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Quiet engines

In the lab at the Technion, the engine of the future is being developed, which operates using sound waves. The result should be cheaper, more environmental and more durable

"Instead of the action of compression and expansion being performed by a moving mechanical component, such as a piston or turbine, we use a sound wave"/ illustration: pixabay.
"Instead of the action of compression and expansion being performed by a moving mechanical component, such as a piston or a turbine, we use a sound wave." Illustration: pixabay.

By Racheli Vox, Angle, Science and Environment News Agency

In the war of attrition, four Mirage planes of the Israeli Air Force made a sortie in the skies of Cairo, during which they crossed the speed of sound over the house of the then president of Egypt, Gamal Abdel Nasser. The resulting supersonic boom caused the windows of the house to shatter. In response, Nasser fired the commander of the Egyptian Air Force.

The event in Egypt is an example of how sound is not just a means of communication, entertainment or a nuisance (the annoying noise from the neighbors' renovations, for example) - sound waves can have a lot of power, and this power can be exploited. In a new development, recently presented at a seminar of the Faculty of Civil and Environmental Engineering at the Technion, the power of sound waves is harnessed to replace the moving parts in the engine - something that may make the engines much cheaper, more durable, and also more environmentally friendly.

Voice drive

An engine is not the only thing that moves our vehicle from place to place. Every time an action is performed that is contrary to the natural state, such as cooling a hot room or moving an inanimate object, energy must be invested in it - and a motor is a device that is able to perform this conversion of energy into work.

The operation of all engines is relatively similar, and is based on the compression and expansion of a material, usually gas. Also, all engines have moving parts. In the car engine, for example, the mixture of fuel and air is compressed by a piston and then ignited, and the resulting explosion moves the piston - which causes a process that moves the wheels of the car. In power plants, the piston is replaced by a turbine, whose blade moves using steam produced by burning combustible materials - which causes magnets to move and thus generate electricity.

The moving parts - the piston, in the case of the car engine, and the turbine in the case of the power plant - are a basic component of the engine, but they require extensive and expensive maintenance and over time they wear out and wear out, and they are expensive: the cost of their production is usually the main component of the cost of the engine. The new development introduced recently may change this situation. "We are based on the same principles, only that instead of the action of compression and expansion being performed by a moving mechanical component, such as a piston or turbine, we use a sound wave," explains Associate Professor Guy Ramon from the Faculty of Civil and Environmental Engineering at the Technion, who began working on the idea already in His PhD under the guidance of Prof. Yehuda Agnon.

A noise ten times louder than an airplane engine

Sound, like any wave, is actually a disturbance that spreads in space. When this disturbance reaches our ears and stimulates our eardrums, the brain knows how to translate it into meaningful auditory information. But sound does not only reach the ears, it can travel through different media, whether they are solid, liquid or gas.

We do not feel the full strength of the sound waves when we speak, because our voices are too weak to cause a significant effect, but the intensities with which we work in Ramon's laboratory are much stronger. "One of the engines we have in the lab is capable of producing a noise that is ten times louder than that of a jumbo plane engine, and the hand is still tilted," says Ramon. A jumbo jet engine by itself produces noise of a magnitude that causes irreversible damage to the human ear.

The mechanism of action of the new patent developed in Ramon's laboratory, known as the "acoustic engine", is based on a temperature difference. Naturally, hot matter expands and cold matter contracts. Such a phenomenon occurs when thunder is formed, for example: following the formation of lightning, the temperature of the air rises suddenly, and the air spreads. The expanded air then comes into contact with the colder air surrounding it, and therefore contracts again. The expansion and contraction naturally cause the creation of a sound wave - which is essentially thunder.

In the acoustic engine, the heated gas expands, then reaches a colder part of the engine - and contracts again. However, unlike lightning, which is a transient phenomenon, and therefore the thunder stops after a short time, in the acoustic engines heat continues to be introduced into the system - and therefore the process repeats itself over and over again. The creation of this powerful sound wave is a well-known physical phenomenon, called thermoacoustic instability.

Usually, thermoacoustic instability is considered a very negative phenomenon, it can be caused as a byproduct in jet engines or rocket engines, and the pressure caused by the sound wave can cause them to explode. Here, on the other hand, the scientists create the phenomenon deliberately and in a controlled manner, using equipment that can withstand it, and exploit it for the purpose of starting the engine.

Cool the house using the solar heater

Source: Associate Prof. Guy Ramon.
Source: Associate Prof. Guy Ramon.

