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Originally Posted by IamIan
That would be the obvious 1st issue I have with that chart.
But to be fair ... I do not know the context of the graph.
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Turned out that book was one I already had.
After looking again at the Heat Transfer in Engines Section ... where this graph came from ... it actually does explain the greater than 100% ... or at least tries to:
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Figure 10-1 Distribution of energy in a typical SI engine as a function of engine speed. Friction losses, which are generally on the order of 10%, add to the other heat losses and make the total energy distribution greater than 100%
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So the % on the left side of the graph is only representing the heat energy content of the fuel ... not all the energy content of the fuel... Which I think they should have included the term 'heat' on the left side to prevent that kind of confusion.
Any chemical energy content of the fuel that does not produce heat during combustion is excluded from the 100% on the left side of the graph ... meaning light energy is not part of that 100% ... pressure changes ( not caused by heat changes ) are also not included in that 100% on the left ... etc... etc.
I think it is a bad approach ... but they are actually not claiming greater than 100% fuel energy content ... they are counting effects of the complete energy content of the fuel in the graph body , but are excluding non-heat energy of the fuel from the % on the left.