Pulsejet

A pulsejet engine is a remarkable jet engine that operates by using combustion in pulses, making it distinct from traditional jet engines. Their simplicity and lightweight design sets pulsejet engines apart, making them ideal for certain applications.

The most well-known example of a pulsejet engine is the Argus As 109-014, which powered Nazi Germany's V-1 flying bomb during World War II. This engine is a valved or traditional pulsejet engine, which uses a set of one-way valves to allow incoming air to pass through. When ignited, these valves close, forcing the hot gases to exit only through the engine's tailpipe, producing forward thrust.

Another type of pulsejet engine is the valveless pulsejet, also known as the acoustic-type pulsejet or aerodynamically valved pulsejet. Valveless pulsejet engines operate by using a series of resonant shock waves between the open end of the engine and a closed end, producing thrust in the process. While less common than traditional pulsejet engines, valveless pulsejet engines are still used in some applications.

Despite their simplicity, pulsejet engines have limitations, including poor compression ratios and low specific impulse. However, researchers are continually working to improve pulsejet engine technology. One promising area of research is the pulse detonation engine, which involves repeated detonations in the engine and has the potential to produce high compression and reasonably good efficiency. Pulse detonation engines are still in the experimental stage, but they hold great promise for the future of jet propulsion.

History

The pulsejet engine has a rich and complex history, spanning several centuries and involving numerous inventors and engineers. The first patent for a steam pulsejet engine was filed by Russian inventor Nikolaj Afanasievich Teleshov in 1867, while the first working pulsejet engine was patented in 1906 by Russian engineer V.V. Karavodin. The valveless pulsejet engine, a precursor to all valveless pulsejets, was developed by French inventor Georges Marconnet in 1908. He patented the engine in 1908, and in 1913, Ramón Casanova in Spain patented a pulsejet in Barcelona. The pulsejet engine gained widespread recognition in the 1930s, with notable contributions from American inventor Robert Goddard and German engineer Paul Schmidt.

 Schmidt's modifications to the intake valves earned him the support of the German Air Ministry in 1933. The valveless pulsejet saw its first widespread use in the Dutch drone Aviolanda AT-21, and the pulsejet was further perfected by the Argus Company during World War II. The Argus As 109-014 was instrumental in the development of jet propulsion technology and was used in the V-1 flying bomb. Despite their limitations, pulsejet engines have made significant contributions to aviation history and continue to inspire new developments in jet engine technology. The legacy of the pulsejet engine can be seen in modern-day aircraft and rocket engines, making it a vital part of technological advancement.

Argus As 014

The Argus As 014, also known as the 109-014 by the RLM, was a pulsejet engine that was utilized in the V-1 flying bomb of World War II. It was the first model of pulsejet engine to be mass produced and was also manufactured under license in Japan during the final stages of the war, where it was known as the Kawanishi Maru Ka10 for the Kawanishi Baika kamikaze jet.

After the war, the United States reverse-engineered the design of the As 014 and used it to power the Ford PJ31 for the Republic-Ford JB-2 cruise missile and the experimental USAAF-developed JB-4 television-guided bomb.

The development of the Argus As 014 began in 1928 when inventor Paul Schmidt started designing a new type of pulse jet engine in Munich. He received a patent for his design in 1931 and received support from the German Air Ministry in 1933. In 1934, Schmidt and Professor Georg Madelung proposed a "flying bomb" powered by the pulse jet engine to the Ministry and received a development contract the following year. In 1938, Schmidt demonstrated a pulse jet-powered pilotless bomber, but the project was ultimately shelved by the Air Ministry due to its lack of range and accuracy, as well as its high construction costs. However, the Argus Company began working on a flying bomb using Schmidt's engine that same year, and Schmidt joined Argus in 1940.

The engine was made from a sheet of mild steel rolled into a tube, and was a resonant jet that could run on any grade of petroleum fuel. At the front of the engine were a spring flap-valve grid, a fuel inlet valve, and an igniter. The shutter system was not expected to last longer than one flight, as it had an operational life of approximately one hour. Contrary to popular legend, the engine could operate while the V-1 was stationary on its launch ramp after reaching minimum operating temperature.

