Diesel Turbocompound Fan propulsion

[Nicknick]

Here is an intresting paper which shows the potential of that:

AIAA Aerospace Research Central

 

[Nicknick]

To give a short summery, the piston engine will be operated with a very high boost pressure with up to 9.4 bar at take off and nearly 20 bar back pressure. The pressure ratio of charge/back pressure is allways around 2. At take off, less than half of the power will be generated by the crankshaft and the turbine will gives the most power output. Therefor a combustion chamber is added, where the exhaust of the piston engine will be reheatet at take off to the maximum turbine entrance temperature (1600° C).

For the weight estimation, two senarios were regarded, one with a specific engine weight of 37 kg per L displacement and one with only 20 kg/L displacement. The 20 kg/L are surly extremly ambitious, and are derived from the old large gazoline aero engines.

It is also noted, that current exhaust emission regulations for turbines can be fullfilled with a Diesel engine without any after treatment systems, so no one should blame die Aero Diesel for beeing dirty...

 

[publiusr]

Sadly, the pilots of such diesel systems suffer side-effects resulting in a type of aphasia:

PILOT: Breaker one-nine…

TOWER: What?

And if you thought a sonic boom was noisy, wait till' you hear their jake brakes…kidding.

 

[Nicknick]

Did you ever drive in a modern Diesel car? You can hardly hear the engine. With the high noise level in planes the engine will be almost unoticeable. Just some low frequency rumbling might be in the background.

The J-Brake releases high pressure air direkt from the cylinders at top dec center, that's why it makes so much noise. Increasing the back pressure will reduce the noise significantly because the pressure fluctuations in the exhaust system are reduced.

 

[red admiral]

Does the paper cover anything in terms of "absolute" power / thrust provision rather than "specific" i.e. hp/kN Vs kN/kg or kN/L

A high power aircraft diesel engine might get you a few 1000 hp/kW but you need way way more than this to turn the fan on a mid size turbofan, hence more engines needed

 

[Nicknick]

Yes of course it does, the existing standard version has a weight of 2745 kg, the compound jet would be between 5010 kg (pessimistic approach) and 3475 kg (optimistic approach). The fan power is 18.5 MW for the compound jet (slightly higher to compensate the weight penalty).

Please regard, that at take off, almost 60 % of the power is comming from the turbine, not the engine, whereas in cruise flight most power is generated by the Diesel engine.