Just a brainfart about igniting fuel, use microwaves instead of spark plugs.

[William Gaatjes]

Just a brainfart.
But would it not be a good idea to replace sparks plugs with RF emitters. Use microwaves to change the energystate of the atoms in the pressurized fuel + oxygen mix . That could be an idea.
The shape of the antenna, or use multiple antenna's would perhaps be a useful method to control the propagation of the combustion wave. Like controlling the flame front.
Is this idea ever done before ?
Is it feasible ? How much power would be needed ?
A dangerous idea would be to place a cup of gasoline+ oxygen mixture in a microwave and see what happens as a crude and dangerous experiment. Dangerous of course because of the explosion.

Perhaps , it could be also used for diesel engines.
To heat up the diesel.
No preheating required.
And the combustion timing could be modified as well for a diesel engine when usinf RF microwaves powerful enough to let the fuel+air mixture ignite timing be controlled.
That is , if it is feasible.

The advantage of this all would be a solid state rf emitter being part of the cylinder head.
If it is feasible, it could also be used for methane + oxygen mixtures.
And especially for 2 piston combustion engines.
Perhaps improved combustion and less harmless output gasses.

 

[Fenixgoon]

I wish I knew more on the topic of combustion physics to give you a more thorough answer, but my initial reaction is that I don't think an RF solution would be able to initiate combustion as efficiently as a spark. The spark itself is a plasma of ~5000-7000C. The operating temperature of the plug is 500-950C. A quick google indicates the instantaneous power for a spark plug spark is on the order of 25kW in the ~1ms time range.

The challenge with regards to emissions and combustion efficiency are manifold. Uniformity of mixing, temperature distribution, and uniformity of combustion (e.g. flame formation and propagation) are critical. Better fuel atomization/mixing and cooler incoming fluids (fuel, air) improve both the efficiency (N = 1-TL/TH) of combustion as well as reduce undesirable combustion products. Direct Injection was a big advancement in terms of keeping the fuel cooler and having better mixing compared to port injection. The combustion temperature can't get too hot either, as that will cause formation of NOX.

I found an EPA primer on NOX reduction (published in 1999, so a little dated at this point). Here's a quick screencap from "Nitrogen Oxides, Why and How They Are Controlled"

 

[alfa147x]

There might be a particular use case where this might yield better results than a rudimentary spark. It reminds me of a recent discussion about using a heat pump instead of traditional heating elements to toast bread. The heat pump, being "advanced" technology, would still take far too long and far less efficient than the toaster oven.

Take a look at this patent:

US20160265502A1 - Microwave spark plug for injecting microwave energy - Google Patents

A microwave spark plug for injecting microwave energy into a combustion chamber of an engine including an elongated housing, including an elongated chamber forming a hollow conductor in an interior of the housing, and including a microwave window arranged at a first end of the chamber in the...

patents.google.com

by this company: https://mwi-ag.com/en/technology/

Looks like they're trying to get into the Porsche Supercup cars:

Microwave ignition combustion engines will be huge says ex-Porsche CEO - Autoblog

The tech cuts emissions by up to 80 percent.

www.autoblog.com

but that was 5+ yrs ago

 

[telesweloB]

Just a brainfart.
But would it not be a good idea to replace sparks plugs with RF emitters. Use microwaves to change the energystate of the atoms in the pressurized fuel + oxygen mix . That could be an idea.
The shape of the antenna, or use multiple antenna's would perhaps be a useful method to control the propagation of the combustion wave. Like controlling the flame front.
Is this idea ever done before ?
Is it feasible ? How much power would be needed ?
A dangerous idea would be to place a cup of gasoline+ oxygen mixture in a microwave and see what happens as a crude and dangerous experiment. Dangerous of course because of the explosion.

Perhaps , it could be also used for diesel engines.
To heat up the diesel.
No preheating required.
And the combustion timing could be modified as well for a diesel engine when usinf RF microwaves powerful enough to let the fuel+air mixture ignite timing be controlled.
That is , if it is feasible.

The advantage of this all would be a solid state rf emitter being part of the cylinder head.
If it is feasible, it could also be used for methane + oxygen mixtures.
And especially for 2 piston combustion engines.
Perhaps improved combustion and less harmless output gasses.

