Combustion Research Group at UC San Diego

Students to test one-of-a-kind, 3D-printed rocket engine advised by Prof. Williams

2013-10-04T13:56:00.000-07:00

The 3D-printed engine designed by the UC San Diego chaper of Students for the Exploration and Development of Space.

San Diego, Calif., Oct. 3 -- A group of engineering students at the University of California, San Diego, will boldly go where no university student group has gone before by testing a 3D-printed rocket engine made out of metal at 10 a.m. on Sunday Oct. 5 at the Friends of Amateur Rocketry testing site in the Mojave Desert.

To build the engine, students used a proprietary design that they developed. The engine was primarily financed by NASA’s Marshall Space Flight Center in Huntsville, Ala. and was printed by Illinois-based GPI Prototype and Manufacturing Services. This is the first time a university has produced a 3D-printed liquid fueled metal rocket engine, according to the students, who are members of the UC San Diego chapter of Students for the Exploration and Development of Space.

“We’ve all been working so hard, putting countless hours to ensure that it all works,” said Deepak Atyam, the organization’s president. “If all goes well, we would be the first entity outside of NASA to have tested a liquid fueled rocket motor in its entirety. We hope to see all of our hard work come to fruition.”

The engine was designed to power the third stage of a rocket carrying several NanoSat-style satellites with a mass of less than a few pounds each. The engine is about 6 to 7 inches long and weighs about 10 lbs. It is designed to generate 200 lbs of thrust and is made of cobalt and chromium, a high-grade alloy. It runs on kerosene and liquid oxygen. It cost $6,800 to manufacture, including $5,000 from NASA. The rest was raised by students through barbeque sales and other student-run fundraisers.

A 3D printed metal rocket engine would dramatically cut costs for launches, said Forman Williams, a professor of aerospace engineering at the Jacobs School of Engineering at UC San Diego, who is the students’ advisor. Williams admits that he was skeptical at first. The design of liquid-propellant rockets is very complex and detailed. But the students surprised him.

“At this stage, I think it’s most likely that the test will be successful,” Williams said.

Watch a video of tests on the engine here on campus

http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1423

Workshop on Interactions between Small and Large Scales in Turbulent Combustion

2013-06-10T18:37:00.000-07:00

Workshop on Interactions between Small and Large Scales in Turbulent Combustion

San Antonio, TX, April 7, 2013

SUMMARY

The workshop started with some introductory remarks by Forman Williams, followed by five 30-minute talks in the morning and two discussion panels in the afternoon, dealing with physical and computational aspects of the problem. The contents of the presentations are summarized below.

The short introduction by Forman Williams set the framework of the workshop by giving basic background information, including a brief review of turbulent combustion regimes and of computational approaches investigated in the past, and he tried to motivate the need for a specific workshop to comment on unresolved issues and on pressing questions to be addressed.

Elaine Oran talked about problems in non-equilibrium reactive turbulence and broadband turbulence and called attention to needed improvements in modeling, including effects of small scales on large scales, such as local blowups associated with chemical reaction, shock/flame interactions, flame/turbulence interactions, and flame collisions in cusps leading to locally enhanced burning rates, which can be interpreted as types of intermittency.

Jackie Chen talked about the role of DNS in elucidating scale interaction in premixed combustion, basing her discussion on detailed computations of a hydrogen/air jet flame. She argued that dilatational effects are more prominent in premixed combustion than they are for diffusion flames. She introduced density-weighted quantities in two-point correlations and derived a 6-term equation for modeling. Her kinetic-energy spectrum showed an anomalous plateau, clearly associated with the combustion but in need of further physical explanation. She also investigate using different scales to collapse the different curves, showing results that differ from results for diffusion flames and that call for further investigation.

Heinz Pitsch discussed the role of intermittency and differential diffusion in soot formation under engine-like conditions. Both effects were shown to require more careful subgrid modeling for LES. The chemistry of soot formation is slow, but soot oxidation in the presence of oxygen is very fast at high temperature. As a result, random differential diffusion may lead to sudden soot destruction, which can have a dramatic effect on intermittent pollution emission from engines.