Replacing the expensive moving parts with sound waves could allow the acoustic motors to be significantly cheaper than those that exist today. This fact will not only affect our pocket, but can also lead to energy savings at the economy level: the engines that exist today consume a lot of energy to operate, which is manifested in the production of heat at very high temperatures. A gas turbine for example, which is mainly used to propel aircraft, operates at a temperature of about 900-800 degrees. According to Ramon, today it is not economically profitable to use low temperatures for driving engines - but with cheap technology like the one being developed in his laboratory, there would be no reason not to do so. Ramon and his team managed to create the temperature difference necessary for the operation of the engine and the creation of the powerful sound wave even at relatively low temperatures. "We are talking about temperatures of about 90-80 degrees, which can be achieved with a simple solar water heater that heats water for showering or cooking," he says.

Such an option will be especially useful on very hot summer days, when the heat is naturally abundant. "During the particularly hot summer days, the consumption far exceeds the annual average," says Ramon. "There is a situation where countries are investing a lot of money in electricity generation infrastructure that is not in use most of the time, but is only supposed to work during these peaks. In Israel this is particularly noticeable." Such an idea will reduce the need for such infrastructures, because it will allow the production of devices that will not rely on the central electricity grid, but will be powered by heat we already have at home, for example from cooking or the solar heater.

Accordingly, the main direction of research today is cooling infrastructures, such as air conditioners and refrigerators, for private houses or apartment buildings. In such infrastructures, the sound wave created by the engine will replace the compressor: in an air conditioner or refrigerator, the compressor compresses the gas in the air conditioner, thus causing it to heat up. When the compressed material comes out of the compressor, it cools again - and thus also cools its surroundings: whether it is the room or the inside of the refrigerator. In the acoustic engine, this compression action is performed by the sound wave.

Of course, saving electricity from power plants, which is mostly produced from fossil fuels, will also lead to reducing the damage to the environment that occurs due to the burning of these fuels. Another environmental advantage of the acoustic engine, when used in cooling systems, is that it does not use materials that are harmful to the environment. refrigerators andAir conditioners Gases are used as part of their operation: the freon gas, which is known to be harmful to the ozone layer (especially in older devices and in developing countries), or the greenhouse gases from the HFC family, which do not damage the ozone but contribute to the greenhouse effect. "We only use materials that are in the environment naturally or that will not harm the environment if they are released into it," says Ramon.

According to Ramon, it will be possible to use the acoustic infrastructure even in places where there is usually no access to electricity, such as remote settlements, or developing countries that do not benefit from the electricity infrastructure that is so obvious to us. "These are people who can't store food or medicine in a refrigerator, they don't have a small lamp to light the cabin and they certainly don't have air conditioning," says Ramon.

In addition to using the sound wave for cooling technologies, Ramon and his team are also testing other uses, such as converting the sound wave directly into electricity. "This is actually what a microphone does: turns sound into an electric current, and in the same way you can take the powerful sound wave generated in the engine and turn it into an electric current," says Ramon.

From science fiction to reality?

Today, the development of the acoustic engine is progressing vigorously: in Ramon's laboratory, working models of the engines already exist, have been published and will be published Articles on the subject and the invention was registered as a patent. Beyond that, Ramon and his team are in talks with investors to turn the development into a commercial product. However, he stresses that much work is still needed. "In the scientific aspect, we have made quite a lot of progress in understanding the mechanisms and basic physics, but there are still question marks", he says. "I think that when we solve them it will be easier for us to move forward on the engineering level as well."

Ramon hopes that once this progress is achieved, the industry will also invest more resources in the development of the technology, similar to the large investment in the development and improvement of the various technological devices around us. "If it will be as good as I think it can be, more and more engineering hours will be spent on development and will take the issue far," he says. "We need to give them the starting point."

Of course, Ramon is aware that his idea is very unusual. "This idea sounds crazy at first, it happens a lot that people don't believe me that it can happen until I show them the engines in our laboratory. It sounds a bit like science fiction, but it is definitely possible", he concludes.

5 תגובות

  1. It is worth noting that a supersonic boom is not created by crossing the speed of sound. The boom is created continuously - as long as the plane is in supersonic flight.

  2. "The operation of all engines is relatively similar" perhaps, if electric engines are ignored...

  3. "that cannot store food or medicine in refrigeration"
    Medicines and stored items (in the warehouse)
    people are staying (in a hostel)

  4. "In the car engine, for example, the mixture of fuel and air is compressed by a piston and then ignited, and the resulting explosion moves the piston" - this is true for a gasoline / gas engine. In a diesel engine there is no ignition but an explosion due to pressure.

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