This would not be very useful in diesel engines since diesel engines do not use a spark plug. Diesel engines burn their fuel entirely by compression.

Edit: I probably would’ve been better if I had simply said that diesel fuel is too dense. It cannot be ignited by a spark plug or this other way.

Diesel requires 1400° temperature for it to thoroughly burn. You get that through the extreme compression.

 

[William Gaatjes]

This would not be very useful in diesel engines since diesel engines do not use a spark plug. Diesel engines burn their fuel entirely by compression.

Edit: I probably would’ve been better if I had simply said that diesel fuel is too dense. It cannot be ignited by a spark plug or this other way.

Diesel requires 1400° temperature for it to thoroughly burn. You get that through the extreme compression.

Of course, diesel engines use compression.
But i was thinking of an interesting idea to modulate the flame front through microwaves.
Like kind of adding energy. Steering the flame front for cleaner burning maybe. it is just a thought experiment.

All combustion fuel, may that be methane , gasoline or diesel.
It is all hydrocarbons. And if possible the hydrogen is kind of excited so that the hydrogen bonds are easier broken.

That is... If it works similar to how a watermolecule is heated.
According to the literature : A watermolecule is an electric dipole following the electric field of a 2.45GHz microwave emitter.
For example methane would not work according to that principle. Because of the molecular setup : CH4.
The electrical field is even out. Non polar. But i am not a specialist in this field.

But it is interesting to find out what would happen. If it is easier to break the bonds...
Then the required temperature would be lower and less compression would be needed.
That would make for lighter engines and easier to design engines. Because with lower compression needed, the materials needed are less exposed to extreme forces...
Increasing durability and reliability. That is... If it is all possible...
Perhaps a different micro frequency would be needed...

Imagine this :
Ideal would be to separate the hydrogen from the hydrocarbons and then let the hydrogen enter the cylinder.
Also, filter the air because current composition of air : a quick google search reveals 78% nitrogen and 21% oxygen.
For a clean burn, you want to separate the oxygen from the nitrogen. And then you have pure oxygen and pure hydrogen.
And you get a clean burn for a combustion engine : Just water vapour...

 

[William Gaatjes]

I wish I knew more on the topic of combustion physics to give you a more thorough answer, but my initial reaction is that I don't think an RF solution would be able to initiate combustion as efficiently as a spark. The spark itself is a plasma of ~5000-7000C. The operating temperature of the plug is 500-950C. A quick google indicates the instantaneous power for a spark plug spark is on the order of 25kW in the ~1ms time range.

The challenge with regards to emissions and combustion efficiency are manifold. Uniformity of mixing, temperature distribution, and uniformity of combustion (e.g. flame formation and propagation) are critical. Better fuel atomization/mixing and cooler incoming fluids (fuel, air) improve both the efficiency (N = 1-TL/TH) of combustion as well as reduce undesirable combustion products. Direct Injection was a big advancement in terms of keeping the fuel cooler and having better mixing compared to port injection. The combustion temperature can't get too hot either, as that will cause formation of NOX.

I found an EPA primer on NOX reduction (published in 1999, so a little dated at this point). Here's a quick screencap from "Nitrogen Oxides, Why and How They Are Controlled"
View attachment 84988

The thing is that this is indeed 24 years old. Technology has progressed. But i understand what you mean.
It is kind of thinking how to get a clean burn. Or to just separate those hydrogen atoms easily.
If i look at this, the main culprit is the nitrogen in the air.
Separate the oxygen form the nitrogen or at least lower the amount of nitrogen and then perhaps less NOx and other nitrogen (di)oxides would be present.
See post above.
This would also be good for stationary powerplants fueled by the methane in natural gas.

 

[Fenixgoon]

The thing is that this is indeed 24 years old. Technology has progressed. But i understand what you mean.
It is kind of thinking how to get a clean burn. Or to just separate those hydrogen atoms easily.
If i look at this, the main culprit is the nitrogen in the air.
Separate the oxygen form the nitrogen or at least lower the amount of nitrogen and then perhaps less NOx and other nitrogen (di)oxides would be present.
See post above.
This would also be good for stationary powerplants fueled by the methane in natural gas.

NOX emissions are still a challenge. I currently work in the HD truck business!

