quote:

The results show very tiny (<2%) improvements in Fuel consumption, thermal efficiency, and smoke opacity when going from 167F to 275F. EGT and NOX emissions were worse at the higher temp.

Good study, useful information. I've concluded that blends of diesel, with VO and/or BD can achieve clean burning without elevated fuel temperatures possibly needed with 100% VO. The tailpipe emission tests on my vehicle support that conclusion.

Besides, with my truck's fuel system, the fuel resides in the hot injector body prior to injection and I suspect that it's very close to the 230°F 'optimum' when it's injected into the hot combustion chamber.

quote:

Here is the best scientific study I have seen that compared D2 and VO at temps of 30C (86F), 75C (167F), and 135C (275F), see post#3:
http://www.frybrid.com/forum/showthread.php?t=3596

The results show very tiny (<2%) improvements in Fuel consumption, thermal efficiency, and smoke opacity when going from 167F to 275F. EGT and NOX emissions were worse at the higher temp.

The reason these charts are good is they are actually measuring engine performance parameters under the varying conditions.

If the actual citations were provided you could see why that particular study is not all that applicable to anything but small (4 hp)low speed single cylinder engines. I encourage you to find the actual study. Even the authors don't conclude what you do from their research.

quote:

with my truck's fuel system, the fuel resides in the hot injector body prior to injection and I suspect that it's very close to the 230°F 'optimum' when it's injected into the hot combustion chamber.

The optimum temp cited is PRE-injector..as BOTH fuels pass through the hot injector and pick up about the same amount of BTUs. I apologise for not making that clear enough in my earlier posts.

quote:

How about we discuss the subject and avoid personal references, OK?

OH PLEASE...I am referring to your "nom de plume" because I was addressing your post. I did not call you a name..I merely asked you to back up your theory.

Yes...please lets discuss the subject...rather than avoid it.

quote:

Good study, useful information.

Since you appear to be claiming to have seen the actual study that the charts (from FB) are alledgedly derived from it would be helpful if you would provide a link to the final report..or better yet the text of the study itself.

This message has been edited. Last edited by: danalinscott,

quote:

Originally posted by danalinscott:
If the actual citations were provided you could see why that particular study is not all that applicable to anything but small (4 hp)low speed single cylinder engines. I encourage you to find the actual study.

Thats still the best info I have seen by far. If you have any better studies, or even results of your own testing that you keep vaguely referring to, this would be the place to post references to them. A viscosity chart alone isn't enough to convince me and probably many others.

quote:

If you have any better studies,

Unless you can read the actual text of a study you cannot determine if it is legitimate or applicable. Best is to have the complete report..second best the final report third best is to have the report summary. If you have none of these you have no way of knowing if the report is legitimate OR applicable in any meaningful way. All one can do in that case is draw conclusions based on the limited information and ones own expertise...and these conclusions are less and less likely to be valid the less information from a study that you have to base them on.

In the worst case the study may be so deeply flawed that the conclusions and charts are completely invalid.

The ACREVO study is considered by thse in the VO fuel research field to be the most advanced and definitive study on VO combustion characteristics to date.

Advanced Combustion Research for Energy from Vegetable Oils (ACREVO).
http://www.biomatnet.org/secure/Fair/F484.htm

The PDF version

The study final report is available at the above link.
Excerpts follow.

quote:

The project was co-ordinated by the Laboratoire de Combustion et Systemes Reactifs, Orleans
(France), in partnership with ESEM/LME, Universite d'Orleans (France), St Etienne du Vouvray (France), Istituto di
Ricerce sulla Combustione CNR, Napoli (Italy), Department of Chemistry, Unversity of Kaiserslautern (Germany),
ICT, University of Karlsruhe (Germany), University College of Wales, Aberystwyth (UK) and Instituto Motori, Napoli
(Italy).

quote:

The objective of the ACREVO project developed by LCSR / CNRS in Orleans (France) is to investigate the burning characteristics of vegetable oil droplets from experiments conducted under high pressure and high temperature conditions. With such investigations, combustion performances of vegetable oils as biofuels for Diesel engines could be improved.