Alan Kerstein talked about new phenomenological modeling efforts, involving hierarchical swaps between neighboring fluid parcels (HiPS). He suggested that the proposed model may reproduce inertia-range cascades. He discussed pdf-transport modeling, in particular, as an example and also indicated that the approach shows potential for more economical computations and improved mixing descriptions. Testing work of the model is underway, actually showing good promise for both channel flow and buoyant convection as introductory model test, in success achieved the day after he workshop.

Parviz Moin talked about transfer spectra and showed extents of backscatter, measured by fractions of negative subgrid diffusivities resulting from dynamic subgrids. He showed how consideration of subgrid budget equations imposes limits on this type of backscatter and how combustion can generate subgrid sources. He also reviewed present challenges and recent advances in LES computation, including studies of jet atomization and supersonic combustion.

The first panel, dealing with physical aspects of the problem, was chaired by Sutanu Sarkar, who introduced the problem by discussing the role of the subfilter field, illustrated by different examples taken from problems of scalar mixing, reacting shear layers, and environmental boundary layers. N. Swaminathan talked about the physics of combustion at small scales and pointed out different phenomena not properly accounted for in current subgrid-scale modeling, along with limitations to present surface-based combustion descriptions, thereby identifying important additional phenomena needing study in connection with interactions between small ad large scales. Javier Urzay used new DNS results of hydrogen-air supersonic mixing layers to discuss subgrid-scale backscatter of kinetic energy, including negative eddy viscosity and compressibility effects. Alexei Poludnenko showed how in the presence of steady-state turbulence of medium intensity, turbulent flames exhibit somewhat irregular periodic oscillations, which need to be better-characterized and understood, with potential implications for subgrid-scale modeling. Peter Hamlington used results of implicit LES as a basis to discuss interactions of turbulence and premixed flames, addressing effects of combustion on velocity fields and scales, from forced-turbulence computations with laminar flame thicknesses in the inertial range, thereby identifying a number of key challenges and questions in need of further investigation. Guillaume Blanquardt pointed out the need for a better understanding of interaction of turbulence with flame instabilities, especially through extensions of triadic-interaction studies to account for effects of non-periodicity and anisotropy, introducing Favre-type spectral decompositions that clearly emphasize the severe complications that arise in such approaches if there are very thin flamelets.

The second panel focused on numerical aspects of the problem. Jay Boris chaired the session and gave an introductory talk explaining the advantages of monotone integrated LES (MILES) and implicit LES (ILES), an explanation that stirred some discussion with the audience, with strong questions raised about the general validity for combustion problems without shocks. Jim Brasseur continued by discussing different physical and computational aspects of triadic interactions, suggesting that they may easily be extended to combustion descriptions, contrary to the apparent implications of the observations of Blanquardt. Carlos Pantano presented new numerical techniques employing edge-flame dynamics to treat local extinction and re-ignition in non-premixed combustion, with applications to lifted flames, emphasizing new aspects that arise. Mathias Ihme talked about subgrid-modelling effects and grid-resolution issues in computations of realistic burners, identifying challenges and open questions that include the need for reducing grid dependences in predictions of important bifurcations such as those in dual-swirl burners. Michael Mueller addressed implementation issues of physically relevant phenomena, such as negative dynamic viscosities, and he pointed out scale-related numerical limitations of descriptions of backscatter energy transfer, suggesting the importance of purposely limiting backscatter in codes in moving towards filtered density functions. Finally, Venkat Raman discussed limitations of predictive capabilities of currently used methods and indicated needed improvements including new validation strategies that emphasize quantifying probabilities of system variability that result in rare events, clearly a difficult task.

