polymerization (coking) when using vo blends?

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scottmartin49
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polymerization (coking) when using vo blends?

Post by scottmartin49 »

Please keep it civil AND reasonably documented...

I've begun running soybean oil blended with #2 diesel in various ratios- mostly chosen to keep acceptable viscosities in varying temperatures.
A serious long term concern might be the formation of engine deposits, even with a pre-chamber type diesel, and I've been doing a lot of research on academic sites but can't really find anything definitive...

Does anyone here have knowledge of long term reliability- say MORE than 40 or 50k- of injectors, valves, rings, and etc.
Anyone ever had an opportunity to open up an engine that had been run on veg oil?

Please note, I am NOT talking about B20, Bio-diesel, or any mixtures including (but not limited to) motor oil, snake oil, Uncle Fred's Miracle Fuel Additive, etc.

If so, please be sure to state the details of the fuel (farm crushed, WVO, etc.) and the engine (beginning miles, condition, etc.) in your post.

Thanks for your input, this information could be genuinely valuable to anyone with an interest in the subject.

Scott; 198? VW Bitsa 1.6 NA Diesel
caveman
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Post by caveman »

I'm sorry this isn't a definitive answer, but when i had just started my shop where i was converting vehicles to run on VO , i had some one come in with their F350. He had done a decent conversion, but was having running issues- poor idle,intermittent low power etc. He had been getting all his WVO from a large restaurant , and about 75% was soybean oil. After doing a quick diagnostic, we pulled one injector which had about 1/4 inch of coke built up on it. We also dumped his motor oil [ which he said was changing fairly regularly ] and found chunks of coke in it also. I can tell you that was an eye opener, and we have avoided using WVO with any blend of soy in it. Other than him i never saw any others with the same problems caused by using soy.
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Fatmobile
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Post by Fatmobile »

I pulled a head off a VW Rabbit,
after 10,000 miles of WVO going through it and there was nothing unusual.
'91 Golf gasser converted to turbo diesel.
'83 Rabbit gasser, converted to diesel, then converted to run on vegetable oil.
2, '84 GTI projects cars
caveman
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Post by caveman »

No dispute here. i'm just addressing what seems to be an issue with soybean oil.
1971 super beetle

1990 t3 transporter 1.9na
1984george
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Post by 1984george »

I have about 8500 WVO miles and recently had looked at my injectors. The bottoms had thin layer of soot on them that i could easily rub off with my finger. I actually think that was nothing more than the fact that I broke down the other day on VO and didn't have a chance to purge my system.

I run canola oil from an Asian Restaurant. I may have run soy but have no knowledge of it.

I thought about blending 50/50 Diesel Veggie Mix during the summer in my main tank, but I'd rather do B100. I think in warmer climates you'd be fine if you checked your compression regularly and changed your engine oil.
Daren
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caveman
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Post by caveman »

No matter what ,halving your oil changes is a must, one of the only draw backs to running on VO. But it won't help coke build up on the injectors and combustion chambers from too much soy oil.
1971 super beetle

1990 t3 transporter 1.9na
scottmartin49
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Post by scottmartin49 »

caveman wrote:I'm sorry this isn't a definitive answer, but when i had just started my shop where i was converting vehicles to run on VO , i had some one come in with their F350. He had done a decent conversion, but was having running issues- poor idle,intermittent low power etc. He had been getting all his WVO from a large restaurant , and about 75% was soybean oil. After doing a quick diagnostic, we pulled one injector which had about 1/4 inch of coke built up on it. We also dumped his motor oil [ which he said was changing fairly regularly ] and found chunks of coke in it also. I can tell you that was an eye opener, and we have avoided using WVO with any blend of soy in it. Other than him i never saw any others with the same problems caused by using soy.
Most of the data I'm finding says veg oil is a definite no on open chamber diesels, but with the VW and Mercs being IDI this shouldn't be an issue. Mercs have the advantage on pumps- rotaries are not recommended.

I have a request in with inter-library loan for a couple of papers written back in the dark days of 1980-81 which should be useful, but it's looking like 40% soy with a cetane improver should be the maximum amount tolerable over the long term.

I'll post more when the research is done, but thanks(!) for the real world data.

Scott
scottmartin49
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data's in...