Many studies have examined the performances and pollutants emissions of Diesel engines using vegetable oils. Due to their physical differences as compared to Diesel fuel (especially a significantly higher viscosity), there are problems such as poor atomisation and coking tendencies in long-term test. It appears, therefore, important to study the mechanisms of deposit formation during vegetable oils combustion.

quote:

The ability of a pure vegetable (VO) oil, the rape seed oil, to be atomised for combustion or engine purposes has been tested. Since the VO is very viscous at low temperatures, it was necessary to heat it to achieve the required increase in atomisation performances.

quote:

As a summary, it may be recommended, for any attempt of using VO in an engine, to use the rape seed oil at relatively high temperature, of order 100-130 °C. An order of magnitude of drop sizes similar for fuel oil and VO may be found. But for Diesel sprays, the sensitivity to ambient air temperature is greater for VO than for FO.

quote:

Due to this stability with the temperature it is possible to preheat the oil up to 150°C where it attains the same viscosity as the diesel oil. Atomisation tests showed that at 150°C the performance of the rapeseed oil are comparable with that of the diesel oil.

It should be noted that one of the reasons the ACREVO study is so applicable is that the engine used was a turbocharged 3-cylinder-direct-injection-Diesel-engine and that the equipment used to monitor the results were state of the art.

This is in contrast to most (if not all) of the studys originating in India and Africa which use small low speed non-turbocharged single cylinder (3-5 hp)"listeroid" type engines. Laymen also often overlook the fact that the "diesel fuel" used for comparsons in those studies is not ASTM quality and has a highly variable viscosity which can ave double the viscosity of th diesel that is sold in the EU and NA. ASSUMING that the comparison charts using that often very high viscosity diesel in extremely inefficient engines is what leads many less familiar with the studies themselves to conclusions that are simply not valid.

For example...the Nwafor, O.M.I. "The Effect of Elevated Fuel Inlet Temperatures on Performance of Diesel Engine Running on Neat Vegetable Oil at Constant Speed Conditions." Renewable Energy. 28 (2003) 171-181, p 178. cited on the Frybrid website used a 304cc single cylinder NA type ar cooled "Petter type" test engine. These are extremely inefficient engines at all but a small rmp range and tend to be jetted for that range. Consequently the data derived from the HP and emissions testing is highly suspect since they are mainly due to the limits of that engine type rather than the fuels being tested. This does not mean that they don't contain ANY useful data. There is however no way to determine exactly WHAT data/charts ARE valid without access to the text of the study itself.

BTW...there is a private discusson group that has access to these studies.
If anyone wishes to join it (and in doing so get access to it's "lending library" which includes most of the studies done in the past 30 years on VO fuel) just email me. I will be happy to sponsor individuals I believe that the current members will approve. As a member I can sponsor up to 3 individuals per year. I have two sponsorships remaining for 2009.

This message has been edited. Last edited by: danalinscott,

quote:

Originally posted by danalinscott:
Due to this stability with the temperature it is possible to preheat the oil up to 150°C where it attains the same viscosity as the diesel oil. Atomisation tests showed that at 150°C the performance of the rapeseed oil are comparable with that of the diesel oil.

It should be noted that one of the reasons the ACREVO study is so applicable is that the engine used was a turbocharged 3-cylinder-direct-injection-Diesel-engine and that the equipment used to monitor the results were state of the art.

The atomization tests from ACREVO you quote where they give the 150C temps were done with an injector in a test rig at ambient pressure, using photography. This is far different than using it in an engine at actual operating temperature, load, and high pressures. Its a stretch to say visual results from an injector in free air are more applicable than tests in an engine measuring actual performance parameters.

Maybe there are some actual measurements at varying VO temps in the other parts of the study you haven't linked. For example, what % improvement in power was noted when going from 160F to 230F VO temps? That seems like a key, simple indicator of better combustion.

then there is this video " The Engine is the Final Heat Exchanger" something to talk about anyway...

The Engine is the Final Heat Exchanger

http://video.google.com/videos...r+&hl=en&emb=0&aq=f#


have a good view
Omar
www.omarsales.com

quote:

The atomization tests from ACREVO you quote where they give the 150C temps were done with an injector in a test rig at ambient pressure, using photography. This is far different than using it in an engine at actual operating temperature, load, and high pressures. Its a stretch to say visual results from an injector in free air are more applicable than tests in an engine measuring actual performance parameters.

