BRISTOL, England — A key part of the fix planned for the British Royal Navy's Type 45 destroyer's unreliable propulsion system is ready to be operationally tested for the first time, according to a top executive at Rolls-Royce's Marine division.

A modified recuperator section installed on one of the two WR-21 gas turbines, which help power each Type 45 anti-air destroyer, has already gone through trials off the British coast, said Tomas Leahy, the director of global naval programs at Rolls-Royce. The warship is scheduled to start operational trials when it deploys later this year, he added.

The recuperator recovers heat from the exhaust of the WR-21 gas turbines and recycles it into the engine, improving fuel efficiency.

"We are confident we have a working solution," Leahy said. "The vessel has done some running around the U.K. We have done an inspection on the recuperator and it's all looking very positive.

"The vessel is due on deployment later this year to warmer [climates] and that will be the official sea trial for the modification. We will do a mid-deployment inspection; when she gets back we will do a further inspection to ensure it is performing."

Leahy briefed reporters about the company's marine activities during a visit to its Bristol, England, site.

Neither Leahy or the British Ministry of Defence would say which of the Type 45 fleets is involved in the test.

The recuperator had undergone extensive modifications with more than 2,000 separate components involved in the change, Leahy said.

Aside from the local sea trials, Rolls-Royce has run a 500-hour test of the heavily modified recuperator at its Bristol site.

However, Leahy said it's what happens during operations that counts.

"Most importantly is how it actually performs during an operational mission. If that is successful, the plan is working with MoD to roll out modifications across the fleet's 11 remaining engines," he said.

Installation of the modifications were carried out in four weeks. Crucially, that's within the warships normal maintenance period, so the work need not impose further stress on the Royal Navy's wafer-thin surface combatant resources.

"We are really quite positive. We believe this will improve the reliability of the WR-21 and the recuperator, which has been a thorn in both our sides," Leahy said.

The Royal Navy's fleet of warships has been dogged with serious propulsion problems pretty much since the first of six of the Type 45s entered service in 2010. The worst of the problems saw ships losing all electrical power and propulsion while at sea.

In a letter to the parliamentary Defence Select Committee last year, Defence Secretary Michael Fallon said power outages were one-third the level they were running at in 2010. He declined to give any precise numbers, however.

The Type 45s use an integrated electric propulsion system with two Rolls-Royce-built WR-21s and two Wartsila diesel generators providing power to the ship.

The otherwise highly successful Type 45s employ what was then a pioneering integrated full-electric propulsion system, which uses gas turbines and diesels to power electric motors, which turn the propellers.

Project Napier

Problems with the systems have generated widespread criticism in Parliament and the media, in particular due to poor MoD equipment specifications that impaired the warship's ability to operate effectively at all times in very hot climates, like the Arabian Gulf.

The MoD is now having to foot a bill of more than £250 million (U.S. $321 million) to fix the problem in a two-pronged program called Project Napier.

The first element of Napier is an equipment improvement plan, or EIP, and the second is the longer-term effort to replace the existing diesels with more powerful generators, known as the power improvement plan, or PIP.

The EIP is looking at a number of individual equipment items within the power propulsion systems. Leahy said improving the recuperator was a key task.

"Improving the reliability of the recuperator is the most important [EIP] task, as it has not reached the level of reliability either the MoD or Rolls-Royce would want," he said.

Leahy said the recuperator has suffered from a series of issues, although they hadn't stopped the gas turbines from working.

"It's not a case of 'it does work or it doesn't'; it degrades. When it does, it gives you operational limitations and ultimately it gets to a point where you have to bypass it. When you do, you still have a functioning gas turbine, but it is just a simple cycle gas turbine, you don't get benefits from having a complex cycle system," he said.

The Rolls-Royce executive declined to give any details on the amount of reliability improvement that company engineers had achieved with the modified system, but he did say: "We are significantly improving the robustness and reliability.

"We are aiming to have a recuperator last two complete overhaul cycles for a WR-21 engine without any failures. That's the target set and the design target [we're] working to."

The WR-21 is designed to be more fuel-efficient across a typical surface combatant operating profile than a simple cycle gas turbine.

Leahy said that to achieve this, the "WR-21 incorporates an 'intercooler' that cools the inlet air after the first stage of compression and a 'recuperator' that recovers heat from the exhaust gas by heating the compressed air before it enters the combustion system."

Intercooler work is being done separately.

"The recuperator provides improved fuel efficiency at part-power conditions, where in the naval application, the gas turbine typically spends most of its time," he said.

Rolls-Royce is not yet under contract to install the modifications, and Leahy said he didn't know when that might happen.

"It's down to the MoD and when they get to a level of confidence they feel they can launch the program. They are very keen but want to make sure they have the right solution," he said.

On the PIP element of the plan, an MoD spokeswomen said the project involves "fitting additional diesel generators to provide further electrical generation capacity."

A competition for the work is currently underway, and the spokeswoman said that "subject to securing the necessary formal approval, our aim is to have completed the competitive process and be in a position to award the contract in early 2018."

Andrew Chuter is the United Kingdom correspondent for Defense News.

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