 

[Paperdoc]

I did research decades ago in Physical Chemistry on how molecules interact with microwaves. This is the basis for how microwave ovens work.

Different types of motion in molecules occur naturally at different ranges of frequency of the applied electromagnetic field. To get the molecule excited in a particular way, you need to apply a field of the right frequency. We are all familiar with using heat to cook food. That means, applying infra-red waves to the food. That frequency range excites several types of vibrations between parts of molecules, especially organic molecules in foods. These motions are stretching, bending and some torsional vibrations of the bonds between atoms. But there is another totally different type of motion that is slower: rotation. That is, rotation of the whole molecule, and also rotation of parts of a molecule with respect to the rest of it. These can be excited by an electromagnetic field in the lower frequencies we call microwaves only if the molecule (or a sub-part of it) has an uneven distribution in space of the electrons in the bonds, producing what we call a electric dipole moment. When that electric dipole is exposed to an electric field which rotates around it at a frequency that closely matches its natural normal frequency of rotation it experiences a torque force that increases its rotational energy. In the real world of things we experience and measure ourselves, we "see" this as higher temperature - the material has been heated, very similar to what happens with infrared, by a different but related mechanism.

As I said, such interactions between an applied rotating field and a molecule (or part of it) only happen if the molecule or fragment has an electric dipole because its structure on NOT symmetrical. Hydrogen, ethane, oxygen, carbon dioxide, carbon tetrachloride, benzene, etc. all are symmetrical and are not heated by microwaves. Water, ammonia, fats, sugars, proteins, and loads of organic molecules all have electric dipoles in them and ARE heated by microwaves in the range from 1 GHz to 150 GHz and higher.

By far the majority of gasoline components are linear hydrocarbons that do NOT have significant electric dipoles. That's why we class them as non-polar. So I am very skeptical of the ability of microwaves to heat such fuel efficiently. I really doubt it can excite those molecules as well as an electric arc spark.

 

[William Gaatjes]

I did research decades ago in Physical Chemistry on how molecules interact with microwaves. This is the basis for how microwave ovens work.

Different types of motion in molecules occur naturally at different ranges of frequency of the applied electromagnetic field. To get the molecule excited in a particular way, you need to apply a field of the right frequency. We are all familiar with using heat to cook food. That means, applying infra-red waves to the food. That frequency range excites several types of vibrations between parts of molecules, especially organic molecules in foods. These motions are stretching, bending and some torsional vibrations of the bonds between atoms. But there is another totally different type of motion that is slower: rotation. That is, rotation of the whole molecule, and also rotation of parts of a molecule with respect to the rest of it. These can be excited by an electromagnetic field in the lower frequencies we call microwaves only if the molecule (or a sub-part of it) has an uneven distribution in space of the electrons in the bonds, producing what we call a electric dipole moment. When that electric dipole is exposed to an electric field which rotates around it at a frequency that closely matches its natural normal frequency of rotation it experiences a torque force that increases its rotational energy. In the real world of things we experience and measure ourselves, we "see" this as higher temperature - the material has been heated, very similar to what happens with infrared, by a different but related mechanism.

As I said, such interactions between an applied rotating field and a molecule (or part of it) only happen if the molecule or fragment has an electric dipole because its structure on NOT symmetrical. Hydrogen, ethane, oxygen, carbon dioxide, carbon tetrachloride, benzene, etc. all are symmetrical and are not heated by microwaves. Water, ammonia, fats, sugars, proteins, and loads of organic molecules all have electric dipoles in them and ARE heated by microwaves in the range from 1 GHz to 150 GHz and higher.

By far the majority of gasoline components are linear hydrocarbons that do NOT have significant electric dipoles. That's why we class them as non-polar. So I am very skeptical of the ability of microwaves to heat such fuel efficiently. I really doubt it can excite those molecules as well as an electric arc spark.

Since chemistry is not my background, but electric engineering is...
I did some google searching and compared that with knowledge of dielectrics from various materials based on the knowledge how a capacitor works.

Then i remembered how much fun the following experiment was many years ago when a sort of relative from the past asked me how to measure the amount of gasoline or diesel or just oil in a tank from a boat or just a bottle in an easy way.
I remembered back then how i did experiments as a young lad to build a tunable capacitor by using a plastic bottle with two sheets of alumunum foil and measuring the capacity of the setup.
Based on the dielectric constant of around 80 for water. More water means more capacity. The capacitance increased with the amount of water in the bottle. And decreased when the amount of water was reduced.
Which fits perfectly with the calculation formula to determine capacitance of a typical parallel plate capacitor.
Fun experiment for eager youngsters, even today.

