Nicolaus Otto patented the first successful compressed charge, four-stroke cycle engine in which year?

1876.

While Alphonse Beau de Rochas described the theoretical principles of the four-stroke cycle in 1861, it was Nicolaus Otto who successfully engineered and patented the first truly functional realization of this concept in 1876. This machine, known as the Otto Silent Engine, required four distinct piston strokes—intake, compression, power, and exhaust—to complete one power cycle. The key to its success, and its dramatic superiority over preceding designs like the Lenoir engine, was the mandatory compression stroke which allowed for far greater thermal efficiency by increasing the pressure before the combustion event.