two-stroke spark ignition engine is an old, and reasonably simple
technology. Sometimes called the Clerk Cycle engine, the concept was
patented in 1881 by Sir Dugald Clerk. In contrast to the four-stroke or
Otto Cycle engine, which produces a power stroke on every fourth stroke,
the two-stroke or Clerk Cycle engine provides a power stroke for every
The original Clerk
two-stroke engine used a second piston as a charging pump. Ten years later
(1891), Day eliminated this device and simplified the engine by using
pressure from a sealed crankcase. This is the version that we see most
often, and is used as a baseline in understanding the technology.
Learn more about him and his engine here!