You have a point..
In fact the very point I raised shortly after seeing the study for the first time.
But the ACREVO study DID include testing that measured actual performace parameters AS WELL as the droplet atomisation testing at atmospheric presures. And as I further researched WHY they did not attmept to test this under higher than atomosheric pressure I discovered that such research HAD been done by researchers testing jet engines in the 1950's and 60's. They discovered that for all practical purposes that droplet size depended almost exclusivly on the viscosity of the fuel and the velocity it exits the atomization nozzle. The pressure of the atmosphere it is injected into only has a measurable effect when it begins to approach the the pressure that the fuel is being injected at and therefore begins to effect the velocity of the fuel as it passes through the nozzle. The pressures in a diesel combustion chamber prior to ignition are no where near that.

By the time that the ACREVO study was being planned it had long been established that a pressure swirl atomiser was the best way to analyze the combustion of fuel droplets. In essence it provides a sinificantly slower combustion event which is therefore much more closely observable and measuable than attempting to record the combustion event inside the combustion chamber of any internal combustion engine. But the ACREVO researchers also want to compare this standard to that of an actual diesel fuel engine injector. Which they did.

ACREVO was very well funded and as a result had very good facilities, thorough planning, and close oversight...as well as massive peer review. Which is why it stands as the most respected study on VO fuel combustion conducted so far. It is certainly possible to find faults with it. But most if not all of those will be based on a lack of undertanding of the amount of research that went into choosing the battery of tests that WERE the ACREVO study or singling out only one test or part of a test without regard for how the other tests relate to it.

quote:

The Engine is the Final Heat Exchanger

A perfect example of the opposite of the ACREVO study.

The theory is poorly thought through and the test was designed to prove the theory rather than actually TEST it and the equipment was incapable of actually measureing or recording what is occurring in the test. So the testor is narrating what he believes is being proved by the test. It much more resembles an advertisment rather than a test. Because that is exactly what it is.

Of course the engine is the final heat exchanger.
Heat is transferred to the injector body by the metal into which that injector body it screwed into.
That heat is in turn transferred to the fuel passing through it.
So the amount of heat transferred to ANY fuel passing through it will raise that fuels temperature and lower its viscosity. Regardless of which fuel is being burned the temperature of the injector body will be the same..and regardless of which fuel is passing through it the same amount of heat will be transferred to the fuel as it passes through. BOTH fuels will be warmed the SAME amount compared to the temp they are ENTERING the injector body. As a result BOTH fuels will experience a reduction in viscosity as hey pass through the injector boy.

The theory presenting in the above video appears to be that both fuels reach the SAME viscosity as they pass through the injector body and this is simply not supported by anything presented in the video. However it can clearly be proven NOT to be possible by applying both simple logic and available existing research.
(Edited for typos)

This message has been edited. Last edited by: danalinscott,

Interesting charts.

This is all dependent on the assumption that one should match the injection viscosity of diesel with the injection viscosity of vegetable oil which may or may not be the case as there are many differences between the combustion of the fuels.

Many kit designers recommend changing the injectors to better handle veggie oil.

As I understand it, the efficiency of Diesel engines increases somewhat with the temperature.

So, it would be possible to boost the operating temperatures of one's engine to 250 degrees or so by changing the thermostat, and increasing the antifreeze content in the coolant.

Unfortunately, our motor oils and etc aren't rated to run at that high of a temperature, and there would be a fear of increased engine wear.

One might be able to design an exhaust based heat transfer system to get the higher temps.

I like the idea of a local feedback/return loop, perhaps with an air bleeder that I've seen discussed elsewhere.

quote:

This is all dependent on the assumption that one should match the injection viscosity of diesel with the injection viscosity of vegetable oil which may or may not be the case as there are many differences between the combustion of the fuels.

What are the differeces between combustion properties of VO and diesel other than viscosity and available energy in a given volume?

quote:

So, it would be possible to boost the operating temperatures of one's engine to 250 degrees or so by changing the thermostat, and increasing the antifreeze content in the coolant.