After presentation of all of this information time did not allow further discussion of the key problems and of the most important future needs. One prevalent theme that emerged concerned intermittency and rare events, which can occur at all scales, small to large to system, and which may be of great practical importance, from pollutant emissions to system failure. Another concerned the importance of time-dependent phenomena in turbulent combustion, calling into question the general applicability of concepts such as Kolmogorov scaling and equilibrium turbulence. A third involved the relative desirability of performing DNS with forced or with decaying turbulence, both having drawbacks but both providing useful, relevant information, thereby motivating further work along both lines. A fourth exposed the variability in the very definition of backscatter in the interactions between small and large scales, with some pertaining only to physical space and others only to spectral space, which are different. A fifth emphasized the remarkable potential capabilities of phenomenological methods for simulation, such as HiPS. And finally a sixth emphasized the exceptionally wide range of ever-growing varieties of subgrid descriptions, from none (ILES) through spectral to intricately detailed and complex, deterministic and statistical, all with different attractive aspects. A significant outstanding future problem is to ascertain more quantitatively the ranges of conditions over which each approach is best suited, in appropriate regime diagrams.

An Old Theory Goes up in Cool Flames

2012-09-14T14:10:00.001-07:00

Read the Combustion and Flame article here.

Before you blow out the candle on your next cake or make a batch of S'mores over a campfire, look closely at the flame. There may be some very cool secrets inside those flames waiting to be revealed. While fire has warmed us and cooked our food for thousands of years, it still holds mysteries that can surprise us and change our understanding of how the world works.

"There are many currently unknown things about the combustion process waiting to be revealed by future scientific experiments," said Forman Williams, University of California, San Diego. Williams has studied combustion for more than 50 years.

After decades of flame studies that have produced well understood theoretical models and numerical simulations, recent flame investigations on theInternational Space Station produced some unexpected results. For the first time, scientists observed large, about 3 mm, droplets of heptane fuel that had dual modes of combustion and extinction. The fire went out twice; once with a visible flame, once without. While the initial burn had a traditional hot flame, the second-stage vaporization was sustained by what is known as cool-flame chemical heat release.

This is the first time scientists observed low-temperature, soot-free cool flames in steadily burning pure fuels. A cool flame is one that burns at about 600 degrees Celsius. To understand how cool this is, consider that a typical candle is about two-and-a-half times hotter, burning at around 1,400 degrees Celsius.

This two-stage burning was not seen in smaller heptane droplets that were less than 2.4 mm in size.

"Thus far the most surprising thing we've observed is the continued apparent burning of heptane droplets after flame extinction under certain conditions. Currently, this is entirely unexplained for heptane," said Williams, FLEX Principal Investigator.

While burning the heptane droplets in the Flame Extinguishing Experiment, or FLEX, investigation, the first stage had a visible flame that eventually went out. Once the visible flame disappeared, the heptane droplet continued rapid quasi-steady vaporization without any visible flame, according to the researchers. This ended abruptly at a point called second-stage extinction. At this point, a smaller droplet was left behind that either experienced normal time-dependent evaporation or sometimes grew slightly through condensation of vapor in the cloud that formed upon extinction.
This result, which was not anticipated when the study was designed, came during the FLEX investigation on the space station using the Multi-User Droplet Combustion Apparatus in the Combustion Integrated Rack, or CIR. More recent FLEX experiments reveal similar two-stage burning phenomena with n-octane and decane fuels.

For the investigation, over one hundred heptane droplets were burned in varying conditions. Some of the videos showing this phenomenon are available on the Glenn Research Center, Cleveland, Ohio, FLEX Website.

The new findings are in press and available online in Combustion and Flame, the journal of the Combustion Institute. This new discovery will help scientists and engineers modify numerical models and better predict the behavior of flames, fuel and combustion. It also has many long-term implications both in space and on Earth.

"There are all kinds of implications for practical applications. For internal combustion engines, it can lead to pollution reduction and better gas mileage," said Vedha Nayagam, FLEX co-investigator, National Center for Space Exploration Research, Cleveland, Ohio. "You could use this cool flame burning to partially oxidize the fuel, like in the HCCI engine."
The Homogeneous Charge Compression Ignition, or HCCI, engine combines diesel ignition with spark-ignition and can be used in any type of diesel engine, both stationary and for transportation. By merging these two technologies, engines could have the efficiency of diesel engines, while also providing reduced particulate and NOx emissions. Basically, this could eliminate the need to burn diesel-fuel sprays, which are notorious for pollutant production, according to the researchers.

