Clean – without any water

Efficient and gentle cleaning of engines at any time of year

Set against a backdrop of increasing aviation traffic and the resultant pollution, particularly in the vicinity of airports, it is in the interests of all parties to minimise kerosene consumption and reduce emissions. With the help of modern engine cleaning, not only can kerosene consumption be reduced and the life of engines extended; emissions of carbon dioxide (CO2) and nitric oxide (NOx) are also reduced. The accumulation of dirt in the engines, arising from insects, dust and aerosols from layers of air close to the surface, leads to a reduction in compressor performance and thus to an increase in the consumption of fuel intrinsic in creating thrust. The increase in kerosene consumption results from an increased firing temperature, causing an increased thermic load on those components within the jet flow along with a shortening of the life of the engine as a whole. A rise in kerosene consumption increases the emission of CO2, NOx and other greenhouse gases.

At present, aircraft engines are being cleaned using the water-based Cyclean® procedure developed by Lufthansa Technik. This procedure has already been used more than 5,000 times and it achieves a significant reduction in kerosene consumption. Cyclean®, however, cannot be used in an ambient temperature of less than five degrees celsius, as any water residue in measuring lines and engine components may freeze during flight, endangering flight safety. To complement the existing cleaning procedure, Lufthansa Technik AG has developed a procedure without any residue based on CO2 dry ice pellets. As with Cyclean®, the cleaning involves the injection of the cleansing agent into the engine intake.

As an alternative to conventional industrial methods, cleaning with CO2 dry ice pellets is as efficient as it is environmentally friendly, and outstandingly non-destructive. When the three by six millimeter pellets hit the blades of the compressor stages in the engine, the kinetic energy released by the impact already loosens some of the dirt. The dry ice pellets then turn into a gaseous state immediately (sublimation), so that no residue remains in the engine. During the contact time, the dirt contracts as a result of the extremely low dry ice temperature, -78.5 degrees celsius; it becomes brittle and is then thoroughly but gently removed. The dry ice jet spray itself does not leave any waste product behind.

In the research project, "Engine cleaning with CO2 dry ice", being carried out in collaboration with the Darmstadt University of Applied Sciences and Pneumo GmbH, a compressed air system is used to inject the pellets into the engine via a rotating cleaning container fitted to the engine air intake. A cleansing effect can be detected as far as the final compressor stages. Several kilograms of pellets are needed per jet spray and nozzle, resulting in several minutes of spraying per engine cleaning operation. Both the quantity and the spraying time need to be fine tuned in order to create a market-ready product. The research project, conducted from the start of 2009 until mid-2013, was funded by the Federal Ministry for Economic Affairs and Energy. An application has been lodged for funding of a successor project researching the use of other spray media, beginning at the start of 2014. Both European and American patents have already been issued for the procedure.

Engine cleaning using CO2 dry ice is initially planned as a complementary method alongside water-based engine cleaning, primarily for use in winter months and in colder regions. As the new procedure is also significantly quicker, engine cleaning can be carried out more frequently in the future. The aim of this development is, apart from weather-independent cleaning, a further reduction in the ground time of customer aircraft by 50 percent in comparison to the Cyclean® procedure currently in use. Compared to the procedure used by engine manufacturers, there is a reduction in ground time of up to 90 percent. This makes it possible to clean the engines of even a medium-haul aircraft between two flights, meaning a significant increase in the number of potential engine cleanings and further improvement in emission reduction.