Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Potential for ultrafast detonations revealed by new computer simulation

24.02.2003


Explosive detonations at speeds faster than current theories predict have been shown to be possible in a powerful new computer simulation developed by a physical chemist and an aerospace engineer at Penn State. James B. Anderson, Evan Pugh Professor of Chemistry and Physics, and Lyle N. Long, Professor of Aerospace Engineering, say their simulation points the way toward the production of ultrafast detonations, which could lead to innovative propulsion systems for space travel and a better understanding of detonations in general, including those that occur at supersonic speeds in the tunnels of underground mines.



With the aid of an innovative chemical model supported by powerful computers, the researchers show that burning particles of highly reactive gas set on fire by an explosive shock wave can leap out in front of the wave and ride it like a surfer, sparking reactions in advance of the wave itself. "All the textbooks say that the velocity of a detonation in a reactive gas mixture can be no faster than the speed of sound in the hot burning gases, but our model shows this assumption may no longer be correct," says Anderson, whose paper is published in the current issue of the Journal of Chemical Physics (volume 118, issue 7, page 3102).

According to the previous prevailing theory, a detonation occurs when a shock wave from an explosion first blasts its way through a reactive gas, heating it until it ignites, then causing a chemical reaction that continues to power the explosive wave forward. The chemical reaction, which proceeds at a slower speed behind the initial shock wave, was thought to be limited to the speed of sound in the hot gases. "Previous models did not predict ultrafast, supersonic detonations, in which the explosion can move even faster than a shock wave in the hot gases," Anderson says.


Anderson and Long’s simulation shows that supersonic detonations can occur in highly reactive gas mixtures if the chemical reaction is fast enough to keep up with the wave, in which case some of the reactive atoms can blast ahead to initiate a reaction in front of the shock wave itself, speeding things up even faster. Now that they have shown it can be done, the researchers predict that experimenters will produce and observe ultrafast detonations in the laboratory. "The most likely gases where ultrafast detonations may occur are in two of the fastest-reacting systems, mixtures of hydrogen and chlorine (H2-Cl2) and mixtures of hydrogen and fluorine (H2-F2)," Anderson says.

The team’s model is the first to simultaneously include the full details of both the chemical reactions and the gas dynamics that occur during explosions, as well as temperature, velocity, density, pressure, and chemical composition of the detonation waves. Earlier approaches, which were based on the use of differential equations, required making approximations that oversimplified the physics and chemistry and were of limited usefulness because of their complexity, the researchers say.

Anderson and Long accomplished their innovation by incorporating finely detailed chemical modeling into a technique known as the Direct Simulation Monte Carlo method, which has been in use for over half a century in gas-dynamics calculations and is in wide use today for solving aerospace problems. Like a lottery in which those who have more tickets have a greater chance of winning, Monte Carlo calculations in Anderson and Long’s model assign to each pair of particles a higher or lower probability of interacting with each other, based on their particular characteristics at any given time. For example, particles that are moving rapidly toward each other are much more likely to be picked for a collision than those that are not moving, and those that are big are more likely to collide with each other than are those that are small.

To add some unpredictability to the game, Anderson and Long also incorporated into their model the technique of using random numbers to pick which reactions actually occur. As a result, the model imitates nature more realistically by allowing particles to interact with each other on a random basis in addition to taking into account their calculated probability of interacting. "The addition of chemical reactions to the Monte Carlo method makes it possible, for the first time, to realistically model simultaneously both the interactive chemistry and the gas dynamics that occur during an explosion," Anderson says.

Anderson and Long’s computer model simulates the chemistry and tracks the movement, temperature, and speed of each particle in a group of about 100,000 as they react with each other. Like frames in a reel of movie film, the calculations in the model are finely detailed snapshots of chemical reactions as they take place step by step. "In these calculations, we break the whole system down into cells to model reactions in very, very small steps in order to model the overall explosion very accurately," Anderson says.

We have treated our model atoms as simple hard spheres without internal structure in order to model the simplest kinds of reactions that one can imagine while still including some of the complicating effects that occur with real systems," says Anderson. "The simplification makes it easier for us to understand and analyze the results, so when our calculations reveal an ultrafast detonation we can know it is not just the result an overly complex model producing extraneous errors."

The researchers say the new model could be particularly useful in understanding situations involving combustion or propulsion in which the chemical reactions in a gas are dynamically coupled with the movement of the gas during an explosion. One such situation involves pulsed-detonation rocket engines, which create propulsion by sending detonation waves rearward through an explosive gas mixture in a combustion chamber, propelling the rocket forward. "The model might also help us to better understand, for example, the reentry of a space vehicle--which involves very complicated gas dynamics and very complicated chemical reactions in the upper atmosphere," Long says. "We expect our model can be used to help make better predictions in such critical and complex situations."


This research was supported by grants from the National Science Foundation.

Additional Contacts:
James B. Anderson: (+1)814-865-3933, jba@psu.edu
Lyle N. Long: (+1)814-865-1172, lnl@psu.edu

Barbara K. Kennedy | EurekAlert!

More articles from Physics and Astronomy:

nachricht A better way to weigh millions of solitary stars
15.12.2017 | Vanderbilt University

nachricht A chip for environmental and health monitoring
15.12.2017 | Friedrich-Alexander-Universität Erlangen-Nürnberg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>