Science Experiment - B0, B5, B50, B100 MPG

JLKunka

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My 7th grade daughter chose to compare mileage in a controlled experiment for various blends of biodiesel. The vehicle was a '99.5 Jetta TDI, 5-speed with 140,000 miles. We carefully planned a route and test scheme to minimize external variables. Ratios were chosen to minimize emptying and filling of the tank while still providing useful results. B5 was included to determine if lubricity alone would affect mileage.

There was a requirement for three trials of each ratio, which dictated route length to keep the time reasonable. We charted an out & back route of exactly 26.0 miles. We used a rural road that is little travelled and locked the cruise on exactly 55 MPH. (For those of you who don't have one, the Jetta holds an amazingly steady cruise speed.) Fuel level was initially topped off and refilled after each run with a graduated cylinder. We filled right up to the neck, using the vent slot as our mark. The results surprised us:
(This table doesn't post well. Original Excel data is linked in this post.)http://biodiesel.infopop.cc/eve/forums/a/tpc/f/419605551/m/678101253

Distance Driven per trial(mi) 26.0
No 2 Btu/gal 129050
Biodiesel Btu/gal 118170
* * * * * * * * * RATIO * * * * * * * * *
ml Consumed Trial # B-0 B-50 B-100 B-5
1 2137 2328 2180 2147
2 1963 2170 2203 1943
3 2049 2151 2084 1931
AVG 2050 2216 2156 2007
Gallons consumed 0.5415 0.5855 0.5695 0.5302
MPG 48.02 44.41 45.66 49.04
% change 0.00% -7.52% -4.92% 2.13%

Theoretical energy 129050 123610 118170 128506
% change 0.00% -4.22% -8.43% -0.42%

Note that the changes in MPG do not correlate with energy content of the blends. We'd love to hear your feedback and questions on the results. More data can be found in the Excel file.
 

Rockwater

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Great science experiment! Ambient air temperature can be an important variable in fuel consumption. What time of year were the tests conducted? Were air temperture effects considered in the design and analysis? Mainly important for winter testing. See the many threads discussing drops in winter fuel economy. Can we count on a new TDI club member when she reaches driving age?
 

JLKunka

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This was January in Virginia. Each day the runs were done starting at noon. The temperature varied a little but ranged from 38 - 42 F. Mostly it dropped during the day, so three runs on a given day saw similar temperature changes.

Yes, it looks like my daughter will want TDI #2.
 

Harvieux

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Very interesting! Where is maktas when we need him? He has always maintained that B5 is useless.:rolleyes: I'm wondering how a B2 run would do in such a test? The Spicer study showed B2 to be the absolute, hands down best lubricity enhancer of all. Best lubricity with a bit more BTUs? Priceless! ;) Later!
 

TomB

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How did you get the exact mix ratios if you only went 26 miles and topped off with a graduated cylinder?

You would have had to run the tank completely empty before each test and then fill with the correct ratio mix.

That would mean running the test on completely different days with completely different variables, possibly weeks apart.
 
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JLKunka

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TomB,

We started with B0, which was easy. The car had run a dozen tanks of B0 so there was no trace of Bio for the first trial. I have done the ventectomy, so capacity of the fuel tank to the neck is 15 gallons.

The first three trials were refilled with B0, using a 2000 ml graduated cylinder as the supply. We poured almost 500 ml into a 500 ml graduated cylinder, and filled the tank with that, recording the amount each time. It took 4+ cylinders to reach our index mark, so the last cylinder was recorded as "starting ml - remaining ml". Adding the numbers gave the total ml for the trial.

To do B50, we disconnected the fuel return line from the filter, started the engine, and let the fuel pump pump 7.5 gallons into a container. We then refilled with B100. This gave us a tank of B50. We drove around a bit to let this mix. We then prepared a B50 mix in the 2000 ml graduated cylinder to use as our refill mix. We topped off and ran our B50 trials.

We repeated the process for the B100 trials, except we pumped the entire tank out and refilled with B100. Our refill mix was neat B100.

