Visualizing Combustion Dynamics: NASA And High-Speed Cameras

By John Oncea, Editor

Combustion is a chemical process in which a substance reacts with oxygen to give off heat. Burning a candle, a fire in a fireplace, pressing the gas pedal … these are a few everyday examples of the result of combustion, all of which happen faster than the eye can see. NASA, however, can precisely and accurately study combustion through the use of high-speed cameras.

Final Jeopardy category: Technology. How much are you wagering? Think about that while we go to commercial.

And we’re back with today’s final Jeopardy question: How long have high-speed cameras been around?

Play Jeopardy think music. Answer? What is since 1878, Alex.

Giddy Up

How many pictures do you have on your phone? According to Photutorial, “The average user has around 2,100 photos on their smartphone.” Beyond that, it is estimated that 1.81 trillion photos are taken worldwide every year. That’s about 57,000 per second or 5 billion per day. By 2030, around 2.3 trillion photos will be taken every year.

While commonplace now, photography is still a rather new technology. Since its invention* in the 1830s, photography has undergone many changes, one of which was the development of high-speed cameras. According to the Atomic Heritage Foundation (AHF), “These cameras allowed photographers to capture and create a frame-by-frame breakdown of events or occurrences too fast for the human eye to discern.

“The first major breakthrough with high-speed cameras was in 1878. Eadweard Muybridge, a British expat and photographer living in California, was commissioned to use photographs to determine whether a horse lifted all four hooves off the ground when galloping.”

Armed with 24 cameras attached to a shutter release system dictated by the horse’s galloping path, Muybridge was able to capture a high-speed motion sequence proving all four of a horse’s hooves do lift off the ground when galloping.

Eight years later, Austrian physicists Ernst Mach** and Peter Salcher published Photographische Fixirung der durch Projectile in der Luft eingeleiteten Vorgänge, a paper that used Salcher’s photo Bullett in Flight to help describe the physics of a shock wave, according to History of Information.

“At the request of Mach, who had not managed to experimentally prove his shockwave theory, Salcher and his assistant Sandor Riegler … conceived an experiment where he managed to record the flight of a projectile shot from a firearm for the first time in history using a specially devised ultra-fast photography technique,” AHF writes. “The recording was done using a method invented in 1859-64 by August Toepler, Salcher’s professor from GrazOffsite Link. The short exposure was achieved using an electric spark, and a total of 80 shots were recorded.”

The steady progression of time and the need to innovate moved high-speed photography from the novelty it was in the 1880s to what it is today: a critical technology being used to ensure many industries – including aerospace – can discover new ways to improve outcomes and lower costs.

* The oldest surviving camera photograph is a heliographic image created by Nicéphore Niépce in 1826 in Saint-Loup-de-Varennes, France titled View from the Window at Le Gras.

** Mach’s work in supersonic motion is why the speed of sound bears his last name.

High-Speed Cameras And Combustion Research

Combustion of explosives is a rapid process that can be utilized in a wide range of applications, from firecrackers to dynamite. Aerospace research involves the study of rocket combustion, such as hot exhaust and thrust creation, as well as supersonic combustion, which occurs when airflow exceeds the speed of sound. A thorough understanding of these phenomena can contribute to the advancement of research on destructive capabilities, power efficiency, and waste reduction.

“When imaging combustion it is important that two key points are considered so the proper advanced imaging technique will be used to acquire the proper data,” writes Phantom. “Most importantly, the researchers need to define what the specific goals are for the study.

“Without understanding the research goals high-speed combustion imaging can become a difficult and expensive undertaking. The secondary point is to understand which part of the combustion action needs to be imaged to obtain the proper data.”

There are, according to Phantom, five critical parts of a combustion event:

• Mechanical Engineering of Valves and Timing – Vibration and other events affecting reliability
• Chemical Engineering During Active Combustion – Wavelength emissions of flame
• Fluid Dynamics Injection and Atomization – Qualifying droplet characteristics
• Fluid Dynamics Under Compression – Study of burn efficiency
• Chemical & Fluid Dynamics in Combustion Qualification – Characterization of flame shape

As with any process, there is a set of unique challenges associated with combustion imaging. One of the most common is extreme speeds. “Because combustion is a chemical reaction that occurs very quickly a minimum of 100,000 fps is required to adequately image the extremely fast movement,” Phantom writes.