I don't believe this will work.
First ... it will be very hard to find a 205F termostat.
Second increasing the antifreeze content of the coolant mix will not increase its' boiling point.

quote:

Many kit designers recommend changing the injectors to better handle veggie oil.

Or modifying them so the angle of the spray "cone" is tighter.
Both are options that help reduce problems associated with not lowering the viscosity of VO enough to allow it to produce as fine a mist as diesel does as it is injected into the combustion chamber.

Changing the injection timing is another way that the less complete/slower combustion of VO that is more viscous than diesel fuel when injected can be dealt with. Of course such modifications of the injectors or timing make the engine more suited to VO fuel at the expense of making it less suited to diesel fuel. Neither modification can be "switched" on/off as heat can. By using heat to simply modify the viscosity of the fuel this undesirable side effect is avoided since the injectors and timing which is correct for diesel fuel is also correct for VO with the same viscosity.

quote:

Originally posted by danalinscott:
What are the differeces between combustion properties of VO and diesel other than viscosity and available energy in a given volume?

The auto ignition temp of D2 is 410F. VO is 690F. This is one reason it burns slower and advancing the timing between 2-4 degrees is best. This is also why VO can make more deposits with extended idling.

quote:

The auto ignition temp of D2 is 410F. VO is 690F. This is one reason it burns slower

Are you certain?
Do you have any referrence material that might support that?

Normally autoignition is applied to liquids and flash pointis applied to vapors.
Since it is the initial flame of the fuel VAPOR that provides the ignition source for the liquid fuel in a diesel combustion chamber I don't see how the auto ignition temp is applicable to this discussion.

The Flash Point of diesel fuel is 62 °C (143°F) and the flash point of Canola oil is 327°C (620°F). Biodiesel has a flash point of 130 °C (266°F). The temp of the compressed air inside a diesel engines combuston chamber is far above all of those. As long as the temperature of compression exceeds 327°C I don't see how the actual combustion of VO is effected by EITHER its' flash point or autoignition temperature. If the flash point of VO were HIGHER than the temp of the compressed air it is injected into I could see how it might effect its' IGNITION characteristics..but it isnt.

As the ACREVO study CLEARLY shows the slower combustion of VO fuel (compared to diesel fuel) is due to the tendecy of VO to not disperse into droplets as fine as diesel does. These larger droplets take a longer time to combust since the combustion of individual droplets proceeds from the outside of the sphere of fuel to the center. The larger the diameter of the fuel droplet the longer complete vaporization and subsequent combustion takes to complete. This is probably why diesel engines tend to sound less "rattely" on VO than diesel at idle. However this difference nearly disappears as the temp of VO is raised to the point where its viscosity matches that of diesel upon injection.

Even cold diesel fuel produces larger droplets than warm diesel fuel. Long enough in fact that cold diesel fuel can produce "wet stacking" more easily than warm diesel fuel. Wet staking is when the droplets of fuel burn so slwly that they are able to reach the cylinder walls without completely vaporizing and the liquid fuel accumulates on the cylinder wall and is scraped off by the rings. Some of this partially combusted liquid fuel then seps behind the rings and causes ring coking..and some seeps past the rings and contaminates the crankcase oil. When VO fuel does this the effects are more serious and progress more quickly.

There IS one documented difference in the combustion characteristic of VO compared to diesel. That is the amount of energy per volume. There is essentially 5% less power in a cc of VO than diesel fuel. This means that to get the same road speed slightly more VO must be injected each combustion cycle (compared to diesel) no matter how hot it is. If you can find documentation of another I woudl be very grateful if you would share it.

quote:

advancing the timing between 2-4 degrees is best.

Best?
In what way?
Compared to what?

What about the undesirable side effects of running diesel fuel in an engine on which the timing has been advance 2-4 degrees past what is recommended for diesel fuel injection?

quote:

Originally posted by danalinscott:

The theory presenting in the above video appears to be that both fuels reach the SAME viscosity as they apss through the injector body and this is simply not supported by anything presented in the video.

