Ultrasonic Fuel Injection

[ginsu]

I was playing with my ultrasonic toothbrush and noticed how small the bubbles become after coming in contact with the toothbrush. This made me wonder if you can use ultrasound to make very fine droplets akin to fuel injector atomization. I realized I couldn't have been the first to think of this so searched the web and found some info.

The do make ultrasonic injectors (from Sono-tek) and they have some very interesting qualities:

Better Control of Spray Shape

The spray can be controlled and shaped precisely by entraining the slow-moving spray in an ancillary air stream. Spray patterns from as small as 0.070 inches wide to as much as 1-2 feet wide can be generated using specialized types of spray-shaping equipment.

Ultra-low flow Capabilites

Since the ultrasonic atomization process does not rely on pressure, the amount of liquid atomized by a nozzle per unit time is primarily controlled by the liquid delivery system used in conjunction with a nozzle.

The flow rate range for the entire family of Sono-Tek ultrasonic nozzles is from as low as a few microliters per second to up to about 6 gallons per hour.

Depending on the specific nozzle and the type of liquid delivery system employed (gear pump, syringe pump, pressurized reservoir, peristaltic pump, gravity feed, etc.), the technology is capable of providing an extraordinary variety of flow/spray possibilities.

Drop-Size Range Selectivity

In general, the drops produced by ultrasonic atomization have a relatively narrow size distribution. Median drop sizes range from 18-68 microns, depending on the operating frequency of the specific type of nozzle. As an example, for a nozzle with a median drop size diameter of approximately 40 microns, 99.9% of the drops will fall in the 5-200 micron diameter range.

Well, I thought that this isn't exactly a fuel injector, but sure enough I found a patent for a "ULTRASONIC UNITIZED FUEL INJECTOR WITH CERAMIC VALVE BODY"

An ultrasonic fuel injector (30) for injecting a pressurized liquid fuel into the combustion chamber of an internal combustion engine that uses an overhead cam



So, they definitely exist, but do they really work? Would they be any good for F1? Are they legal?

Certainly, 18-68 microns is very, very small for a droplet. I don't know how it compares to diesel fuel injected at 1000+ psi. but it sounds small to me. So, it seems promising.

[Ciro Pabón]

What a great idea, ginsu! Just an afterthought: back in school, when we measured the electron charge, we passed droplets through an electric field and then deflected them with a magnetic field to find its velocity.

In principle, you could, not only create small droplets, but also direct them through the cylinder volume with a magnetic field. Care to make a new patent together?

[ackzsel]

In principle, you could, not only create small droplets, but also direct them through the cylinder volume with a magnetic field. Care to make a new patent together?

Isn't that made somewhat impossible due to the magnetic field inducted bij the spark coils? Those EM fields would kinda interfere with each other, I think.

[Ciro Pabón]

In principle, you could, not only create small droplets, but also direct them through the cylinder volume with a magnetic field. Care to make a new patent together?

Isn't that made somewhat impossible due to the magnetic field inducted bij the spark coils? Those EM fields would kinda interfere with each other, I think.

You are right, it could be a problem. There are probably a thousand things that make this unworkable, but actually, thinking about it, the disruption of spark plug's electric field only happens after the fuel has been (in theory) "magnetically" distributed. The spark coil, where the magnetic field builds meanwhile, is far away from the block and could be easily shielded by an Gauss cage, or whatever its name is in English.

The idea of an ultrasonic droplet creator seems good in itself, as I read in other threads that the combustion properties of the mix is one of the main barriers to get higher RPMs. If you have more combusting "surface" by making smaller droplets, you should, maybe, get a mix that combusts faster.

Unfortunately for this "grand scheme" you will find that (1.5 Mb PDF) droplet size in a Diesel nozzle is between 6 and 13 microns, which seems the same as the "ultrasonic" droplets. Gasoline injection could be promising as I found droplet size of 50 microns, which is an order of magnitude greater. Of course, the gadget would be useful for normally aspirated engines, I suppose, but I am not sure if you can get the same droplet size with gasoline injection as with diesel injection if you use a different nozzle.

What could be interesting here is that you do not need such high pressures to create the droplets. Ever heard of the Miller-cycle engine? You keep open the inlet valve while the piston is compressing (for a while, of course, it finally closes before ignition) which should give you around 15% increase in HP. This thing has to operate with a supercharger to avoid the piston pushing the mix out of the cylinder (it was "hot" when we had turbo back in the 90's). This could help to avoid the supercharger part, I suppose, but I do not know. It has been a long day...

But back to my "idea", I guess that somebody could check if the EM force you could develop is enough to actually move the droplets in the 1/20.000 of a second you have (at high RPM), which I think is the major problem. Given the high pressures, I find this not very feasible. But it is an idea to fill the areas that does not combust well or to help with the "CFD-only" distribution of the mix in the cylinder. Probably the "aero" guys had this distribution dominated, but you never know.

