"Spring hasn't really arrived until you are awakened by the first lawn mower."
Source unknown
To some it is the one of the most annoying sounds made by machines, while to others it has an almost musical quality. We are talking, of course, about the buzzing noise of the two-stroke engine. From motorbikes to lawn mowers this invention has been the model of simplicity in the world of internal combustion, and its modern design originated with British engineer Joseph Day (1855-1946).
An earlier two-stroke engine had been devised by Dugald Clark in 1880, but it lacked the simplicity of Day's version. Using just three moving parts, Day's engine used the pressure below the piston to force the fuel and air into the combustion chamber while simultaneously pushing the exhaust gases out. This meant that a pulse of power could be sent along the drive shaft with every revolution—an efficiency improvement over the four-stroke, which sends a pulse of power every two revolutions.
The simple design of the two-stroke has led to its wide popularity. Most high-performance motorbikes use them, as do outboard motors for boats. But despite the advantages of its high power-to-weight ratio, the two-stroke is actually more polluting than the four-stroke. Each time a fresh charge of fuel, air enters the combustion chamber, a small amount leaks out with the exhaust, which can be seen as the oily sheen on the water around an outboard motor and smelled as a distinctly oily aroma at go-kart tracks. Current environmental concerns mean that, unless significant improvements are made to two- stroke technology, we may not see them around for much longer.
