Silicone oil in engine

[HardbodyLoyalist]

Yes, you can have non-solid SiO2, but only if you melt it. If I recall from my solid-state chemistry class, this happens somewhere around 1600 Celsius!

It is also possible that the SiO2 is colloidal (very small particles suspended in solution), but this isn't what that paragraph seems to describe.

I suspect that they're actually describing the deposition of solid SiO2, and you're absolutely right that it would cause serious problems.

Furthermore, ethyl silicate is probably susceptible to hydrolysis (i.e. it reacts with water), which wouldn't do much for its shelf life.

 

[mojo]

You also need to remember that silicone oils/fluids as a class are very poor on metal to metal contact. Anotherwords, they will create real wear problems.

 

[kilou]

Hi,

This is what I found on http://www.aeroconsystems.com/misc/motor_making.htm

"Oxygen motors generally run hot, and heat transfer to the walls is at a fantastic rate. This had been a problem from the beginning, even with regenerative cooling, but in the spring of 1948 experimenters at General Elextric came up with an ingenious fix. They put 10 percent ethyl silicate in their fuel, which as, in this case, methanol. The silicate had the happy faculty of decomposing at the hot spots and depositing a layer of silicon dioxide, which acted as insulation and cut down the heat flux."

Well two things bother me a little bit about this silicone oil:

- It "breakdowns" in a layer of SiO2 deposit. If it's a deposit, then it is likely it can clogg oil galleries and/or filter no?

- The decomposition product is SiO2 and this is..........sand!!!!! So this should drastically increase wear on hot spots no????? I dont like the idea of having SiO2 in the engine. Is it possible to have a non solid form for SiO2?????

Thanks

 

[MolaKule]

For the interior casings of rocket motors, where you want some insulation, this additive would be a good idea.


But depositing SiO2 on rings, cylinder walls, and valves is a bad idea.

 

[XS650]

In general, it's not a good idea to use rocket engine fuel in your otto cycle engine.

 

[Kestas]

Rocket motors have a design life measured in minutes.... your piston engine is measured in thousands of hours.... roughly four orders of magnitude difference!

 

[labman]

I don't think ethyl silicate is what is sold as a silicone oil. The SiO2 deposits are not meant as lubrication, but as insulation, like the tiles on the space shuttle. As long as it stays put, it would be all right in an engine. Think of the ceramic coated pistons. Silicone lubes have their uses, usually where heat resistance and stability are more important than preventing heavy metal to metal contact. Great for brake parts along with graphite doing the heavy metal to metal work.

 

[kilou]

So maybe this additive is not what is called a silicone oil. But I've heard about an additive (Mecacyl) which contains a lot of silicone and this additive is used in Europe with very good results and since a long time. It is almost impossible to find a bad opinion from those who are posting things about it that's why I'm particulaty interested in this one.

Recently there has been a test of this additive made by a french car-bike magazine and they pointed out very promising results of this additive (drastically decreased wear of the engine etc....) and the oil anylsis pointed out that this additive is mainly based on silicone (2025ppm of Si in the oil...............).

Well all seems very interesting but this high content of silicone is somewhat strange and I'd like to know what it makes on the engine. But as I said, people who use this additive are all very enthousiastic about it.

If you want to read the test (in french) with results of the oil analysis, you can find it here (scanned images in jpeg)

http://www.argus-nc.info/

So this is really why I ask all these questions about silicone additives because it seems these are really working. But I'd like to know if there are drawbacks with silicone and I can't find anything on the net. Solid SiO2 of course would be a large drawback but as the lab measured a real decreased wear in the treated engine, this shouldn't be apply to the additive I'm speaking about. Do you know any other drawback? Plugging of oil galleries? Lambda sond contamination?

 

[kilou]

Moreover silicone is used as an anti foaming agent in all engine oils so it shouldn't be bad for the engine no?

 

[Kestas]

I'm confused... are we talking about silicone or SiO2? Both are completely different animals. Even SiO2 has many different crystal forms, each with its own character and set of properties.

 

[kilou]

Imagine the additive uses 100% organo polysiloxanes similar to anti foaming agent. If you have a 3% mix of this additive in your engine oil, would this cause any troubles?

I've heard that too much antifoaming agent may result in foaming.......... True?

 

[MolaKule]

Hey guys, listen to mojo, he's right on.

The molecular weight of this product is so high that too much polydimethylsiloxane (PDS)
interferes with the lubricity of the base oil and tends to thicken it. These silicon fluids do not do much to lower friction.

Sometimes you may see as much as 100 ppm in so-called "shock" fluids, but the average treatment rate for engine oils is 3-10 ppm.

BTW, the higher the viscosity of the base fluid, the greater the foam inhibitor treatment level required.

Be aware that PDS' are sometimes substituted with vinyl acrylates as foam inhibitors. In other cases, both types of foam inhibitors are used.


The only silicon fluids I am aware of that are used in lubricants are the polyflurosiloxanes; very specialized, very expensive.

[ August 12, 2004, 02:36 PM: Message edited by: MolaKule ]

 

[mojo]

When silicone is used as an antifoaming additive,it is used in extremely small quantities like in the 1-10 or more parts per million range. Further, this is an organo polysiloxane product not to be confused with the inorganic version mentioned above.

 

[kilou]

Well the confusion mainly comes from the fact that on the webpage regarding the "rocket engine additive" (see first post), it is said that silicone will produce a layer of SiO2 on hotspots thus cooling down them. I do not know if the additive I'm speaking about (Mecacyl) will produce SiO2 but for sure it contains a lot of silicone (2025 ppm Si in the oil sample!!!).

Of course there are a lot of different silicone molecules and obviously it is not possible to know which one is used in the additive but is there general precautions regarding silicone in an engine? I suppose that silicone would coat the engine internal parts so there may be a risk of piston rings sticking no?

As a rule of thumb, chlorinated additives are not good in engine despite the fact it exists a lot of different products too. So is this the same for silicone?

For me it is really important to know because this additive has a very very good publicity around Europe and the test has shown that it works really great!

 

[kilou]

Mecacyl costs almost 30 USD for 100ml.......so it is very expensive

Is there something to do to know what type of silicone is used in this additive? May an oil analyser know what is used in this stuff?