To do the B5, we pumped out 14.25 gallons of the tank's B100 and refilled with petro-diesel. We prepared a mix of B5 in the 2000 ml graduated cylinder for the B5 trials.

The time it took for all this pushed the trials over 4 days, all during Christmas break - one ratio, three runs per day. We had a stretch of consistent dry weather that week, so temperature only varied a couple degrees which was the best we could do.

Read some of the replies on the previously linked Biodiesel & SVO Discussion Forum site for some interesting statistics on our results.
 

Lug_Nut

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Harvieux said:
Very interesting! Where is maktas when we need him? He has always maintained that B5 is useless.:rolleyes: I'm wondering how a B2 run would do in such a test? The Spicer study showed B2 to be the absolute, hands down best lubricity enhancer of all. Best lubricity with a bit more BTUs?
What friction source does the fuel reduce? Rolling resistance? Air resistance? If a 5% (or 2%:rolleyes:) biodiesel proportion is enough to reduce ALL resistance (at 55 mph!) by enough to account for the 2% fuel consumption reduction, then just how much frictional resistance is coming from the only item that liquid B5 contacts: The injection pump?
For this amount of increase in fuel economy to come solely from reducing wear on the pump when using biodiesel, I am quite skeptical that a pump without any bio, would last a week.
I still don't buy that "lubricity" improvement is the root cause of better fuel economy with the addition of a hint of bio. Put me down as being in Maktas camp on that hooey.

I use biodiesel but it ain't for ludicrous claims like "lubricity".
 

JLKunka

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how much frictional resistance is coming from the only item that liquid B5 contacts: The injection pump?
I tend to agree. Look at it this way: It takes energy to pump the liquid fuel, and it takes more energy to pump a more viscous liquid. Couple that with reduced energy content of biodiesel, and it's no wonder bio blends give poorer fuel economy.

Now, B-5 is barely different energy-wise than B-0 BUT biodiesel is supposed to have a high cetane number, so could we see improved performance (and mileage) due to the more "advanced" start of ignition and more complete combustion?
 

TomB

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The energy difference between Dino and B100 does NOT cause a reduced MPG in older diesels. It may actually increase. The older engines just were not as efficient at utilizing all that energy whereas the B100 burned more completely.

The impact of the energy content reduction does not become apparent until you get into an engine such as the 2.0L TDI in the 2004-5 Passats. These engines and newer are so much more efficient and clean burning that the reduced energy content does indeed impact MPG since they utilize every bit of that energy to perform.

The Passats show about a 10% decrease.

As well, cetane does not equate to higher MPG directly. My understanding is that it changes the burn pattern in the cylinder, resulting in quieter performance, but not necessarily helping improve MPG.
 

TomB

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JLKunka said:
TomB,

We started with B0, which was easy. The car had run a dozen tanks of B0 so there was no trace of Bio for the first trial. I have done the ventectomy, so capacity of the fuel tank to the neck is 15 gallons.

The first three trials were refilled with B0, using a 2000 ml graduated cylinder as the supply. We poured almost 500 ml into a 500 ml graduated cylinder, and filled the tank with that, recording the amount each time. It took 4+ cylinders to reach our index mark, so the last cylinder was recorded as "starting ml - remaining ml". Adding the numbers gave the total ml for the trial.

To do B50, we disconnected the fuel return line from the filter, started the engine, and let the fuel pump pump 7.5 gallons into a container. We then refilled with B100. This gave us a tank of B50. We drove around a bit to let this mix. We then prepared a B50 mix in the 2000 ml graduated cylinder to use as our refill mix. We topped off and ran our B50 trials.

We repeated the process for the B100 trials, except we pumped the entire tank out and refilled with B100. Our refill mix was neat B100.

To do the B5, we pumped out 14.25 gallons of the tank's B100 and refilled with petro-diesel. We prepared a mix of B5 in the 2000 ml graduated cylinder for the B5 trials.

