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Go Back   TDIClub Forums > VW TDI Discussion Areas > Alternative Diesel Fuels (Biodiesel, WVO, SVO, BTL, GTL etc)

Alternative Diesel Fuels (Biodiesel, WVO, SVO, BTL, GTL etc) Discussions about alternative fuels for use in our TDI's. This includes biodiesel WVO (Waste Vegetable Oil), SVO (Straight Vegetable Oil), BTL (Biomass to Liquid), GTL (Gas to Liquids) etc. Please note the Fuel Disclaimer.

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Old July 2nd, 2004, 15:38   #1
VW Derf
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Default Biodiesel FAQ

Thread update:

VWDerf's original Biodiesel FAQ has been merged at top of this thread. AF section has too many stickies.


Q) What is B100, B33, B20, etc

B100 stands for 100% biodiesel. The first B stands for Biodiesel and the number after that is the percentage. B20 is 20% biodiesel and 80% regular diesel (sometimes called dyno Diesel)

Q) Will biodiesel void my warrenty.

Maybe...and maybe not. During the last few years, VWoA has repeatedly stated to North American TDI owners that use of any Biodiesel fuel will void warranty claims for fuel-related problems/failures. VW owners manuals state that warranty claims for damage/failure due to the use of any bad fuel will not be honored. VWoA justifies its position stating that, unlike in Europe, North American Biodiesel types vary widely, and unregulated for quality. However, more than a few VW service departments are informed enough to know that Biodiesel usage reduces the probability of intake manifold clogging due to the use of sulphur-laden fuel. Some U.S. states are now beginning to mandate the use of Biodiesel-blended fuel in percentages from 2% to 5%. Thus, expect VWoA to revisit its official Biodiesel policy.

Q) What is biodiesel made of?

Biodiesel can be made up of many items from recycled fryer fat to Soy Beans, Rape Seed, etc. In the US, commercially available Biodiesel is often made up of Soy beans. In Germany it is often made from Rape Seed (similar to Canola oil).

Q) What is Biodiesel?

Biodiesel is a non-petroleum based diesel fuel (oil) derived from renewable sources like animal fats and vegetable oils.

Q) How is Biodiesel made?

Biodiesel is made thru a process called transesterification. This process separates usable diesel fuel from unwanted oil components, like glycerin.

Q) Is waste vegetable oil (WVO) or straight vegetable oil (SVO) the same as Biodiesel?

No. Both WVO and SVO contain glycerin. Glycerin can be corrosive to some fuel components. While Biodiesel can be made from either WVO or SVO, the glycerin has been removed in Biodiesel.

Q) Can Biodiesel be used in any climate?

RUNNING ON B100 IN COLDER WEATHER IS NOT RECOMMENED. Biodiesel will generally begin gelling at temps below 4C/40F. To use Biodiesel below this temperature, heating must occur to prevent gelling or additives can be used to reduce the gelling point. NO KNOWN ISSUES WITH USING B20 (WITH WINTERIZED PETRODIESEL) HAVE BEEN NOTED. Biodiesel will generally begin gelling at temps below 4C/40F. To use Biodiesel below this temperature, heating must occur to prevent gelling or additives can be used to reduce the gelling point.

Q) Will using Biodiesel fuel harm my engine?

Volkswagen TDI powerplants from 1996 through the 2003 model years run very well on Biodiesel. One thing to know is that with vehicles that have never used Biodiesel, the older the vehicle, the higher the probability of microbial growth accumulating in its fuel tank. Biodiesel, being the terrific solvent that it is, can and will loosen these growths/deposits and send them downstream to the fuel filter. Anyone who is just starting to use Biodiesel in an engine which hasn't previously used it is cautioned to have at least one spare fuel filter standing by in case of fuel starvaton due to clogging. In new or near-new vehicles, microbes should not be a problem.

Q) Is Biodiesel harmful?

No. Biodiesel is not toxic or harmful to people or pets. Be aware that Biodiesel, when spilled on body paint or rubber parts (hoses, tires, etc.), can do damage, no differently than dino-diesel fuel.

Q) Is all Biodiesel the same in regard to quality?

Like dino-diesel fuel, the Biodiesel fuel you buy is as good...or not good as the way it was made and the way it was stored. Most Biodiesel is made by firms specializing in its manufacture. However, there are also many individuals who have become "backyard biodieselers" by making their own, usually from waste vegetable oil. Whatever your source of Biodiesel, good judgement and caveat emptor applies.

Q) Biodiesel costs more than dino-diesel fuel. Why use Biodiesel?

