Engine of internal combustion without crankshaft

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Merlyn
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Re: Engine of internal combustion without crankshaft

Postby Merlyn » Mon Nov 23, 2015 4:16 am

What happened to the Wankel engine invention? No crank here.
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Big Pete
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Re: Engine of internal combustion without crankshaft

Postby Big Pete » Mon Nov 23, 2015 11:39 am

The Graphics are excellent and it certainly looks to be a very compact engine.

Not sure about the Physics/ Applied Thermodynamics of your assertions:

The work done on the piston, by the gas pressure is = piston area x mean pressure x length of stroke.
That determines the amount of power transferred to the crankshaft.

You can not get more power out of the crankshaft than you put in the piston!

Fuel is injected before TDC partly because of the ignition delay, ignition of the fuel is not instantaneous, and by starting combustion just before TDC I always understood that this reduced the shock loading on the combustion chamber and allowed the combustion to take place at the most efficient pointy, TDC i.e. at constant volume, combustion after this point is inherently less efficient as the gas does not fully expand before exhaust and therefore potential energy is wasted.

To me it appears that there is still a tangential force on the piston because the crank throw is rotating and does not remain lined up with the centre of the piston.

If the angle of the connecting rod is changed to produce more torque at the crankshaft, then greater pressure will be required to move the piston.

The principle increase in efficiency would appear to be due to maintaining "constant volume" long enough for all the fuel to be burnt, the reason this is not done in conventional engines is because all the components have to be much heavier to support the higher pressures generated and would also have to be ceramic coated to resist the high temperatures produced.
The reason traditional diesel engines burn fuel at both Constant Volume and Constant pressure is because although burning fuel at Constant Volume is more efficient, in terms of the Carnot cycle, it cannot generate much power. Burning fuel at Constant pressure as the gas expands during the power stroke maintains the temperature and pressures at the maximum permitted by the material design and therefore enables the engine to produce worthwhile power outputs in relationship to its weight and cost.

I think your logic in suggesting that such an engine would produce 1.83 times as much power as a conventional engine and have an efficiency of over 73%, compared to the 40% efficiency of modern Marine Diesels, is flawed.

BP
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Merlyn
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Re: Engine of internal combustion without crankshaft

Postby Merlyn » Fri Dec 04, 2015 5:58 am

Not convinced that this non duplex chain drive is entirely Gorviendo valve oscillation free here? Anyone?
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JollyJack
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Re: Engine of internal combustion without crankshaft

Postby JollyJack » Sun Dec 06, 2015 9:02 pm

Pescara Muntz had a free piston engine, opposed pistons with air cushioning linked by pivoting levers attached to the pistons.

https://books.google.ca/books?id=kCKMy7 ... tz&f=false
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Big Pete
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Re: Engine of internal combustion without crankshaft

Postby Big Pete » Mon Dec 07, 2015 1:41 am

I remember studying a "Free Piston Gasifier" Engine as a Cadet. It was a conventional engine with a crankshaft but no power output from the engine!
Instead the exhaust gas was used to drive a power turbine, which did all the work, it sounded pointlessly complicated to me at the time and still does!!

I just followed the link above again but now it is showing a different engine so I am a bit confused.
The first one I looked at had a "Crankshaft" but no connecting rods, instead the throws of the crank acted as gudgeon pins and, if I remember correctly, ran in eccentric bushes in the piston to allow for the changes in alignment during the stroke. So in effect these bushes were performing the role of very short connecting rods, but this idea could only work with an engine with a large bore and short stroke.

BP
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JollyJack
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Re: Engine of internal combustion without crankshaft

Postby JollyJack » Tue Dec 15, 2015 6:42 am

Starting the Pescara-Muntz compressor was a bit of an adventure. The outer crown of one of the pistons was within an enclosed cylinder and the piston acted as an air spring. The other piston pumped air as a compressor and the twp were connected by a rocking linkage.. Starting consisted of cranking a handle to pull the pistons apart and to compress a bloody great spring.,.,...as I remember, it was 21 1/2 turns. That number was very important to know, because that's when the spring released, throwing the pistons together at Mach 2.5! If everything was set up right, the air would be compressed between the pistons, fuel would be injected and off we'd go!
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