Pressure gain combustion

Last updated

Pressure gain combustion (PGC) is the unsteady state process used in gas turbines in which gas expansion caused by heat release is constrained. First developed in the early 20th century as one of the earliest gas turbine designs, the concept was mostly abandoned following the advent of isobaric jet engines in WWII. [1]

Contents

As an alternative to conventional gas turbines, pressure gain combustion prevents the expansion of gas by holding it at constant volume during the reaction, causing an increase in stagnation pressure. The subsequent combustion produces a detonation, rather than the deflagration used in most turbines. Doing so allows for extra work extraction rather than a loss of energy due to pressure loss across the turbine.

Several different variations of turbines use this process, the most prominent being the pulse detonation engine and the rotating detonation engine. In recent years, pressure gain combustion has once again gained relevance and is currently being researched for use in propulsion systems and power generation due to its potential for improved efficiency and performance over conventional turbines. [2] [3] [4]

History

Early history

Prototype of the Holzwarth Explosion Turbine. Deutsches Museum - Holzwarth-Gasturbine.JPG
Prototype of the Holzwarth Explosion Turbine.

Gas-powered turbines have been researched since the late 18th century, starting with John Barber's 1791 patent. Over a century later, Ægidius Elling built a turbine in 1903 which generated 11 bhp (8.2 kW), the first gas turbine to produce net positive work. In 1909, the first pressure gain combustion turbine was built by Hans Holzwarth. Initially operating at 200 bhp (147 kW), subsequent improvements to the engine increased its power output to 5000 bhp (3728 kW) by 1939. However, the aptly named Explosion Turbine would lose popularity among engineers and inventors as continuous combustion designs gained traction due to their use in jet engine prototypes. [5] [1]

Renewed Interest

The concept of pulsed propulsion is neither new, nor exclusive to pressure gain combustion. In fact, the German V1 missile utilized a pulse jet operating at 45 Hz. During the space race, NASA's Project Orion concept utilized force from nuclear explosions ignited behind the spacecraft to generate thrust. This process is known as nuclear pulse propulsion and is stylistically similar to the pulse detonation engine. [6]

PGC powered aircraft PDE-powered aircraft.jpg
PGC powered aircraft

In the mid-20th century, US aeronautical scientists and engineers were trying to study the properties of detonation waves. To do this, a primitive rotating detonation chamber of created. This development became the basis for the rotating detonation engine, one of the leading PGC engine concepts, although it was largely ignored at the time due to its instability. [7]

However, as gas turbines are becoming more and more optimized, PGC research is now gaining traction in aircraft propulsion, power generation, and even rocket propulsion. In January 2008, a pulse detonation-powered plane completed its first flight as a cooperative project between the Air Force Research Laboratory and Innovative Scientific Solutions, a research and product development company. Currently, various organizations have developed working PGC engines (mostly RDEs), but none have been put to commercial use due to developmental challenges. [7] [8] [9]

Concept & Comparison to Convention Turbines

Overview of Conventional Turbines

From points 2 to 3, the pressure increase stops while volume increases, limiting the net work being done by the Brayton cycle. T cycle Brayton.png
From points 2 to 3, the pressure increase stops while volume increases, limiting the net work being done by the Brayton cycle.

The majority of gas turbines consist of an intake through which atmospheric air enters the turbine. The air is then pressurized through a compressor before mixing with fuel. The air-fuel mixture, also known as the working fluid, is combusted in a deflagration (a combustion reaction propagating at subsonic speed), which causes the mixture to expand in volume while maintaining constant pressure. Finally, the combustion product is ejected out of the exhaust to produce thrust. This process is known as the Brayton Cycle and has been used as the standard method of jet propulsion and turbine design for about a century. [10] [11]

Humphrey Cycle

The same pressure to volume graph for the Humphrey cycle shows a pressure increase at constant volume, maximizing its net work. T cycle humprey.png
The same pressure to volume graph for the Humphrey cycle shows a pressure increase at constant volume, maximizing its net work.