One reason is that Biodiesel use pruports to lengthen the life of an engine. One interesting study summary about this from the University of Saskatchewan is available here. Buying Biodiesel supports the farmer who grew whatever your Biodiesel is made from (beans, seeds, pigs, cows, etc.). Another reason is that Biodiesel, which contains no sulphur, burns cleaner than dino-diesel fuel, thus no sulphuric soot which contributes to acid rain, lung problems, etc. Biodiesel usually has higher cetane content than dino-diesel. Of course, dependence on Middle Eastern oil is somewhat reduced by Biodiesel usage. Biodiesel sales have dramatically climbed every year since records have been kept.

Q) Can I use Biodiesel with my new '04 Pumpe Duse engine?

While Biodiesel can be safely used with VW TDI model years 1996 thru 2003, little is currently known about Biodiesel use in the new Pumpe Duse (PD) engine, other than VW's guidance not to use Biodiesel, both in North American and European PD models. The main difference between the PD and earlier engines is that the PD injects fuel into the cylinder at pressure up to 29,000 PSI, where older TDI injection systems (pre-2004 in North America) operate around 16,000 PSI.

What about SVO and WVO? What's the difference?

WVO means waste vegetable oil, or vegetable oil that is recycled, typically from restaurant fryers. SVO means straight vegetable oil, oil that has not been used yet. Biodiesel can be made from both sources of oil. Some people who "homebrew" biodiesel reclaim WVO from their local restaurants for free. Commercially manufactured biodiesel is usually (although not always) made from SVO. Biodiesel made from WVO typically has a higher gel point than biodiesel made from SVO, which means that WVO biodiesel will gel (and potentially clog fuel lines and filters) at a higher temperature than SVO biodiesel. Untreated petroleum diesel fuel can also gel in low temperatures, usually at temperatures lower than biodiesel. See the TDI FAQ entry on "winterizing" (http://tdiclub.com/TDIFAQ/TDiFAQ-3.html#c) for more details on this phenomenon. Proper care must be taken to operate diesel vehicles on biodiesel in cold temperatures, either by adding anti-gel agents to your biodiesel, or lowering then blend of biodiesel used.

Can diesel engines can run on vegetable oil?

The original prototype of Rudolf Diesel's engine, demonstrated at the World's Fair in Paris in 1900, was powered by peanut oil. Diesel envisioned farmers growing their own fuel to power their tractors, or generators. (Henry Ford also envisioned his cars powered by farm-grown biofuels; the Model T was designed to run on ethanol). Modern diesel engines, however, operate at much higher pressures that Diesel's original designs. The viscosity of both WVO and SVO is insufficient to operate the relatively delicate fuel injector pumps. However, there are aftermarket conversion kits by Greasecar (http://www.greasecar.com), and Elsbett (http://www.elsbett.com) that will allow operation of some TDI engines on pure vegetable oil. Any such operation will require a tank heater. Some configurations require a second tank for starting and stopping the engine on regular diesel (or biodiesel). Details of such operation is beyond the scope of a mere FAQ, however, interested individuals are encouraged to do much more research before making a decision to convert any diesel vehicle to operate on pure SVO or WVO.

Additions to the FAQ can be suggested in this topic.

Last edited by nicklockard; May 1st, 2011 at 16:33. Reason: updating posting status and reason.
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Old March 10th, 2008, 19:29   #2
nicklockard
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Default Experimental and Alternative Fuels: an Overview

Scope: This overview is intended to address some of the fundamentals by defining terms and phrases commonly heard in the community. It intends to address member’s desire for a clearly defined, healthy forum discussion of the usage of alternative experimental fuels in the Volkswagen Tdi (turbo-direct injection) diesel engine.

Background: There is a desire to have a collaborative and healthy forum discussion area for running, preparing, and troubleshooting of alternative experimental fuels such as vegetable oil and waste vegetable oil in Volkswagen diesel vehicles.

Commercially sourced, ASTM-compliant “Biodiesel,” as defined below, is not considered an experimental fuel. However, it is still considered an alternative fuel. This distinction must be drawn because of Volkswagen’s stated warranty policy which strictly prohibits the use of biodiesel blends over 5% by volume fraction for their present and current diesel technology offerings (as of 3/3/08.) Implicitly then, it can be stated then that the vehicle manufacturer does not categorically view biodiesel as harmful to their (existing) diesel engine platforms. Volkswagen, insofar as this author is aware, strictly and explicitly prohibits the use of any amount of any vegetable oils as fuels or fuel extenders. Un-assayed home-brewed biodiesel which may be incompletely reacted or contain free fatty acids or other contaminants is equally experimental and not Volkswagen-approved. Use at your own risk.

Gasoline usage or gasoline fuel blending in a Tdi is expressely prohibited by Volkswagen and will void your warranty on fueling system and related components. Check your manual for specific clarification. Gasoline does not have adequate lubricity and will damage most modern injection pumps and injectors. Use of gasoline in vegetable oil blends can be dangerous, as the gasoline will flash to vapor in accordance with Raoult's law inside high temperature heat exchangers--it is very unsafe and strongly recommended against.

