Ultrasonic transducer on diesel injection line...would it oscillate fuel at the nozzle?

Question

heating is causing polymerization of fuel resulting in coking deposits.

I'm also heating the fuel in the line first, which causes the coking. Will the ultrasonic oscillations from the transducer on the injection line flow all the way into the injector through the fuel to the nozzle?

WOW! Thanks 'Dr. R'. That is a fantastic explanation! and with pictures too! I wish you explained all the answers here.

One more question if thats ok with you. I didn't want to build an injector from scratch, I'm gonna use a cummins injector.

I know, I know, construction details with harmonics are key. Would you know if services, say at my local university or laboratory that could determine the optimal position of the transducer on the injection line or top of injector. Got any tips to do it myself(ha, ha!).

With another pick of your savvy brain, do you think intense heat would interfere with the oscillation as well.

Answer 1

Yes, it will oscillate the fuel, and that may be a good thing. If you approximate the injector as a cylinder and put a piezo vibrator on the back end (opposite the nozzle), drive it at the first compressional harmonic. That will put nodes at 1/4 and 3/4 the way along the injector length. mount the fuel feed at the 1/4 point from the vibrator, and a thin mounting flange at the 3/4 point. That will minimize acoustic loss. You'll need to learn about harmonic analysis to grok all this. The nozzle is a converging sort so the vibration will impart an oscillating axial velocity to the fuel as it ejects. This may improve atomization by breaking the spray into short squirts of higher velocity than normal. It may prevent coke from forming at the end by literally shaking off the polymerizing goo before it hardens.

I'm an experimental physicist who specialized in continuum dynamics of all phases of matter, I'm telling you this is a great idea that may not have been tried before (find out!). I encourage you to pursue it. There is a great demand for clever ways to improve fuel economy and use alternate fuels (like bio-diesel). Don't be discouraged by naysayers who poo poo the idea. Read between the lines; most likely they simply assume it won't work because, if it did, someone else would have thought of it already, and there'd be a kit for it you buy on the internet.

Re " Will the ultrasonic oscillations from the transducer on the injection line flow all the way into the injector through the fuel to the nozzle? ". Yes, if you do it right. The idea is to set up a compressional standing wave the length of the injector with excitation at resonance. Antinodes (surfaces of greatest deflection) will be at the driver, nozzle, and about 1/2 between if you set it up as described above. The driver must be precisely tuned to the right resonant frequency for this.

Check out my sketch at the link below. D_z, here, is the peak axial displacement of the injector as a function of distance z along the axis (It's suppose to be a sine wave). The piezo element is just a disc of cermamic metalized on both sides that expands and contracts when an oscillating voltage is applied (leads not shown).The mass provides something for the driver to push again, and is part of the resonant structure.

If you're looking for an easy upgrade to your personal vehicle, give it up now and let someone else reading this post pursue it. I doubt modifying an exisiting injector would be very productive since there would be no regard to decoupling the harmonics from the rest of the engine, and that's kinda the key. The basic problem is that you've stumbled on a good idea that *may* have never been investigated before, but you have no experience with doing research and need to be more educated about the physics. Pursuing it would basically be a research project. I can only give general advice. The first thing you need to do is a literature search to see what's been done. If it's original then learn a bit about acoustics. There are finite-elements math packages that can help you model the resonant eigenfunctions of an elastic solid. I don't think heat is a big problem. Piezos use ceramic materials, which are generally refractory (heat resistant). The leads could be insulated with braided glass cloth. The acoustic response (elastic properties) of metals depend very little on temperature. Simple prototype injectors can be machined on a lathe with the right resonant structure. Buy a cheap oscilloscope to tune the acoustics. A proof of principle injector doesn't even have to work in an engine. Mock it up; prove it self cleans before coking with a propane torch or something.

If things look promising after such "simple" activities, learn about what's going on in engine research today. Find out how people are funded. Write a proposal. Maybe an SBIR (you'll need to be incorporated).

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Please email me you contact information. I've discussed your idea with a mechanical engineer who may be interested in helping you with acoustic modeling and machining. I've temporarily enable Yahoo Answers email contact permission.