Shrad wrote ...

it also takes the huge benefit of oil thermal inertia

the energy needed to launch the system is quite important, but once it is running, the energy needed to sustain the reaction is quite low actually

as hot water in oil will be pressured in micro-bubbles, get calories needed to evaporate but be kept under pressure, the vapor will be generated all at once when it reaches the combustion chamber which has greater volume, no?

it has not the same drawbacks as standard vapor turbines with super saturated vapor, water droplets, entropy etc... without mentioning the maintenance required by a turbine

Patrick wrote ...

Fourth, i about 10 years ago investigated concentrating heat from pipes in the ground, since the ground is a constant heat source the deeper you go and doesnt rise and fall on the horizon. energy isnt a problem, but concentrating high volume to small value while increasing temp (not volating E conservation) is...

2bytes wrote ...

But as a MO S&T alumni I wish them the best of luck! I think testing beforehand to show energy output would have helped.

BigBad wrote ...

That's called a "ground source heat pump", and it's fairly well known tech, you can buy them off the shelf.

You can power them from electricity, and they're much more efficient than normal space heaters. Also, there's "air source heat pumps" that suck the heat out the air, which work down to about 7C.

Jrz126 wrote ...

I wonder if the flammability of oil will be a problem.

Dr. Slack wrote ...

The "re-inventing the steam engine" post hit the nail on the head.

If they are planning to get the oil to 700F, then that's plenty high enough for efficient use of a steam turbine. They are only using a small IC engine as that's what they had to hand, and their machining facilities probably don't run to turbines. I think a major design issue they have is going to be the operating temperature of that high thermal conductivity cylinder head. If cool, it will sap the thermal energy content of the oil and wreck the efficiency. If hot, it will be injecting steam rather than water. I suspect that a much lower thermal conductivity and thermal capacity head will fit better with their "oil boils water" heat transfer mode.

But then why have all that fiddly internal combustion/boiling mylarky, when external engines like Stirling, steam turbine or old skool reciprocating steam engine would probably be simpler to optimise?

By the way, don't use low grade heat "concentrated" by a heat pump to power a thermal (Carnot) engine. You've just connected the up side and the down side of a thermodynamic not-perpetual motion machine.