Moreover, Volkswagen has stated explicitly that no amount of biodiesel nor vegetable fuels usage of any kind will be allowed in their yet-to-be-released new Tdi-‘Common Rail’ Tier-2, Bin-5 emissions-compliant diesel offerings. As a counterpoint to this, recognize that EPA emission certification tests are performed on industry standard (i.e. petroleum based) diesel fuel. Use of fuel other than that which the emission certification procedure was performed on could cause the emission profile to change (i.e. potentially fail the Federal Test Procedure or the durability testing). Since the original engine manufacturer cannot account for this, they cannot legally allow the use of fuels other than originally specified while warranting that the vehicle meets applicable emission standards. This is different from saying the vehicle physically cannot run on something else … it’s just not proven and not legally certified to meet emission standards. At this point, in view of this situation, there is no way to know what would happen to the vehicle if you ran it on something else.

As a community of Volkswagen diesel enthusiasts, we emphatically and overwhelmingly recommend against running of experimental fuels in a Volkswagen Tdi diesel powered vehicle. There may be a small, dedicated group of ultra-diligent users of experimental fuels here; however they do not represent the norm. The use of experimental fuels in a modern diesel engine such as the Tdi is very much a high-risk affair, with dire financial consequences for ‘getting it wrong.’ And, it is very easy to get wrong as many former fuel experimentalists and pioneers can attest to.

Much user experience has shown that more often than not, YOU WILL GET IT WRONG. If you can not afford to remedy catastrophic engine breakdowns, this is not a hobby for you. A conservative estimate is that if you are not prepared to replace your engine at a typical installed cost of $3,500-$5,000 (used, depending on model year,) and you do not have a backup vehicle, you can not afford this risky hobby.

Any discussions contained herein and within any place of this forum pertaining to the modification of your vehicle’s fuel system and the use of experimental fuels are strictly YOUR opinions and your opinions only. They are NOT condoned in any way, shape, nor form by the administrators, moderators, owners, nor by the vast majority of users. Use of any such information for any reason whatsoever is at YOUR OWN RISK. In oft-repeated words here, except in very special circumstances where a “kit” manufacturer may expressly state otherwise and you conform strictly to their operating requirements, “you are your own warranty”.


However, this is a place of learning, thus the desire for this discussion sub-forum and a free-ranging, healthy, respectful discussion area. Be advised that as experimentalists going against the norm, you should expect, as with any such endeavor in life, to catch a lot of flak. You will have to have a thick skin. Your efforts and goals will be criticized by most. You will have constant reminders of fundamentals of physics, chemistry, and thermodynamics. The possibility always exists that you’ll pay for a mistake, however small, the hard way. A learning atmosphere with healthy debate requires ‘rising above the fray’ by both posters and critics.

This means: learn first, debate second.



Definitions of terms and phrases:

Biodiesel: Quality biodiesel is a chemically converted form of vegetable oil wherein the ‘arms’ of the parent triglyceride have been separated from the backbone (glycerol, a byproduct) as ‘fatty acid alkyl esters.’ Biodiesel is an alternative fuel in use since WWII whose reactions have been known since Emil Fischer’s day in the 1800’s. It is considered an alternative fuel and not an experimental fuel.

SVO: SVO stands for “Straight Vegetable Oil:” this means virgin, unused, pure vegetable oil. Typically these would be edible cooking oils. These oils are dephosphatized and degummed prior to sale to you at the store. This enhances shelf life so that stores do not have to turn over product due to spoilage. These cooking vegetable oils fit for human consumption are typically the types of oil that people are interested in using as a fuel source for their diesel vehicles. This is because they are widely available and already degummed and dephosphatized. However, not all edible cooking oils are the same.

In the most basic sense, all have the same chemical structural motif: they consist of 3 polymer chains (much like diesel fuel) attached to a central 3-carbon backbone by something called an ‘ester’ linkage. This structure is called a “triglyceride.” The 3 individual “arms” of the triglyceride are called “fatty acid residues.” Don’t get intimidated. Fatty acid residues are nothing more complicated than polymer chains with a “carboxylic acid” at one end. Vinegar is another example of a carboxylic acid. Carboxylic acids are very common in foods, medicines, and elsewhere in daily life.

Now when a plant makes these oils, it is intended as a food source for its seeds: the seeds are equipped with enzymes to ‘hydrolyze’ the oils to more basic components and eat the residues when conditions are just right. This tides the seed over until it can root, germinate, and establish itself as a small seedling plant capable of securing food (sunlight and soil nutrients) on its own. As you can imagine, no plant is a perfect machine. It does not make millions of copies of the exact same fat/oil molecule. What it does is make several variations of the basic structural motif, wherein the individual “arms” or fatty acid residues will differ slightly in chain length and in the placement of double bonds. We would say that each vegetable oil produces a “distribution profile” of different triglyceride oil molecules. This even differs from one planting season to the next—plants are not like machines. They make the oils that seem to match the conditions best at the time depending on their own health and nutrients available to them.

