What's wrong with external combustion?

Question

I'm not talking about the classic steam engine, but a variation using a low boiling point liquid/gas to drive a turbine. It could be heated electricaly to provide vaporization.
The advantages of this system would be no polution ( it's a closed system) and less oil use. The only disadvantages I could think of would be the high pressure lines/tank and a possible lack of horsepower.
Let me know what you think.

To clarify, I'm thinking of using a liquid like freon that boils somewhere near -40c. To reliqifiy it use a compressor like an A/C unit. The heater dosn't have to be an open flame, just enough heat to boil it.
And yes, I know what is involved in producing electricity.

To clarify, I'm thinking of using a liquid like freon that boils somewhere near -40c. To reliqifiy it use a compressor like an A/C unit. The heater dosn't have to be an open flame, just enough heat to boil it.
And yes, I know what is involved in producing electricity. Also, using an electric motor would use many times the amount of power that a small heater would.

Answer 1

External combustion turbines are exactly how most electricity is generated in the US. The problem with your idea is that since these generators are at best 50% efficient, if you run your engine on electricity you are using twice the fuel (and generating twice the pollution) as you would heating the fluid by burning fuel directly. Also, since your engine has the same constraints on efficiency, it will be much less efficient than simply using an electric motor.

New engine ideas in general face an uphill battle because existing engines are already doing the job and have proven cost and reliability. To take business away from existing designs, yours has to have some compelling advantage, plus overcome customer fears about unknown cost and reliability issues. The laws of thermodynamics make it hard to make major improvements in efficiency, and the existing designs have the advantage of many years of refinement and an extensive support system.

Additional comments: A "small heater" will produce only a small amount of power. The facts of life (aka the laws of thermodynamics) for thermally powered engines are that you will get out as mechanical energy less than half what you put in as thermal energy. Electric motor efficiency, on the other hand, can be better than 95%.

Answer 2

heres your flaw:

To get the gas back into a liquid you would need just as much energy if not more due to heat and friction loss. now you are using twice the energy to do half the work. very inefficient.

you also say there would be no pollution because you are using electricity and its a closed system. why not just use an electric motor? it only uses electricity and creates no pollution. the thing is, electricity is not made pollution free. 80% of all electricity is created from coal furnaces, which put out more pollution than gasoline.

Answer 3

It's not clear what you are trying to accomplish. But an external combustion engine for automotive use was invented about 200 years ago -- it was called the Stirling engine. See below.

Answer 4

Electricity is a very expensive way to heat anything.