Heat Engines

Sun Powered Turbo Generator Idea by Peter L. Peres

Internal injection flash steam heat engine.

David Wells says:

1. Mechanical engines life time is improved dramatically if there is LUBRICATING FLUID allowed to keep sliding parts from touching. The process is called hydrodynamic film lubrication, and is the reason why pistons don't wear out, why you need oil in your crank case if you want to drive more than 10 km, and so on. So, if you have to run on steam, you have to have an oil that is compatable with steam to keep things lubricated. Such oils exist.
2. The "mechanical efficiency" or "adiabatic efficiency" of mechanical expansion machines reduces in known and predictable ways in proportion to the "break mean effective pressure" and in proportion to the operating speed.
2A: Generally, the "ideal efficiency" will go directly as the mean operating pressure,
2B: friction will generally go up or down proportionally as the speed.

So, say the numbers on the expander show it to have a 70% efficiency running on air at 8 atmospheres of pressure, and it puts out, say, a kilowatt according to the vendor. You want to make some estimates for the same device running in other conditions.
Your goal: to estimate the "ideal mechanical output", the estimated frictio n, and estimated ideal output and actual output running at the same rotational speed but with half the supply pressure.
By 2A, That means the device has effectively a mechanical drag or loss of roughly 0.3 kW, and the "ideal mechanical output" was 1 + 0.3 or 1.3 kW. If you take the same machine, run it at the same SPEED, but run it at half the pressure, the theoretical ideal mechanical output would be reduced by half, or 1.3 kW x 0.5 = 0.65 kW. BUT, since you are running it at the same SPEED, the mechanical frictional losses will be expected to be identical, i.e. 0.3 kW, and you would expect the device to put out about 0.65 - 0.3 kW or 0.25 kW.
So, the "adiabatic efficiency" or the "mechanical efficiency" at the same speed but half the operating pressure drops to 0.25/0.65, or to about 34%. Quite a drop!