These differing distribution profiles from different plants lead to vastly differing physical properties such as:

· viscosity
· compressibility
· internal bond energy (btu’s)
· auto-ignition temperatures

For example, Olive oil is very much unlike Canola oil. Both are even more unlike diesel oil.

WVO: WVO stands for “Waste Vegetable Oil.” This typically just means oil which has already served a useful purpose (usually cooking) and is no longer fit for human consumption. After oil is used in cooking, it absorbs many impurities from salt, food, spices, and other ingredients. Moreover, the presence of water and heat degrades the oil through hydrolysis (same mechanism the seeds use to eat the oil.) Whereas the seeds use enzymes to hydrolyze the oils to fatty acid residues, heat and water can do the same.

Fatty acid (residues): As described before, fatty acid residues are the “arms” that have been broken off of the triglyceride’s ‘backbone.’ These Fatty acids have VASTLY different physical and chemical reactivity properties than the original oil. They also make a great food source for microbes, which will be attracted to them, populate old oil, and turn it even more rancid. Used cooking oil can smell absolutely horrid from the microbes which populate it.

As you can imagine, an acid reacts to different things much differently than a non acid like triglyceride (oil) molecules do. Being acids, they react with bases to form water and carboxylic acid salts, i.e. “SOAP!” Moreover, they have different solubility(s) in different solvents.

Secondly, fatty acids are more ‘polar’ than their parent molecules the triglyceride oil molecule. This changes their physical properties and chemical solubility properties significantly.

Viscosity: Viscosity is how “thick” a substance is. It is dependent on temperature and pressure. Honey in winter is thicker than honey in summer. The thickness of a fluid determines how much pressure it takes to squeeze it through an opening. As you can imagine, it would take a lot more pressure to squeeze a jet of honey ten feet with your hands than a jet of water ten feet. Self experiment: collect an old honey bear plastic jar and clean it. Fill with water. Collect another honey bear jar full of honey. Holding one in each hand, squeeze each as hard as you can and measure the distance each jet flies. You can probably guess the water will fly twenty to forty times as far for a given effort.

Vegetable oil at 160f, depending on type, varies between 25-30 centistokes kinematic viscosity. Diesel fuel at the same temperature is between 2-6 centistokes kinematic viscosity. Let’s look at Frybrid’s graph below (which cuts the lower part of the graph off, quite unethically, in an apparent effort to deceive, by the way.) We can see that (the unspecified) vegetable oil at 160f is thicker than diesel fuel at -10f!



Compressibility:Compressibility of a liquid depends on many things. Water is almost perfectly incompressible: a hydraulic ram designed to use hydraulic fluid will break itself trying to compress water! Typically, ‘oily’ substances are very compressible, while watery substances are less compressible or hardly compressible at all. Compressibility affects the speed of sound and its transmission loss through a fluid. Sound travels very much faster (and longer) in water than it does in air. A compressible fluid acts very much like a shock absorber and attenuates sound waves through it. This is one of the reasons a diesel engine gets quieter when running vegetable oils or biodiesel. This is not necessarily a ‘good’ thing though. Quietness does not automatically equal ‘goodness,’ as the very high pressure direct injection systems in use today have specifically been tuned to work with diesel fuel only—the pressure wave dynamics effecting wave peak arrival times, injection cracking pressures, injection needle timings, lift height and lift duration, as well as leakage rate, and spray pattern (cone width, droplet breakup time and distance) are ALL crucially and critically dependent on fuel compressibility as well as viscosity. Recall the honey experiment: honey is both more viscous AND more compressible. It took a great deal more effort to shoot the honey than the water, partly because it is simply thicker, but also because the honey acts like a shock absorber and attenuates your hand pressure.

Internal Bond Energy (btu’s):

All fuels combust like:

Hydrocarbons (and derivatives—don’t get hung up on semantics!) + Oxygen (O2) + ignition source à Carbon Dioxide (CO2) in gas form + water vapor in gas form + heat.

The amount of heat a fuel will release is equal to the total bond energy of the reactants minus the total bond energy of the products. Hydrocarbons with just carbons and hydrogens have more total bond energy than hydrocarbons with oxygens and double bonds in their structures.) This is called the ‘reaction enthalpy.’ Vegetable oils have more total reaction enthalpy per ‘mole’ of molecules than either diesel oil or biodiesel. However, on a weight (mass) or volume basis, vegetable oil has less reaction enthalpy than its counterparts.

