UK-based Ilmor Engineering has improved the power density of a general aviation diesel engine by applying technologies and design solutions from the motorsports world.

The work is part of an EU Clean Sky 2 (CS2) programme, aimed at finding innovative ways to reduce CO2, gas emissions and noise pollution from aviation.

Ilmor Engineering creates engines for Formula 1 and IndyCar and has a growing aerospace capability, which includes the development of a UAV engine, as well as work for Boeing.

Ilmor Engineering’s Clean Sky 2 programme had two interdependent aims. The first was to improve power density on a certified engine by increasing power and reducing weight while also maintaining fuel efficiency. The second was to identify and apply new design techniques and technologies.

Improving power density

Power density is a function of engine mass and power. Reducing mass for the same power improves power density; increasing power for the same mass has the same effect. The result is reduced fuel consumption, with a residual benefit in lower emissions and lower operating costs, plus potentially improved aircraft performance.

Ilmor collaborated with SMA, the piston engine division of Safran Aircraft Engines. SMA supplied the EASA-certified SR305-230E engine, a 227hp, four-cylinder, four-stroke, horizontally-opposed engine most commonly fitted to the Cessna 182.

Ilmor met the initial goal to reduce mass and increase cooling performance to allow the engine to operate at a higher power output for the duration of its life. The overall mass of the engine was reduced by 2.6%, mostly by replacing the iron liners with a plasma bore coating.

New components

The Ilmor team designed new components and redesigned existing components to meet the increased demand on the engine. It also reduced the number of these components by 35%, thus improving machinability and serviceability. The team also identified a possible further mass reduction of 1.6% through the use of a steel piston and redesigned con-rod.

Almost 100 hours of testing in France proved the power increase and basic reliability, and at the same time highlighted elements that needed further refinement.

Ian Whiteside, Ilmor’s Chief Engineer – Advanced Projects, who led the CS2 programme, said: “Increasing the power from a diesel engine is quite straightforward – you simply put more fuel in. But that generates much higher loads, so while increasing the power is easy, ensuring the engine stays together at that increased output is a challenge… and it was more of a challenge again because the requirement was to make it simultaneously lighter”.

Motorsports techniques take off

An Ilmor statement notes: “Ilmor was able to introduce design solutions, technologies and materials used in Motorsport’s constant quest for high power output, light weight and fuel efficiency.  Many are unfamiliar to the aerospace industry and the CS2 programme demonstrated they can contribute towards improving the performance and efficiency of the next generation of aero diesel engines.”

Finite element analysis was used to predict that all components will survive for the ‘time between overhaul’ life of the engine, whilst operating at a higher power output than currently required for certification.

Computational analysis was used to assess design changes and verify that the cooling performance of the engine increased, keeping the higher temperatures under control. Mass flow of air through the cylinder head has increased by 5%, and barrel surface area has increased by 39%.

Ilmor was able to introduce design solutions, technologies and materials used in Motorsport’s constant quest for high power output, light weight and fuel efficiency.

Test measurements recorded a drop in temperature in the cylinder head material around the combustion chamber of, on average, 19°C.

To improve the robustness of the engine over its lifetime, Ilmor applied an alternative combustion seal commonly used in motor racing applications. The seal is more durable at higher temperatures and pressures. The company also introduced a DLC coating on the stiffer gudgeon pin.

As well as being lighter and more robust, the crankcase, cylinder barrels and cylinder heads were cast using printed cores, which reduced development times. Assembly of these parts was simplified for a reduced number of parts overall.

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