The time it took for all this pushed the trials over 4 days, all during Christmas break - one ratio, three runs per day. We had a stretch of consistent dry weather that week, so temperature only varied a couple degrees which was the best we could do.

Read some of the replies on the previously linked Biodiesel & SVO Discussion Forum site for some interesting statistics on our results.
That was some science project. :)

How about the fuel left in the lines to the engine, did you purge that some way to the same percentage?

If you ran all three test of the same % right after each other, then you may need to discard the first run for each one to prevent skewing from the "purging" run which sent through some of the old.
 

Harvieux

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Lug_Nut said:
What friction source does the fuel reduce? Rolling resistance? Air resistance? If a 5% (or 2%:rolleyes:) biodiesel proportion is enough to reduce ALL resistance (at 55 mph!) by enough to account for the 2% fuel consumption reduction, then just how much frictional resistance is coming from the only item that liquid B5 contacts: The injection pump?
For this amount of increase in fuel economy to come solely from reducing wear on the pump when using biodiesel, I am quite skeptical that a pump without any bio, would last a week.
I still don't buy that "lubricity" improvement is the root cause of better fuel economy with the addition of a hint of bio. Put me down as being in Maktas camp on that hooey.

I use biodiesel but it ain't for ludicrous claims like "lubricity".
I don't think you understood what I am referring to and maybe it's because I didn't make it clear enough. It is not the better lubricity factor that would increase fuel mileage beyond minute amounts, it would be the btu factor in bio vs. D2. My reference to B2 is solely for the lubricity improvement over straight D2, all other diesel fuel additives, and even B100 as shown to be the case from the Spicer research data. My meaning of B2 over B5 was only a trivial, if any improvement due only to the fact that B2 would have a tad more btus than B5. I also think it is an argument of whether the sky is really blue or not when referring to B2/B5 being useless when there is data to prove otherwise. Any questions?:rolleyes: Later!
 

Lug_Nut

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B2 and B5 will have FEWER BTU than Bzero. If it were heat energy content only, the decline in MPG would be nearly linear to increase in the bio proportion. That didn't happen here in this trial. That doesn't happen in most other trials of this type.
B2 and B5 can reduce pump friction, but there isn't enough pump friction to allow reducing the entire car's resistance by the 2% this trial shows or whatever percentage that the Spicer trials show. The fuel injector pump simply isn't that great a percentage of the entire car's energy consumption to have such a dramatic effect.
There is something that happens at the B2 to B10 ratio, but it isn't from MORE heat energy than D2, and it isn't all from injector pump friction reduction.

"Data to prove otherwise"? No. There are ample anecdotes and a general consensus, but no explanation as to why. It's an explanation that addresses the result that that I find to be blatantly lacking in the assertion that low bio amounts are a benefit to fuel economy.

The sky isn't blue simply because everyone says so. It's blue due to provable, physical, optical properties that can be explained, measured and reproduced.
Low percentages of biodiesel appear to improve fuel economy versus no biodiesel far more than the "it improves lubricity" mantra should have it. I still haven't heard a logical, defensible explanation as to why.

If someone were to show that the injector pump requires 1500 watts of energy to spin at 2000 rpm and compress x cc of fuel to 300 bar per revolution, and that 5% bio lowers that requirement to 500 watts, than I'd be able to see that the 1000 watt saving is a bit over 1 hp and a substantial proportion of the 15 or so hp needed to move a car at 55 mph.
That I can buy....

I'll leave D2 (no bio) pump lifetime for ... later.
 

Harvieux

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How's this response to keep it simple? Lubricity advantage of B2 vs. straight D2. Answer = B2 backed with data resulting in such and therefore the claim that B2/B5 is useless = bunk, period. Fuel mileage advantage of B100 vs. B2, B5, or straight D2. Answer = B2, B5, & straight D2. Fuel mileage advantage of B2 vs. B5. Answer = No data but, with general consensus that negligible increases in btus of B2 over B5 may have a minute advantage in overall fuel mileage. Later!
 

