Electronics in Diesel

Question

I was wondering if there will be any adverse effect on electronics functionality-wise when it is dipped in diesel and operated. Since diesel is non-conductive, the functioning should not be affected. What other factors should I consider? What is used in industry to protect such circuits?

Also even though diesel is not very easy to ignite, its flammability should be considered too. — Eugene Sh., Oct 13 '21 at 18:20
Fuels are usually organic solvents, so I wouldn't be surprised if it dissolved certain components' packaging over time. — Hearth, Oct 13 '21 at 19:00
You will seriously need to consider [Intrinsic Safety](https://en.wikipedia.org/wiki/Intrinsic_safety). — jay, Oct 13 '21 at 19:01
Fuel diesel is not pure - it has both contaminants and deliberate additives which are attracted to powered electronics floating in it and result in the electronics becoming contaminated with "gunk" which maybe be somewhat conductive. — brhans, Oct 13 '21 at 19:14
Diesel in a relatively full tank is difficult to ignite but a near empty tank may allow an explosive mixture to form. Recall TWA Flight 800 as an example of what can happen. — jwh20, Oct 13 '21 at 19:26

score 4 · Answer 1 · answered Oct 13 '21 at 18:53

The epoxy seal is perhaps the biggest risk to ingress, especially on LED's. The lower the dielectric constant the better for high slew-rate signal crosstalk. Air is 1 , Parylene is 2~3, epoxy and oil products are 4 , water is 80. All plastics are hydroscopic, some transmit less than others. Any fluids can be a carrier to contaminants that cause failure.

COnsult with a Conformal coating engineer for advice and verify the results. [Get EE and coating risk specs ] Don't guess.

Random example https://pctconformalcoating.com/lp/conformal-coating-services

Thanks. Will see what conformal coating/ potting compound solutions are rated for this kind of application. — aaditpj, Oct 18 '21 at 04:28

score 2 · Answer 2 · answered Oct 13 '21 at 19:26

Since diesel is non-conductive, the functioning should not be affected.

Directly (instantly) affected - unlikely. But can it be latently, indirectly affected? I think likely.

I do not know the peculiarities of diesel fuel in this regard. But one of the worst contaminants for PCB's is hydraulic fluid. While it is "just an oil" and "oils are non-conductive so should be fine", hydraulic fluid will cause severe PCB damage over time. The reason why is: 1) It's mobility is so high that it can get under the solder resist, even under the traces themselves, and 2) Hydraulic fluid is hygroscopic, so adsorbs water. Oil, carrying water molecules, to bare copper, corrodes the copper traces readily.

What other factors should I consider?

Is there any explosion/fire hazard from any conceivable failure? Vibration?
What can/will happen at the expected temperature extremes?
What contaminants (oils, solids, other chemicals) can be in the diesel fuel?

What is used in industry to protect such circuits?

For (limited) exposure, conformal coating might be used. This is a dip, spray, or paint-on material which dries or cures and resists most chemicals. Compatibility with diesel fuel would need to be verified against the specific product.

Another option is potting or total encapsulation. Again, check for compatibility. This is usually an epoxy compound which is poured into a box, covers the circuit board, and hardens, totally encasing everything. If potted, nothing can get to the components, not even a service technician. Special care may have to be taken at the interface between potting compound and exiting wiring, such as RTV silicone sealant. (Some materials may still be able to enter from the microscopic gap between wires and the potting compound.) Also, circuits operate hotter when potted, as the potting compound acts as a thermal insulator.

These are a lot of variables to consider. Wouldn't it be easier and safer to just keep the board away from the fuel?

Thanks. I have thought of keeping the PCB away, but I require the flowing fuel to cool the electronics too. Keeping it away would require me to have a separate cooling system which I don't think would be feasible in this project. I'll explore what conformal coating options I can find that would work. — aaditpj, Oct 18 '21 at 04:26

score 0 · Answer 3 · answered Oct 13 '21 at 18:22

Thermal dissipation will be different. Dielectric properties also change, affecting capacitance, an aspect that may be relevant in systems with frequencies higher than HF. And of course since diesel is not pure, dissolved components in it can sulfate or corrode the contacts and components.

Electronics in Diesel

3 Answers3