Timing changes with blending

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

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Postby coachgeo » Sun Nov 30, 2008 4:25 pm

bio_cowboy wrote:...Also, since quite a few people who blend gasoline with VO, find greater power and fuel economy than one would expect if one were to just add up the BTUs of the components in a blend of VO and gasoline, then the third conclusion suggests that adding gasoline to VO causes faster evaporation and combustion of the blend particles as compared with pure VO. This conclusion sounds theoretical and not experimental. The other possible mechanism might be the hypothetical decrease of surface tension by adding a light fraction that might improve atomization of the base fuel, which is in this case VO. However, the fourth conclusion would not hold for gasoline, because it is cheaper than diesel fuel....
Another hypothetical on why Gas/Petrol blends act as you noted... could be because of a dual flame front during combustion in the cylinder.

For example the fuel "oil" igniting due to compression under heat (AKA Diesel engine combustion) and the second one (petrol) lighting off due to the flame created by the compression combustion. This second light off helps the first combustion reach full fuel burn thus increasing power.

Now that is assuming it would be the compressed fuel "oil" that ignited first.

There has been discussions on this but I forget which fuel is thought to combust first.

If it is the petrol that combust first then maybe it's combustion further automizes the fuel oil being compressed thus when it lights off it gets a more full burn?
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Postby 240Volvo » Sun Nov 30, 2008 7:22 pm

If I recall correctly, petrol retards the timing of ignition. As one must advance the timing of injection of VO in order to gain a more complete combustion, this is a curious puzzle, indeed.

Thoughts?
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Postby John Galt » Sun Nov 30, 2008 8:55 pm

@#$*&^%$!!!
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Postby 240Volvo » Sun Nov 30, 2008 9:49 pm

I'm sure that is true of your blend, John. I was referring strictly to the combustion characteristic of VO in regard to injection timing and that of RUG. It puzzles me.
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Postby bio_cowboy » Mon Dec 01, 2008 7:45 am

coachgeo wrote:Another hypothetical on why Gas/Petrol blends act as you noted... could be because of a dual flame front during combustion in the cylinder.

For example the fuel "oil" igniting due to compression under heat (AKA Diesel engine combustion) and the second one (petrol) lighting off due to the flame created by the compression combustion. This second light off helps the first combustion reach full fuel burn thus increasing power.

Now that is assuming it would be the compressed fuel "oil" that ignited first.

There has been discussions on this but I forget which fuel is thought to combust first.

If it is the petrol that combust first then maybe it's combustion further automizes the fuel oil being compressed thus when it lights off it gets a more full burn?
Hey coachgeo, you make some good points. But, to clarify, since we are now on the topic of timing, I have read (and it seems correct) that gasoline (petrol) most probably advances the timing; whereas VO supresses the timing, so a proper blend of the two would produce a fuel mix that is properly timed for said vehicle, thus precluding the need to adjust the timing, as Mr. Galt pointed out. So, in this case it would suggest that if there is a hypothetical dual flame front, that the gasoline is most probably the first, which helps ignite the VO flame front. But, if there is such a dual flame front then it must be in quick succession, because blenders observe smooth operation, and often a quieter engine.
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Postby coachgeo » Mon Dec 01, 2008 9:41 am

bio_cowboy wrote:... if there is such a dual flame front then it must be in quick succession, because blenders observe smooth operation, and often a quieter engine.
and it has been said if you end up with a quiter engine then you need to adjust your timing till it sounds more diesel like because this is the point that things are combusting most effciently.
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Postby SunWizard » Mon Dec 01, 2008 9:55 am

The timing change depends on viscosity, cetane and auto-ignition temperature of the components of your blend.

From the RUG blending isn't as good thread:

RUG lowers the cetane of a blend compared to using D2 in your blend. Low cetane causes symptoms such as poor fuel economy, excessive smoke and engine noise, excessive emissions, misfiring, rough running and hard starting. These symptoms are usually worse or more noticeable in colder weather. VO has a very low cetane (38 for most VO) to begin with, its interesting that all those symptoms commonly listed are the very things you get if you have too high% VO in your blend.

The figure that matters for diesel engines is the auto-ignition temp, where lower is better: 410F = diesel. RUG is 536F. VO is 690F. This temp is the main thing that affects cetane.

Auto-ignition temps:
http://www.engineeringtoolbox.com/fuels ... d_171.html
Which shows that almost all of the additives used by blenders will raise the auto-ignition temps compared to D2. This means lower cetane, lower MPG and it can also make your timing off by being retarded.

The combustion quality and timing in a diesel depends mainly on cetane. As long as you have your viscosity thin enough that you get proper atomization, which is a separate discussion here:
Viscosity testing of WVO & blends since viscosity is the other main factor along with cetane.
Last edited by SunWizard on Fri Sep 24, 2010 10:54 am, edited 1 time in total.
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Postby coachgeo » Mon Dec 01, 2008 10:20 am

were back to math cetane, Octane etc etc..... this has been said. Butt...least from what I've read in reality.... the math that should add up .... DON"T.

