Stirling engine coupling with electric propulsion

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Mathew
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Stirling engine coupling with electric propulsion




by Mathew » 21/11/12, 19:48

Good evening everyone.
I thought during my studies of a propulsion mode for cars. Surprisingly, I haven't found anything about it on the web. Yet I search in English, so I should cast a wider net.

The basic idea is as follows:
1 / Under the hood, a Stirling engine that can rotate at two speeds: normal and fast.
2 / Still under the hood, an electric motor.
3 / In the trunk and / or under the floor: batteries.

It is not a hybrid, but a 100% electric powered car. The stirling engine is not connected to the wheels, but to an alternator to charge the batteries.

At start-up, batteries fully charged, the Stirling engine does not run. The batteries are discharged. After a few kilometers, when the battery charge reaches a certain threshold, the Stirling engine starts at normal speed, and provides enough power to recharge the batteries while continuing to drive.
And if you want to drive faster for long journeys on the motorway, for example, the engine goes into second gear to provide enough power.
When the ignition is switched off, the Stirling stops.

Rapid heat balance: internal combustion engine, n = 35%

This system: stirling engine, n1 = 40%
electric motor: n = 90%
losses in cables and batteries: 10% -> n3 = 90%

N = n1 * n2 * n3 = 32.4%

Not necessarily better than the conventional heat engine. But I don't teach you anything about electric propulsion: power available from start-up, silence in use.
Benefits of Stirling:
* external combustion, so much easier to control
* quiet
* in absolute terms, can use any energy source
* At constant speed (only two speeds) the output can be optimized.

In the 70s, 40 years already, Ford had put a Stirling in a Torino. The error was to want to replace the gasoline engine directly, and to fight against the muscle cars of the time, which made 400cv without worry. Only electric propulsion can do better in terms of performance.

This car would theoretically be silent, have a long range thanks to the standard fuel tank, and pollute less than a conventional engine thanks to its external combustion.

Here. It's just a principle. I do not have the details of the type of stirling, power, capacity of the batteries, functioning of the regulation for the ignition of the engine ....

What do you think?
Me it's evening : Mrgreen:
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by chatelot16 » 21/11/12, 20:31

with the stirling the passage by the electricity is almost obligatory, because the stirling is too slow to control its power

of the said 40% stirling yield? the stirling does not have a constant output for all the stirling ... it has a yield limited by log according to the hot and cold temperature of its cycle: and as the heat must pass through a wall it is necessary that the materaix supports the cycle temperature

with the internal combustion or diesel engine the material of the engine does not reach the temperature of the cycle, that is all the advantage of the alternative engine: the materials of the cylinder take only the average temperature

there are already diesel engines up to 50% efficiency ... for stirling I can hardly believe

to make a high yield in stirling you need very expensive materials to go up to high temperature ... in diesel we do the performance we want with cast iron
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by Gaston » 22/11/12, 10:30

Agree with chatelot16 (with a small downside: diesel at 50% efficiency are huge engines made to propel container ships).

I would add that at equal power, a Stirling engine is much heavier than an internal combustion engine.
Weight is really an enemy for a car.
In the end, we have a car that consumes little (thanks to better efficiency) compared to a vehicle of equivalent weight, but which risks consuming more than an equivalent thermal vehicle which will be lighter :|

In addition, the calculation of yield seems to me to ignore the generation of electricity?
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by chatelot16 » 22/11/12, 13:02

it's not just the huge boat engines that reach 50% efficiency

we find smaller, with 47% which is already not bad
http://international.schnellmotor.de/sm ... 1040kW.pdf
of course it's 1000kW ... still a little too big ... it's a V12 ... with a single cylinder we would have the same efficiency and therefore 83kW

for a good output it takes a large cubic capacity so that a small proportion of the heat is lost by the walls of the combustion chamber: this is what makes the advantage of large engines

to seek the maximum output in small power you need only one cylinder: alas it makes the engine 2 or 3 times heavier than a 4 cylinder because it requires at least a large flywheel, and in addition a lot of weight in the whole engine do not vibrate too much: it is a good solution for a fixed engine ... more difficult but not impossible for a vehicle engine: you need a high speed flywheel turning in the opposite direction to the engine ... balancing shafts as on single cylinder motorcycles

another problem, to reach this output schnell uses not only a turbo compressor, but an additional turbine to finish the relaxation: with a single cylinder the turbines work badly, it is necessary to fire these compression and expansion by piston, well synchronized with the main cylinder. .. it is a good way because the piston has better efficiency than the turbine ... if schnell is 47% with turbo, a single cylinder with additional piston could do even better in yield, but much less good in power weight ratio

this increase in efficiency by compression and expansion separated from the main cylinder can also be done with petrol, with the advantage of being able to turn faster therefore making it lighter

I see a lot more hope to increase the yield by these additional piston than by the stirling

in addition these improved engines will remain usable with conventional transmission
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by chatelot16 » 22/11/12, 13:24

schnell achieves this 47% efficiency with a smaller engine
http://international.schnellmotor.de/sm ... _265kW.pdf
it is a 6 cylinder it lets hope the same performance on a 44kw mono

or a 88kw twin cylinder better balanced than the mono
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by Woodcutter » 22/11/12, 20:34

chatelot16 wrote:it's not just the huge boat engines that reach 50% efficiency

we find smaller, with 47% which is already not bad
http://international.schnellmotor.de/sm ... 1040kW.pdf
of course it's 1000kW ... still a little too big ... it's a V12 ... with a single cylinder we would have the same efficiency and therefore 83kW [...]

I'm not at all sure that such a simplistic linear interpolation can be done!

Otherwise, these SCHNELL engines are interesting, but their particularity is above all that they are Diesel cycle engines, but GAS!
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by chatelot16 » 22/11/12, 20:48

it is not an interpolation: a single cylinder works exactly the same as 12 cylinders together in the same engine

yes the schnell engines are built like diesel, but only inject a small proportion of fuel oil to ignite and swallow methane through the air intake ... that doesn't change much in terms of efficiency. it’s just a good place that performs better than other manufacturers
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by Remundo » 22/11/12, 21:15

High performance diesel should ideally have a very large PME (effective average pressure), rotate slowly and a high compression ratio. In general, they must be overfed.

The connecting rod / crankshaft must also be mounted on a bearing rather than on a lubricated bearing.

Ideally, the connecting rod should be long to limit the transverse piston / sleeve forces. Also limit the powers of the auxiliaries (in particular mount the valves on rollers / latch)

These characteristics are rather found on the monstrous Diesel Marins.
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by Woodcutter » 22/11/12, 21:25

chatelot16 wrote:it is not an interpolation: a single cylinder works exactly the same as 12 cylinders together in the same engine [...]
Well except that some things that eat power are distributed on a single cylinder instead of 12 and that on the other hand, as you have sketched, supercharging does not work on a single cylinder ... So no, this is not that simple.
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by chatelot16 » 22/11/12, 21:45

turbo supercharging works badly on single cylinders, but it's not just turbines, we can do the same thing with pistons, and if we do 47% with turbo and turboconpound, it is hoped to do better with pistons

I will do it for small fixed engine, where there is no problem of weight, but I think that it can then be useful for vehicle
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