Anyway...
I then found out that measuring capacity with oil works really lousy. Of course because of the low dielectric value.
And that connects with having almost no dipole moment. The material is non-polar.
I then found a chart with dielectric values of different substances and compared my finding and it was obvious.

I remember now and understand.
And i fully agree, based on dipole moment.
If i say : The dipole moment determines the dielectric behavior with these kinds of fluids / substances.
This is sort of correct yes ?

As an example a list of dielectric constants for other people reading this :

Liquids - Dielectric Constants

Dielectric constants or permittivities of some fluids or liquids.

www.engineeringtoolbox.com

 

[Paperdoc]

Yes, The magnitude of the dipole moment has a direct bearing on the rate at which the material can absorb energy from an applied field. If the material's molecules have a high dipole moment, then it will absorb energy from an alternating field at a faster rate; NO electric dipole and it will absorb very little. Nevertheless, at very low frequencies (or DC, which is just zero frequency), any material HAS a dielectric constant. So your capacitor measuring device still CAN work with oils.However, with such a low dipole moment its dielectric constant is MUCH lower than water's, so your calibration graph of fluid level versus capacitance measured will be quite different, with ALL capacitance readings for oil much lower than for water at any particular level.

Now here's where it gets complicated - this was my field of research. The dielectric constant of any material is NOT a constant! It becomes less as the frequency of the applied field is increased, and drops substantially over the frequency range where the applied field interacts with the molecules to excite them. Energy is absorbed from the alternating field by the molecules. Mathematically we express the "Dielectric Constant" (symbol the Greek letter epsilon, ε) as a complex number with real and imaginary parts:

ε = ε' - i ε" where i is the square root of -1.

In the limiting cases, for near-zero frequency the max value of ε is called ε(0) and is the value commonly encountered. At some very high frequency (typically below infrared and visible light) we call that the "infinite" frequency for this purpose and the minimum value of ε is called ε(∞). The Debye-Pellat Equations describe the relationships between the ε' and ε" parts to the angular frequency ω (Greek omega) of the applied alternating field and the characteristic relaxation time τ (Greek tau) of the molecular process causing absorption of energy from the field.

Now, the Maxwell Equations say that the Refractive Index of a material is just the square of the Dielectric Constant, and both really are frequency-dependent complex numbers. Even over the frequency range of visible light the Refractive Index of most materials changes slightly, and that is why a glass prism can "split up" white light into its separated range of colours - the Refractive Index of the glass changes over that frequency range and thus bends different light frequencies by different angles. For purposes of studying molecular rotation and microwave fields, we approximate the upper-frequency low-limit value of ε(∞) as the square of the refractive index of that material measured specifically in the middle of the visible light region at the orange D lines in the Sodium atom emission spectrum.

These factors have become much more important in our daily lives and in modern technology which relies heavily on electronic devices operating in the Gigahertz region. Insulating materials in circuit boards and inside capacitors must be made of materials that do NOT interact with those high-frequency alternating fields; to interact and absorb energy from the field would reduce the field intensity and cause delays in the speed of signal transmission. It impacts our ability to transmit high-frequency signals for high rate data transfers (think of the 2.4 GHz and 5 GHz bands used for WiFi everywhere, and for many communication systems) because such signals are absorbed and reduced by many molecules in living matter AND by that VERY ubiquitous substance, water!

Back when I was doing that lab work we were doing fundamental research to measure the rates of rotational motion of certain molecules and of their substituent groups and relate that information to the physical sizes of the rotating items and to the energy interactions they have with their surroundings and with the rest of the host molecule. Using some of those results we then pursued a relatively new field at that time, Far-Infrared Absorption. This is the frequency range between high microwaves and low-end infrared light, and there was no good understanding of what processes at the molecular level could absorb energy from fields at that frequency. We devised experimental conditions to slow the rotational motions substantially and shift their energy absorptions to well below the Gigahertz region to make it easier to examine the Far-Infrared Absorptions that occur over 100 GHz.