Contrasting against the Brayton Cycle used in most turbines, Pressure Gain Combustion is based on the Humphrey Cycle. Instead of an isobaric system in which gas volume expands as heat is added to the combustion chamber, the volume of working fluid stays constant as its pressure increases during combustion. [12] While the Brayton Cycle describes a subsonic deflagration, the Humphrey Cycle occurs in a detonation (A combustion reaction propagating at supersonic speed). [13] The reaction occurs so quickly that the mixture doesn't have time to expand, causing a pressure gain, before being ejected through the exhaust to produce thrust. The whole process occurs rapidly, and turbines will produce anywhere from 20 to 200 detonations per second. [14] [15]

Because the working fluid is combusting at a constant volume, there is no pressure loss across the turbine, which increases the net work generated by each cycle. However, since work is done by a series of detonations, rather than a constant reaction generating thrust, the process is naturally more unsteady compared to a conventional turbine. [3] [16]

Designs & Variations

Pulse Detonation Engine

The simplest modern PGC turbine is the Pulse Detonation Engine. Consisting of almost no moving parts, the PDE is externally similar to a ramjet, a type of jet engine without compressor fans that is viable only at supersonic speeds. First, air enters the intake nozzle and travels directly to the combustion chamber to be mixed with injected fuel. There, the mixture is ignited while the front of the chamber closes, producing a detonation wave which both compresses and combusts the mixture, before the working fluid is ejected at supersonic speeds through the exhaust. [17] [6]

Because of the engine's simplicity and anatomical similarity to ramjets and scramjets, pulse detonation engines can be implemented as a combined-cycle engine, which can improve the performance and reliability of ramjets. Conventional combined-cycle engines have complex moving parts that are essentially rendered useless at high speeds, an issue that PDE/ramjet drives will not have. [17] [6]

Rotating Detonation Engine

A prototype RDE developed by NASA for rocket propulsion NASA RDE.jpg
A prototype RDE developed by NASA for rocket propulsion

Apart from PDEs, there exist multiple other PGC engine concepts, including Resonant Pulse Combustors, and Internal Combustion Wave Rotors to name a few. However, the majority of modern PGC research is concentrated around the rotating detonation engine (RDE), which aims to solve many of the issues encountered by PDEs. [3]

The main drawback of pulse detonation is the intermittent nature of the combustions. Not only is the reaction hard to control, but the intermittent combustion also loses power due to the time it takes to refuel the combustion chamber after purging, in which no thrust is produced. [17] [6] The rotating detonation engine aims to address both these problems. While PDEs involve a series of repeating detonations to ignite batches of air that enter the combustion chamber, RDEs can circumvent this by utilizing a single detonation wave that rotates around the space in between concentric cylinders. A continuous air intake flows through the cylinders, which compresses and combusts as it passes through the rotating detonation wave. This eliminates the need to constantly produce detonations since it only uses a single cyclic detonation, and it allows for a steadier constant flow, instead of the pulsing thrust produced by PDEs. [18] [19]

Applications & Technical Challenges

Propulsion

Modern chemical rockets still utilize deflagration reactions to generate thrust, which are getting increasingly optimized to their limits. As a result, pressure gain combustion engines, mostly RDEs, to garner significant attention as a possible method of improving rocket performance. Currently, pressure gain rocket engines are being researched by space agencies in multiple countries, including NASA and JAXA, as well as numerous universities and private companies. [9] Detonation propulsion, which is more energy efficient than conventional deflagration reactions, may increase efficiency by 5-10%, which can both reduce rocket mass and increase payload size. [20]

As mentioned previously, pressure gain turbines have also been researched and developed extensively for use in aircraft propulsion. Pressure gain combustion engines can both improve the performance and reduce the complexity of combined ramjet/scramjet engines through their shared design similarities. Furthermore, this may even allow PDE/RDE combined ramjets to be utilized at conditions unsuitable for conventional ramjets. In addition, pressure gain turbojets require significantly less complexity, especially in the compressors, compared to regular turbines. This will not only save resources in manufacturing but also allow for designs to produce higher thrust in smaller engines. [6] [19]

