Thayer School's Fire Bug
JAMES A. BROWNING '44 of the Thayer School of Engineering is making a study of flame stability for the Government that involves setting off explosions which can't be heard and taking pictures of flames which the camera cannot see.
All this may sound a bit unusual, but so is his study, a piece of basic research for Project "Squid," sponsored by the Office of Naval Research, the Office of Air Research and the Ordnance Department.
"Squid" itself is a cooperative effort, with headquarters at Princeton, in which a number of college and university scientists, some commercial laboratories, and various government laboratories, are all directing their attention to different aspects of the general subject of jet propulsion. Much of this is so-called basic research - that is propulsion itself without regard to how knowledge gained may be applied specifically to pushing an aircraft more efficiently and rapidly through the air.
Browning is not the kind o£ man who is content to strike a match, light his living room fire and settle back in comfort. He wants to know just what happens from t e moment the match flares up until the last ember of the fire has died away. He is already well established in high temperature engineering circles with his invention three years ago of the Browning Tore , a device using gasoline and oxygen to produce a temperature of 5500 degrees Fahrenheit.
An Assistant Professor of Mechanical Engineering, he graduated from Dart mouth in 1944 and from Stanford University School of Engineering in 1948. His present work is not so surprising m view of the subject of his thesis - "The Effect of Light Radiation on Detonation.'
Some have called him, in good-humored jest, "Hanover's own fire bug." He is happiest when he is making a bigger, or a hotter, or a smaller or a cooler flame than anyone else, and then studying its characteristics.
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Wkat's tke significance of all this? Browning himself, with a cautious scientist's preface, provides part ok tke answer:
"I very frankly don't know what applications the results of this research may have. That's up to a methods or development engineer, or somebody interested in applying results to existing mechanisms.
"But I would make the point that the pilot of a jet plane is personally concerned with flame stability. He depends for his power on a relatively unstable flame of kerosene or gasoline being burned under high temperature and pressure. One thing he particularly fears is a flame-out. If he does have a flame-out at 40,000 feet he can't get his engine started again until he drops down to ten or twenty thousand feet. I don't know the exact figure, and besides I suppose it is militarily classified. At high altitude he can't get his engine spinning fast enough to scoop in sufficient air to start combustion again.
"And when he does reach an altitude where the air is dense enough for him to start his engine, he has a list of two dozen things to do. He even has to point the nose of his plane up so that any unburned fuel in the engine's combustion chamber will drip out of the tail. If he doesn't he is likely to blow the tail right off the plane.
"The pilot has time for two tries at starting his engine. If he fails, he then has to bail out. I can well understand why pilots dread a flame-out. In this project we are concerned with the characteristics of flames and their stability. There is the connection."
Browning's work is a sample of how technical progress often demands a re-examination, in the light of experience or need, of basic knowledge. Engineers have for years known much about combustion, but now that we are propelling our airplanes with the thrust from a jet of fire, we are going back for another long and detailed look at basic combustion processes.
The carburetor in an automobile sprays a mixture of air and gasoline into the cylinders. The drops are of different sizes, some very large and some very small. If the drops are too big for the amount of time allowed for burning, or if there is too much fuel, you get a wasteful, yellow, dirty flame, but one that tends to be quite stable.
What happens if you put into the combustion chamber a "fog" of droplets all very tiny and all the same size? This is what Browning has been concentrating on.
To do it, he first vaporizes his fuel, heating it up so that it turns into a true gas. Then in a fog chamber he expands his vapor and condenses it into tiny particles. He burns these at a measured rate and with a measured amount of air in a large nozzle, something like a Bunsen burner.
Engineers have made many observations of how gaseous fuels burn. One reason is that the scientist can easily and accurately control the amount of fuel and air he is using. But it's another story with liquids. Just an ordinary spray won't work - the resulting mixture is too full of variables to satisfy the researcher.
And that's the reason Browning hit upon burning a fog of fuel, actually a liquid fuel, but in very tiny droplets. "The drops I am using," he says, "are between a half and one and a half microns in diameter." If you can't remember back to college physics, a micron is a thousandth of a millimeter. That's small.
To produce a fog that is satisfactory for his research work, Browning has converted his first-floor laboratory room at Thayer into a kind of Dante's inferno of pipes, pressure tubes, valves, gas tanks, metering devices, air and fuel pumps and expansion chambers - all culminating in a long tube surmounted, at times, by the flame being studied.