Auto-ignition point:

This is the temperature at which a fuel will auto-ignite in the presence of an oxidizer such as air. Vegetable oils have typical auto-ignition temperatures ranging from 675-725f,[1] whereas diesel fuel has auto-ignition temperatures ranging from 375-425f.[2] A cold diesel engine struggles to get in-cylinder temperatures in the combustion range. A warm diesel engine typically has temperatures of 705 C [3] at the end of the compression stroke. This means that vegetable oils have auto-ignition temperatures much closer to the maximum attainable compression temperatures in the diesel cycle, leaving a much lower margin for error. Any cold spots within the cylinder, e.g. the nozzle itself, which is at a lower temperature than the compressed air in the cylinder at this point, are prime locations of possible droplets that can accumulate without igniting and burning away.

No one can say for sure at what precise running/load conditions this may happen, but generally speaking at light load when average cylinder temperatures are lower, you will see the largest cooling effect at the nozzles. This may have catastrophic consequences, insofar that vegetable oils combusted at lower local temperatures (in a cold spot) are likely to undergo partial decomposition ‘pyrolytic’ reactions. One example is the formation of acrolein—a toxic glassy and gummy organic substance. These partial decomposition pyrolytic reactions can lead to formation of nozzle hole clogs, ‘crud,’ gum, varnishes, and other non-combustion reactions, none of which are desirable, normal, or tolerable inside your expensive diesel engine.

Because vegetable oil is thicker, has vastly different compressibility, and has a higher auto-ignition point, this can lead to some problems. The following comments in green text are unsubstantiated. They belong to the author only and are just his informed opinions.

In the rotary pump diesel engine, the different compressibility of vegetable oil causes the peak pressure arrival times to be off—leading to a poor spray pattern (narrower cone) with poorer droplet penetration.

As the shock wave travels to the injector, it may reflect off the injector back toward the pump head before the injector has had a chance to inject all the fuel for that stroke! This means that the injector may dribble and trail off in injection pressures toward the end of the injection event, causing injector streaming. In practical effect, this makes the car’s ‘brain’ the Electronic Control Unit (ECU) struggle to maintain correct timing. Using a program called ‘Vag com,’ you can check the ‘smooth running fine adjustments’ and see the ECU struggle on vegetable oil and alternative fuels that the system was not designed for. There has been widespread reporting on this fact here at Tdi club and elsewhere.


As the vegetable oil travels out the injector nozzles, the droplets have less energy to penetrate into the combustion chamber—they have less mixing with air molecules and fewer collisions, which leads to poorer burning. The thicker fuel forms larger droplets, which have less kinetic energy for effective mixing because they were ejected with weaker pressure than diesel droplets would be. This means that a greater number of the droplets must burn in a 'diffusion-limited' manner (at their periphery) which is slow. It also means that a greater number of droplets will remain unburned and strike the pistons or stick to cold spots such as the nozzle itself. Any oil which adheres to cold spots is likelier to undergo partial decomposition pyrolytic reactions than combustion reactions, forming hard, crusty matter (likely polycyclic hydrocarbons PAH’s,) or gummy, glass-like and/or resinous matter (possibly acrolein, soaps, cross-linked fatty acids, etcetera…)

In theory, compressibility and viscosity should have less of a detrimental effect within the ‘Pumpe-Duse’ unit injection scheme, as the energy dissipation path is so short, and pressures much higher. But, since the Pumpe Duse cars use an in-tank lift pump and a secondary transfer pump, these may be more susceptible to chemical attack from Free Fatty Acids in Waste Vegetable Oil (WVO.) Moreover, reaction rates are sensitive to temperature AND pressure: the high pressure within the PD unit injector could catalyze hydrolysis reactions (between Free Fatty Acids and entrained water)and other reactions of Free Fatty Acids, which could lead to varnishing, formation of ‘soap scum’ and other problems within the injector unit itself.
In counterpoint, the compressibility and viscosity will have a greater detrimental effect in a system with a greater 'dead volume' such as Common Rail designs due to it having a longer dissipation path--there is just more fuel volume for things to go wrong.


What constitutes a “normal” versus unhealthy looking engine?

Let’s fill this section in. Please contribute photos of normal/abnormal engine conditions, regardless of cause if you have them. Thanks.





[1]Fire Research and Engineering: Third International Conference Proceedings


[2] Googled ‘diesel auto ignition temperature’ Several references

[3] http://hyperphysics.phy-astr.gsu.edu...mo/diesel.html Rough estimate.

Last edited by nicklockard; March 24th, 2008 at 12:47.
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Old March 10th, 2008, 20:02   #3
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Here are pictures of my engine's valves and intake at 178K after a head gasket failure.

Notes: The intake had been cleaned at ~145K miles and EGR *somehow got disabled also at that time. Car has only run D2 or biodiesel since I've owned it (took posession at 138K miles.) I don't believe it had ever had any other fuels.








