How efficient is steam power compared to internal combustion? Can you get a steam engine that provideo the same power per pound as an internal combustion?
What about a practical sterling engine?
I'm not an expert on engines. From my understanding of chemistry:
Burning black coal (~90% carbon), the equation of combustion is
C + O2 -> CO2; /\H = -30kJ/mol
In the case of octane, the main component of normal car petrol:
C8H18 + (12.5)O2 -> 8CO2 + 9H2O; /\H = -5054kJ/mol
So what does all this mean?
For every mole of black coal burned, approximately 30 kJ of energy is released.
For every mole of petrol burned, 5054 kJ of energy is released.
One mole of carbon is defined as being 12 grams. Extending this, 1 mole of octane is 114 g.
:. 30k/12 = 2500 J of energy per gram of coal (actually about 1.1g of coal due to impurities).
5054k/114 = 44333 J of energy per gram of petrol (actually about 1.05g of petrol due to impurities).
So, to have an engine that provides same power per unit mass, you would need to condense the coal into a space of about 1/18 of its normal size. Which is a bit ridiculous. A much more practical way of doing this is to upsize the engine to be 18 times bigger. A normal car engine, after a quick internet search, is approximately 1000 cm3, or a cube of 10cm side length. For a steam engine of the same power, one would need a cube of side length 26.2cm.
I don't know how the engine sizes would scale in the case of a tank, but using the simple idea that a tank requires 10 car engines, due to having a mass ten times greater, this engine would now have a side length of close to 60cm (2 ft).
Simply put, the engines can be done. The fuel (coal), is the most difficult aspect for steam engines.
- BNC