Hybrid turbo compounding

Kate invented one day that why the turbo compounding could not be implemented with electric motors, because that way the usually unfeasible gearbox from normal turbo compounding becomes unnecessary and the gearing is instead implemented with the electric motor and the generator where the generator rotates at higher revolutions than the motor that is used to decrease the load the combustion engine sees.

We were in assumption that this was a new invention, but it seems that it has been used in heavy machinery already, e.g. by Catepillar. This in turn also means that it is feasible.

The challenge would be how to place the generator to the shaft of the turbo. Usually turbos do not have a place where to fit the generator but they are closed packages which are not easily modifiable.

The idea would be to increase fuel efficiency with the compounding and increase the shaft horse power without loading the combustion engine anything more. The electric motor could have an additional lithium polymer batter pack which could increase the power even more on takeoff, so the plane would have on critical take off situation somewhat more power than the combustion engine can output, so in other words, for example getting 80 hp out of a 60 hp HKS700E.

This would result that using impossibly small engine power would become a possibility in a wider variety of airframes. On a twin 2 x 80 hp is a lot more than 2 x 60 hp, single engine performance on 60 hp is very poor in any case without any tricks done to increase the power temporarily.

A quite small lithium polymer battery pack would be enough since assuming 300 fpm climb rate on a single engine, this results 3 minutes to 1000 feet AGL where it should be safe to turn back to the runway and perform landing even with a very low power output of a single engine. So it would be well enough for the extra power from the battery pack last only for 3 minutes. This kind of battery pack would not be that heavy, and the brushless DC electric motor is also pretty lightweight.

Any comments on this?

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    • Matthew
    • January 27th, 2009

    Thats a fantastic idea, offering and additional short-term boost in power for single engine climbing.

    The concept is good, but I think the idea of a battery powered turbo would be a complex piece of equipment that would be heavy for the the amount of time it would be used.

    I might sugest you look at Nitrous oxide injection as a cheaper, simpler, lighter and more reliable, solution?
    (it was used by Allied and Axis fighters and recce. aircraftin the second world war)

    The parts are already easily available from the automotive industry and all that would be required is a tank for the nitrous oxide, some extra piping and solenoids and an injector per cylinder.

    I’ve just had a look at some nitrous injection manuracturers websites and I think 1.5kg (aprox) of nitrous oxide would produce the extra 20hp for 3min.

    It might not be the best solution for all aircraft, but for the idea of a ‘Minimal twin’ it might be the best solution, and certainly worth looking into.

    • Matthew
    • January 27th, 2009

    Thats a fantastic idea, offering and additional short-term boost in power for single engine climbing.

    The concept is good, but I think the idea of a battery powered turbo would be a complex piece of equipment that would be heavy for the the amount of time it would be used.

    I might sugest you look at Nitrous oxide injection as a cheaper, simpler, lighter and more reliable, solution?
    (it was used by Allied and Axis fighters and recce. aircraftin the second world war)

    The parts are already easily available from the automotive industry and all that would be required is a tank for the nitrous oxide, some extra piping and solenoids and an injector per cylinder.

    I’ve just had a look at some nitrous injection manuracturers websites and I think 1.5kg (aprox) of nitrous oxide would produce the extra 20hp for 3min.

    It might not be the best solution for all aircraft, but for the idea of a ‘Minimal twin’ it might be the best solution, and certainly worth looking into.

    • dodlithr
    • January 27th, 2009

    Why not? Everything is possible. But why to have several different power sources. Why not to make directly a lipo powered airplane? Just some time and all planes could be electric.

    Mr. Csaba Lemak is allready flying full electric. Check ->

    http://www.marksparaglidingpages.com/index.php?action=news&newsid=188

    • dodlithr
    • January 27th, 2009

    Why not? Everything is possible. But why to have several different power sources. Why not to make directly a lipo powered airplane? Just some time and all planes could be electric.

    Mr. Csaba Lemak is allready flying full electric. Check ->

    http://www.marksparaglidingpages.com/index.php?action=news&newsid=188

    • Karoliina Salminen
    • January 30th, 2009

    Matthew:

    1. short term boost with nitrous oxide has nothing to do with reliability, if that is used on aircraft engine, the engine TBO might drop from the 1500 hours to 50 hours. Absolute no-no for frequent use and even in emergency use there is a risk that the only remaining engine breaks before the aircraft reaches safe altitude. I have been thinking that, but that would only work for absolute emergency in case of engine failure. All other times the system would be just dead weight.

    2. Electric motors are everything else than heavy. In fact, they are very lightweight, if we are talking about modern brushless DC motors. For example a 5 kW motor weights only 1.35 kg (not 13.5 or 135 kg, but 1.35 kg!).

    3. Lithium polymer batteries weight about nothing. Look the RC plane or mobile phone batteries, combine a pile of them and see how much it weight, still quite little compared to a tank that contains nitrous oxide, all the plumbing and pump.

    4. If turbo that is turning only the generator fails, it does not make the engine to stop.

    dodlithr:

    Lipo batteries are already pretty good and so are the small brushless electric motors. One engine does not produce enough output, but a reasonable electric aircraft would be quite feasible with distributed trailing edge propulsion, so that there are multiple engines attacted to the wing trailing edge (e.g. 10 * 5 kW = 50 kw, which is a quite reasonable number already).

    Here is one link for one brushless DC that has reasonable power output

    Using big old-fashioned industrial electric motors would not work, but the low cost RC technology could possibly enable all kinds of interesting concepts. The downside currently is the very high price of the lipo batteries. Because they are expensive, I was rather thinking of this hybrid system.

    • Karoliina Salminen
    • January 30th, 2009

    Matthew:

    1. short term boost with nitrous oxide has nothing to do with reliability, if that is used on aircraft engine, the engine TBO might drop from the 1500 hours to 50 hours. Absolute no-no for frequent use and even in emergency use there is a risk that the only remaining engine breaks before the aircraft reaches safe altitude. I have been thinking that, but that would only work for absolute emergency in case of engine failure. All other times the system would be just dead weight.

    2. Electric motors are everything else than heavy. In fact, they are very lightweight, if we are talking about modern brushless DC motors. For example a 5 kW motor weights only 1.35 kg (not 13.5 or 135 kg, but 1.35 kg!).

    3. Lithium polymer batteries weight about nothing. Look the RC plane or mobile phone batteries, combine a pile of them and see how much it weight, still quite little compared to a tank that contains nitrous oxide, all the plumbing and pump.

    4. If turbo that is turning only the generator fails, it does not make the engine to stop.

    dodlithr:

    Lipo batteries are already pretty good and so are the small brushless electric motors. One engine does not produce enough output, but a reasonable electric aircraft would be quite feasible with distributed trailing edge propulsion, so that there are multiple engines attacted to the wing trailing edge (e.g. 10 * 5 kW = 50 kw, which is a quite reasonable number already).

    Here is one link for one brushless DC that has reasonable power output

    Using big old-fashioned industrial electric motors would not work, but the low cost RC technology could possibly enable all kinds of interesting concepts. The downside currently is the very high price of the lipo batteries. Because they are expensive, I was rather thinking of this hybrid system.

    • Karoliina Salminen
    • January 30th, 2009
    • Karoliina Salminen
    • January 30th, 2009
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