Your corrections / additions make it sound more like you know what you are doing. The OP sounded to the contrary, and not consistant with your other posts in other threads ( where you did sound like you knew what you were talking about ).

Sorry if I made a rush judgement. Your OP sounded non-reliable to say the least. I still have a problem with a "1.2 mile" test procedure. That is still a very small sample size.

The fact that you collect 1 sample per second is very good. This is very good sample resolution but not a measure of sample size.

Someone could repeat your experiment with a different computer that recorded 1000 samples per second, but the sample would still be a very short, very small, 1.2 mile sample.

I think a resolution of 2 is sufficient. The gasoline used from point A to point B is all that is required, yes? The amount of gas used from point A to point 0.01B is not helpful. What is helpful, is to make the distance between point A and B much larger. Do you agree?

Nontheless, it will all be interesting.
Thanks for sharing.

Oh, I used the "groundwater" example to mean any impurities that may contaminate the original gasoline that may detract from its performance. There are probably countless other things ( rust, dirt, chemicals, ) that could be present in your gas tank. And yes, water will separate from gasoline when allowed to sit still. But how often is this the case with a car in motion? I suggest that water droplets would be suspended in the gasoline as a mixture ( dirt in water ) vs. a solution ( sugar in water ).
These water droplets would pass through the fuel injectors, contributing zero useful btu, energy, or power to the ICE. (The water droplets would not contribute to the miles, but they would contribute to the "gallons".) Again, not a sign of a poor manufacturer ( brand ) but of a poor storage, or delivery system ( poor particular station).

 

Unfortunately, the nearest larger hill is about 50 miles away near Stevenson AL. It has a 980 ft rise, nearly double the size of my nearest hill. I have gone there for other hill climb testing but found I still get usable, not perfect, data from the local hill.

This remains an interesting if somewhat intractable problem. I'm reminded of the gas sample tank on light airplanes. We would draw a sample as part of the pre-flight to look for water and sediments before each flight. Unfortunately, no such fuel quality system is built into our vehicles. However, if gasoline density turns out to be a useful metric for energy content, a well design gasoline quality tool might be possible.

I could see a clear plastic, tank filler extension. The fuel would pass through a vortex separator so any particulate or immiscible contaminates could be seen. A small micro processor with a piezoelectric and thermistor could measure the density and report fuel energy quality. Within seconds, you could tell if there was a problem and decide to top-off or move on. Caps for each end could seal the unit to minimize the vapor problems during storage.

BTW, I appreciate the comments and will look at editing the intermediate report to clarify details about the data and methodology.

Bob Wilson

 

Agreed, but also remember that stations have to add markers to their tanks to make them "un-same". So you have (total guess here) 9999 gallons of same gas, and 1 gallon of marker additive. Chevron's marker is Techron. If the marker is inert it might effect the energy content of the gas. I don't recall how many parts per million is marker, but I'll concede that it would make a difference.

11011011

 

I went back today and made three runs up the hill in 88F weather. To increase the number of samples, I averaged two injector times on either side of two ICE power settings to make an intermediate watt_sec/gram sample. This cut the sample interval down to just a little over half a second.

I checked the averages of each run against the average of all runs and they were within less than 2%. The 'power' trendlines were of similar shape, only slightly offset. If the samples were random, I would expect the averages and trendlines to be off substantially.

Hopefully, I'll get three runs in the morning in the mid 60s to compare to the 88F runs. This will test the hypothesis that the ambient temperature has an effect upon the apparent specific energy of the same lot of fuel.

Bob Wilson

 

Very cool. I began my Shell testing Friday by finally finding a Shell station in my area that was around the basement price for gas here ($3.45) instead of paying a large premium like I would have at other Shells nearby. I don't have any of Bob's equipment so my stats will be showing up by the tank on the GreenHybrid DB with Shell 87 in the Notes.

Bob, thanks for all the rigorous testing, it's not trivial to pay such close attention to detail in a hobby fashion. I have a request on your graphs to make them more readable to the average forum reader - try to group colors by brand and group them in the key. For example Shell right now is scattered around the key and seems to use pink and green. If it instead was the first 3 entries in the key and all of its lines were shades of red, while another brand's 3 lines were all shades of green, it would be a much easier read to less data-minded readers. I don't know if this is possible in the software you're using, however.

 

Hi folks,

The graph color code is fixed:

1. Reds - highest energy (three samples)
2. Greens - high octanes (two samples)
3. Blues - lowest energy (four samples)

Thanks 'SoopahMan'.

If you take the highest energy values, ~16,000 W_s/g, and assume a 33% thermal dynamic efficiency, this gives ~48MJ/kg, which is pretty close to the 46-47MJ/kg listed in Wiki. As the specific energy decreases at high rpm, this is consistent with a fall off in ICE efficiency at higher power settings.

It looks like this protocol does not spin the ICE faster than ~4,200 rpm. Yet other, maximum power runs have achieved red line 4,500 rpm (specific to 2001-03 Prius.) The newer NHW20s have a higher red line, 5,000 rpm. I will look at the 4,200-4,500 rpm range to see if this explains a precipitous drop in MPG seen with my 2003 NHW11 Prius.

It also looks like this protocol can evaluate ICE modifications like testing ICE oil. I can run one series pre-oil change; change the oil; and run a second series and compare the results. A significant improvement in ICE efficiency means it was past time to change the oil. I can compare 0W-20, 5W-30 or other oil brands and grades. I can also test a performance muffler with the protocol providing a direct readout of the effectiveness.

Bob Wilson

 

bwilson4web — Did I miss your final report, or have you not yet completed the gasoline comparison tests that you were conducting? You were waiting for a hydrometer, as I recall.

Stan

 

Thanks for reminding me. I have some data to share but will need to resume the testing in a couple of weeks:

In the above chart and my latest data, I compared three brands previously not compared: Exxon, Chevron and Shell. The first surprise was how similar their energy contents came out. This is in stark contrast to Shell versus Conoco, BP, Texaco and Citco in April-May. Back then, Shell and only Shell 87 came out with these energy numbers.

I did get my hydrometer and found:

What surprised me was Shell and Chevron having similar densities and slopes but Exxon appears to have a slightly greater density. The theory is that energy density is tied to fuel density yet I can not find a strong correlation with the energy testing other than Exxon showed up on the high side of the energy curves but not by much.

What I need to do is retest the other brands, Texaco, Conoco, Citgo and BP, using this new methodology against Shell 87. However, it will take me almost two weeks to burn off this tank.

So far, my mileage with Shell 87 remains high. I would expect Exxon and Chevron to do the same. I need to retest the other four brands.

Bob Wilson

 

Bob Wrote:
"The theory is that energy density is tied to fuel density yet I can not find a strong correlation with the energy..."

Now why would you say that?
Water has 30% more density than gasoline, and 100% less energy.

 

LOL! Or lead!

It actually comes from a Dept. of Energy report that stated the energy of hydrocarbon fuels is a function of density. This makes sense in that longer chained hydrocarbons will have more energy bonds and be denser because of their higher molecular weight. The energy per gram is fairly constant but having more grams per gallon goes further . . . or that is the theory. But the Exxon numbers have me wondering.

What I need to do is find some of that low energy gasoline I was testing back in April-May, the Conoco, BP, Texaco or Citgo, and measure their relative densities. Then I'll be able to see if there is a strong or weak correlation. If so, we'll have a simple, non-destruct means to test gasoline quality. If not, . . . another beautiful theory crashes into hard reality.

Bob Wilson