Otto cycle and Otto engine are common terms used interchangeably to represent a four-stroke internal combustion engine as seen on most cars. The term arose from the original engine's inventor, Nikolaus Otto. He created an engine that would evolve into the four-stroke engine mass produced for most vehicles. Running in an ideal state, the engine is meant to be thermally efficient, meaning it produces a low amount of heat and waste in proportion to the material it consumes. Key characteristics that define Otto engines are the use of cylinders and spark plugs to ignite the gaseous mixture which will drive the vehicle forward.
In 1862, a man by the name of Alphonse Beau de Rochas earned a patent for the invention of the four-stroke engine. He had the ideas and design for it, but he never built an actual working engine. German inventor Nikolaus Otto began expanding on Alphonse Beau de Rochas' ideas, and 14 years later, in 1876 he assembled the first four-stroke internal combustion engine along with the help of two gentleman named Wilhelm Maybach and Gottlieb Daimler. The original Otto engine used only one cylinder and several parts were mounted on the outside of the engine, which caused problems due to the collection of dirt and grime that interfered with the engine's performance.
What makes the Otto cycle special is the use of internal combustion to power it. The engine works smoother than previous engines, converts energy efficiently, and does not misfire or break constantly as previous engine types often did. The Otto cycle involves four steps, which is where the term "four-stroke" comes from. The first stage is the intake stage, in which air and gasoline fill the cylinders of the engine. Next, in the compression phase, pressure is applied to the gaseous mixture.
The next phase, the ignition phase, is what sets the Otto cycle apart from the diesel cycle. In the ignition phase, a spark fired from a spark plug causes the air and fuel mixture to ignite and turn the wheels to push the vehicle forward. Finally in the exhaust phase, the cylinder opens and releases the leftover mixture through the vehicle's exhaust system.
Diesel cycles are similar to the Otto cycle because it also uses a similar cycle of four stages, however diesel engines use compression instead of a spark to create the explosion which powers the vehicle. The engine compresses the air in the diesel engine's cylinder and adds heat. Fuel combustion creates heat in the cylinder and under the intense pressure the mixture begins combustion and forces the cylinder back up, which in turn rotates the vehicle's wheels. Though similar, the key difference is the diesel cycle's lack of a spark that differentiates it from the Otto cycle.