And intake:



And from a recent discussion here on "WVO intake valve soot pics" thread:

Quote:
Originally Posted by aNUT
Here are a few from a WVOed ALH that got run out of oil. (broken pan + neglecting to shut down when the oil pressure warning light came on)

This is a Greasecar fitted car with coolant/veg oil heat exchanger only (no electric heat)

I don't have details about purge/switch over times. I have also forgotten how long the customer said the car had been run on grease. No clue on my end about which crank case oil he was running, or what the OCI was.

"Up to now I have been pouring the raw oil through a 5 micron gravity filter into a settling barrel, wait >24 hours, heat to 100 degrees than pump through a 1 micron filter into the car. Now I heat the oil to about 130 then pour through a 1 micron gravity filter into the barrel. I then pump through another 1 micron filter after letting it settle."

As you can see there is significant soot build up on the intake valves, as well as oil residue in the combustion chamber.
Keeping in mind that this car ran for several miles without oil, I found the the piston rings stuck, and the con rod bearings wiped out. There was some scoring on the crank at the con rod bearings. There was minimal bore damage as far as I could tell. I did not break out the micrometer, but most factory honing was intact. (all but one cylinder - that one had a small rub)

The customer said it was running fine prior to the oil pan incident. After installing a longblock, his injector balance was within spec and stable.

One thing baffling me is about how the soot got so high up the intake valves, though I've seen this before on a handful of other greased cars. Is this build up a result of extremely sooty exhaust? His intake was obstructed, though not any more than I'd expect on a car with it's mileage.












*Edit: Removed 2 somewhat redundant photos (available for viewing in original thread*)


Last edited by nicklockard; June 12th, 2008 at 12:03.
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Old March 11th, 2008, 14:06   #4
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Hello Nick,

Very comprehensive start - Many of the points you make are valid and well presented, however, don't I detect a bit of an 'anti' SVO tone?

I did notice some points that are incorrect or could be disputed.

To start the wheels of discussion rolling.....

Quote:
Originally Posted by nicklockard
Compressibility: Compressibility of a liquid depends on many things. Water is almost perfectly incompressible: a hydraulic ram designed to use hydraulic fluid will break itself trying to compress water! Typically, ‘oily’ substances are very compressible, while watery substances are less compressible or hardly compressible at all. Compressibility affects the speed of sound and its transmission loss through a fluid. Sound travels very much faster (and longer) in water than it does in air. A compressible fluid acts very much like a shock absorber and attenuates sound waves through it. This is one of the reasons a diesel engine gets quieter when running vegetable oils or biodiesel. This is not necessarily a ‘good’ thing though. Quietness does not automatically equal ‘goodness,’ as the very high pressure direct injection systems in use today have specifically been tuned to work with diesel fuel only—the pressure wave dynamics effecting wave peak arrival times, injection cracking pressures, injection needle timings, lift height and lift duration, as well as leakage rate, and spray pattern (cone width, droplet breakup time and distance) are ALL crucially and critically dependent on fuel compressibility as well as viscosity. Recall the honey experiment: honey is both more viscous AND more compressible. It took a great deal more effort to shoot the honey than the water, partly because it is simply thicker, but also because the honey acts like a shock absorber and attenuates your hand pressure.
and

Quote:
Originally Posted by nicklockard
In the rotary pump diesel engine, the higher compressibility of vegetable oil absorbs mechanical work and dissipates it as heat (shock absorber effect) which means that the peak pressure values are less—leading to a poor spray pattern (narrower cone) with poorer droplet penetration.

As the shock wave travels to the injector, it loses peak amplitude (loses energy,) and slows down! This means that the injector will open less forcefully, and later, since the speed of sound is slower in a more compressible fluid. As soon as it opens, pressure decays very rapidly, and when it drops below cracking pressures, the injector will close early. In practical effect, this makes the car’s ‘brain’ the Electronic Control Unit (ECU) struggle to maintain correct timing. Using a program called ‘Vag com,’ you can check the ‘smooth running fine adjustments’ and see the ECU struggle on more viscous, more compressible fuels.

As the vegetable oil travels out the injector nozzles, the droplets have less energy to penetrate into the combustion chamber—they have less mixing with air molecules and fewer collisions, which leads to poorer burning. The thicker fuel forms larger droplets, which have less kinetic energy for effective mixing because they were ejected with weaker pressure than diesel droplets would be. This means that a greater number of the droplets must burn in a 'diffusion-limited' manner (at their periphery) which is slow. It also means that a greater number of droplets will remain unburned and strike the pistons or stick to cold spots such as the nozzle itself.
Vegetable oil apparently has a higher bulk modulus (resistance to compression) than diesel fuel. So the inverse of many of the above points are true. see

http://www.sciencedirect.com/science...1fc033424e99e9

http://pubs.acs.org/cgi-bin/abstract...ef049880j.html

It should be made clear that spraying unheated vegetable oil from a fuel injector will provide an inferior spray. As I understand it this is largely due to cold vegetable oils having a viscosity and surface tension that is much higher than diesel fuel.

