Blending with gasoline

Single Tank WVO systems and blending SVO WVO to thin it.

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Blending with gasoline

Postby John Galt » Wed Apr 09, 2008 7:04 pm

Things to consider when using gasoline in diesel engines:

http://www.turbodieselregister.com/mixi ... diesel.htm

TDReprint
MIXING GASOLINE AND DIESEL
(Issue 26, pages 14 – 15)

My wise old mechanic who has worked on Mercedes for years told me that if I put one gallon regular gas to a diesel tankfull after about every four tanks that it would perform essentially the same job as a fuel injector cleaner at a fraction of the cost.

I would like to hear a technical opinion.

Bill Carson , e-mail

Bill, I’ll turn the answer to your request for a technical opinion over to Brian Kmetz. As a mechanical engineer, Brian’s daily task at work is to extract BTUs through oxidation from mass quantities of methane and fuel oils. Needless to say, he knows how the fuel “stuff” works. Brian writes:

We hear this one all the time. Another version is to add one gallon of gasoline to 20 gallons of diesel fuel as a cheap easy anti-gel for winter fuel. I’ll include alcohols in this discussion because a lot of guys add it instead of gasoline. Both fuels have the same detrimental effect on diesel fuel and are very close in weight and BTU content.

The mechanic meant well and probably never saw a fuel pump or injector failure due to improper blending of fuels. But that doesn’t mean one is not risking damage, even in small dosages.

Gasoline and alcohols hit diesel fuel right where it hurts the most. Those light thin fuels will lower the cetane number and lubricity. To explain how octane and cetane DO NOT work together, I’ll have to review more crude oil and fuel fundamentals.

The light distillates that gasolines are made from have a natural high-octane index. The middle distillates that diesel fuels come from have a high cetane index. The octane and cetane indexes are INVERSE scales. A fuel that has a high octane number has a low cetane number, and a high cetane fuel has a low octane number. Anything with a high octane rating will retard diesel fuel’s ability to ignite. That’s why each fuel has developed along with different types of engine designs and fuel delivery systems. Gasoline mixed in diesel fuel will inhibit combustion in a diesel engine and diesel fuel mixed in gasoline will ignite too soon in a gasoline engine.

A lot of old-time mechanics added some gasoline to diesel to supposedly clean the carbon deposits out of the cylinders. I have never read anything that said it worked. Gasoline will make the fuel burn hotter, and hotter burning fuels burn cleaner. That’s probably where the theory got started. In the older diesel engines that belched lots of black smoke even when properly tuned, the result of adding gasoline was probably more white smoke instead of black. This might lead one to believe the engine was running cleaner. Maybe so, probably not. Here’s what happens.

Gasoline will raise the combustion temperature. This might or might not reduce carbon deposits in the cylinder. This also might or might not overheat the injector nozzle enough to cause coking on the nozzle. That’s a clogged injector tip in layman’s terms. The fuel being injected is the only thing that cools the nozzle. Diesel fuel has a lower combustion temperature than gasoline. The fuel injectors depend on the fuel burning at the correct rate and temperature for a long life. If the combustion temperature is raised long enough, the gums and varnishes in gasoline will start to cook right in the fuel injector and turn into carbon. These microscopic carbon particles will abrade the nozzle. High combustion temperatures alone will shorten fuel injector life, gasoline makes the problem worse.

Gasoline and alcohols do have an anti-gel effect on diesel fuel, but these fuels are too thin and will hurt the lubricity. Alcohols work as a water dispersant in small amounts, but also attract water in large amounts. Diesel fuel is already hydrophilic (attracts water) so why add to the problem. The old timers got away with this because high sulfur diesel fuel had enough lubricity to take some thinning. Today’s low sulfur diesel fuels have adequate lubricity, but I wouldn’t put anything in the tank that would thin out the fuel, reduce lubricity, or attract water.

Opposites do not attract in this case. Use any of the diesel fuel additives available to clean out carbon deposits, not gasoline or alcohols.

While we’re on the subject of fuels, let’s discuss another common question. What is cetane?

