Nope, sorry. Such assumptions are not very, very conservative. They are very, very unrealistic, to the point of being a fantasy. As I have said before, the exercise become unhelpful when you assume there is fuel but no tanks or burners.
There are heat producing machines at 100% thermal efficiency, and rockets at 96% fuel content. Why quibble over 5% ?
As I've said again and again, these are UPPER BOUNDS which CANNOT be exceeded.
What should one do ... postulate a design and say that "the fuel content is 50%" -- then someone will pop up and say "but I can design it with 50.5% efficiency, so your conclusion is wrong."
eg http://newenergytimes.com/v2/conferences/2011/ICCF16/pres/ET01Grabowski-RobustPerformanceValidation.pdf
"The test should be conducted for a sufficient continuous period to
strongly exclude the possibility of stored chemicals generating the
observed energy output."
Where do you put "strongly exclude" ? 50%, 50% ? 49% 51% ?
Setting it at 100% fuel 100% efficiency puts it BEYOND argument.