A second challenge is the bright light that comes as a result of energy output at the moment of combustion. High-speed sensors are light-sensitive and often oversaturation is a concern that can be solved through multi-camera setups and low exposure times.

Finally, there are non-visible reactions involving air and heat movement. “They are not easily visible and require unique imaging methods, such as Schlieren, to ensure accurate and visible imaging data,” Phantom writes.

The right high-speed cameras can help overcome the challenges described above because of their ability to capture rapid processes, allowing them to provide detailed information about the behavior of materials under high-stress conditions. Using their high frame rates and high-resolution sensors, these cameras contribute to safer materials and improved performance. They also can help to:

• Understand the impacts of minute design adjustments
• Measure velocities, temperature, and concentrations more precisely
• Capture and identify detrimental conditions that might be rare in occurrence and defining in leading to failure
• Characterize fuel injection, ignition, and combustion in internal combustion engines (ICE), gas turbines, or jet engines
• Provide insights into combustion efficiency, pollutant emissions, and the optimization of energy production processes

Can You Take Me Higher?

NASA considers high-speed cameras as a valuable tool for analyzing the performance of aerospace propulsion systems. They are also useful in investigating other aspects of aerospace engineering, such as studying the aerodynamic characteristics of wings and airfoils, as well as examining the effects of wind and turbulence on aircraft structures.

High-speed cameras can be used to measure velocities, temperature, and concentrations with greater precision. The enhanced temporal and spatial resolution they provide is crucial for obtaining more accurate data for computer-based models and theoretical models can be developed using this data to gain further insight into important topics such as fire control and flame-burning efficiency.

NASA has used high-speed cameras to record the ignition and combustion processes in rocket engines, including the Space Launch System (SLS) and various experimental engines. These cameras provide valuable data on combustion stability, performance, and safety. They are also used to study combustion instability in engines, capturing high-frame-rate images and videos which allow them to analyze the vibrations and fluctuations that can affect engine performance and safety.

High-speed cameras are essential for studying the behavior of flames in microgravity environments, such as those on the International Space Station (ISS). Understanding flame dynamics in space helps improve spacecraft safety and propulsion systems.

NASA has conducted research on supersonic combustion, including scramjets and hypersonic vehicles, using high-speed cameras to observe the complex combustion processes at high speeds and provide insights into improving efficiency and performance. Lean burn combustion, which involves using less fuel to reduce emissions, can be better observed by high-speed camera technology and is crucial for developing more environmentally friendly and fuel-efficient engines.

High-speed cameras are also used to capture the rapid spread of flames and test fire suppression methods, as well as in conjunction with Particle Image Velocimetry techniques to measure the velocity and flow patterns of combustion gases in various engine types, allowing for better optimization of engine designs.

The Future Of High-Speed Cameras

The future of high-speed cameras remains bright. Optica reports, “Researchers have developed a new method for capturing the complex behavior of turbulent flames produced during combustion. Insights provided by this high-speed 3D imaging approach could be used to develop more efficient and cleaner combustion systems for cars, airplanes, factories, and power plants.”

Qingchun Lei of Northwestern Polytechnic University in China told Optica, “The high-speed imaging approach we developed provides detailed insights into flame dynamics, ignition processes, and combustion behavior. This can provide insights into combustion efficiency, pollutant emissions, and the optimization of energy production processes that could be used to improve the design and operation of power plants, engines, and other combustion devices, leading to reduced environmental impact and enhanced energy efficiency.”

And Science Daily reported earlier this year that a University of Gothenburg research team “developed one of the world's fastest single-shot laser cameras, which is at least a thousand times faster than today's most modern equipment for combustion diagnostics. The discovery has enormous significance for studying the lightning-fast combustion of hydrocarbons.”

These discoveries have broad applications in physics, chemistry, biology, medicine, energy, and environmental research beyond combustion.