Energy Generation

Apart from nuclear fission, natural gas contains the highest energy density of widely used fuels. [21] As such, to reduce carbon emissions, electricity-generating plants are increasingly turning to gas turbines from crude oil and coal. While conventional turbines generate large amounts of energy more efficiently than other fossil fuels, just as in aerospace, they are beginning to reach their limits. [22]

Similar to its potential use in propulsion, pressure gain combustion turbines can offer an improvement to gas power plants. In addition to better efficiency, RDEs can operate at much higher hydrogen concentrations, further improving performance because of hydrogen's higher energy density compared to petrochemicals. The relative simplicity of RDEs can also improve reliability and ease of maintenance, though that may be counterbalanced by the increased stress put on the engine by the process itself. [22]

Engineering and Implementation Challenges

While PGC offers improved performance and efficiency, there are serious flaws and challenges that researchers were initially unable to solve, preventing the technology from being widely used.

Since PDEs are effectively intermittent explosion drives, the cycle they run on is far more unsteady and harder to control than conventional turbines. This makes PDEs very difficult to integrate into airframes, as the high energy pulsing of the engine can cause the inlet to unstart and stop the reaction, in addition to putting high stress on the nacelle or any other adjacent parts. The noise from the exhaust is also a concern. In testing, the highly energetic detonations produced up to 122 dB at a distance of 3 m in a 20 Hz PDE. For scaled-up commercial units operating at higher power and frequency, noise pollution will be a serious issue if effective damping measures are not implemented. [6]

Moreover, due to the high energy required to initiate detonations, PDEs with shorter combustion chambers will need to utilize deflagration combustion at initial ignition and accelerate pressure waves through a process called Deflagration to Detonation Transition (DDT). This requires placing obstacles in the path of the deflagration wave to induce turbulent flow, which speeds up the wave but requires more complexity in the engine structure. [17]

While RDEs solve many of the problems encountered in PDEs, it isn't without its flaws. The constant flow of the engine, coupled with the need to sustain the detonation, requires a tremendous intake of air to be rapidly mixed with the fuel in a shorter distance than most PDEs, which are normally quite elongated. In addition, the stress placed on the engine by the detonation process was simply too much for the engine to withstand during the early years of development. However, advancements in material science and manufacturing processes have improved the feasibility of RDEs to the point where research and development is believed to be worthwhile by many organizations. [9] [18] [19]

See also

Related Research Articles

<span class="mw-page-title-main">Jet engine</span> Aircraft engine that produces thrust by emitting a jet of gas

A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.

<span class="mw-page-title-main">Ramjet</span> Supersonic atmospheric jet engine

A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to Mach 6.

<span class="mw-page-title-main">Pulsejet</span> Engine where combustion is pulsed instead of continuous

A pulsejet engine is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically. The best known example is the Argus As 109-014 used to propel Nazi Germany's V-1 flying bomb.

<span class="mw-page-title-main">Aircraft engine</span> Engine designed for use in powered aircraft

An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Aircraft using power components are referred to as powered flight. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many small UAVs have used electric motors.

<span class="mw-page-title-main">Turbojet</span> Airbreathing jet engine which is typically used in aircraft

The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine. The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.

A pulse detonation engine (PDE) is a type of propulsion system that uses detonation waves to combust the fuel and oxidizer mixture.

<span class="mw-page-title-main">Detonation</span> Explosion at supersonic velocity

Detonation is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with speeds about 1 km/sec and differ from deflagrations which have subsonic flame speeds about 1 m/sec. Detonation is an explosion of fuel-air mixture. Compared to deflagration, detonation doesn't need to have an external oxidizer. Oxidizers and fuel mix when deflagration occurs. Detonation is more destructive than deflagrations. In detonation, the flame front travels through the air-fuel faster than sound; while in deflagration, the flame front travels through the air-fuel slower than sound.

<span class="mw-page-title-main">Brayton cycle</span> Thermodynamic cycle

The Brayton cycle, also known as the Joule cycle, is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. It is characterized by isentropic compression and expansion, and isobaric heat addition and rejection, though practical engines have adiabatic rather than isentropic steps.