Cetane is to diesel fuel what octane is to gasoline. It is a measure of the fuel’s ignition quality and performance. Cetane is actually a hydrocarbon chain, its real name is 1-hexadecane. It is written as C16H34, or a chain of 16 carbon atoms with 34 hydrogen atoms attached. All HC chains are also referred to as paraffins. Cetane is a hydrocarbon molecule that ignites very easily under compression, so it was assigned a rating of 100. All the hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. There is very little actual cetane in diesel fuel.

All the hydrocarbons in diesel fuel have similar ignition characteristics as cetane. Cetane is abbreviated as CN. A very loose way to think about cetane is if the fuel has a CN of 45, then the fuel will ignite 45% as well as 100% cetane. Diesel engines run just fine with a CN between 45 to 50. There is no performance or emission advantage to keep raising the CN past 50. After that point the fuel’s performance hits a plateau.

Diesel at the pump can be found in two CN ranges: 40-46 for regular diesel, and 45-50 for premium. The minimum CN at the pump is supposed to be 45. The legal minimum cetane rating for #1 and #2 diesel is 40. Most diesel fuel leaves the refinery with a CN of around 42. The CN rating depends on the crude oil the fuel was refined from. It varies so much from tanker to tanker that a consistent CN rating is almost impossible. Distilling diesel is a crude process compared with making gasoline. Gasoline is more of a manufactured product with tighter standards so the octane rating is very consistent. But, the CN rating at the diesel pump can be anywhere from 42-46. That’s why there is almost never a sticker on a diesel fuel pump for CN.

Premium diesel has additives to improve CN and lubricity, detergents to clean the fuel injectors and minimize carbon deposits, water dispersant, and other additives depending on geographical and seasonal needs. More biocides added in the south in summer, more ant-gel added in the north in winter. Most retailers who sell premium diesel will have little brochures called POPs (Point of Purchase) at the counter explaining what’s in their fuel. Please don’t ask the poor clerk behind the counter any technical questions after reading this discussion. All they need to know how to do is sell you beer, milk, cigarettes, lottery tickets, and take your money.

Texaco and Amoco are two big names who sell premium diesel in limited markets. Amoco primarily sells its Premier to specialized industrial and agricultural markets. I cannot get either in my area. Most fuel retailers buy additives or buy treated fuel. In the Northern plains states, Koch is a well-known marketer of premium diesel. I buy it when I travel into Northern Wisconsin.

Because there are no legal standards for premium diesel yet, it is very hard to know if you are buying the good stuff. I have good news. An ASTM task force has drafted standards for premium diesel. When the new specifications are accepted, information will have to be posted on the fuel pump. Retailers will no longer be allowed to label cheap blended diesel as ‘premium.’ They will have separate pumps with clear labels on both informing the customer what is being sold. The marketing and labeling will be the same as with regular and premium gasoline. Retailers selling the real thing use this system now. Enforcement of all fuel standards is done at the state level in the USA.

Diesel fuel is an international commodity for industry. Therefore, you should be picky about where you fill up. Shop for price from a large volume retailer so you have the freshest fuel. That’s about the best advice I can give.

The 1994 legislation and reformulation of diesel fuel in North America is due to an international effort for lower emissions. Cleaner diesel emission laws are on the way. Diesel fuel is going to be reformulated into a cleaner fuel in general. Without getting too technical (this is over-simplified and very generalized), diesel fuel for the most part is made up of two different hydrocarbon families: paraffins and aromatics. The paraffins have a naturally high cetane index, burn clean, but cause the annoying gel problem in winter. The aromatics have a naturally high lubricity, low cetane index, and cause a lot of diesel emissions and soot. Reformulated diesel will have a higher paraffin content, higher cetane number, and a much lower aromatic and sulfur content. It will also be more prone to jelling and have a lower lubricity. Big oil is working on improved additives as I type this.

The reason nothing has happened yet is because of infighting in the EPA on its new Tier II Emissions standards for gasoline and diesel. Ultra-clean technology for gasoline and diesel engines is almost ready to go, but the refiners have to lower the sulfur level drastically in both fuels. The EPA should formally set something by year 2000.

