Why the thermal efficiency is low in 2-stroke engine?

The thermal efficiency of a 2-stroke engine is generally low due to its design, which leads to incomplete combustion and significant unburned fuel escaping during the exhaust phase. In 2-stroke engines, the intake and exhaust processes occur simultaneously, resulting in a loss of fuel and energy as fresh fuel can mix with exhaust gases. Additionally, the lack of a dedicated stroke for exhaust and intake reduces the time for proper combustion, further diminishing efficiency. These factors contribute to lower thermal efficiency compared to 4-stroke engines.