A Pulse Detonation Engine was an engine that used detonations to combust fuel. It was more efficient than a turbofan.
(Note: The background section of this page uses most of the same words as Terra Futura's page on turbofans to save time.)
Early airplanes used piston engines similar to those used in cars, buses, and trains. As planes became common in the 1930s, radial engines started being used. In the early years of air travel, the radial engine was the dominant aircraft engine. The radial engine was used to turn a propeller which helped the airplane fly. After World War II, gas turbine engines started being used for propulsion. The earliest were turboprop engines which continued to use a propeller. In more large scale aircraft, the turboprop was initially replaced with the turbojet. But turbojets were inefficient and noisy. So they were replaced with turbofans.
Turbofans became commonplace after they were first used on the Boeing 707. The jet age was born. This was followed by the 727. Early turbofans were low bypass. The fan had multiple stages. It could go faster. In the 1960s, turbofans became high bypass. There was only one fan. They more efficient than ever before. By the early 21st century, the fastest turbofan used for passenger travel was the Boeing 787. It reached Mach .89 once it finally got in the air. In the 21st century, turbofans were mainly used for subsonic travel. Other engines went supersonic.
Tech Level: 10-11
While a turbofan mixed air and fuel together, a pulse detonation engine used shockwaves to blow up a mixture of fuel and air. The shockwaves went through metal tubes. The first explosion was similar to a conventional turbofan. The process was called deflagration. The explosion was then funneled through a second chamber. This process detonated the fuel. A pulse detonation engine was 5-20% more efficient than a turbofan. It could travel up to Mach 4 or better. There were no valves because valves wore down quickly in these engines. These engines were not very common because of the jackhammer-like noise created by the engine. There were other engines that were better.