why biodiesel has high lubricity?

Why does the sun shine?

Huw

Because its real slippery?

Chemically and physically, because the molecular chains are relatively long.

Long chains are usually 'oily';that is, they have increased viscosity over water, and they move slowly or sluggishly compared with shorter chained or smaller molecules. They usually have little mutual solubility with water.

When such a molecule gets into an area where friction is an issue, it tends to wet the surfaces and stay in place (re sluggish) , reducing friction.

Some molecules are better at reducing friction than pure oils or hydrocarbons, in particular those containing phosphorus, sulfur, halogens, and sometimes metal components.

I have a feeling that he may want to know why the molecular chains are relatively long.

Huw

Good question.

Extemporaneously, most natural oils, from soybeans, peanuts, trees, etc, contain mixtures of fatty oils having chains from something below about 14 carbons (coconut oil having fairly low chain lengths) to something over 22 carbons,

18 being most normal. The unsaturated oils tend to be liquids, the saturates are often like waxes.

These are the same types of oils you cook with, put on your salad, etc.

The human body makes and stores fats of about the same length. Eat too much, and your body makes these same types of fats as glycerin esters.

Why an average of 18 carbons? Much longer and the fats tend to become waxy and not too conducive to the health of the organism.

Shorter ones are produced too, like the 4 and 5 carbon butyrates (butter) and valerates. These tend to be highly odiferous, somewhat volatile. The shorter ones dont seem to be as useful for either plants or animals as far as energy storage is concerned, but they are useful as odorants, etc.

Plants (and animals) can be somewhat genetically manipulated to produce somewhat more or less of the specific fats, but the cost goes up.

For fuel purposes, the best option is to use what you can get cheaply and with the least modification and processing necessary. Hence, the biodiesel systems that are common today.

Could plants make something like gasoline? Yes, they already do, but only in limited quantities. Terpenes like turpentine, dipentene, limonene, etc could be blended and burned with relatively little processing, but they are expensive. Some esters might also be useful as gasoline substitutes.

Probably could be enhanced, but not worth it until the cost of fuel goes up drastically. Maybe never.

Long hydrocarbon chains are moored to polar functionality that binds to metal. Biodiesel strongly adsorbs to metal surfaces, presenting a forest of lubricious hydrocarbon tails to the outside world.

Sounds good enough to eat.

Huw

Does it means that if it binds to metal ,biodiesel is partly ionic?

Polar is a better description. The components may not display any appreciable ionic character, but they do have polar sites....

Well said, Uncle Alan... Apparently some of the chemistry and physics involved in these systems are still not easily explained.

My ex husband-in-law (ex wifes ex husband) worked for a lubricant company in the Los Angeles area. He says that the poly(isobutylene) compounds hold onto the surfaces in a manner that is still not fully explained, but the effects are measurable and positive. With all the branching, one could surmise that the lubricity would be good, but why it adheres the way it does is perhaps interesting.

Snakeoil is one of the best of lubricants;>)

UA: Long hydrocarbon chains are moored to polar functionality that binds to metal. Biodiesel strongly adsorbs to metal surfaces, presenting a forest of lubricious hydrocarbon tails to the outside world. ================================================= Does anyone know if there is a biodiesel engine lube? Is regular old B100 with less thinning suitable as a crankcase lubricant?

John Deere market both an engine and transmission oil. Have a look at their web site.

Huw

Not exactly. Modern engine lubricants are better and more stable than an unformulated vegetable oil blend would be. In the distant past, highly refined and formulated castor oil was used as an engine lubricant, as a matter of fact. This would be closely related to fatty oils used in biodiesels.

There was some previous discussion as to whether the Castrol name might have been derived from this product, and I am not sure we ever got to the bottom of that one.

Taking this a little in the OT direction, but these claims for pre-oilers always gave me a giggle. They claim that when the engine sits for some time, the oil drains COMPLETELY into the oil pan, and even cranking the engine with the starter does far more damage than many miles worth of running. Actually I have a hard time getting metal surfaces completely clean of oil :-)

snipped-for-privacy@nospam.nix wrote: snip

It was.

Castor oil is/was an excellent lubricant, but deteriorated quickly. Hence it was used for racing engines for one race - and the smell of 1920/30s race tracks was a sweet smell of burnt castor oil.

Stupid idea. A lube must survive, not merely work, and perform from winter storage temps in a storage sump to all Hell breaking loose at high engine temps under high shear and compression in a chemically aggressive environment. If you want the best synlube for your car, use Mobil 1 (though NOT in aircraft engines. Application matters). Citrate polyester is a good lube base. It will swell and crack your elastomeric seals and conduits unless well-diluted with hydrocarbon base lube.

If you want an Enviro-whiner lube dripping hype, use sucrose polyester (Olestra). All natural! Any failure in use is a test of faith.

I tend to agree. A properly engineered preoiler wouldn't hurt anything, especially if it came as an OEM addition from the manufacturer so that the warranty would not be in jeopardy. I don't know that it would help anything either.

True drysump systems would, I would think, take into account that it might take a moment to get oil flowing from the remote sump. Then, there aren't many dry sump systems in the sorts of cars most of us drive. In my slanted view, the more complex a system becomes (and the greater the number of individual parts), the more troublesome it promises to be, especially as it ages. Just like us humans.

Went through the Olestra plant about a year ago, Al. Very interesting. The time and expense they have spent on this product is amazing.

Well, the issue is just how long it sits, and how much weight/force is on the bearings when you start turning things.

Large stationary power units use 'pre-oiler' pumps that keep the oil circulating at a very low pace all the time. Then on a loss of power, the pump obviously stops. But because it was 'recently' running, the engine can be automatically started and broght on line in as little as 10 seconds.

If the engine had sat for a month or two without any 'soak-back', you can bet the bearings would wipe on such a start up (especially considering the amount of oil it takes to fill all the crank passages and oil galleries).

But yes, the typical claims of a lot of these small units, and the 'super-oils' that claim to prevent such damage are mostly BS.

daestrom