James
Correct, DC is dielectric constant.
No problem on the avgas. A racer brought some by for testing; I remembered you wanted to know, so I made a note. I wish I'd asked him what brand of avgas it was, or at least where he got it, but I was doing something else at the time and didn't think of it until he was gone.
Keep in mind that out reagent test chemicals were suspect that weekend, so we didn't use them. That sample of avgas or either of the street fuels may have failed one or both of the reagent tests.
If any of you guys are going to be at the Runoffs, and want to check a particular fuel, bring it by the tech building and look me up (when I don't have a batch of miatas torn apart) and I'll introduce you the folks at fuel test central. Best if you do it early in the week, once qualifying starts they get pretty busy.
Bill
Maybe you are confused because I haven't been clear. I'm not an expert, but I'll try again.
We run three tests on fuel at the track.
The first is done with an electronic test meter. The meter measures the dielectric constant (DC) of the sample. The DC is a measure of the sample's relative effectiveness as an electrical insulator. The DC of pure gasoline is known. The addition of other substances will change the DC. As it turns out, oxygen bearing compounds added to fuel will raise the DC, hence the table in the GCR specifies a maximum DC by class. Adding oxygen to the fuel can increase the power output of the engine burning such fuel. Unfortunately, the really good (in terms of power increase) oxygen bearing compounds are pretty toxic. Also unfortunately, oxygen bearing compounds such as alcohol or MTBE are often added to street fuel to reduce air pollution, and they will change the DC just as paradioxane will. More sophisticated test methods would allow the club to determine exactly what is added to any given fuel sample. The downside to that is cost and convenience. A quick browse around the internet tells me that a gas chromatograph would cost around $25-$30K. It would probably need to be used in an air conditioned building (cost?) and be operated by a chemist (average freshly graduated chemist salary ~$36K; probably $75/hr from a temp agency). The DC test we do now takes about one minute (including cleaning and rezeroing the meter between samples). I have no idea how long a laboratory analysis would take, but I'd bet a lot of racers would leave the track for home with their group's results still listed as 'provisional'.
OK, the next two tests are easier to explain. We put a few mL of the sample fuel into two test tubes and add a drop of test chemical (commonly called a reagent) to the sample. If a precipitate forms in the bottom of the test tube, the fuel sample fails. This tells us if certain other chemicals have been added to the fuel. I have no idea what the test chemicals are, or what they are testing for. IT, SM, SS, T and SRF (I think) are a little different; if a precipitate forms in the 'A' test that is white (or anything other than black) the fuel doesn't fail. I believe this is to allow street fuel in those classes. The next time I talk to Chemical Ira, I'll see if I can get any more details on the reagent tests (but don't hold your breath, see below).
You ask why we can test
Eric
I think you've summed it up nicely in your first paragraph. In your second paragraph you ask if better equipment could test for everything, and if it's really necessary to test for everything. I'm not really sure, but I believe that a gas chromatograph or possibly a mass spectrometer could tell you the exact makeup of the sample. I, personally, don't think that's necessary and the club must not either; as we're not doing it now.
OTOH, if you start testing by looking for specific adulterants, as soon as the cheaters figure out what you're looking for they'll find something different that your test won't detect. I suspect this is why I haven't been able to find out what the current reagent tests are, or what they're looking for. The company that supplies the test chemicals won't sell them except to a sanctioning body. That only slows the determined cheaters down, of course, it won't stop them.
Finally, what you say in the third paragraph makes a lot of sense. Is it practical? I don't know, but this is exactly the sort of thing I was thinking of when I called for questions. The people I can ask aren't rule makers, but they're probably the closest thing the club has to fuel test experts. The rule makers aren't fuel test experts, but they probably would be open to information from someone who is. I really believe that they (the CR
have our best interests at heart in this matter, and they want to do their best to keep us from poisoning each other in our quest for a plastic trophy without going too far overboard in either money or time expended.
On a side note, SCCA isn't the only sanctioning body to use the same instruments and chemical tests to screen fuel, so if we're doing it wrong, at least we're not alone.
Keep 'em coming.