The idea of changing fuels at F2C midrace pitstops can be traced back at least 35 years, the intention being to change to a fuel having a more suitable ignition timing for the engine as it gets hotter throughout a race, thereby avoiding the need to fly the early part of the race undercompressed or to fiddle with compression settings. Grant has developed this idea to a new level of sophistication with his multi-chambered pressurized refuelling tank, allowing him the choice of 3 or more fuels at every pitstop.
Grant writes:
My multi chambered arm tank has been done before, although I didnt know it had before leaving for France but I assumed it would have been done before. So its not new, but winning a world championships with one was new. Not many people were interested in it before we won, but interest rose sharply after! Since coming home there are at least 5 others now in use that I know of and competitions haven't even started in Europe yet as its still winter.
There are four holes in the arm tank, with 2 holes joined together. The two holes joined together make the cavity for the main fuel supply ie practice and race fuel. The second tank is for a lower cetane diesel fuel mix. and the third an even lower cetane fuel mix.
There was 4cc of fuel between the new selected tank and the finger valve. So effectivley I had 5 different fuel mixes. By not clearing the fuel line between the arm tank and finger valve there would be 2 different fuel mixes go into the tank and I would get a combination and half the difference of compression.
The different fuel mixes were achieved by adding a lower cetane kero to the original mix. ie a shorter length carbon chain or a lower boiling point. I added D60 to Jet A1. 7.5 mls for the 1st tank and 15 ml for the second.
This was done to avoid having to back off the engine compression during a race. We found that the second and third tank was hotter than the first but this way we could run at maximum settings for tank one and effectively reduce the comp by changing fuel for tank 2 and 3 as required.
1. Pic 1 is the starting blank solid 2011 aluminium it has been bored and od has been finished and ready to parted off.
2. Pic 2 Looking at the top holes are drilled right through to btm for setup later and the holes finished for the top threads and pressure gauge.
3. Pic 3 looking at setup holes drilled right thru. Its in the lathe and these holes are used to true up ready for boring out to the finished diameter.
4. Pic 4 Dial indicator getting the third hole true
5. Pic 5 drilling the 3 rd hole before boring out to finished diameter
6. Pic 6 drilling pressure transfer passages. these were to allow the air pressure to be the same in all cavities but had a vertical chamber so any fuel that might get pushed through would be caught and so the fuel in each chamber would not get contaminated with another. At the btm they had a schrader valve to dump any fuel caught in this area.
7. Pic 7 is a top view. Into the holes were fitted stainless steel threads, one for pump, 2 for presuure gauge, 3 cap, and 4 cap.
Bolted to the bottom was a slide valve that I was able to use to switch between the tanks. There are photos of the slide valve and bottom on the next page.