Exactly how did you reach this conclusion???
"Appears" ??? The point is made repeatedly that what is being discussed is temperature. The appearance of anything else would be a product of your own personal imagination and nothing to do with the facts or points presented in the video.

I have seen that video several times before and I watched it again just now and NOWHERE do I see or hear any reference to Viscosity. Due to this I would totally agree with you that nothing in the Video supports YOUR viscosity argument because it is never mentioned or implied. The only thing the narrator (whom you constantly seem to take unfounded issue with) mentions is temperature.

I suggest you watch the video again more closely and pay attention to what is actually being said rather than draw your own flawed conclusions to base an argument on that is purely a product of your creation and nothing that was put forward in the first place.

Perhaps you should make some videos of your own to put your theories forward in a more entertaining and easily digestable manner.

quote:

Perhaps you should make some videos of your own to put your theories forward in a more entertaining and easily digestable manner.

Thanks for the suggestion but I am much more interested in clearly communicating well researched information then producing entertaining videos. I don't think that serious research translates well into entertaining video. There are those who will devote the time and intellect it takes to understand a real study...and those that will not.

I ty very hard to present information in as clear a manner as possible and the charts I have prepeared and presented in this discussion do that. I ALSO try to provide clear explanations of related information for those who have more qhestions on the subject. I am in the "good information" business and I am sure my clients would not refer to me as "entertaining". Engineers in general tend to have a prefferrence of clarity over entertaining or humerous and I am certainly not much of an exception to that rule.

This message has been edited. Last edited by: Shaun,

quote:

Originally posted by danalinscott: Posted 29 June 2009 01:04 PM
Normally autoignition is applied to liquids and flash pointis applied to vapors.
Since it is the initial flame of the fuel VAPOR that provides the ignition source for the liquid fuel in a diesel combustion chamber I don't see how the auto ignition temp is applicable to this discussion.

The Flash Point of diesel fuel is 62 °C (143°F) and the flash point of Canola oil is 327°C (620°F). Biodiesel has a flash point of 130 °C (266°F). The temp of the compressed air inside a diesel engines combuston chamber is far above all of those. As long as the temperature of compression exceeds 327°C I don't see how the actual combustion of VO is effected by EITHER its' flash point or autoignition temperature. If the flash point of VO were HIGHER than the temp of the compressed air it is injected into I could see how it might effect its' IGNITION characteristics..but it isnt.

The flash point of the vapors from combustible material is only applicable when there is an ignition source. Generally a flame or spark but a charged glow plug would apply. The hot air in a diesel engine does not constitute an ignition source. AIT is responsible for ignition in all the vast majority of diesel engines.

Thanks, Geno

My italicized words are not correct but I think the gist of the post got through. (AIT is what matters)
Correction: The hot air is what causes ignition but not until AIT of the fuel being introduced is reached.

This message has been edited. Last edited by: Turbogeno,

quote:

The flash point of the vapors from combustible material is only applicable when there is an ignition source. Generally a flame or spark but a charged glow plug would apply. The hot air in a diesel engine does not constitute an ignition source.

I do not believe that is correct.

One should remember that although we generally refer to the engines we convert to VO fuel as "Diesel engines" they are actually referred to as "compression ignition" engines. Consequently the "hot air DOES constitute an ignition source. http://en.wikipedia.org/wiki/Diesel_engine

This is in refference to the fact that the the heat produced by the compression of the air in the cylinder before the fuel is injected into it. Because that air is above the temp required for the spontaneous ignition of the vapors produced when the fuel droplets hit it those vapors spontaeously ignite.

This initial ignition in turn raises the temperature in the combustion chamber to much greater temperatures which accellerate the vaporization and ignition process of the small droplets (speres) of fuel being propelled toward the cylinder walls by the momentum which was imparted by the injection process. I the fuel droplest are small enough they completely vaporize and combuat before they reach the cylinder walls. If however they are not small enough to completely combust some DO reach the cylinder wall and begin the process of ring coking/crankcase oil polymerization. Some also exit the compression chamber and create accretions on exhaust valves or create higher than normal EGTs as the combustion process continues at near atmoshperic pressure.

