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Sunday, October 1, 2006

Engine Washing

New on-wing washing using an atomized mist of water penetrates deeper into the engine and promises to be environmentally friendly

It may be one of the great ironies of modern aviation that turbine engines work most efficiently at temperatures more than hot enough to vaporize water, but periodic washing of the engine at room temperature makes the efficiency possible.

By the term "washing" is meant the use of water and, in some cases, detergents, flowed through the engine to clean the turbine blades and the core. By this means, carbon buildup is minimized and operating efficiency is maximized. In this respect, the term "washing" does not refer to cosmetic cleaning of the engine exterior, but to a process applied to the interior components to ensure economical operation through the life of the engine.

Traditionally, the engine wash process has featured the use of detergents and solvents mixed with the water, and applied to the engine during overhaul, when the engine is removed from the airplane. The engine components are rotated and the fluid is sprayed into the inlet. Engine manufacturer Pratt & Whitney, which is also in the business of servicing engines, has developed a means of conducting these engine washes while the engine is "on the wing," as it were. Company officials claim the process is superior in terms of cleaning efficiency, environmentally friendly with no harsh effluents to sweep or suck up in the area, and it can be done in a fraction of the time taken for traditional engine washes.

Not surprisingly, the technology is dubbed EcoPower, suggestive of both the procedure's cost-effectiveness and its benefit to the ecology.

"We are focusing on introducing clean technologies for aerospace manufacturing, repair, and maintenance that lower customer cost with little or no environmental impact," declared Anapam Bhargava, general manager of line maintenance services for Pratt & Whitney.

For the engine cleaning process, he said, "We go to the aircraft vice bringing the aircraft to the wash."

Basically, a cart is pulled up to the parked airplane containing everything needed to wash the engines. The cart features a storage container for effluent, as well, so the whole process is a "closed loop" where water is injected into the engine and recovered at the exhaust end.

Key to the application is an array of injectors that is fitted to the engine inlet. Featuring four nozzles, the injector array is sized for the particular engine being washed -- with a smaller radius used for, say, business jets, and a larger one used for engines powering wide body aircraft. The array consists of three nozzles arranged to spray into the center of the engine, thereby reaching the core, and a fourth nozzle to cover the outer diameter, thereby covering the fan.

Jim Keenan, a Pratt & Whitney senior vice president explained, "The system uses atomized water in a fine mist." As a result, there are no toxic chemicals, hazardous wastes or detergents involved. There is another benefit of using a spray of atomized water: there are no adverse chemical reactions to gas path coatings and sealants in the engine. This is an especially important consideration for hot section components that may have expensive thermal barrier and corrosion resistant coatings.

Not the least consideration by any means, technicians don't have to don personal air supplies or filtering equipment.

The engine is rotated, using the electric starter motor, to about 20% of its idle speed, and the mist is sprayed into the inlet. Pratt & Whitney claims that the mist penetrates deeper into the engine core, saturating and cleaning all surfaces. Conventional washing methods, the company asserts, are not as effective because the denser washing mixture is partially centrifuged out into the bypass fan duct and therefore does not reach into critical gas-path components.

The effluent is collected during the wash process and the water is purified for re-use. The engine wash process is not limited to Pratt & Whitney engines; it can be applied to all turbine engines, and a selection of injector arrays has been designed to fit just about any engine size.

According to Bhargava, the new EcoPower system can wash engines in as little as one quarter the time (roughly 60-90 minutes), and the water used is between 16-42 gallons (60-160 liters), depending on the size of the engine. With multiple-engine cleaning capability, a commercial twinjet can be cleaned in approximately two hours at the end of the flight day. The service is typically offered overnight, while the aircraft is parked at the gate.

Applying the wash takes two mechanics. They receive one week of formal training and undergo three additional months of on-the-job training, at which point they are authorized to perform the engine washes on their own.

According to Pratt & Whitney, its patented system has a number of payoffs. First, efficiency is increased in both low- and high-pressure compressors. Exhaust gas temperature (EGT) is reduced by up to 15�C, thus providing longer revenue service time.

Fuel economy is also improved by as much as 1% (which is significant given rising fuel costs), and cleaner engines are better for the environment, as they burn less fuel and at the same time emit less exhaust pollutants.

The EcoPower engine wash service is presently offered at seven locations around the globe, the most recent being the first in Europe at Amsterdam's Schiphol Airport. Dutch carrier Martinair completed a pilot program at Schiphol, washing its PW4000 engines. Paul Horstink, Martinair's vice president of maintenance and engineering, was enthusiastic about the results. "The EcoPower pilot program met all of our desired results," he said. "We now plan to clean all of our engines regularly with this new method."

Pratt & Whitney Service Centers Offering EcoPower Engine Washes for P&W, GE, IAE, CFMI and Rolls Royce Engines



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