<span class="mw-page-title-main">SABRE (rocket engine)</span> Synergetic Air Breathing Rocket Engine - a hybrid ramjet and rocket engine

SABRE is a concept under development by Reaction Engines Limited for a hypersonic precooled hybrid air-breathing rocket engine. The engine is designed to achieve single-stage-to-orbit capability, propelling the proposed Skylon spaceplane to low Earth orbit. SABRE is an evolution of Alan Bond's series of LACE-like designs that started in the early/mid-1980s for the HOTOL project.

A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, burner can, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high-pressure air by the compression system. The combustor then heats this air at constant pressure as the fuel/air mix burns. As it burns the fuel/air mix heats and rapidly expands. The burned mix is exhausted from the combustor through the nozzle guide vanes to the turbine. In the case of ramjet or scramjet engines, the exhaust is directly fed out through the nozzle.

<span class="mw-page-title-main">Jet propulsion</span> Thrust produced by ejecting a jet of fluid

Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet. Reaction engines operating on the principle of jet propulsion include the jet engine used for aircraft propulsion, the pump-jet used for marine propulsion, and the rocket engine and plasma thruster used for spacecraft propulsion. Underwater jet propulsion is also used by several marine animals, including cephalopods and salps, with the flying squid even displaying the only known instance of jet-powered aerial flight in the animal kingdom.

<span class="mw-page-title-main">Valveless pulsejet</span> Simplest known jet propulsion device

A valveless pulsejet is the simplest known jet propulsion device. Valveless pulsejets are low in cost, light weight, powerful and easy to operate. They have all the advantages of conventional valved pulsejets, but without the reed valves that need frequent replacement; a valveless pulsejet can operate for its entire useful life with practically zero maintenance. They have been used to power model aircraft, experimental go-karts, and unmanned military aircraft such as cruise missiles and target drones.

A jet engine performs by converting fuel into thrust. How well it performs is an indication of what proportion of its fuel goes to waste. It transfers heat from burning fuel to air passing through the engine. In doing so it produces thrust work when propelling a vehicle but a lot of the fuel is wasted and only appears as heat. Propulsion engineers aim to minimize the degradation of fuel energy into unusable thermal energy. Increased emphasis on performance improvements for commercial airliners came in the 1970s from the rising cost of fuel.

<span class="mw-page-title-main">Components of jet engines</span> Brief description of components needed for jet engines

This article briefly describes the components and systems found in jet engines.

Deflagration to detonation transition (DDT) refers to a phenomenon in ignitable mixtures of a flammable gas and air when a sudden transition takes place from a deflagration type of combustion to a detonation type of explosion.

An airbreathing jet engine is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air, which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle. Compression may be provided by a gas turbine, as in the original turbojet and newer turbofan, or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet.

<span class="mw-page-title-main">Humphrey cycle</span> Thermodynamic cycle

The Humphrey cycle is a thermodynamic cycle similar to the pulse detonation engine and pulse compression detonation system cycles. It may be considered to be a modification of the Brayton cycle in which the constant-pressure heat addition process of the Brayton cycle is replaced by a constant-volume heat addition process.

Space Engine Systems Inc. (SES) is a Canadian aerospace company and is located in Edmonton, Alberta, Canada. The main focus of the company is the development of a light multi-fuel propulsion system to power a reusable spaceplane and hypersonic cruise vehicle. Pumps, compressors, gear boxes, and other related technologies being developed are integrated into SES's major R&D projects. SES has collaborated with the University of Calgary to study and develop technologies in key technical areas of nanotechnology and high-speed aerodynamics.

<span class="mw-page-title-main">Rotating detonation engine</span> Type of rocket engine

A rotating detonation engine (RDE) uses a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. Computational simulations and experimental results have shown that the RDE has potential in transport and other applications.

<span class="mw-page-title-main">Fickett–Jacobs cycle</span>

The Fickett–Jacobs cycle is a conceptual thermodynamic cycle that allows to compute an upper limit to the amount of mechanical work obtained from a cycle using an unsteady detonation process (explosive). The Fickett–Jacobs (FJ) cycle is based on Chapman–Jouguet (CJ) theory, an approximation for the detonation wave's velocity during a detonation. This cycle is researched for rotating detonation engines (RDE), considered to be more efficient than the classical combustion engines that are based on the Brayton or Humphrey cycles.