Fire safety in space can also benefit from this new discovery. Since the flame continues to produce combustion after the hot-flame goes out, fire suppression techniques will need to consider the possibility that the pure-fuel flame is not really out, even with no visible flame. It could behave like a solid that smolders and reignites into open flame under the right conditions, leading to the need for space-specific suppression techniques.

Thanks to the FLEX investigation in the reduced gravity environment of the space station, we have new insight into the mysteries of flames and fuel. Whether it's a candle, a campfire, or some other blaze, the combustion process may be waiting for the right investigation to pry loose more secrets. Microgravity research may prove to be the tool that helps force free those secrets.

Mike GiannoneNASA's Glenn Research Center

http://www.nasa.gov/mission_pages/station/research/news/cool_flame.html

How Do You Fight Fire in Space? Experiments Provide Some Answers

2012-02-02T21:17:00.000-08:00

Prof. Williams research was featured recently in the UCSD News: Link.
Read about it below:

Research on the International Space Station also aims for a better understanding of fuel combustion here on Earth

Color image of a burning droplet
Photo: NASA/Glenn Research Center

Improving fire-fighting techniques in space and getting a better understanding of fuel combustion here on Earth are the focus of a series of experiments on the International Space Station, led by a professor at the Jacobs School of Engineering at the University of California, San Diego. A first round of experiments ran from March 2009 to December 2011. A second round kicked off in January and is set to last a year or more.

Forman Williams, a professor of mechanical and aerospace engineering, has been working on fire research and fire safety with NASA since the 1970s. You will not, however, find him on the space station. The experiments are run by remote control from NASA’s John Glenn Research Center in Cleveland. Williams and colleagues at Princeton, UC Davis, the University of Connecticut and Cornell analyze the results at their home institutions. They will present findings based on the first series of experiments this summer at a symposium in Poland.

“Research leads to a better understanding of fire behavior,” Willams said. “And better understanding ultimately leads to better safety designs.”

FLEX Chamber Insert Assembly Apparatus
Photo: NASA/Glenn Research Center

All the experiments take place in a chamber located in the Destiny module of the International Space Station. The chamber is part of a piece of equipment called the Combustion Integrated Rack, which is roughly the size of a 5.5-foot bookcase and weighs close to 560 lbs. The rack is crammed with sensors and equipped with video cameras that record experiments. The chamber is equipped with a device called the Multiuser Droplet Combustion Apparatus that can generate and ignite droplets from different fuels in different atmospheric conditions.

Fire safety on the space station

The Flame Extinguishment Experiment, known as FLEX, ran in the chamber from March 2009 to December 2011. The goal was to get a better understanding of how fire happens on a space craft, where there is no up or down and where atmosphere and pressure are tightly controlled. The ultimate goal was to improve fire-fighting techniques in space.

To help understand how flames behave and burn in space, FLEX researchers ignited a small drop of either heptane or methanol. As this little sphere of fuel burned for about 20 seconds, it was engulfed by a spherically symmetric flame. The droplet shrank until either the flame extinguished or the fuel ran out.

Test #1 - Droplet diameter of 4 mm, with no support fiber. Droplet deployment was successful with a brief burn before radiative extinction. An afterglow from condensing vapor cloud and scattered backlight occurred approximately 30 sec after extinction. This afterglow phenomena typically occurs following radiative extinction. (NASA/JSC)

Flames in space can burn at a lower temperature, at a lower rate and with less oxygen than in normal gravity. This means that materials used to extinguish fire must be present in higher concentrations. The slow flow of air from the fans mixing air in a spacecraft can make flames burn even faster.

The space station is equipped with carbon-dioxide fire extinguishers, so researchers investigated how fuel droplets burn in the presence of different amounts of CO2. Also, ambient air can become completely fire safe when there is not enough oxygen for fuels to ignite. This threshold is called the limiting oxygen index. Williams and colleagues pinpointed this index for methanol and heptane on the space station.

