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Power Density improvement demonstrated on a certified engine

Periodic Reporting for period 2 - SMM (Power Density improvement demonstrated on a certified engine)

Reporting period: 2017-07-01 to 2018-03-31

The objective of the project is to look at methods of improving the power-weight ratio of a diesel fuelled piston engine for light aircraft use. Improving the power-weight ratio of the engine will increase aircraft performance as well as reducing fuel consumption / CO2. This has obvious environmental benefits as well as reduced operating costs for the aircraft owner. These improvements would make the engine more competitive in the market which should lead to more sales and in turn the potential to increase employment.

Increasing the engine performance of the engine is easily achieved by changes to the fuel injection system on the engine. However, this increased performance results in higher loads on the engine due to the increase in pressure and temperature within the cylinders during combustion. The design of the base engine for this project had been optimised for its current performance level and increasing performance results in a reduction in the life of many of the main structural components of the engine.

The project is therefore challenging in that it requires many of the components to have increased strength and stiffness but also reduced mass. This was achieved by careful detail design of the components, alternative materials and methods of construction of the engine. FEA stress analysis was used to validate that the revised components could meet the durability requirements with the increased loads.

The engine was tested during the final Work Package of the project , it suffered no failures and completed the test schedule defined in the periodic report, running for a total of 96 hours.

The prototype engine was confirmed as being 5Kg lighter than the existing engine, and thermocouple readings revealed that the revised cooling systems were effective in reducing the temperature of the cylinder heads and barrels.

The Crankcase package has manufacturing benefits such as reduced part count, a more simple assembly process and reduced cycle time for machining, which should also enable some cost saving.

Overall, these outcomes show that the changes have been effective in improving the power density of the existing engine. If implemented, they have the potential to have environmental benefits in terms of reduced CO2 emissions, and socio-economic benefits in terms of making the SMA engine more competitive.
Work Package 1 was the preparation phase, where the existing engine was examining and discussions help with the supplier about know weak points. Some preliminary FEA stress analysis was carried out on a couple of engine components to understand the potential challenges and opportunities for weight reduction. Using this information and via regular meetings with the engine supplier and detailed scope of work was defined and a project timing plan produced.

Work Package 2 was the main technical phase of the project where the engine components defined in WP1 were redesigned to improve their strength and reduce their mass. An alternative method of construction was utilised for the main engine crankcase, this was done to improve its strength as well as simplify the manufacturing of the part. The cylinder barrels very also redesigned around an alternative manufacturing method as these parts were targeted as the item with the largest potential for weight saving. A by-product of the alternative design was also an improvement in the cooling of the cylinder barrels. The cylinder heads were redesigned to reduce their mass and CFD analysis was carried out to also improve the cooling of these parts. A number of smaller components were also redesigned to reduce mass and accommodate the changes made to the other engine components. The FEA stress analysis showed that all components could achieve the desired engine life at the increased loads for the project. The CFD results also demonstrated improved cooling for the engine which would also have a positive impact on the engine durability.

Work Package 3 was the manufacture of parts to the new design so that a prototype engine could be assembled and tested in Work Package 4. Castings were procured for the major structural components of the engine and as of the end of Reporting Period 1 ( 30/6/17 ), the castings had been received and they were part way through the process of being machined into finished components.

During Reporting Period 2, the machining of all crankcase, cylinder barrel and cylinder head castings was completed at Ilmor. For the cylinder barrels this also meant sending the parts to an external supplier for plasma spray coating the bore, then to the honing supplier.
Two cylinder heads and barrels were machined to accept thermocouples (37 per cylinder), to allow temperature measurement during engine testing. The majority of other components were manufactured by companies within Ilmor’s supplier base.

Work Package 4 comprised the assembly, testing and final inspection of the engine. The engine was assembled at SMA with the aid of an Ilmor prepared build manual. Engine testing took place at external test facility. The engine completed a running-in cycle, then performance characterisation and thermal testing, at the desired power output. Further testing included a durability cycle which brought the total engine test duration to 96 hours.

The engine was returned to SMA for disassembly and inspection. The majority of new parts were also returned to Ilmor for more detailed analysis.

The complete prototype engine, despite being designed to cope with higher combustion pressures and temperatures was 5.4Kg lighter than the existing engine.

Ilmor will disseminate information regarding the details of the project to the wider aerospace community via a dedicated section on the website. In addition, an aerospace specific PR company will put together a press release, and create a technical article detailing the novel features introduced to the prototype engine. This will be published in one of the leading aerospace media publications.
An alternative construction has been used for the design of the crankcase which is novel within the air-cooled light aircraft engine market. Analysis work in WP2 has shown that there is a significant increase in the strength and stiffness of the crankcases by using these new techniques with only a small penalty in mass. The new design of crankcase is also significantly simpler to manufacture which will reduce the cost of manufacturing the engine and make it more cost competitive.

The design of the cylinder barrels is also unique within the air-cooled light aircraft engine market. The new methodology reduces the mass of the cylinder barrel assembly by over 35% which will improve the power to weight ratio of the engine. The number of unique parts in the barrel assembly has been reduced by 67%, which will reduce manufacturing costs, logistics and assembly time.

Both of the above two innovations should make the redesigned engine more competitive in the market which should lead to more sales and the potential for increased employment.

The reduced mass of the engine should result in a fuel cost saving to the customer and reduction of CO2 emissions, which is obviously beneficial to the environment.