References

  1. 1 2 Escobar, Joe (2006-04-14). "Turbine Engine History". Aviation Pros. Retrieved 2023-10-21.
  2. ↑ "Pressure gain combustion". Frazer-Nash Consultancy. Retrieved 2023-10-21.
  3. 1 2 3 Paxson, Daniel E. (July 9, 2018). "Pressure Gain Combustion 101" (PDF). NASA. Retrieved October 16, 2023.
  4. ↑ Rankin, Brent A.; Fotia, Matthew L.; Naples, Andrew G.; Stevens, Christopher A.; Hoke, John L.; Kaemming, Thomas A.; Theuerkauf, Scott W.; Schauer, Frederick R. (January 2017). "Overview of Performance, Application, and Analysis of Rotating Detonation Engine Technologies". Journal of Propulsion and Power. 33 (1): 131–143. doi:10.2514/1.B36303. ISSN   0748-4658.
  5. ↑ "The Evolution of Gas Turbines From the First Designs to the Latest Environmentally Friendly Development Trends: Part 1 | Turbomachinery blog". blog.softinway.com. 2022-04-19. Retrieved 2023-10-26.
  6. 1 2 3 4 5 6 Sweeney, Joseph (December 5, 2009). "Pulse Detonation Engines" (PDF). www.colorado.edu. Retrieved October 29, 2023.
  7. 1 2 McAlpine, Kate (2017-03-30). "Rotating Detonation Engine: The Old Is New Again". Michigan Engineering News. Retrieved 2023-10-29.
  8. ↑ "Scaled Composites Long-EZ "Borealis"". National Museum of the United States Air Force™. Retrieved 2023-10-29.
  9. 1 2 3 "NASA's rotating detonation rocket engine posts record test results". New Atlas. 2023-01-31. Retrieved 2023-10-29.
  10. ↑ "3.7 Brayton Cycle". web.mit.edu. Retrieved 2023-10-23.
  11. ↑ "Power Turbine Thermodynamics". www.grc.nasa.gov. Retrieved 2023-10-23.
  12. ↑ Bulat, Pavel (March 13, 2014). "About the Detonation Engine". American Journal of Applied Sciences. 11 (8) – via ResearchGate.
  13. ↑ Machine, Smart (2021-11-06). "The Transition Of Deflagration To Detonation | Smart Machine Technologies". Smart Machine | SMT. Retrieved 2023-10-26.
  14. ↑ Wei, Lu (August 26, 2015). "Operation of a pulse detonation engine system at high frequency". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 230 (5): 886–894. doi:10.1177/0954410015601693.
  15. ↑ "Pulsed Detonation Engine – ISSI" . Retrieved 2023-10-23.
  16. ↑ Gutmark, E. J. (2021-10-01). "Pressure gain combustion". Shock Waves. 31 (7): 619–621. doi: 10.1007/s00193-021-01053-3 . ISSN   1432-2153.
  17. 1 2 3 4 "Pulsed Detonation Engines". arc.uta.edu. Retrieved 2023-10-30.
  18. 1 2 "Dr. Venkat Raman on the Rotating Detonation Engine, the frightening-sounding technology of tomorrow". aero.engin.umich.edu. 2020-11-11. Retrieved 2023-10-30.
  19. 1 2 3 Zhou, Rui; Wu, Dan; Wang, Jianping (2016-02-01). "Progress of continuously rotating detonation engines". Chinese Journal of Aeronautics. 29 (1): 15–29. doi: 10.1016/j.cja.2015.12.006 . ISSN   1000-9361.
  20. ↑ Richards, Geo. A. (June 23, 2014). "New Developments in Combustion Technology, Part II: Step Change in Efficiency" (PDF). cefrc.princeton.edu. Retrieved October 22, 2023.
  21. ↑ "Energy density - Energy Education". energyeducation.ca. Retrieved 2023-10-31.
  22. 1 2 "NETL Advances Rotating Detonation-Wave Combustor Technology". netl.doe.gov. Retrieved 2023-10-31.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.