This is why it is very important to reduce the viscosity of VO to that which equals the diesel fuel being injected into the combustion chamber. Unless it is of equal viscosity the injectors produce much larger droplets of fuel.

quote:

Originally posted by danalinscott:

quote:

The auto ignition temp of D2 is 410F. VO is 690F. This is one reason it burns slower

Are you certain?

Yes. Auto-ignition temp (AIT) is what matters for a diesel engine, because it is compression ignition. There is no spark, so flash point (FP) makes no difference. From:
http://en.wikipedia.org/wiki/F...of_fuel_flash_points
Gasoline (petrol) is designed for use in an engine which is driven by a spark. The fuel should be premixed with air within its flammable limits and heated above its FP, then ignited by the spark plug. The fuel should not preignite in the hot engine. Therefore, gasoline is required to have a low FP and a high AIT.

Diesel is designed for use in a high-compression engine. Air is compressed until it has been heated above the AIT of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high FP and a low AIT.

The low AIT insures it ignites very quickly after its injected, the higher AIT of VO makes it ignite slightly later. Advancing the timing by 2-4 degrees is to compensate for this small delay. Higher AIT also means lower cetane which is a measure of ignition delay.

quote:

Do you have any referrence material that might support that?

http://en.wikipedia.org/wiki/F...of_fuel_flash_points
http://www.engineeringtoolbox....peratures-d_171.html

quote:

Normally autoignition is applied to liquids and flash pointis applied to vapors.

Untrue, see discussions of AIT and diesel engines such as the ones I gave above.

quote:

quote:

advancing the timing between 2-4 degrees is best.

Best?
In what way?

Best for higher power and mileage, less engine deposits due to higher cylinder temps.

quote:

Compared to what?

Compared to an engine that wasn't advanced, and set to factory spec.

quote:

What about the undesirable side effects of running diesel fuel in an engine on which the timing has been advance 2-4 degrees past what is recommended for diesel fuel injection?

Its a trade off, you want to optimize it for the fuel you use most, in my case its VO about 90% of the time, so I optimize for VO. 2-4 is such a small amount that you will probably not notice any side effects on D2. If you go beyond this amount of advance, you will see:
Decrease exhaust temperature
Increase cylinder temperatures/pressures
Increase fuel economy
Increase your output of NOx (a pollutant)
Decrease your output of Hydrocarbons (a pollutant)
Increase the amount of black smoke at peak torque
I wouldn't consider all of these to be bad side effects, some are very good.

Here is an old thread by crossbones who is an expert at diesel timing, and gives good examples of how the 2-4 degree advance was determined and tested:
http://biodiesel.infopop.cc/ev...641054012#9641054012

We will have to agree to disagree regarding flash point and autoignition point significance.
I tried to explain why the ignition depends on flash point temp rather than autoignition temp in a deiesel engines combustion cycle. Your own citation provides corroboration of that. "The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air."

quote:

quote:

What about the undesirable side effects of running diesel fuel in an engine on which the timing has been advance 2-4 degrees past what is recommended for diesel fuel injection?

Decrease exhaust temperature
Increase cylinder temperatures/pressures
Increase fuel economy
Increase your output of NOx (a pollutant)
Decrease your output of Hydrocarbons (a pollutant)
Increase the amount of black smoke at peak torque
I wouldn't consider all of these to be bad side effects, some are very good.

Its a trade off,

An unneccesary trade off.
If you can optimise VO fuel to match diesels vsscosity no timing change is neccesary for the engine to be optimized for BOTH fuels. In this way you can obtain the "good effects" of advancing the injection timing..without the bad ones.

quote:

2-4 is such a small amount that you will probably not notice any side effects on D2.

Most diesel technicians would disagree with that.

quote:

Fuel delivery timing is extremely critical in a diesel engine and impacts power, fuel economy, and emissions. If the injection timing is overadvanced, a loss of power will be experienced, along with possible internal engine failure such as piston damage. Excessive gray/black smoke can be a sign of an overly advanced pump setting.

http://www.dieselpowermag.com/..._injection_pump.html

I have always liked the ACREVO study, and in fact brought it to the attention of the SVO community a long time ago. However, this thread, and Dana’s interpretation of some of the conclusions of that study, have made me curious about it, so I read through it again.