Maybe the fuels are igniting at different times as if they were on their own.... another words.... the math of their cetan/octane etc. being added up gets negated because.... they become seperated just prior to combustion and act INDEPENDENTLY?
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Postby SunWizard » Mon Dec 01, 2008 11:29 am

You can't figure any of this with math, too many variables. If blend components act independently (2 flame fronts as you said before), then a D2 portion will ignite sooner than a RUG portion, and sooner than the VO portion, due to the lower auto-ignition temp.

The viscosity will also affect timing, since if its too thick it causes worse atomization and later combustion. Different vehicle types can handle thicker viscosity better than others and are less affected by it.

Is there some part of those 2 factors that you disagree with? (if thats what you mean by don't add up?)
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Postby John Galt » Mon Dec 01, 2008 1:45 pm

@#$*&^%$!!!
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Postby John Galt » Mon Dec 01, 2008 8:33 pm

@#$*&^%$!!!
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Postby coachgeo » Mon Dec 01, 2008 9:15 pm

SunWizard wrote:...Is there some part of those 2 factors that you disagree with? (if thats what you mean by don't add up?)
not sure the VO/Diesel seperate out. My guess is they stay combined while the petrol seperates out and ignites seperately.
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Postby coachgeo » Mon Dec 01, 2008 9:18 pm

John Galt wrote:... not armchair quarterbacking.
There was a very long detailed thread with "if I recall right" evidence that showed the point I brought up on need to keep the "diesel sound" via tuning. If I recall right the thread was; or brached off of, one of those on infopop that was discussing using the glow plugs as sensors to measure efficency of combustion.

Sorry I can't quote the exact thread.
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Postby SunWizard » Mon Dec 01, 2008 9:21 pm

Welcome back Jeffrey Brooks, AKA Mixer who was banned here, now back with a new IP and name. You have the same writing style, same long list of links, and have now have started posting nearly the same axe grinding about RUG as before. And as I warned before please don't start posting a repeated long list of links on every post or it will be considered spam.

bio_cowboy wrote:there are significant reliable reports of improved economy, increased power and decreased emissions with VO/RUG blends.

If there are, please post some of them. I went through your long list of links and if they are reliable reports of better mileage, why are most of the reports of worse mileage and power? I saw only 1 post who said better MPG (by DCS), and V95/RUG 5 but he didn't answer more power compared to what when I questioned him.

To be reliable, they need to state what blend ratios were used, what vehicle, and test methods. And if they say better mileage/power, compared to what? I saw no posts meeting those simple standards, except mine where I reported less power with V80/ RUG20 blends compared to V80/D20 on my 300D which is very underpowered and the change is very noticeable.

Any mileage claims are extremely hard to verify since few ever follow good test procedures, leading to large variations in mileage even on the same fuel. Dyno tests of different blends is the best test, thats what I would like to see.
...the blend itself acts as a single entity having its own viscosity, flash point, and auto-ignition temperature that closely matches that of #2 diesel fuel.

A blend will never closely match the D2 auto-ignition temp (AIT) since everything we are adding has a much higher AIT than D2. Unless we are talking about very low % blends like V20.

Flash point doesn't affect a diesel engine, it merely means a fuel is more or less hazardous to handle, and has more/less evaporative emissions. This is why the laws for D2 require the flash point be much higher than RUG, so they don't have to deal with the extra safety and complex evaporative emissions systems and cost required on gas engines.
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Postby coachgeo » Mon Dec 01, 2008 9:30 pm

bio_cowboy wrote:...Our best bet now, is to come up with an explanation. I personal believe that we do not have two flame fronts, but the blend itself acts as a single entity having its own viscosity, flash point, and auto-ignition temperature that closely matches that of #2 diesel fuel....
Problem with that theory is.... when you do the math you can do.. cetan Octane addition/subtractions.... of the components in the RUG/WVO/diesel blendyou come up with a number that would agree with Sunwizards and others that follow the same path, that such a blend should NOT be performing better or at least equal too.

If I recall right somone ( I think Kugel) found a reference in a very very old diesel theory book about the two flame front with petrol added. I may be wrong on who though.

There has been yearrrsss of discussions on this topic at infopop. Going way back long before they created a blenders forum. I tried to copy links etc. into the blenders forum referencing those old good topics from the other forum but gave up cause of all the pissing back and forth. Heck think I even did some under an annonymous name to help that forum get off on a good foot.

In those discussions only a few tried to think of ways to explain why RUG blends worked as good as some seem say they do while a lot of others kept shooting them down saying they must be wrong due to cetane octane mathmatics.

Sorry .... again..... were going WAY WAY WAY back so I cant quote a reference.
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