Why is the two-stroke engine less efficient than the four-stroke engine?

The two-stroke engine is generally considered less efficient than the four-stroke engine primarily because of the less complete intake and exhaust processes. In a two-stroke engine, the design requires that both the intake and exhaust processes happen in a shorter time frame, and often they occur simultaneously. This means that there can be a significant amount of unburned fuel and exhaust gases being expelled with the fresh charge of fuel-air mixture entering the combustion chamber.

This overlap leads to inefficiencies, as not all of the fresh fuel is used in the power stroke, and some exhaust gases can dilute the new charge, resulting in incomplete combustion. As a result, the engine tends to produce less power and has lower fuel efficiency compared to a four-stroke engine, which has a dedicated cycle for intake, compression, combustion, and exhaust, allowing for more efficient and complete combustion of the air-fuel mixture.

In contrast, the other options suggest scenarios that are not the primary factors for the inefficiency of the two-stroke engine. The characteristics of the fuel mixture or the rate of combustion don’t play a central role in the fundamental design difference leading to efficiency disparities between the two engine types. The higher power-to-weight ratio is actually seen as an advantage in specific