You don't patent the thermodynamics, or even the concept of a car engine. You would patent the specific schematics, which, if you engineered in an original way, then you should own the rights to it for a period of time.

Everyone who labored to provide food, housing, utilities, etc. while you worked on it already got their piece of the pie when they accepted the wages they agreed to work for or the price they set for the goods. (The unfairness of wage labor is a separate issue to be addressed separately; it has nothing to do with IP laws, and it's the employers who are on the hook to compensate them more fairly, not the end consumer).

Anything else and suddenly you owe every grocer, farmer, and fieldworker a royalty for every dollar you make at your job; which you can clearly see is a foolish idea. You buy the fucking food and you eat it; it's yours, and whatever you decide to do with the energy it provides is no business of the people you bought it from.

Patents are supposed to be pretty specific and open to alternative implementations that don't infringe, but the USPTO has made some pretty awful decisions, especially around early home computers.