I also don't think the ECU will have any problems maintaining the correct opening time - generally the standard ECU in a Tdi engine is left with quite a bit of room for manoeuvre to achieve the correct injection timing
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Last edited by DarrenUK; March 12th, 2008 at 09:49.
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Old March 11th, 2008, 16:30   #5
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Quote:
A warm diesel engine typically has temperatures of 750f


http://www.vka.rwth-aachen.de/PDFs/P..._Esslingen.pdf

This paper shows peak cylinder pressure of a Tdi and should allow us to calculate a 'ball park' peak temperature using the ideal gas law.

http://hyperphysics.phy-astr.gsu.edu...degasc.html#c1
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Old March 11th, 2008, 17:52   #6
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It is worth considering that many 'upgraded' VW Tdi engines are running in Europe on SVO - aka pure plant oil PPO - many with 'single tank' conversions.

This presentation from Ireland February 2007 gives some details of the technologies involved, fuel production and level of uptake.

p.24 details some high mileage Tdis

http://www.biofuelsfortransport.ie/d...ingSeminar.pdf

**** for some reason this
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Old March 12th, 2008, 06:34   #7
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Quote:
Originally Posted by DarrenUK
Interesting post. I like how they specifically mention micro-CHP units which utilize PPO, like the Dachs. I've known about the Dachs for a couple years, wishing I could get one stateside. We're just barely getting into micro-CHP of any sort here, with Honda making a nice scalable domestic unit. Only gas, though. No oil ones at all that I can find.
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Old March 13th, 2008, 16:50   #8
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Quote:
Originally Posted by nicklockard
As the shock wave travels to the injector, it loses peak amplitude (loses energy,) and slows down! This means that the injector will open less forcefully, and later, since the speed of sound is slower in a more compressible fluid. As soon as it opens, pressure decays very rapidly, and when it drops below cracking pressures, the injector will close early. In practical effect, this makes the car’s ‘brain’ the Electronic Control Unit (ECU) struggle to maintain correct timing. Using a program called ‘Vag com,’ you can check the ‘smooth running fine adjustments’ and see the ECU struggle on more viscous, more compressible fuels.
.
I cannot say that this has been my experience. I have been logging " Smooth fine running adjustments" for six months on diesel, B100, B20 and SVO and have noticed no real difference. The only way I changed the value significantly in the smooth running was by releasing the torque on the injector to vary an air leak that I had. The fuel has never made a jot of difference if anything they became more even on SVO. If you have a bad cylinder either through an air leak/compression loss or a nozzle blockage it shows up
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Old March 13th, 2008, 16:55   #9
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Quote:
Originally Posted by nicklockard
Volkswagen’s stated warranty policy which strictly prohibits the use of biodiesel blends over 5% by volume fraction for their present and current diesel technology offerings (as of 3/3/08.) .
This is not totally correct. B100 biodiesel is approved for use in most VAG TDI's between 1996 and 2003. I will scan my VAG user manual when I get to a scanner. Its only with the introduction of particulate filters that its fallen to B5 and even then you get conversion kits for these cars.
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Old March 13th, 2008, 17:24   #10
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Quote:
Originally Posted by nicklockard
Because vegetable oil is thicker, more compressible
I agree with Darren regard the compresibility, the reverse is true. Vegetable oil and Biodiesel has a higher Bulk modulus of compressibility than diesel. Bulk Modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to effect a given relative decrease in volume

Further reference here

http://www.eere.energy.gov/vehiclesa...er_boehman.pdf

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Old March 15th, 2008, 15:10   #11
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The post has a great deal on the fuel properties e.g. viscosity, but more need to be added and an explaination of the issues with each and the impact on the engine.
e.g.

Viscosity measured is mm2/s @ 40°C is a measure of the fuel flow resistance. A higher viscosity is also associated with poorer fuel atomisation from injectors and increased engine deposits. It also impacts energy requirements and wear of fuel pump and injectors;

Carbon residue is an indicator of the tendancy of a fuel to form engine deposts.

Pour Point measured in °C (°F) is the Minimum temperature above which fuel can be poured, i.e., is still a liquid and can be pumped. Its affects a fuels use in cold climates

Cloud Point measured in °C (°F) is the temperature at which fuel begins to cloud (i.e., increases in turbidity), indicating wax is beginning to form. This can plug the fuel filter and stop the engine running.

Cold Filter Plugging Point, °C Temperature at which fuel will plug a fuel filter and stop the engine running.

Cetane number is a measure of ignition delay of a compression ignition fuel. Higher values indicate shorter ignition lags, fewer deposits, lower starting temperatures, reduced engine roughness.

Lubricity is a measure of the lubricating quality of the fuel. A higher values indicate better lubrication

Oxidation Stability is a measure of change in fuel oil quality and is an indicator of the shelf life of the fuel
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Old March 15th, 2008, 18:44   #12
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An ongoing discussion on another thread brings up another point that should probably be made.