Fuel combustion experiments

Williams is now working on a new series of experiments, called FLEX-2, which aims to recreate conditions that are closer to what actually happens in a combustion engine. Findings could lead to new designs for cleaner fuels that have a smaller carbon footprint and emit fewer pollutants, among other applications.

Astronaut Mike Fincke pictured to the left of the Combustion Integrated Rack facility installed in the Destiny module of the ISS shortly after installation. Photo: NASA

While the original FLEX experiments looked at fuels with only one component, FLEX-2 will run tests on fuels with two components, more similar to fuels used in real-life conditions, which usually have multiple components. While FLEX examined the behavior of single fuel droplets, the new round of tests will also look at the interaction of two fuel droplets.

But Williams said he isn’t quite done with the original FLEX experiments. He and colleagues still need to explain some of what they observed. For example, when the flame around a fuel droplet extinguishes, that droplet should stop shrinking because combustion has essentially stopped. But in about a dozen instances during the FLEX experiments, heptane droplets kept shrinking at the same rate as when the flame was still burning. Williams, who has studied combustion for the past 50 years, said he has never seen anything like it.

Tests on the space shuttle

This is not Williams’ first round of tests to be run in space. His work includes several experiments that ran on Spacelab, a science module flown in the cargo bay of U.S. space shuttles. The holy grail of combustion science is a flame around a fuel droplet that looks like a perfectly symmetrical sphere. That is very hard to achieve here on Earth. It is however a common occurrence in microgravity. Spherical symmetry makes it easier to observe droplets’ behavior and to craft the calculations that explain it, Williams said.

Forman Williams is a professor of mechanical and aerospace engineering at the Jacobs School of Engineering at the University of California San Diego.

During the space shuttle missions, he and colleagues used to work around the clock at the Marshall Space Flight Center in Huntsville, Ala. Williams and colleagues also took their families to Cape Canaveral to watch space shuttle Columbia take off in July 1997, when it was carrying a microgravity combustion experiment they designed.

William’s interest in combustion dates back to his undergraduate days at Princeton. He was taking a graduate-level course. His professor wrote out on the blackboard the conservation equations of combustion. “When I realized how complicated they were, I said to myself that there is enough there to last me a lifetime,” Williams explained.

Willams’ colleagues on the FLEX and FLEX-2 experiments are: Frederick Dryer, of Princeton; Mun Choi, of the University of Connecticut; Benjamin Shaw at UC Davis; Tom Avedisian of Cornell; Vedha Nayagam at the National Center for Space Exploration Research; Michael Hicks, Daniel Dietrich and others from NASA’s Glenn Research Center.

Symposium in Honor of Professor Stanford S. “Sol” Penner

2012-01-20T13:52:00.001-08:00

The Department of Mechanical & Aerospace Engineering is pleased to announce a symposium in honor of

Posted in

Professor Stanford S. “Sol” Penner

This symposium is being organized to recognize Dr. Penner, who made important advances in thermophysics, applied spectroscopy, combustion, propulsion, and energy.

Please join us to celebrate his 90th birthday by reflecting on his research and university contributions.

2:00 p.m.-5:00 p.m.
Wednesday, February 1, 2012
CMRR Auditorium
UCSD

Microgravity Combustion Experiment Featured on Space.com

2012-01-10T15:30:00.000-08:00

Space.com recently feature NASA’s Flame Extinguishment Experiment, or FLEX which has conducted more than 200 tests since March, 2009 to better understand how fire behaves in microgravity. The research could lead to improved fire suppression systems aboard future spaceships, and it could also have practical benefits here on Earth.

"We hope to gain a better knowledge of droplet burning, improved spacecraft fire safety and ideas for more efficient utilization of liquid fuels on Earth," project leader Forman Williams, of the University of California, San Diego, said in a statement. "The experiments will be used to verify numerical models that calculate droplet burning under different conditions."