Who knows, maybe somebody has the money... Hey, I can help you with this (with the spending of money, I mean... ) We could build a nice, heavy, magnetic ferrite-iron block and cylinder heads... (this is a joke, pleeeze, and not very good).

[ginsu]

Thanks for the enthusiastic response, Ciro. I'm glad you posted some numbers on the droplet size for diesel direct injection, as that was the benchmark as far as I'm concerned. No, it wouldn't beat the diesel droplet size, but lets remember that they have to pressurize that fuel to the extreme, and are very, very vulnerable to particulates at that pressure. Not to mention, they need an engine driven mechanical pump to get the pressure that high, so you do lose power.

Also, diesel direct injectors probably have a very wide range of drop sizes, whereas the ultrasonic injector is able to make quite uniform drops:

As an example, for a nozzle with a median drop size diameter of approximately 40 microns, 99.9% of the drops will fall in the 5-200 micron diameter range.

One of the primary benefits of the Sono-tek Ultrasonic injector is that it requires very little energy to operate, I remember them quoting 15Watts.

Also, I don't think that you would need to guide the fuel all that much. As I see it, it would operate above the intake trumpet, directly in the center. And due to the velocity of the intake flow, I believe the fuel would be guided quite well, as this is one of the benefits that Sono-Tek advertise:

The spray can be controlled and shaped precisely by entraining the slow-moving spray in an ancillary air stream.

Another benefit of the Ultrasonic injector is it's very wide flow range, which seems very ideal for an Internal Combustion engine. I'm wondering if this would allow a 'throttle-less' intake. It seems feasible, as you can easily control the combustion by adding whatever amount of fuel you desire.

Since the atomization mechanism relies only on liquid being introduced onto the atomizing surface, the rate at which liquid is atomized depends solely on the rate at which it is delivered to the surface. Therefore, every ultrasonic nozzle has an inherently wide flow rate range.

Now, does anybody know if this type of injector is explicitly forbidden in F1?

[Ciro Pabón]

Well, you probably already know that the general rules only say this about injection:

5.7 Fuel systems
5.7.1 The pressure of the fuel supplied to the injectors may not exceed 100 bar. Sensors must be fitted which directly measure the pressure of the fuel supplied to the injectors, these signals must be supplied to the FIA data logger.
5.7.2 Only one fuel injector per cylinder is permitted which must inject directly into the side or the top of the inlet port.

And that's it. There are some paragraphs on air inlets and mixes of anything with the fuel, but they do not apply.

I looked around the titles of the appendixes to the rules, but I could not find anything on this subject.

So, my guess: yes, they are legal. At least, until Ferrari uses them and the other 11 teams protest. But you know, if you cannot be a useful member of society, you could always become an attorney.

My mother is a lawyer, and visiting my house today, immediately spotted the words "inject directly" in the rules (when I joked with her about the previous phrase) and told me "well, you could have a case against Ferrari here... but you are crazy, son".

Finally, I insist, for any compassive nerd that reads this: do you know of any example of "magnetic" distribution of fuel in the combustion chamber? After all, this is a 100 years old industry, everything has been tried once... even if the aero specialist probably have a hard time trying to imagine that you could guide the flow with something different from fins and wings.

I think this could be useful, even if ginsu thinks that "you do not need to guide the fuel that much". I am sure that the engine designers fight for keeping the fuel out of the cylinder walls (to avoid cooling it), so a magnetic field would be ideal here to do the task.

Besides, look at the pictures in the PDFs links I gave, to appreciate how much the nozzle can guide the fuel: it seems at the same sophistication level than my garden-hose, but I am an amateur.

Sorry for Senna's anniversary, ginsu.

[ginsu]

Ciro, I agree with you on the distribution of the spray in the pdf that you linked. It seems that we are very far from ideal when it comes to injecting fuel. There is enough information in that paper to digest for awhile. I've never really thought that fuel injection was a bottleneck, but I know they can now push for higher revs in F1, and combustion events are more and more important when they have to occur during shorter durations.

I do believe you are aiming down the right path by trying to keep the fuel from sticking to any walls of the inlet ports. It seems in F1 that the inlet velocity would be stratospherically high, but I'm sure there's still some tendency for fuel to stick to the walls. I've heard you can cure this with 'dimpling', similar to golf balls. But, I don't think anybody has dimpled an entire inlet tract. Also, how about electro-static repulsion? Although, I'm sure this could be dangerous with fuel. You could also do some sort of teflon coating.

I don't know much about the magnetic repulsion, it seems complicated, but I'm not really that informed about the subject.

Also, I believe it would be very important to find a way for the fuel to keep from sticking to itself, thus not forming any clumpy droplets and obtaining the largest surface area with individual spherical droplets. The ultrasonic injector looks to help with this. I wish I could do some research with one of those things, it'd be interesting to see if it would work. Perhaps I'll come back to this topic in grad school.