THE QUESTION OF FUEL
PART 2 -
Passing Gas the Clean Way

 

By John Copeland

Last month we talked about some of the factors that influence the way fuel performs in your engine and, consequently, how it makes your engine perform. We talked about octane rating, flame speed, vaporization and a lot of other stuff and, hopefully, we didn't lose you in all the technical stuff. After all, all you really want to do is go fast and pass tech, right? Well, this time we're going to look at the passing tech part.

Since the fuel legality issue began, race officials and tech people have spent sleepless nights trying to figure out how to catch the cheaters. They've used baby bottles and fuel "sniffers" and all manners of chemical tests. The oldest test in common usage is the baby bottle test. Before many racers had access to some of the more sophisticated additives, we had methanol.

Add enough methanol to gasoline (less than about 40 percent and you didn't gain anything) and a McCulloch or a West Bend, or a Clinton would really fly. It mixed well with gasoline, and with most oils in common usage at the time. Those of you who started karting after the Digatron meter was introduced in 1983 probably have never seen this test performed, but it really works.

You see, while methanol is soluble (it mixes well) in gasoline, it is even more soluble in water. Add to that the fact that gasoline doesn't mix at all with water and you've got yourself the makings of a way to detect methanol in gasoline. All the tech man has to do is take a sample of fuel and put it in a container with volume markings on it.

You could use a fancy graduated cylinder, or a measuring cup for that matter, but we mostly used baby bottles because they were cheap, had screw on caps, and were readily accessible. Anyway, you put a fuel sample in the baby bottle and you note the volume, say 4 ounces. Then you add an equal amount of water and shake gently. When the mixture settles down in the bottle, the water will be on top and the gas and oil mixture will be on the bottom. Since you put in 4 ounces of fuel and 4 ounces of water, the dividing line between the two should be at the 4 ounce mark. But remember, methanol is more soluble in water than it is in gasoline. In fact, it likes water enough more than gas that it will leave the gasoline and dissolve in the water. If your 4 ounce fuel sample is 25 percent methanol, when the fuel/water mixture in the bottle settles out, there will only be about 3 ounces of gasoline on the bottom and 5 ounces of water/methanol mix on the top. Pretty neat, huh?

It was messy, and it took some time, but it worked pretty well, and it still does. The baby bottle test is still a pretty good way for 4 cycle tech guys to spot stuff in the methanol that's not supposed to be there. Of course, in that case, you expect to see all the fuel absorbed into the water. Anything that doesn't, probably isn't supposed to be there in the first place.

With the introduction of the Digatron Fuel Meter, fuel checking went high tech. What the meter actually measures is called the "dielectric constant" of the sample. Some folks mistakenly think that the dielectric constant and conductivity are the same, but they are very different. Conductivity is the ability to pass an electric current between two electrodes and is measured as 1 /resistance with a direct current. Dielectric constant is a measure of capacitance measured with an alternating current. While both distilled water and iso?octane have very low conductance, the dielectric constant of distilled water is 80 and isooctane is 1.94!

Anyway, the Digatron meter measures the dielectric constant of the fuel sample. The national tech officials have specified that the meter be calibrated to ?55 with the probe immersed in cyclohexane, which has a dielectric constant of 2.023. After this calibration, the probe is immersed in the fuel sample and it may not read 0.0 or higher. Additives like alcohols, Propylene Oxide, or others tend to align themselves with an electric field (chemists say they're "polar") and they have higher dielectric constants. It only takes a drop or two of these rascals to make the meter read in the positive range and you're illegal. Setting the meter at ?55 gives you plenty of room for minor variations in gasoline composition or for different oils, but it will blow the whistle on most of the funny stuff.

By the way, while we're on the subject of the fuel meter, it is very important that the person doing fuel tech do it right, or he may end up tossing out innocent competitors. After the meter is calibrated, there is no need to put the probe back into the cyclohexane between every reading. In fact, doing so will mess up the calibration, because every time you take the probe out of the fuel tank and put it back into the cyclohexane jar, you dilute the cyclohexane with gasoline. You keep adjusting the meter for this contaminated cyclohexane and the calibration goes straight to "you know where." It's only necessary to re-immerse the probe and check the calibration if the reading comes up illegal. Then it's a good idea to recheck the meter and recheck the fuel.

The Digatron meter is very effective at detecting polar compounds used as additives, but there are two important shortcomings with this method. First of all, there are some chemicals that folks are experimenting with in their fuel that are non-polar, or that have a dielectric constant close enough to legal gasoline that the meter may not spot them. Some competitors have also found ways1to use material with low dielectric constants to mask the presence of other additives with higher constants.

Fortunately, only a few karters have the knowledge to circumvent the rules in this manner, and fewer still are desperate or dishonest enough to do so. A larger concern for the reliability of the Digatron meter is that the oil companies' never-ending search for more mileage and fewer emissions has led to the addition of a host of new components to readily available pump gas. Some of these components may alter the dielectric constant of the fuel enough to read over 0.0 on the meter. No tech man wants to see an innocent competitor tossed out because the fuel he or she purchased had something in it that it shouldn't have. The problem is that the poor tech man has no way of knowing whether the fuel fails the meter because of something the oil company put in it or something the karter put in it.

There is another way, however, to use the Digatron meter, and it borrows somewhat from the "baby bottle test" as well. If we take a fuel sample and add a roughly equal amount of water to it, then agitate it, like in the baby bottle test, we should get two clearly separated layers of liquid in the container, water on top and fuel on the bottom. Then take a reading with the Digatron meter on the fuel portion of the fuel/water sample and a reading on the fuel-only sample from the tank. If nothing has migrated from the fuel to the water, the meter readings should be exactly the same. However, if the fuel contains anything that leaves the fuel to dissolve in the water instead, the reading of that fuel will be different than the fuel that was not exposed to water.

It's probably a good idea to allow five points of leeway, plus or minus, on the reading to allow for any minor absorption of elements in the oil, but anything more than that is an excellent indicator that something is in the fuel that shouldn't be there. This test won't be able to tell you who (oil company or karter) put whatever in there, but it's a reliable test for most of the commonly used illegal additives.
Finally, there are now, and have been, a number of chemical reaction tests for various illegal additives. Most involve adding a sample of fuel to a test tube containing some chemical. Tech officials must then look for some specified reaction, such as a color change or bubbling. If properly designed and performed, these reactions can provide undeniable proof that the specific additive is present. The problem is, most tests like these require controlled conditions, or very accurate measurements of quantities, or experienced personnel to interpret them.

Unfortunately, we rarely have any of these things at the track, conditions are marginal, it is impossible to measure quantities accurately enough, and we lack trained, experienced technicians to perform and interpret the tests. Furthermore, many of the chemicals required for tests like these are dangerous in their own right. Acids and hydrides are commonly used for detecting specific hydrocarbons, and both families of chemicals may react dangerously with unexpected ingredients in fuel, or even with water! As an additional test, and in the hands of trained, experienced personnel, they can provide a valuable additional tool for the fuel-tech man. But in the wrong hands, or under the wrong conditions, they can be more dangerous than the fuel additives they were designed to find.

Next month we'] l start looking at specific additives and what they do. We'll also discuss how to spot them in tech. We'll probably end up doing some basic chemistry along the way, but 1 hope that you'll bear with me and see where this whole fuel thing is headed. See you next month!