Talk:Thermal efficiency

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What in blazes is going on in the thermal efficiency section? E_hp - E_r = 1 ?!?!

So E_hp was greater than one to begin with?! Something needs explanation or changing here! —The preceding unsigned comment was added by 165.124.116.206 (talk) 23:06, August 22, 2007 (UTC)

Internal combustion engines are not "thermal devices" like furnaces or steam engines. Heat is a byproduct of burning fuel to generate pressure. Heat is actually unwanted, thus radiators and so on. External combustion engines are "thermal devices" because they specifically use heat, to generate pressure. —Preceding unsigned comment added by Arantius (talk • contribs) 16:44, 3 January 2008 (UTC)[reply]

Pressure (useful work) is generated by the heating of the air inside the piston of an internal combustion engine by the perfect gas law P=Rho*R*T. ...so it is a cyclic thermal device as it converts heat to work and obeys the 2nd law of thermodynamics. The "unwanted heat" is due to the inherent inefficiency, as stated by the 2nd law