Electrostatics Under the Hood
October 1961 Popular Electronics

October 1961 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

Dr. Frank Stuetzers 1960s electrostatic oil filter, as presented in this 1961 issue of Popular Electronics magazine, was an ambitious attempt to revolutionize engine maintenance. It employed an electric field to capture metallic particles and carbon deposits from circulating oil, theoretically allowing for dramatically extended oil change intervals - potentially over 100,000 miles. The concept was innovative but flawed in practice. A major limitation was its inability to handle non-conductive contaminants like sludge and water, which still required conventional filtration. This necessity for a hybrid system added cost, bulk, and complexity under the hood. Consequently, automakers showed little interest, and the device saw only limited fleet testing. It never achieved commercial production. While the idea occasionally resurfaces, modern lubrication systems rely on highly efficient mechanical and synthetic media filters, making Stuetzer's invention a footnote in automotive history.

Electrochemistry Quiz

By James G. Busse

An engineer from Chicago recently drove his car into a service station in southern Minnesota and asked for an oil change. The attendant put the car up on a ramp and promptly drained the oil. But when he lifted the hood to replace the oil filter, he got the surprise of his life.

"There's something wrong with your car," he told the driver, excitedly. "The oil filter's missing!"

"Oh, it's there, all right," said the engineer, reassuringly. He leaned over and disconnected a heavily insulated wire from a small plastic cylinder attached to the fire wall. Picking up a wrench, he opened the bottom of the cylinder and tapped it gently. Out slid three months' accumulation of oil sludge.

He closed the cylinder, and the fresh oil was added. He then reconnected the insulated wire and packed up samples of the new oil, the old oil, and the sludge. In a few minutes, he was on his way again, leaving the service station attendant more bewildered than ever.

The engineer from Chicago is one of several now driving around the country, testing a new electronic device which promises to make your present oil filter as out-of-date as a hand crank or a running board. Besides eliminating the inconvenience and expense of conventional oil filters, it will mean less frequent oil changes. In short, this new device could easily add years to the life of your car.

Electronic Pump

The story of this ingenious gadget begins several years ago in Minneapolis. Hidden away in the basement of a building occupied by the Mechanical Division of General Mills was a tiny laboratory. In it, Dr. Otmar Stuetzer, an ex-German scientist, was busy studying the operation of a dielectric pump, a device which pumps dielectric liquids directly without moving parts (see Popular Electronics, April, 1959, p. 99).

In front of Dr. Stuetzer lay a plastic container filled with ordinary motor oil. Inside were two small metal rings separated by a short piece of glass tubing. Wires ran from the rings to a high-voltage d.c. power supply.

Dr. Stuetzer switched on the supply and adjusted its output to 10,000 volts. Slowly, the oil moved toward one electrode. The "pump" worked!

In the days and weeks that followed, Dr. Stuetzer spent many hours watching the oil move around the container, passing through the rings. And every now and then he saw something which puzzled him. A tiny particle of dirt moving along with the oil would suddenly dart toward one of the rings, pass through it, and then settle to the bottom of the container. Soon, a significant deposit of impurities could be seen there.

40,000 Volts

Eventually, Dr. Stuetzer had a glass blower make a special tube in which the electrodes were sealed in walls directly across from one another and at right angles to the oil flow through the tube. The lower ring surrounded the opening of a small glass bulb or "trap" attached to the main tube.

Connecting the electrodes to the power supply, he used a conventional pump to direct the motor oil past the electrodes. The oil wasn't dirty enough to suit him, so he gathered up all the dust and dirt he could find around the lab and dumped it in, tossing in some ground-up ashes from his cigar for good measure. Then he switched on the high-voltage supply and sat back to see what would happen.

Although a steady stream of dirt particles was passing between the electrodes, the color of the dirty oil flowing through the tube did not change. Dr. Stuetzer hopefully raised the voltage on the electrodes; several particles of dirt shot down into the trap. Cautiously, he increased the voltage to 40,000 volts. In a short time, a cloud of dirt appeared in the trap, and it continued to increase in size and density. Soon, the oil flowing through the tube became translucent again. The oil was being filtered electronically!

Two Electrodes

Conventional oil filters clean the oil in your car by forcing it through layers of tightly packed fibers and screens. As more and more dirt accumulates in the filter, its efficiency decreases. Finally, it becomes so clogged that it allows dirt to remain in the oil returning to the engine.

But in the electrostatic filter, two electrodes accomplish this filtering electronically. The high voltage applied to the electrodes produces an intense electrostatic field between them, and any dirt particle entering this field is of course affected by it.

If the particle is conductive-a piece of carbonized motor oil, say - its electrons are actually drawn towards the positive electrode. If the particle is non-conductive - a tiny piece of sand, for instance - its charge is similar to that of the dielectric in a charged capacitor: its orbiting electrons are repelled by the negative electrode and attracted by the positive one.

Once the particle is within the electrostatic field, it begins to move toward the negative electrode - the higher the voltage on this electrode, the faster the particle moves. But because this electrode is circular in form, the dirt particle has passed out of the electrostatic field by the time it reaches the electrode. And since it's out of the moving stream of oil, too, it settles to the bottom of the "trap."

"Corona" Point

In the original electrostatic filter, a large portion of the dirt particles were attracted to the upper electrode and thus would fall back into the oil stream, untrapped. But by substituting a pointed conductor for the upper ring electrode, Dr. Stuetzer killed two birds with one stone. For one thing, the pointed conductor concentrated the electrostatic field. And at the same time, it forced all of the dirt particles to move toward the lower electrode and the trap.

Why? Simply because the amount of static electricity on any conductor is proportional to the curvature of the conductor's surface. (This explains why all types of high-voltage electrical apparatus have smooth, rounded surfaces.) And when a high voltage is applied to a conductor with a pointed surface, the electrical charge concentrated at the tip is so intense that everything near it becomes strongly charged.

In air, this "corona" point charges and repels the atoms, generating a wind strong enough to blow out a candle. Similarly, in the electrostatic filter, the "electrical wind" charges even the smallest particle of dirt and literally "blows" it at the lower ring electrode. And this concentrated electrical field around the corona point also makes it possible to clean oil which is flowing through the filter at a relatively fast rate.

Power Source

Powering an electrostatic oil filter in a car is no problem. The current drain of one prototype filter is only a few microamperes at 25,000 volts, and this can be easily supplied through a filter choke and a couple of capacitors connected to the car's generator.

Although you can't buy an electrostatic oil filter for your car just yet, the time may not be too distant when they'll be installed in every new car rolling down the production lines. In fact, the day may come when a service station attendant will lift the hood and remark, "But, sir! This car has a non-electronic oil filter!"