"Vegetable oil" is not one single material with one set of properties. Canola is different from soy is different from palm, etc. And they are all different from the "mystery goop" that comes out of the fryer at the local greasy-spoon restaurant, which is loaded with contaminants and probably has a fair amount of animal fat in it and a certain amount of hydrogenated vegetable oil (a.k.a. "margarine"!) which is much thicker and turns solid at a much higher temperature.

What that means is that just because one particular person claims success running "vegetable oil" in some particular (usually simple) way, does NOT mean you will get the same results by doing the same thing in a different climate with the unknown mixture you drained out of a deep-fryer.

Dissolved solids, or dissolved heavier materials (e.g. animal fat or hydrogenated vegetable oil) have a way of coming out of solution and wreaking havoc at the worst possible times and places.

The climate and the operating conditions have an influence, too. Someone in a warm climate may be able to get away with things that could never be done in a cold climate.

When you hear of someone running their engine on "vegetable oil" (or high percentage blends of vegetable oil and diesel fuel) and claiming that they've done nothing to the engine, bear this in mind. Perhaps under some conditions (light-viscosity oil, mild climate, etc.) this CAN be done, at least for a while. But if your climate differs, or your source of oil differs in composition, or your luck differs ... well, "your mileage may vary". Cold-climate operation on waste vegetable oil will need MUCH more equipment and attention to keeping the fuel hot throughout the whole fuel system - and has less tolerance of operator error - than warm-climate operation on light "virgin" vegetable oil.
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Old March 24th, 2008, 08:53   #13
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Default In cylinder temperatures

"A diesel engine is a reciprocating-piston engine with internal (and thus heterogeneous) mixture formation and auto-ignition. During the compression stroke intake air is compressed to 30...55 bar in naturally aspirated engines or 80...110 bar in supercharged engines, so that its temperature increases to 700...900 °C. This temperature is sufficient to induce auto-ignition in the fuel injected into the cylinders shortly before the end of the compression stroke"
From Bosch Electronic Automotive Handbook Robert Bosch GmbH 2002
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Old March 24th, 2008, 09:23   #14
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Well done Darren. That one has had me scratching my head for a while.

Handy link for the theoretical temperature at the end of compression

http://hyperphysics.phy-astr.gsu.edu...mo/diesel.html

Clearly real world temp is lower and the turbo is not running during starting but for the millisecond of max compression not much heat is tranfered through the cylinder wall or else it would melt at full load. Bosch number looks good to me.

Brings up the question.... if you run with a blended fuel say 50% SVO and 50% diesel does the diesel light first and help the SVO ignition get underway.

Never seen a study on autoignition temperatures of mixed fuels.

Clearly winter diesel is a lighter blend that has a lower autoignition temperature. But if you add 50% diesel to 50% SVO does the autoignition point lower to halfway in between? Or can you just add say 2% diesel let that ignite and assist with the ignition of the SVO. My limited experience is the latter.

And the next thought.... if you add petrol does it flash off to vapour when if goes through the SVO/WVO heat exchanger? It certainly can't do the lubricity in the fuel pump and injectors much good if you do it for long periods. (Note I have never added petrol to SVO) ! Probably need a general recommendation not to add petrol/gas to SVO?
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Old March 24th, 2008, 12:37   #15
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Quote:
Originally Posted by TDICult
Well done Darren. That one has had me scratching my head for a while.

Handy link for the theoretical temperature at the end of compression

http://hyperphysics.phy-astr.gsu.edu...mo/diesel.html

Clearly real world temp is lower and the turbo is not running during starting but for the millisecond of max compression not much heat is tranfered through the cylinder wall or else it would melt at full load. Bosch number looks good to me.

Brings up the question.... if you run with a blended fuel say 50% SVO and 50% diesel does the diesel light first and help the SVO ignition get underway.

Never seen a study on autoignition temperatures of mixed fuels.

Clearly winter diesel is a lighter blend that has a lower autoignition temperature. But if you add 50% diesel to 50% SVO does the autoignition point lower to halfway in between? Or can you just add say 2% diesel let that ignite and assist with the ignition of the SVO. My limited experience is the latter.

And the next thought.... if you add petrol does it flash off to vapour when if goes through the SVO/WVO heat exchanger? It certainly can't do the lubricity in the fuel pump and injectors much good if you do it for long periods. (Note I have never added petrol to SVO) ! Probably need a general recommendation not to add petrol/gas to SVO?
Temperature at end of compression stroke depends on block temperature, incoming air temperature, combustion chamber design, and compression ratio from what I understand.

If by petrol you mean gasoline, yes it will flash off to vapor in accordance with Raoult's law. Thanks for the heads up. Gasoline in modern diesel engine = waaaaaay bad idea AFAIK.
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