Regular Engine Wash Plan For Sustainable MRO

Four engine washes per year strikes the best balance between reducing emissions and costs to operators say researchers from German aerospace center DLR following an analysis of the environmental impact of maintenance on commercial airliners.

The study, conducted by the DLR’s Institute of Maintenance, Repair and Overhaul (MRO), focused initially on engine washes as part of a broader effort to develop a modular framework for life-cycle assessment of aircraft maintenance. Engine washes remove contaminants from compressor blades, vanes and stators, improving overall performance, reducing fuel burn and maintenance.

However, although the procedure can cut fuel burn by 1.5% and result in significant reductions in annual CO₂ emissions, the wash process also represents cost and time to operators. To assess the optimum number of washes for an Airbus A321 “we looked at every single maintenance step and collected the inputs and outputs,” DLR researcher Antonia Rahn said. Inputs for the engine-wash process included water and cleaning agents, plus the energy required for the power-wash equipment and the fuel used to perform an engine run after the process. Outputs were waste-water and emissions.

“We put the inputs and outputs into our global inventory to normalize them,” said Rahn, who was speaking at the American Institute of Aeronautics and Astronautics virtual Aviation Forum in early August. “The environmental impact calculated per liter of water can be reused for other maintenance tasks using water as well. For one engine wash, we calculated an environmental impact of almost 2,000 kgs of CO₂ equivalents.”

The DLR study used an in-house life-cycle simulation tool to evaluate the impact of the wash against the context of the A321’s operation over an entire life-cycle. “Every flight event has an individual cost and an emission output depending on different parameters, such as the flight range or the fuel-burn rate. Together with the environmental input for the engine wash, it is now possible to calculate an economic and an environmental footprint over the whole life-cycle of the aircraft,” Rahn said.

The impact of an engine wash on overall operations was then calculated based on how exhaust gas temperature (EGT) gradually increased over flight cycles as contaminants accumulated inside the engine. An engine with no washes will typically experience an EGT rise of up to 10C before the first shop visit at around 9,000 cycles. An engine that was washed once a year, by comparison, would see an EGT rise to around 7C before resetting to zero, thereby improving performance and lowering fuel burn for a longer cumulative period.

“The more often the operator performs an engine wash, the more cost and emissions can be theoretically saved. But this must be weighed against the engine-wash cost and its ecological impact,” Rahn added. The study next looked at 12 scenarios with different intervals between the engine washes and compared them to a case with no washes. “With only one wash per year, we achieved the best economic result for the airline. Here, we got the highest cost savings but also the lowest emission savings.”

To achieve the best environmental result, the study showed an operator would have to wash 11 times per year, but that would be more costly. “Looking at the single differences between every scenario we investigated, [we found] that four engine washes per year would be a good choice for the operator. Because here we can save more than 5,000 tons of CO₂ over the entire engine life-cycle with only a very small economic and operational investment.”