Brian Kmetz
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Postby SunWizard » Wed Apr 09, 2008 7:56 pm

I agree with that article, and its why I blend with 20% winter diesel or kerosene only. RUG lowers the cetane, which means harder starting, and lower MPG, which are 2 added things that article didn't mention.

Lubricity they mention isn't a concern, since >2% VO gives outstanding lubricity.
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Postby David » Thu Apr 10, 2008 2:18 am

Of course the first thing that has to be remembered here is that the conclusions of the entire article are based on Petrol in DIESEL, Not vegetable oil.

As pointed out, the part about lubricity we know to be wrong for a start. That applies to diesel NOT Veg oil. What we don't know is what other conclusions are also incorrect.
The other possible discrepancy's in the article may be related to it's age. It mentions EPA standards by the year 2000. Here in oz at least, the current low sulfur Diesel wasn't introduced till later than that. In any case, what is refered to here is not relevant to what the majority of people here are doing which is mixing petrol with VEG which we know has very different properties to Diesel.

Before getting all fussed about the WVO/ULP that is in the startup tank of my car right now, I'd have to see tests done on the mixing of WVO and petrol that said that was detrimental to be worried it was a bad thing.
Much is made of the cetane of Diesel but I haven't seen ( although I don't doubt the info may be out there) what the cetane of WVO is. This areticle says the cetane of Diesel is variable, I'll bet is is a whole lot more stable than your average mix of WVO! :D

I have seen statements to this effect before but still don't understand how the conclusion is arrived at:

"A fuel that has a high octane number has a low cetane number, and a high cetane fuel has a low octane number. Anything with a high octane rating will retard diesel fuel’s ability to ignite."

A low compression Diesel engine will run 16:1 compression ratio. A High compression Petrol engine will run maybe 13:1 but that would be a pretty rare engine and not a production version.
The problem with petrol engines and high compression is self ignition resulting in untimed burning. If the petrol is going to self ignite in an engine running maybe 13:1 compression, how the hell is it going to retard the diesels ability to ignite in an engine running something like 20 to 25:1 compression? I'd be more thinking the problem would be with the petrol component lighting off too quick not retarding the diesels ability to light off.

The article says petrol in Diesel leads to harder starting but with veg, I have found the exact opposite to be the case on more than one vehicle.
Mercedes also have a list in their W123 model handbook for mixing petrol with diesel in cold weather so at least back then, they could not have seen too much risk in this blend in those engines.
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Postby BMW Fan » Thu Apr 10, 2008 6:55 am

ASG Analytik-Service GmbH, Germany has shown a Cetane values of 54 for rapeseed oil.
Makes sense to me since Dyno tests on veggie always show an increase of power.
If I blend I use Diesel and not gas. I did use gas for some time in the range of less then 10% with no ill effect.

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Postby ROLLGUY » Fri May 09, 2008 6:57 pm

[quote="David"]Of course the first thing that has to be remembered here is that the conclusions of the entire article are based on Petrol in DIESEL, Not vegetable oil. [/quote]

As pointed out, the part about lubricity we know to be wrong for a start. That applies to diesel NOT Veg oil. What we don't know is what other conclusions are also incorrect.
The other possible discrepancy's in the article may be related to it's age. It mentions EPA standards by the year 2000. Here in oz at least, the current low sulfur Diesel wasn't introduced till later than that. In any case, what is refered to here is not relevant to what the majority of people here are doing which is mixing petrol with VEG which we know has very different properties to Diesel.

Before getting all fussed about the WVO/ULP that is in the startup tank of my car right now, I'd have to see tests done on the mixing of WVO and petrol that said that was detrimental to be worried it was a bad thing.
Much is made of the cetane of Diesel but I haven't seen ( although I don't doubt the info may be out there) what the cetane of WVO is. This areticle says the cetane of Diesel is variable, I'll bet is is a whole lot more stable than your average mix of WVO! :D

I have seen statements to this effect before but still don't understand how the conclusion is arrived at:

[b] "A fuel that has a high octane number has a low cetane number, and a high cetane fuel has a low octane number. Anything with a high octane rating will retard diesel fuel’s ability to ignite."[/b][i][/i]

A low compression Diesel engine will run 16:1 compression ratio. A High compression Petrol engine will run maybe 13:1 but that would be a pretty rare engine and not a production version.
The problem with petrol engines and high compression is self ignition resulting in untimed burning. If the petrol is going to self ignite in an engine running maybe 13:1 compression, how the hell is it going to retard the diesels ability to ignite in an engine running something like 20 to 25:1 compression? I'd be more thinking the problem would be with the petrol component lighting off too quick not retarding the diesels ability to light off.