A Schlieren camera is aimed at the flame, and this is where the photographing of the flame that the camera can't see comes into the work. The next few paragraphs are a bit complicated, but if you will stick with it, you'll better understand the relationship between this work and jet flameouts.
Browning is interested in what happens just inside the inner cone of his flame. Look at the flame on your gas stove, if your kitchen is so equipped, and you'll see the inner cone, just above the hole in the burner. No combustion occurs inside the cone, only on its outer surface.
When a liquid fuel is used, the droplets change to vapor just along the inner surface of that cone - and from there on out is the area where combustion will be supported. Now, when a liquid vaporizes, a cooling effect takes place. If you pour some gin on your hand and then blow on it, you can feel the coolness as the liquid alcohol vaporizes.
Combustion is a chemical reaction, and the colder the temperature, the slower the reaction rate. Your college chemistry text postulated, you may remember, that a chemical reaction could not take place at absolute zero temperature.
To find out what is happening in this area of vaporization just inside where the fuel begins to burn, Browning beams a ray of light through the flame and then picks it up with a system of lenses called a Schlieren camera. This records the action within the inner cone and excludes all the light from the flame itself.
What he is actually doing is photographing a part of the flame without showing any of the actual flame itself. None of the light captured on the film comes from the burning flame.
By measuring from his photographs the angular shape of the inner cone, and knowing the rate of fuel flow through the burner, Browning can determine the flame velocity or the speed of the chemical reaction. He has discovered that it does not differ appreciably between the fog flame and that produced by a gaseous fuel.
He has discovered that the cooling effect of using a liquid fuel and depending on the heat of the flame itself to vaporize the fuel is not nearly so marked as had previously been theorized.
As to the explosions he touches off which can't be heard, these occur inside a heavy cylinder or bomb. Browning wants to know the maximum and minimum concentrations of fuel that will support combustion. He does this by adjusting the "leanness" or "richness" of his fog-air combination and then pumps it through the bomb. He shuts a pair of valves, capturing a known concentration within his bomb, and then touches off an electric spark.
What happens then is similar to what happens in the cylinder of an automobile engine, except that there isn't a sound. The reason is that the bomb is so heavy and is entirely enclosed. Of course, if the container itself exploded there would be plenty of noise.
"The only way I know there has been an explosion," Browning explains, "is by watching a pressure gauge. If the pressure goes up, then I know that the fog-air mixture has supported combustion."
It takes only half a jog on the imagination to get the idea of how important to jet propulsion is any study of fuel ignition or flame stability of different liquid fuels under various conditions. "Squid" gets its name, incidentally, from the method that the peculiar sea creature uses to get around. Mr. Squid gulps in quantities of water at one end, and then shoots the water out of a nozzle. Instead of using a whirling compressor and a high temperature flame to create the jet, he uses his muscles - but the result is true jet propulsion.
Browning has just embarked upon the definitive stage of his project. So far he has been working out the steps of his procedure, using kerosene and propane gas both cheap fuels, one liquid and the other gaseous, and both extremely like one another.
Now he has begun to use the same fuel for both the liquid and the gaseous sides of the experiment. This is methyl naphthalene, a compound which is liquid at room temperatures and can best be described as smelling like "gasoline soaked mothballs." Its odor, which is very clinging, is now Browning's trademark in the halls of Thayer's laboratory wing.
He has not yet had an uncontrolled explosion. So far they've all been confined silently to his heavy steel bomb - and he expects to keep them there throughout the program. But he does admit, with some chagrin, to one small fire. It wasn't much, didn't even demand use of the magnificent, and large, red fire extinguisher which is prominently fixed to the wall near the door of his laboratory. It was caused purely through carelessness, he says, and was easily stamped out.
When Browning's work is completed, he expects that a process or methods engineer will review the results to see if anything may be applied specifically to jet engines. Then in another laboratory a second series of experiments will begin, possibly using as their starting point some finding made by Browning, and quite probably combining it with the results achieved by some other researcher, or group o£ researchers.
In this way, the work of one scientist here at Dartmouth may influence the progress of the great air age in which we find ourselves. The headlines in the papers will go to the development engineers or to the airplane companies, but what they do isn't possible without the foundations laid by scientists like Browning working in the area of basic information.
Prof. James A. Browning '44 in his Thayer School laboratory where flames, controlled explosions and moth-ball smells are part of his research for Project Squid.
Professor Browning seated before a pane! of flow and pressure meters used in his flame stability tests. Behind him sits a Thayer School student assistant. A fire extinguisher is handy on the panel board and a bigger one is just outside the door.