Dana has stated that:


“As the ACREVO study CLEARLY shows the slower combustion of VO fuel (compared to diesel fuel) is due to the tendecy of VO to not disperse into droplets as fine as diesel does.”

Interesting conclusion. Here is what the authors of the study actually say:


"The study was reduced to atmospheric pressures, since this is the condition generally used use for this kind of injector (industrial furnaces for example). For Diesel sprays, the exact influence of the complex processes involved in liquid jet break up are not yet sufficiently known. Hence, the exploitation of the results was necessarily more elementary."

(In other words, they had to simplify it, and err on the side of caution, not having, at that time, the large number of converted engines operating successfully long term, not having emissions tests that showed good emissions reductions, etc., available, and needing to make some sort of recommendations. )

"Nevertheless information of primary interest for the practical use of VO in engines could be found in this work."

Indeed...primary interest. A starting point. Not the be all and end all.

"For use with pressure swirl atomiser, similar values of discharge coefficients may be obtained for fuel oil and heated (90-130 °C) VO."

(Ok - 90C works fine for that aspect….)



"But the injection pressures needed to reach a stable zone (zone of pressure in which these angle or coefficient are independent of injection pressure) are much higher for VO than for fuel oil. This results in greater exit velocities and atomisation processes which are certainly complex."


Indeed. Complex. As in, extremely difficult to map and extrapolate across engine families.



"In addition, values of SMD are systematically greater at a given pressure for VO than for fuel oil. Even if these values begin to be comparable between VO at 130 °C and fuel oil, this is only obtained for high injection pressures (more than 20 Bar)"

20 Bar? Injection pressures typically found in a diesel engine are much higher than that – 150-160 bar on an old Merc to maybe 10 times greater than that, or more, on a new common rail engine. What's the effect of that? Clearly, higher injection pressures have a profound influence on atomization, combustion, and emissions.

Otherwise, they would not have become the primary means by which diesel engines have been made cleaner in the years since ACREVO was done on that old-school, small-displacment, DI tractor engine (one of the most difficult types to get good atomization and minimal cylinder wall impingement on).

The quest for cleaner diesel engines has been a quest for ever-higher injection pressures, not fuel temperatures. If raising the fuel preheat temperature ever higher was the path to better atomization, it would have been used with diesel fuel.

Here is another famous and oft-cited quote from ACREVO:

"Due to this stability with the temperature it is possible to preheat the oil up to 150°C where it attains the same viscosity as the diesel oil. Atomisation tests showed that at 150°C the performance of the rapeseed oil are comparable with that of the diesel oil."

Nice. But it seemed this was done, as they state earlier in the document, at atmospheric pressure.

So the relevance of the ACREVO study to what is going on inside an actual engine, one under load, one that is already warmed up, especially, as in 2-tank conversions is, in my opinion, minimal.

Which really begins to put the entire thing into the category of the Olsson/ Chalmers University study, which caused a big uproar a number of years back, when Reuters reported the results in the mainstream media to the world. Also not done in an engine. Rejected by other researchers, and eventually retracted by Chalmers University, and embarrassment, and swept under the rug never to emerge again.

I think that it places too much faith in the ACREVO study to use it as a main pillar for the argument that fuel temperatures of higher than 80C or perhaps 90C at most are necessary.

quote:

Originally posted by danalinscott:
We will have to agree to disagree regarding flash point and autoignition point significance.
I tried to explain why the ignition depends on flash point temp rather than autoignition temp in a deiesel engines combustion cycle. Your own citation provides corroboration of that. "The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air."

That is ignitable by a spark, there isn't a spark in diesel engines. Without a spark, it won't ignite until it reaches the AIT. Thats why they care about the AIT being low and have an ASTM spec for cetane on all D2 fuel. (cetane is a measurement of ignition delay, and is a direct relationship to AIT, higher cetane = lower AIT.)

