How a two-stroke engine works
Used in leaf blowers, lawn mowers, chain saws, mopeds and jet skis, the two-stroke engine is lightweight and powerful
— but it's one inefficient, dirty little machine.
Simplicity and its drawbacks
With an upstroke and a downstroke, the engine completes one cycle of internal combustion; hence the name. Automobile engines require four strokes to complete a cycle and are much heavier because they require extra systems and components, which make them cleaner and more efficient.
Two-cycle engines use metal fins to radiate heat from the motor. The fuel is a mixture of gasoline and oil, which lubricates the engine.
Exhaust is pushed out of the combustion chamber by fresh fuel, some of which escapes with the exhaust, giving two-stroke engines their characteristic oily, aromatic odor.
A greener option
Electric motors are a quieter, cleaner alternative, but they are less powerful and require recharging or extension cords. Although emissions are released by the coal-fired power plants that generate electricity, these gases are much less polluting than those from a two-stroke engine.
Fuel intake for air/fuel mixture
Transfer port ---------
On the downstroke, the piston compresses the air-fuel mixture in the crank case, forcing it through the transfer port into the combustion chamber.
As the crankshaft rotates, it powers fans, mower blades, wheels or propellers.
Exhaust pollutes the air with carbon monoxide, acid-rain-forming nitrogen oxides, particulate matter and unignited fuel.
SOURCE: United Nations Environment Program.