Lug_Nut

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Driving at 55 mph steady state will use fuel at some rate. That can be measured with VAG-COM, scanguage, other fuel consumption devices.
The engine RPM can also be measured and will be just a shade under 2000 rpm.
The difference in fuel used in maintaining 2000 rpm in neutral with the vehicle at a stand-still, and in driving in 5th (or 6th) at 2000 rpm is the vehicle resistance. Subtracting driving fuel use rate from same rpm, but at a stand-still fuel use rate, separates the engine resistance out and provides the fuel used to move the vehicle. The percentage of engine consumption to vehicle consumption at 55 mph is now quantifiable.
If the engine consumes 10% and movement of the vehicle at 55 mph uses 90%, then a B5 improvement of 2% of the total at 55 mph implies that the engine has improved by 20%.
Because the fuel doesn't affect the piston rings, oil pump, power steering other parasitic engine drag, the logic is that the injector pump resistance has to drop by a much greater percentage to allow the engine consumption to drop 20%. Then it stands to reason that only a percentage of fuel pump energy consumption is friction, and the rest is fuel sucking and pressurizing. So how much would you guess? 50/50? Pump friction would need to be cut by what? 80% to reduce engine consumption by 20% to reduce the 55 mph consumption by 2%?

That belief that fuel pump friction resistance is nearly eliminated with 5% bio is not "simple", that's ignorance.
 

JLKunka

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Stats on our data from another thread:

TDIST (B0,B5) =TTEST(C6:C8;F6:F8;2;2) 0.647
TDIST (B0,B50) =TTEST(C6:C8;D6: D8;2;2) 0.091
TDIST (B0,B100) =TTEST(C6:C8;E6:E8;2;2) 0.163
TDIST (B5,B50) =TTEST(F6:F8;D6: D8;2;2) 0.080
TDIST (B5,B100) =TTEST(F6:F8;E6:E8;2;2) 0.133
TDIST (B50,B100) =TTEST(D6: D8;E6:E8;2;2) 0.416

Quoting keelec on Biodiesel & SVO Discussion Forum: (where our results were also posted)

Ok, I think what this gives me is that:
B0&B50 are different within a 90% confidence interval (91%)
B5&B50 are different within a 90% confidence interval (92%)
B0&B100 are different within an 80% confidence interval (84%)
B5&B100 are different within an 80% confidence interval (87%)

B0&B5 are not statistically different.
B50&B100 are not statistically different.
He ran statistics on our results which allow us to make the above conclusions. Within the limits of our measurements, we cannot say that B50 is worse than B100, only that Bio blends > 50% are worse than B0.

Originally Posted by TomB
How about the fuel left in the lines to the engine, did you purge that some way to the same percentage?

If you ran all three test of the same % right after each other, then you may need to discard the first run for each one to prevent skewing from the "purging" run which sent through some of the old.
Technically, the car has the previously ratio in the lines from the pump to the injectors. This is a tiny quantity, probably used up before we get in gear and start driving. The fuel in the filter and lines to/from the tank is recirculated very quickly back into the tank. This volume is again, small compared to the entire tank and was ignored in the calculations.

Originally Posted by Lug Nut
Because the fuel doesn't affect the piston rings, oil pump, power steering other parasitic engine drag, the logic is that the injector pump resistance has to drop by a much greater percentage...
Here's something to chew on: The other vehicle I run with biodiesel blends is a 70's International Harvester tractor. It regularly gains "oil" between changes. The unburned biodiesel is getting past the rungs during operation. Now, piston side loads are a significant source of friction in an engine, so it stands to reason that if a fuel "lubricant" is getting into the crankcase, then that lubricant will be reducing the friction of the pistons and rings....

Thoughts?
 

RalphVa

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It appears that mileage is a function of BTU/gallon except for the slight improvement with B5 (e.g. saw some information that says bio has less BTU/gallon than B0). Could this be a combustion improvement thing?
 
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