The article says petrol in Diesel leads to harder starting but with veg, I have found the exact opposite to be the case on more than one vehicle.
Mercedes also have a list in their W123 model handbook for mixing petrol with diesel in cold weather so at least back then, they could not have seen too much risk in this blend in those engines.[/quote]

I agree. I have been blending (80% VO 20% RUG) with stale gas from a boat shop, and it works great. The best part is the price (FREE). I am not at all concerned with lubricity, as VO is loaded with it!
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Postby David » Fri May 09, 2008 11:53 pm

The "Stale" aspect of the Unleaded is also interesting.
I'm not sure what the altered properties of the fuel would be, I imagine it would lose some of its vapor flammability which would seem a good thing in this respect but it should still have the same thinning properties.

All good for blenders I'd say.
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Postby SunWizard » Sat May 10, 2008 9:44 am

The best thing about RUG being stale is that it lowers the octane, which means it hurts the cetane value of the blend less than fresh RUG.
YVORMV - Your veg. oil results may vary.
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not complete data

Postby coachgeo » Sat May 10, 2008 4:30 pm

Numbers dont lie, the cetane is lowered by octane therfore little less punch would occure in a diesel factor WHEN NO OTHER THINGS ARE CONSIDERED.

If I calcuate how much a gymnast can flip, then have a kid do 3 x that cause... he's on a trampoline, the math would not be be wrong.... just forgot to take into acount "springs" on the trampoline.

If one was to calculate the cetane value of vegetable oil and tune the engine according to that....and tested it in alaska with no fuel heating system..... the cetane numbers would not be lieing.. but it still would not work.

That is the problem with the cetane octane thing. It is only ONE THING and in to itself not enough to base an itso facto decision.

What is not being considered in the numbers game of cetan/Octane is combustion characteristics of the two fuels which are different.

Way I heard it theorized is when taking flame fronts into account even though the cetane number is lower, due to a secondary flame front (ignition of the gas comes at a different time than the Veg oil) the result is an improved overall combustion of the veg oil resulting in you actually get simular results to diesel and sometimes even BETTER RESULTS by you blending with gasoline.

This if I recall right was also shown to be true with diesel long long long ago. Someone (Kugel I think) sited having seen it in an acient book of diesel combustion studies. Of course one could easily see that there is a point of dimenishing return such as when the ratio of gasoline to vegoil or diesel gets too hight.
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Postby ROLLGUY » Sat May 10, 2008 6:06 pm

[quote="SunWizard"]The best thing about RUG being stale is that it lowers the octane, which means it hurts the cetane value of the blend less than fresh RUG.[/quote]

Yes, that is why I say "the staler, the better". The boat shop guy can't understand this, but thats OK. I think with all or most of the aromatcs gone, RUG still has the capacity to thin the VO, without degrading the Cetane value of the VO (something like you said).
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Postby David » Sat May 10, 2008 6:44 pm

The minimum CN at the pump is supposed to be 45. The legal minimum cetane rating for #1 and #2 diesel is 40.


BMW Fan wrote:ASG Analytik-Service GmbH, Germany has shown a Cetane values of 54 for rapeseed oil.



If the veg oil number is correct ( and I assume it is) then even if the unleaded does knock the cetane value off a bit, from what the diesel number is supposed to be, we have a bit of extra cetane to start with so the likelihood is that we are still finishing up no worse off (and I would guess probably better) given the low amounts of unleaded normally used.
If the unleaded is stale to start with, then the Veg/ ULP blend should be significantly better than Diesel!

