I was a huge supporter for Bio-Diesel really I was all for it and after seeing long term havoc yes havoc that Bio-Diesel will do to a modern Diesel and I mean B20 and Higher ,I was done and will never use it again . Google for one's self and see what I am talking about . In any old school diesel , have at but not in a modern Diesel.
Another key difference is not all Biodiesel is the same.
The wide variation even in Soy (SME) Biodiesel makes it impossible to hit uniform specification.
Rapeseed which is the only "Biodiesel" sold in Europe has COMPLETELY different characteristics that Soy and other types produced here in the US.
The key difference with Rapeseed (RME) Biodiesel is superior oxidation stability.
Most of the proponents of Biodiesel here in the US refuse to accept the issues associated with Oxidation stability. With the newer fuel systems especially those found in the PD, fuel temperatures skyrocket.
The problems really reside inside the injectors and other components of the fuel system that are exposed to high temperatures. In older VE TDI's the problem areas are the fuel nozzles and internal ares of the injectors.
In the PD engine the problem areas are the hundreds of microscopic laser drilled holes in addition to the same nozzle issues of the VE engines.
In the Common Rail there is a 10 fold increase in issues making it nearly impossible to run (reliably) high percentages of US grade Biodiesel and even European Rapeseed Biodiesel. Just like the VE engines the nozzles and internal components of the injectors are exposed to continious heat. The fuel temperatures are in north of 150-200C in most cases. The Rail due to high pressure spike the fuel temperatures and presents the possibility of forming varnish and gum in the rail and the pressure regulating valve(s). The High pressure pump in my opinion is perhaps the only part (just like the VE) which may benefit from B100 and the increased viscosity.
In addition the post injection strategy to elevate the DPF temperatures as well as the poor combustion characteristics of the Biodiesel in the DPF leads to rapid contamination of the DPF systems, pressure sensors as well as Oxygen and NOx sensors. Even with the more robust SCR systems they too cannot tolerate anything beyond B5 reliably.
With the High pressure and Low pressure EGR, unburned fuel re-ingested is a very bad thing considering the Low Pressure EGR is injected into the turbos compressor inlet. The recirculation of unburned heavy Biodiesel residues presents a recipe for disaster since the B100 will not burn off in the DPF due to its higher flash point, leading to varnish and gum formation in the catalysts and the EGR systems.
The key will be fuels that mimick conventional Diesel fuel derived from Bio-mass.
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.
Due to Bio Diesel Use!
They say a pictures say a 1000 words: Here is a really good reason why not to use ANY Bio-Diesel .
Biodiesel is simply too unstable to be run in a Direct Injected engine without forming Varnish and oxidation break-down residues from the intense heat generated in the fuel system.
Deposits and varnish can form in just a few thousand miles. Extensive use usually leads to gummed up springs and components that cause irregular operation of the injector leading to an exstensive cleaning or overhaul.
I would never buy a TDI That run on ANY percentages of biodiesel, the experiences and observations of failure don't lie, it damages/rusts everything in the fuel system and injection system over time.
I am of the opinion that the solution is Bio-GTL aka Synthetic high grade diesel fuel produced ENTIRELY from Biomass. 75-80 cetane, 0% sulfur, ZERO running issues in any modern and future diesel engines permitting lower emissions that what are possible today.
But why havent they started producing this fuel in mass? People won't pay $5 a gallon when they can get fuel for $3 a gallon.
People can put the conspiracy theories away and need to put on a business hat for a bit.
Oil companies are there to produce one thing, fuel that the market will support (ie Buy).
There is no reason for an oil company to jump in feet first and produce $5 fuel when everybody else is selling fuel that does the same thing for $3.
I know for a fact that Bio-Jetfuel is coming and will be in use before it reaches the automotive industry. Unlike the automotive industry a uniform product with very unique qaulities is a BIG deal. Also the volume of fuel consumed in aviation allows for the incentive to invest in the infrastructure required to produce these synthetic fuels from Biomass.
The US Government has been spending BILLIONS $$$ to nail down the standards for these Biofuels and this came back when Bush was in office. The Democrats (hate to push this in any one direction or another) carry the full blame for derailing diesel technology in the US via CARB and California. The issue is the threat of reducing the tax revenues from the more efficient cars disguised as "clean" emissions laws.
After5.JPGBefore3.JPGFuel_Inlet_ports_Before.jpgFuel_Inlet_ports_closeup.jpgOpen_bore.JPGPoste_Solvent_Wash.JPG
If you really want a solution, shift the taxes so that everybody pays per unit of energy consumed. Think about this for a minute, a more efficient car (read one that travels further on less consumed energy) will not impose as much wear and tear on the roads. Sure this will reduce the tax revenues but it will also force the 8.0L V8's to pay their fair share for the 8,000# of damage they do to the roads. This will also force a shift to smaller lighter vehicles thus improving the congestion and increasing the efficient use of available space cars take up in the city and urban areas.
Look at the VW 1L concept, this is a glimpse of where the future of cars needs to go, no batteries required!