The only effect FP has in a diesel is safer handling while fueling, and thats why the ASTM D2 spec requires FP to be higher than a high # (>125F). If the flash point was what they cared about for combustion quality (as you claim) they would have the opposite: a spec requiring FP to be below a certain low # (<-40F) as they do for gasoline engines. See the wiki link I gave above for much more explanation.

Cetane is another important property you missed in your statement:
"What are the differeces between combustion properties of VO and diesel other than viscosity and available energy in a given volume?"

This message has been edited. Last edited by: SunWizard,

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That is ignitable by a spark,

Clearly diesel fuel/fuel oil can be much cooler than it's flash point of 143F before it is ignitable by a spark. Fuel oil cooler than room temp is routinely ignited by a spark in fuel oil furnaces.

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Diesel flash points vary between 126 °F and 204 °F

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Here is another famous and oft-cited quote from ACREVO:

"Due to this stability with the temperature it is possible to preheat the oil up to 150°C where it attains the same viscosity as the diesel oil. Atomisation tests showed that at 150°C the performance of the rapeseed oil are comparable with that of the diesel oil."

Nice. But it seemed this was done, as they state earlier in the document, at atmospheric pressure.

And WHY they did this..and WHY the ersults are valid for atomizationin diesel engines is explained in an earlier post.

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So the relevance of the ACREVO study to what is going on inside an actual engine, one under load, one that is already warmed up, especially, as in 2-tank conversions is, in my opinion, minimal.

What study/research do you believe is MORE valid then Ed?

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The quest for cleaner diesel engines has been a quest for ever-higher injection pressures, not fuel temperatures. If raising the fuel preheat temperature ever higher was the path to better atomization, it would have been used with diesel fuel.

And it has.

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Clearly, higher injection pressures have a profound influence on atomization, combustion, and emissions.

Otherwise, they would not have become the primary means by which diesel engines have been made cleaner in the years since ACREVO was done

Actually it isn't just higher injection pressures that is responsible for that. ACREVO (and other) researchers documented that well timed multiple bursts of fuel burned more efficiently and produced lower levels of pollutants than the single burst a mechanical injector is capable of. Higher pressures produce finer atomization..as does heating diesel fuel to higher temps. The same rules on combustion of liquid fuels apply to VO as petrodiesel.

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"Nevertheless information of primary interest for the practical use of VO in engines could be found in this work."

Indeed...primary interest. A starting point. Not the be all and end all.

I agree.
Unfortunately it is the BEST research available.

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I think that it places too much faith in the ACREVO study to use it as a main pillar for the argument that fuel temperatures of higher than 80C or perhaps 90C at most are necessary.

Can you produce BETTER documentation that 80 or 90C (at most) is neccesary for optimal combustion efficiency of VO fuel? Or are you just pulling that number out of thin air?

I recall similar arguments when I first suggested that suspended water in VO could cause IP and injector damage. Each and every advance in VO knowledge tends to be met with resistance by those that simply do not want to believe that what they currently believe may no longer be "state of the art". No conversion kit vendor wants potential customers to believe that what they claim is the most advanced technology available ... isn't. When it was acceptable suspended water levels in WVO fuel each vendor claimed (as some still do) that customers do not need to "worry" about suspended water levels. It eventually became clear through discussions like this (and later through cases of IP and injector damage via high suspeded water levels in VO fuel) that the concerns I raised were deemed VALID by the VO fuel community in general.

Later when I raised concerns regarding piston ring/land/groove coking the same vendors raised the same objections. Yet....eventually through discussion like this (and later through cases of piston ring/land/groove damage being documented) those concerns too were deemed VALID by the VO fuel community in general.

Wehn I produced this chart I expected the same resistance to its' implications as nearly every advance in VO fuel knowledge/understanding that I have presented and from mainly the same individuals. Reason and logic eventually prevail.

C'mon Ed...we have both been in this field long enough to remember when the belief that if it is liquid it is warm enough prevailed. It is a shame that kit vendors don't value progress enough to plow back some of the profits from kit sales into research that makes conversion bitter. It appears that each and every one is waiting for "someone else" to do that. Or maybe they all beleive that the conversoin THEY sell is the BEST possible conversion and no technological advancement are possible.

That's just not reasonable.
There are ALWAYS technological advancements that are possible.