As I initially pointed out, the test shown at the begining of the thread was based on DIESEL with ULP, NOT blending VEG with Ulp. What has come to light since in this interesting discussion highlights what a significant difference this is and why. It would also seem to suggest that much of the gloom and doom spread about ULP/Veg blends is completely ill founded and misunderstood because people are most likely basing their conclusions on the tests done with Diesel which is obviously a far different and in this case, irrelevant material to VEG which is what we are all concerned with here. :D
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Until then, it's just more endless gloom and doom Veg folk law.
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Postby SunWizard » Sat May 10, 2008 8:43 pm

Most sources of cetane values for VO show much lower numbers like 38 for soy and rapeseed. See Fuel properties of fats and oils here:
http://journeytoforever.org/biodiesel_yield2.html

A number of 54 sounds like b100 made from rapeseed, I would like to see the source.

Elsbett who is well respected says this:
"Cetane Number: No sufficient testing method existing, because the engines for the standardising tests are all conventional diesel engines. When measured with conventional method, Cetane number is worse, nevertheless practice shows, that ignition delay is shortened in comparison to diesel fuel."
http://www.elsbett.com/us/vegetable-oil/vegetable-oil-standard.html

So what that means is we really don't know what VO cetane is.

A good test would be with a dyno, compare D2, V100, V80/D20 and V80/RUG20. I haven't seen any research testing blends with dynos so every blend idea is speculation. But our only info we have is that RUG lowers cetane and turps (and cetane boost) raises cetane, based on mixing them with D2 in research that was done. And that cetane is important in a diesel engine, and long stroke slower RPM engines like the cummins can handle lower cetane better than a VW TDI or any higher revving engines.
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Postby SunWizard » Sat May 10, 2008 10:19 pm

Another thing to consider with blending RUG is that in the US, most RUG is now 7-10% ethanol by law. There are many reported problems with using ethanol in diesel engines, here are some from detailed research that Cummins reports here:
http://regions.cummins.com/sa/pages/en/ ... C4A8F00000
This is for higher % of ethanol than we blend (through our RUG), but many of these issues are likely to happen with any % ethanol:
"Alcohol is a reactive chemical and can cause fuel system corrosion. Alcohol also will deteriorate and affect the performance of gasket and/or seal materials. There are confirmed accounts of ISB engine fuel pump failures due to the effects of alcohol induced de-lamination of an internal timing sensor component. Robert Bosch, the fuel pump manufacturer prohibits alcohol blended fuel in the VP44 fuel pump on the ISB/QSB Cummins engine."
"The fuel pump, a Robert Bosch VP44, failed an internal timing sensor (IAT) due to delamination of the foil caused by the presence of alcohol."

"Vapors in the fuel tank containing a mixture of ethanol with diesel will readily burn under conditions where diesel vapors alone will not combust."
"WARNING: UNDER NO CIRCUMSTANCES SHOULD ALCOHOL BE USED TO DILUTE DIESEL FUEL. THIS PRACTICE CREATES AN EXTREME FIRE HAZARD AND UNDER CERTAIN CIRCUMSTANCES, AN EXPLOSIVE HAZARD."
"Since E diesel is more volatile, it is more likely that the vehicle will experience pump and injector cavitation and hot fuel re-start problems. " (RUG is much more volatile as well as ethanol.)
YVORMV - Your veg. oil results may vary.
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Postby BMW Fan » Sun May 11, 2008 7:34 am

I try to go with the time and follow companies doing actual research.
I admired the late Elsbett all my live and had the pleasure to know him in person.
I collected tons of information.
I know his sons running the Elsbett company now.
They don't do any actual analytical research but ASG does.
ASG has a reputation as one of the best in the analytical market using up to date equipment.

There are two methods for obtaining CETANE values.

The old “ TEST MOTOR “ and a newer so called “ CHAMBER “ method.

I called ( 12.October 2007 ) ASG Analytik –Service Gesellschaft mbH and got the following information :

Based on their experience the method with a test motor
produces Cetan values from 37 – 41 on veggie oil ( +/- )

The new method ( chamber test ) shows 44-46 if identical samples are used.
All of their tests are done with the new method.
If veggie oil is used as a fuel ( in Germany ) the new pre-Norm is 41 Cetan

The value of 54 was given to me as results ASG has seen with some of the oils they have analyzed.

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