as the volume increases as the piston comes down after the ignition in a cylinder of an engine, how much is th

Question

How much is the pressure drop as the piston comes down after an ignition..let's say starting pressure is 800psi....stroke is 4in. and the area of the piston is 4in. diameter...?
looking for feasability using hydraulic fluid rather then connecting rod and crankshaft and using a 6in diameter gear/driveshaft instead.....

Answer 1

Mr JOM is right. The piston is forced down by the ignition of the feul, not by the rotation of the crank shaft.

BUT heres your answer. If the chamber pressure is 800 PSI at TDC, The pressure at BDC would be zero. If the piston chamber was sealed there could be a starting pressure, but like mrjom said, you need another motor to turn the crank sharf to drive the piston and make compression, or pressure.

Using hydrolic fluid instead of a conn rod wouldnt work. The conn rod gives the power from the piston to the shaft and limits the pistons travel in both directions. Let me put it this way, you could do it with hydro, but why? there wouldnt be a gain of any sort, and you still need another source of energy to push the fluid. Thats the point of an internal combustion engine.

Without knowing what your goal is, I can say that if you reeeeeally wanted to use hydro power to drive a piston, you could make a water wheel that does that and it could be made self driven by using the piston to pump fluid to the top of the wheel. It would need a little help getting started but could run on its own. also, the exhaust valves open on the exhaust stroke, just before TDC, and not at BDC on the combustion stroke (power). If it opened on the combustion stroke all the power from combustion would be lost.

Answer 2

The is a direct relationship between pressure and volume ( assuming the temperature remains unchanged). i.e. If you increase the volume by, say, a factor of 3, then you decrease the pressure to 1/3. This, unfortunately, doesn't do much good in your calculations because the volume and pressure of the exploding gases rapidly increases as the piston goes down until the exhaust valve opens near the bottom of the stroke

Answer 3

Actually the pressure increases, because you have experienced a controlled explosion in the cylinder.
I believe you are talking about building a type of hydraulic motor that would need to be driven by another engine. Hydraulic fluid is virually incompressible, this why hydraulics are more efficient than pneumatics when it comes to work movement.

Answer 4

this might help:
http://www.tfxengine.com/NaturallyAspiratedEngineData.html
It demonstrates the pressure in the cylinder as it is running.