Ignition was initiated by an automotive-type spark plug located about 0.75 m (2 ft 6 in) behind the shutter system, with electricity supplied from a portable starting unit. Acetylene was used for starting, and a panel of wood or similar was often held across the end of the tailpipe to prevent fuel from diffusing and escaping before ignition was complete.

Once the engine was started and the temperature rose to the minimum operating level, the external air hose and connectors were removed, and the resonant design of the tailpipe kept the pulse jet firing. Each cycle or pulse of the engine began with the shutters open, with fuel injected behind them and ignited, and the resulting expansion of gases forced the shutters closed. As the pressure in the engine dropped following combustion, the shutters reopened and the cycle was repeated, roughly 45 to 55 times per second. The electrical ignition system was only needed to start the engine, as a V-1 carried no coils or magnetos to power the spark plug once launched.

While the engine was simple and produced a good amount of thrust at 2.7 kN (660 lbf), it was inefficient, limiting the range of the V-1 to 240–400 km (150–250 mi). The resonant frequency of the combustion process was around 45 Hz, giving the V-1 its nickname "buzz bomb" or "doodlebug" due to the sputtering sound it produced.

SNECMA Escopette Pulsejet Engine

In 1943, SNECMA began working on pulse jets to create a simple jet engine. The Escopette (Carbine) model was the first of SNECMA's pulse-jet models and is considered an artefact of this early work. Unlike a ramjet engine, it is capable of developing power while static. It is of the resonant-duct type and has no moving valves. Power is obtained through the successive bursts of a carbureted mixture produced at a rate of 100 per second. The pressure waves caused by these bursts are carefully controlled and are reflected in expansion waves on both ends of the engine.

In 1950, an Emouchet glider fitted with four Escopettes made its first flight. SNECMA continued to develop higher-powered pulsejets in the 1950s for target drones, helicopter rotor-tip propulsion, and other industrial uses.

Design

Pulsejet engines are an intriguing area of engineering that has captured the attention of enthusiasts and researchers alike. These engines are known for their simplicity and high noise levels, and they operate on the Lenoir cycle, which employs acoustic resonance to drive compression and limits the maximum pre-combustion pressure ratio. Pulsejet engines have found use in a variety of applications, including experimental helicopters and model aircraft. Valved engines use mechanical valves to control the flow of expanding exhaust, which allows fresh air and more fuel to enter through the intake. Valveless engines, on the other hand, excel in flight due to their lack of valves, enabling them to operate at high speeds without interruptions. Thrust in pulsejet engines can be increased by using an augmenter, a specially shaped duct placed behind the engine that harnesses aerodynamic forces in the pulsejet exhaust to even out the pulsating thrust.

While the larger the augmenter duct, the more drag it produces, it can significantly increase the thrust of a pulsejet with no additional fuel consumption. Despite their limitations, researchers are continually working to improve pulsejet engine technology, with promising developments in pulse detonation engines. These engines involve repeated detonations in the engine and have the potential to produce high compression and reasonably good efficiency. Although pulse detonation engines are still in the experimental stage, they hold great promise for the future of jet propulsion. Overall, pulsejet engines are an exciting area of study and innovation. From their unique design to their remarkable capabilities, these engines have contributed significantly to aviation history and continue to inspire new developments in jet engine technology.

Future

Pulsejets are used today in target drone aircraft, flying control line model aircraft (as well as radio-controlled aircraft), fog generators, and industrial drying and home heating equipment. Because pulsejets are an efficient and simple way to convert fuel into heat, experimenters are using them for new industrial applications such as biomass fuel conversion, and boiler and heater systems.

Some experimenters continue to work on improved designs. The engines are difficult to integrate into commercial crewed aircraft designs because of noise and vibration, though they excel on the smaller-scale uncrewed vehicles.

The pulse detonation engine (PDE) marks a new approach towards non-continuous jet engines and promises higher fuel efficiency compared to turbofan jet engines, at least at very high speeds. Pratt & Whitney and General Electric now have active PDE research programs. Most PDE research programs use pulsejet engines for testing ideas early in the design phase.

Boeing has a proprietary pulsejet engine technology called Pulse Ejector Thrust Augmentor (PETA), which proposes to use pulsejet engines for vertical lift in military and commercial VTOL aircraft