Check out some videos of droplet combustion aboard the space station and the article at http://www.space.com/13766-international-space-station-flex-fire-research.html

Updated San Diego Mechanism

2011-11-23T11:09:00.001-08:00

On November 22nd, 2011 a new version of the San Diego Mechanism was released and posted to the mechanism webpage.

Several changes were made to the ethanol chemistry that were detailed in Li at al. (2004) and Saxena et al. (2007). A few reactions were added dealing with the C3 chemistry. Those are detailed in J. C. Prince et al. (2011).

If you would like to subscribe to future updates to the mechanism by email, please email san-diego-mechanism+subscribe@googlegroups.com to subscribe to our mailing list.

Prof. Williams to deliver plenary lecture at 2011 Fall Meeting of the Western States Section of the Combustion Institute

2011-09-30T12:39:00.000-07:00

The 2011 Fall Meeting of the Western States Section of the Combustion Institute will be held October 17 and 18, 2011 at the University of California, Riverside. Prof. Forman A. Williams will deliver the plenary lecture at the conference:

Short Chemical Mechanisms in Combustion
Professor Forman Williams, University of California, San Diego

Seminar by Amable Liñán: The initiation of detonations in reactive gases

2011-08-07T13:30:00.000-07:00

The initiation of detonations in reactive gases

Amable Liñán
ETSI Aeronáuticos, Universidad Politécnica de Madrid

Wednesday, August 3, 3 – 4pm EBU2, Room 584

Abstract:
The presentation will be devoted to the analysis of the initiation, by external, concentrated, energy sources in gaseous reactive mixtures, of cylindrical and spherical self-moving detonation waves.  These waves are led by a shock wave, moving radially outwards at supersonic speeds, and heating the mixture so that the reaction is ignited behind the shock wave, and goes to completion in a layer of thickness lr large compared with the thickness of the shock wave; whose radius coincides with the radius rd(t) of the detonation wave when we use the reactive blast wave model (corresponding to the limit, ld/rd → 0, of fast reaction rates).

The energy E0 of the external source defines a characteristic value rc of the detonation radius, for which the chemical energy released by the detonation wave is equal to E0. For concentrated external energy sources, with a radius rh small compared with rc (and a deposition time th small enough), a strongly heated core, of radius re(t), is formed; this has a gas density very small compared with the initial density, a very high temperature and near-uniform pressure. This heated core pushes the gas, so that it moves outwards with an inviscid radial motion in the region, re < r < rd, bounded outside by an “overdriven” denotation wave.

The overdriven detonation is reached from behind by expansion waves, represented by the acoustic characteristics C+, that attenuate the detonation velocity D; in such a way that at a finite time t0 (after the initiation of the external heating), when the detonation radius is rd = r0 (of the order of rc) the detonation velocity has decreased to the Chapman-Jouguet valued DCJ.

For t > t0 the detonation surface, moving with the constant velocity DCJ, is no longer reached by any of the characteristics (the three characteristics originate at the detonation and are left behind the front).The last characteristic surface C0+ that at t = t0 reached, tangentially, the detonation wave, at t > t0, is left behind the wave, and bounds, together with the detonation front, a shell of reacted gases with a self- similar motion, independent of the external deposition energy and of the deposition time. (On the other hand these determine r0 and t0 and also the non self-similar motion of the reacted gases bounded externally by C0+).

Outside the characteristic surface C0+, the flow structure coincides with the Zeldovich-Taylor self-similar structure behind a Chapman-Jouguet detonation of constant velocity DCJ , originating at r = 0 at t = t0 − r0/DCJ . (The self-similar Z-T structure is reached everywhere for large values of t/t0).

We shall also indicate in the presentation how finite reaction rate effects represented by the small, but non-negligible, value of the ratio lr/r0 at t = t0 determines, together with the deposition time, the minimum energy needed to initiate a self- moving Chapman-Jouguet detonation.

Welcome to our New Website

2011-07-23T10:28:00.000-07:00

Welcome to our recently re-designed website.