Final answer:
The theoretical power advantage of a 2-stroke engine over a 4-stroke engine is that it can complete its power cycle in just two strokes, potentially offering twice the frequency of power strokes and theoretically twice the power of a similarly sized 4-stroke engine.
Step-by-step explanation:
The theoretical power advantage of the 2-stroke engine over the 4-stroke engine lies in its cycle completion. In a 4-stroke engine, as depicted in Figures 15.17 and 15.19, the heat transfer into work happens through four distinct strokes: intake, compression, power, and exhaust. These steps complete the cycle of the engine, bringing the air-fuel mixture back to its starting condition.
On the other hand, a 2-stroke engine completes a power cycle with just two movements of the piston, achieving an intake and exhaust stroke combined with the compression and power stroke. This leads to one power stroke per revolution of the crankshaft, as opposed to the 4-stroke engine which produces one power stroke every two revolutions. Therefore, theoretically, a 2-stroke engine could produce twice as much power as a 4-stroke engine of the same size, because it has twice the frequency of power strokes. However, in practical applications, various factors like fuel efficiency, emissions, and engine wear can affect the actual performance difference.