nelitahtisia

Nelitahtisia is Finnish for four-stroke engines. The term refers to engines that complete a combustion cycle in four piston strokes over two crankshaft revolutions. In Finnish technical usage, nelitahtisia may describe four-stroke engines as a class, often contrasted with kaksitahtisia (two-stroke) engines.

Operation: The four strokes are intake, compression, power, exhaust. The intake stroke draws air, the compression stroke increases the mixture's pressure, the power stroke ignites and expands the gases, and the exhaust stroke expels spent gases. Valve timing is synchronized by a camshaft. Most four-stroke engines use separate lubrication and a crankcase oil sump; they may have overhead or side-valve configurations. Modern engines may use fuel injection and catalytic converters.

History: The four-stroke cycle, known as the Otto cycle, was developed in the 1870s by Nikolaus Otto and Gottlieb Daimler and became the basis for the modern internal combustion engines. Adoption spread to automobiles, motorcycles, aircraft, and industrial machinery. Improvements over time include variable valve timing, direct injection, turbocharging, and advanced emissions controls.

Applications and characteristics: Nelitahtisia engines are generally more fuel-efficient and produce less emissions per unit of power than two-stroke engines; they offer smoother operation, better torque distribution, and lower emissions with proper aftertreatment, but are typically heavier and mechanically more complex. Common applications include cars, trucks, motorcycles, lawn equipment, generators, and small industrial machinery.