Post by scottmartin49 »

The three main factors affecting longevity in 1.6na diesels would be;

1. increased viscosity of vegoil and vegoil blends and their effect on injector pumps and fuel atomization.
2. the iodine value of the different oils that are being used- these affect polymerization rates, volatility, and atomization. They also produce an effect on plastics, seals, and rubber due to the drying effects of oxidation
3. lowered cetane value of vegoil/blends, leading to late and incomplete combustion with associated injector fouling and ring buildup.

Note that different oils have different values, but for our purposes liquid soy and sunflower are equivalent- liquid corn and canola are somewhat "better", and the solid fats are better yet- IF you have a fully heated system.

Lets start with viscosity. Straight veg WILL shorten pump life- couldn't find definitive data attributable to this one thing, but I'd speculateabout 60% the normal life span, with blends of 50% veg lasting about 80% as long as straight diesel. An important thing to note is that even 30% diesel added to veg does great things for viscosity. Viscosities effect on atomization is negligable on a warm IDI engine with single point injectors but long idling periods and cold starts aren't great; it's probably easiest to think of this as "December in July". Incresed fuel viscosity is like a straight diesel start up on a Minnesota morning in a cold month, everything's relative!

Iodine values are a measure of the "drying value" of an oil- think linseed oil- and then think of what's happening to your engine and fuel system if that's what's in there. Fortunately, not all oils are so drying. Soy and Sunflower have values of about 130, Corn and Canola about 100, and the solid oils lower still, and the recomendations run about like this;

a. if you want 80-100% of diesel fueled life-span keep your overall Iodine values below "50" i.e., a blend of 60%diesel and 40% Soy oil (approx.)

b. blends between 50 and 100IV may produce a loss of as much as 50% of useful operating life. This appears to be the case with straight canola as a long term fuel. It's your call- consider your costs and make your decision. THIS is the reason for processing veg into bio-diesel, it strips the gunk that causes the damage right out.

Cetane's the easy one. Our Bunnies, Golfs, and etc. are designed to run on a fairly high cetane stock- even higher than prevailing U.S. pump levels- and ANY vegoil will lower that even more. Most oils will run no higher than 40, with 37-39 being a closer approximation, so a cetane improver is a necessity for clean efficient combustion. There is evidence of piston and ring damage due to late combustion using low cetane fuels, especially when heavily fueled. This would relate to Hagar's claim that we should rev not lug. Those little pre-chambers can only burn so much fuel so fast, and if it floods out and burns on the piston top it's potentially damaging. Worse yet, it doesn't burn at all.

Again, this is all VW IDI specific, and by no means exhaustive. This is maybe 5% of what I've plowed through, but it's probaly enough for us to avoid mistakes we'd rather not make.

In the warm months i'm going to run a 60-40 blend of #2 diesel/soy oil with enough cetane improver to get the full 6 pts. improvement the manufacturer claims. It's running well so far...


Scott
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Post by Mr. Natural »

What kind of cetane booster do you use with WVO? I am not aware of any off the shelf cetane booster that is VO compatible.

Elsbett asserts that only canola oil meeting specific criteria are known to run reliably in single tank converted IDI engines. They do advocate blending as necessary to avoid gelling. Their kits include proprietary injector nozzles with spray patterns intended to minimize coking, and special glow plugs/relays that add heat to combustion as needed. These two items (spray pattern and added heat) appear to be what distinguishes them...

I have read that using a block heater to warm the engine up whenever the ambient temperature is below 70 degrees farenheit, anecdotally, minimizes coking. Cold starts with VO or WVO appears to be an invitation to coking.

An alternative would be an eberspracher (diesel powered engine coolant pre heater). These are common in Northern Europe as a factory or dealer installed option; and are practically essential on the TDI if one lives in the cold North.
Mr. Natural
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scottmartin49
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Post by scottmartin49 »

The Elsbett kits are nice, but beyond the level of cost-effectiveness I think most VO burners are looking for. They don't do anything about the IV values either.

I'm using "Diesel Kleen with Cetane Boost" by Powerservice for the cetane improver. I blend it with the VO before adding the #2 diesel. Seat of the pants says that cold starts and power are better than without it, but no real data.

We're still getting 30-40 degree mornings here.

Scott
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