A few questions.

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iron_goober
Posts: 27
Joined: Tue Jul 24, 2007 7:57 pm
First Name: John
Last Name: Roehling

A few questions.

Post by iron_goober »

Now, I am not an expert in these engines by any means, I have built a
few, and would like to build some more, but currently do not have the
means. But I have a couple of questions.

First question, with a pressurized engine, how large does the buffer
region have to be compared to the working volume of the engine to get
the thing to run. ( I have never built one, I am just guessing that if
the buffer region is the same size as the working volume, or smaller,
the engine wouldn't run because the expansion of the working volume
would be compressing the buffer region, and this would be too great a
resistance to overcome.)

Secondly, is there a problem with lack of leakage in a pressurized
engine? Say for example, you pressurize the buffer region and allow it
to slowly leak into the working volume. It then equalizes and you then
fire up the engine. BUT..because the working space is getting hotter,
the mean pressure in the working space gets higher and pretty soon,
because of lack of leakage to the buffer space, the buffer space
pressure is too low to push the power piston down for the compression
stroke.... Can this happen? I thought I read somewhere that a
pressurized engine would only run for about 15 minutes before
stopping, and I figured this was the reason.

I'd appreciate any input you can give me.
rtopf
Posts: 21
Joined: Fri Jun 28, 2002 6:49 am
First Name: Richard
Last Name: Topf

Response to A few questions.

Post by rtopf »

John,

There are few hard and fast rules for buffer space volume. It usually depends on the particular configuration. Engines with kinimatic linkages normaly require substancial space to fit the drive linkage. These would typically be much larger volumes and not a problem for buffer space pressure variations.

In a free-piston engine, the buffer space is purposly kept small so to provide a gas spring necessary to operate.


On the second item, I doubt that this would happen. You are also cooling the working fluid. If you don't provide enough cooling, the engine will quit when it gets hot. The pressure is always relitive. It will always equalize at some value with little difference between the average intrernal and buffer space pressure.
With a kinimatic engine, the flywheel does most the work of commpression.

Rick
iron_goober
Posts: 27
Joined: Tue Jul 24, 2007 7:57 pm
First Name: John
Last Name: Roehling

Response to A few questions.

Post by iron_goober »

Thanks Rick, I appreciate your input. And just for clarification I meant I read somewhere about a particular pressurized engine that would only run for about 15 minutes.
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