If you do as said in the Military Ahem "Embrace The Suck" as you will be asking for trouble. I hope this clears a few things up.
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Another key difference is not all Biodiesel is the same.
The wide variation even in Soy (SME) Biodiesel makes it impossible to hit uniform specification.
Rapeseed which is the only "Biodiesel" sold in Europe has COMPLETELY different characteristics that Soy and other types produced here in the US.
The key difference with Rapeseed (RME) Biodiesel is superior oxidation stability.
Most of the proponents of Biodiesel here in the US refuse to accept the issues associated with Oxidation stability. With the newer fuel systems especially those found in the PD, fuel temperatures skyrocket.
The problems really reside inside the injectors and other components of the fuel system that are exposed to high temperatures. In older VE TDI's the problem areas are the fuel nozzles and internal ares of the injectors.
In the PD engine the problem areas are the hundreds of microscopic laser drilled holes in addition to the same nozzle issues of the VE engines.
In the Common Rail there is a 10 fold increase in issues making it nearly impossible to run (reliably) high percentages of US grade Biodiesel and even European Rapeseed Biodiesel. Just like the VE engines the nozzles and internal components of the injectors are exposed to continious heat. The fuel temperatures are in north of 150-200C in most cases. The Rail due to high pressure spike the fuel temperatures and presents the possibility of forming varnish and gum in the rail and the pressure regulating valve(s). The High pressure pump in my opinion is perhaps the only part (just like the VE) which may benefit from B100 and the increased viscosity.
In addition the post injection strategy to elevate the DPF temperatures as well as the poor combustion characteristics of the Biodiesel in the DPF leads to rapid contamination of the DPF systems, pressure sensors as well as Oxygen and NOx sensors. Even with the more robust SCR systems they too cannot tolerate anything beyond B5 reliably.
With the High pressure and Low pressure EGR, unburned fuel re-ingested is a very bad thing considering the Low Pressure EGR is injected into the turbos compressor inlet. The recirculation of unburned heavy Biodiesel residues presents a recipe for disaster since the B100 will not burn off in the DPF due to its higher flash point, leading to varnish and gum formation in the catalysts and the EGR systems.
The key will be fuels that mimick conventional Diesel fuel derived from Bio-mass.
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.
Due to Bio Diesel Use!
They say a pictures say a 1000 words: Here is a really good reason why not to use ANY Bio-Diesel .
Biodiesel is simply too unstable to be run in a Direct Injected engine without forming Varnish and oxidation break-down residues from the intense heat generated in the fuel system.
Deposits and varnish can form in just a few thousand miles. Extensive use usually leads to gummed up springs and components that cause irregular operation of the injector leading to an exstensive cleaning or overhaul.
I would never buy a TDI That run on ANY percentages of biodiesel, the experiences and observations of failure don't lie, it damages/rusts everything in the fuel system and injection system over time.
I am of the opinion that the solution is Bio-GTL aka Synthetic high grade diesel fuel produced ENTIRELY from Biomass. 75-80 cetane, 0% sulfur, ZERO running issues in any modern and future diesel engines permitting lower emissions that what are possible today.
But why havent they started producing this fuel in mass? People won't pay $5 a gallon when they can get fuel for $3 a gallon.
People can put the conspiracy theories away and need to put on a business hat for a bit.
Oil companies are there to produce one thing, fuel that the market will support (ie Buy).
There is no reason for an oil company to jump in feet first and produce $5 fuel when everybody else is selling fuel that does the same thing for $3.
I know for a fact that Bio-Jetfuel is coming and will be in use before it reaches the automotive industry. Unlike the automotive industry a uniform product with very unique qaulities is a BIG deal. Also the volume of fuel consumed in aviation allows for the incentive to invest in the infrastructure required to produce these synthetic fuels from Biomass.
The US Government has been spending BILLIONS $$$ to nail down the standards for these Biofuels and this came back when Bush was in office. The Democrats (hate to push this in any one direction or another) carry the full blame for derailing diesel technology in the US via CARB and California. The issue is the threat of reducing the tax revenues from the more efficient cars disguised as "clean" emissions laws.
After5.JPGBefore3.JPGFuel_Inlet_ports_Before.jpgFuel_Inlet_ports_closeup.jpgOpen_bore.JPGPoste_Solvent_Wash.JPG
If you really want a solution, shift the taxes so that everybody pays per unit of energy consumed. Think about this for a minute, a more efficient car (read one that travels further on less consumed energy) will not impose as much wear and tear on the roads. Sure this will reduce the tax revenues but it will also force the 8.0L V8's to pay their fair share for the 8,000# of damage they do to the roads. This will also force a shift to smaller lighter vehicles thus improving the congestion and increasing the efficient use of available space cars take up in the city and urban areas.
Look at the VW 1L concept, this is a glimpse of where the future of cars needs to go, no batteries required!
If you do as said in the Military Ahem "Embrace The Suck" as you will be asking for trouble. I hope this clears a few things up.
