I'm in the large diesel engine business - I have to guarantee efficiency values every day. Today's large diesels, both two stroke and four stroke, (I mean LARGE, like 10,000 - 100,000 HP) achieve an efficiency measured at the crankshaft of 50%. That is to say that for every 100 units of fuel energy burned in the engine, 50% goes to mechanical power. The other 50% is mostly rejected by heat. Heat into the block cooling circuit, the lube oil, and the charge air cooler (intercooler). Some heat is just radiated also.

The large diesel is the most efficient prime mover available commercially today. A smaller diesel might achieve a shaft efficiency on the order of 40 - 45%.

A gasoline engine such as those commonly used for automotive use is in the region of 30 - 35%, typically.

A gas turbine (i.e. "jet engine") is generally less efficient. In simple cycle use, which means no heat recovery from the exhaust, the most efficient gas turbine today is approximately 40 - 41% while most average considerably less. Some very small turbines, like helicopter engines, are down in the 28 - 30% range or worse. But large gas turbines used for power generation typically are placed in "combined cycle" wherein the hot exhaust goes through a boiler to make steam, which is then used to drive a steam turbine and make more electricity. Doing this, efficiency today can reach approximately 60%. This is only practical for stationary use.

Hope this info helps.

Rgds,
Chris W.
I do it for a living.