The new engine employs a three-module concept, which results in a standardized generator set comprised of the engine itself, a generator and an auxiliary module, all produced at GE’s Jenbacher plant. The engine maker claims the electrical efficiency of the 20-cylinder J920 engine has been raised by 1.5 percentage points on the “industry standard” to 48.7 per cent largely due to the combination of an advanced, electronically controlled combustion system with a two-stage turbocharging system.

While two-stage turbocharging is common for diesel engines, this is its first application in a large-scale gas engine, says GE Jenbacher. This technology was first used to raise the output of the J624, which had previously been the largest Jenbacher gas engine, from 4 MW to 4.4 MW and to increase its electrical efficiency to 46.5 per cent.


The two-stage system employs intercoolers at every stage of turbocharging, giving a very high efficiency by producing more usable heat and reducing gas exchange losses. Having two turbochargers rather than one raises the boost pressure of fuel to the combustion chamber by about a third. This also gives the advantage of increasing the temperature of the air-fuel mixture to about 70 à‹Å¡C.

Karl Wetzlmayer, product management leader for GE Jenbacher gas engines, says the J920 has a unique combustion concept, different from all other gas engines in the Jenbacher range. “All other gas engines feature a gas mixture and the gas is mixed before entering the turbocharger,” he said. “With the J920 air is first compressed and the natural gas is then injected before the cylinder head. The gas mixture is then fed into the combustion.”

The J920 could be particularly attractive for operation in warmer climates where condensation can be a problem because of the high humidity of ambient conditions, says Wetzlmayer. “With the J920, the mixture temperature can go up to 70 à‹Å¡C as opposed to 40 à‹Å¡C”45 9à‹Å¡C,” he said. “This is only possible with the higher boost pressure inherent with a two-stage turbocharger, as it allows a greater amount of fuel into the combustion chamber.”

GE Jenbacher admits that the two-stage turbocharger system has a cost impact on the J920, but says the engine concept is designed to be cost-effective. “I believe we have the best cost position in the 9″10 MW market with this J920 engine,” says Wetzlmayer.

The two-stage system should have little impact on maintenance scheduling. “The serviceability of this engine compares to others on the market. The J920 is very easy to assemble and disassemble. There is no defined service regime for the J920. It’s variable. We inspect the engine first and then we decide what needs to be changed.”

So why choose a potentially more expensive, two-stage turbocharged engine over a single-stage system? Mainly because of the high electrical efficiency, says the Austrian, who holds a bachelor’s degree in business and engineering from the University of Applied Sciences in Linz.

“If you are 1.5″2 per cent above the average industry standard, it gives the customer a huge benefit. A customer who buys the engine saves roughly €200 000 [$270 000] on fuel costs every year. If you have a CHP [combined heat and power] application with 90 per cent efficiency, the benefits are even higher. Other manufacturers provide only around 87 per cent, maximum 88 per cent.

“In Europe, CHP is a very hot topic. For power generation alone, the J920 would be a good solution for peaking power in conjunction with wind power. For developing countries, the J920 is being targeted as a solution for independent power projects for baseload power generation up to 200 MW, particularly in combined-cycle operation at over 50 per cent efficiency.”


Wetzlmayer says the structure of the J920 is actually designed to go beyond 49 per cent efficiency. The two-stage turbocharger facilitates this, but some components of the Jenbacher combustion system will have to be developed further before this level of efficiency can be reached. The development of the combustion system would be done in-house by Jenbacher engineers, added Wetzlmayer, saying that 49 per cent efficiency should be attainable with ease in due course.

“The whole concept of the J920 is not to just deliver an engine, but a solution,” he said. “Combined with the modular powerhouse, the J920 offers customers a compact solution.” The compactness of the J920 is down to the power density of the 6-litre, 20-cyclinder engine, which is designed to run at 1000 rpm, compared to similar, slower engines that run at 500″750 rpm.

“Power density is mainly driven by the speed of the engine. Take a Series 6 engine, a 6-litre, 20-cylinder engine operating at around 1500 rpm. Other engine manufacturers may use a 9-litre, 20-cylinder engine running at 1000 rpm. They have the same power output, but the 6-litre engine has a much smaller footprint.”


Prady Iyyanki, CEO of GE Jenbacher gas engines, says that he has entered a “$1 billion space” with the J920 engine. Quite what this exactly means is unclear; it could loosely be described as the total annual sales of ‘large’ gas engines worldwide, but GE Jenbacher has high hopes for its new engine, particularly in developing countries in urgent need of baseload power.

Prady Iyyanki, Steve Bolze, Georg Knoth, Volker Schulte and Karl Wetzlmayer at the launch of GE Jenbacher’s J920

GE Jenbacher is targeting three main applications for the J920: independent power production; peak shaving/grid balancing for renewables because of its ability to reach full output in only five minutes; and CHP, for which it claims the J920 could achieve efficiency of about 90 per cent.

As ever with gas engine manufacturers, GE Jenbacher is keeping schtum over the cost of the J920, but GE Power and Water CEO Steve Bolze told PEi that GE Jenbacher had invested a large amount on developing the J920.

“We have invested more than $100 million over the past three to four years ” that’s not just on the technology, but also on test facilities, getting the supply chain together to build the engines and the support of the launch of those engines,” said Bolze.

“So we have invested more than $100 million on a new, large gas engine with no return on investment for at least five years in testing market conditions and, four years later, here it is. We see great potential for the J920, particularly for distributed generation in emerging markets like Brazil, India and Indonesia.”

The J920 engine is not replacing an existing engine, added Bolze. Rather, as it is now the largest engine in the GE Jenbacher range, it is viewed by its manufacturer as an expansionary product.

While the J920 is primarily designed to run on natural gas, like all GE Jenbacher engines it will be fuel flexible, offering the ability to run on alternative fuels such as syngas, flare gas, coal bed methane and so on.à‚ 

In CHP applications, GE Jenbacher rates the J920’s efficiency as well above industry norms Source: GE Jenbacher

The J920 will be built and shipped from the Jenbach factory, where the 1200 GE Jenbacher employees finish around 1000 gas engine units a year. It is expected that the J920 could take around 300 to 500 hours to assemble versus around 200 hours, not including machining hours, for the smaller 4.4 MW two-stage turbocharged engine.

The engine will undergo a testing process with seven steps ” four mechanical and three electrical ” before shipping. Such is the size of the J920, GE Jenbacher will have to use a special wide-load truck and seek permission from the local authorities before transporting it.

Testing, testing

A prototype of the J920 has been undergoing successful testing on a purpose-built test bench at GE’s Jenbacher manufacturing facilities in Austria since late summer.

A large-scale pilot programme will put the new engine into operation for the first time at the Stadtwerke (municipal utility company) of the town of Rosenheim, Germany, during the first quarter of 2011. Volker Schulte, GE Jenbacher’s general manager for engineering, says he is in the middle of a validation process for the J920.

The J920’s installed dimensions Source: GE Jenbacher

“This is one of the most extensive programmes that we have ever done worldwide,” said Schulte. “It’s a short time-cycle for commercialization, but there is a lot of parallel testing being conducted on different levels of test facilities. The engine that will be installed at Rosenheim in early 2011 is part of that programme.

“We are working closely with Rosenheim Stadtwerke in order to gain real-field experience with the engine and to make sure that it achieves the targets that we have set in terms of performance, durability, lifecycle suitability and costing.”

Following this test phase, set to last all year, serial production is scheduled to begin, and the new engine should be available for use in applications in 50 Hz and 60 Hz countries in 2012.

More Power Engineering International Issue Articles
Power Engineering International Archives
View Power Generation Articles on PennEnergy.com