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The aerospace industry has been making significant strides in recent years to address the environmental impact of air travel. With growing concerns about climate change and the need for sustainable practices, the aviation industry is actively seeking ways to reduce its carbon footprint and increase fuel efficiency. One crucial aspect of this pursuit is the role of abradable coatings in improving the efficiency of aircraft engines. In this article, we will explore the basics of aircraft engines, the concept of thrust, the significance of Specific Fuel Consumption (SFC) and how abradable coatings contribute to improved fuel efficiency and lower emissions.
The Basics of Aircraft Engines
An illustration of the parts of an aero engine.
To understand the significance of fuel efficiency, it is essential to grasp the basics of how an aircraft engine operates. Modern jet engines consist of several components, including the cooler “front end” fan, low-pressure compressor, and high-pressure compressor sections and the hotter “back end” high-pressure and low-pressure turbines. Between the fan and compressor sections and turbines is the combustor section where high pressure gases are mixed with fuel and burned to produce high-pressure gases.
The “business end” of an engine is the high-pressure turbine, or HPT, which is typically a one or two stage bladed rotor that is driven by the high pressure, high temperature gases generated in the combustor section which blow onto the HPT rotor blades. The HPT rotors are connected through a drive shaft system to the front “cooler end” of the engine and drive the fan and compressors which force air into, and around, the engine. The inlet air compressed by the low-pressure and high-pressure compressors is forced into the combustion chambers, mixed with fuel, and ignited to produce a high-velocity high temperature gas for injection into the HPT. Finally, the low-pressure turbine extracts additional energy from the exhaust gas, propelling the aircraft forward.
Thrust and Specific Fuel Consumption
Thrust is the force that propels an aircraft forward, generated by the expulsion of high-velocity exhaust gases from the engine. In a large portion of engine designs, air is also accelerated around the outside of the engine by the fan, producing thrust. The power required to produce this thrust is linked to the amount of fuel consumed. Specific Fuel Consumption (SFC) thrust is a metric used in the aviation industry to measure the fuel efficiency of an engine. It quantifies the amount of fuel required to produce a unit of thrust over a specific period. Lower SFC values indicate more efficient engines, as they require less fuel to generate the desired thrust. Therefore, reducing SFC is a key criterion for the industry to achieve greater fuel efficiency
The formula of Specific Fuel Consumption.
Closing the Gaps with Abradable Coatings
In the quest for enhanced fuel efficiency, engineers over the past half century have identified and developed a crucial area for improvement within aircraft engines. The gaps between the rotor blades and the casing of the engine play a significant role in determining overall engine performance. If these gaps are too large, they allow gases to leak around the rotor tips instead of being compressed and expelled. This results in a “leaky engine” with reduced gas compression, lower engine temperatures, decreased fuel burn efficiency, and reduced engine thrust or power. To mitigate this issue, abradable seals are employed in compressor and turbine sections of the engine.
Abradable coatings are specifically designed to be cut by the rotor blades as they rotate. This property helps to mitigate blade tip wear damage and reduce repair costs while enabling tighter sealing. When the rotor blades encounter the abradable coating, they create a temporary seal, minimizing the air leakage around the tips. By reducing the size of these gaps, abradables contribute to increased compression ratios (Engine Pressure Ratio - EPR) with resulting higher engine temperatures, improved fuel burn efficiency, and increased engine thrust or power. This enhancement plays a vital role in achieving greater fuel efficiency for aircraft engines.
Aerospace Engine Makers and Reduced Carbon Monoxide Emissions
The dots represent engines that are in-service and include both new engines in production and older engines that are no longer being produced but are still in use. Improved EPRs boost Specific Fuel Consumption (SFC) and reduced unwanted emissions such as Carbon Monoxide. EPRs are boosted by the use of improved sealing, using abradable sealing systems - a key technology in use by all Aero Engine OEMs.
Aerospace engine manufacturers have heavily invested in the development of engines with improved fuel burn efficiency using abradable sealing technology.
These advancements not only enhance fuel efficiency but also have a positive impact on environmental pollution. For example, in a report by Zürich Airport, titled "Air Quality Assessment Sensitivities," the need for technological advancements to enhance environmental protection is highlighted and the need for reducing aircraft engine harmful emissions, which are produced because of inefficient fuel burn, is emphasized (Zürich Airport, 2012).
These are “by-product” gases such as Carbon Monoxide (CO) and hydrocarbons (HC) as well as smoke particles. By improving the overall fuel burn efficiency of engines through improved sealing, less fuel is required to generate thrust with fewer unwanted “by-product” emissions.
Conclusion
The aerospace industry is embracing the challenge of making air travel more sustainable by focusing on increasing “fuel burn” efficiency and reducing unwanted emissions. By understanding the fundamentals of aircraft engines, the significance of thrust, Specific Fuel Consumption (SFC), and the role of abradable coatings, we can appreciate the efforts to improve fuel efficiency in the aviation industry. Through advancements in engine design and the utilization of abradable seals, aerospace engine manufacturers are not only enhancing performance but also reducing carbon emissions. With ongoing research and innovation, the aviation industry is poised to achieve a more sustainable and fuel-efficient future.
References: 2012-05_zrh_air-quality-assessment-sensitivities_v2.pdf (flughafen-zuerich.ch)