Yay, you guys bit the bait
![Grin ;D](https://www.fieldlines.com/Smileys/default/grin.gif)
And so the difference shows there too - 90MPG vs 3000MPG - there's more than just the aerodynamics in that. LOL Not sure, call me crazy, but the engine having to zip along @ 9000RPM continuously to keep 27MPH may have had something to do with it... Huh
One other question about your car I can't quite make out - the O2 sensor. Don't they have to be up to temperature to provide useful information to the computer? It would seem that 2 or 3 seconds wouldn't be enough to get it hot enough to give good data... ?
The best mpg would be at a constant speed, since air drag is exponential ( squared ) in terms of mpg. Also, for the difference in mpg, look at these numbers: 10-15 x less weight, a CD * A of only 0.04 instead of 20-30 times higher (wikipedia has lots of info on this). Transmission is about 95-98% efficient, also there is no alternator. The Rolling resistance coefficient is also much lower, which 0.0008-0.0024 instead of 0.006-0.008 for a car.
As for the O2 sensor, we program the computer to have a start up mode pretty much, in which the software can learn the "fuel map". Apparently the O2 sensor works pretty quickly, but I didn't build the engine.
Sheesh... 3000 mpg?
The record is about 3,000, but if last year's 1st place car actually ran well, they could of had 4000+ mpg. The record for any type of ICE engine is significantly higher but I don't know the number... the record for a hydrogen fuel cell with the equivalent amount of energy is 12,000 mpg, but their rules were a little looser than ours.
For the building of the frame and body using the carbon fibre , could you post some of the pics over in the transportation area too Grin
Umm... I wish my school's website would be accessible to you guys. It has about 130 pictures and 20 videos... Maybe if I have more time this week end.
As for the carbon fiber, the stuff is best stuff in the world. It's easy to make and requires no skills. Basically you mix the 2 part epoxy to the directions and add glue to your carbon fiber fabric. The hard part is not to get anything stuck the to carbon fiber, so for this problem you use lots of ceran (plastic) wrap. Anything made of the same plastic will not stick to the glue (like bubble wrap). Lexan is good for making shiny smooth surfaces.
For the cost, 1 yd of 60" wide is $20-50, so it's worth it for small projects. I'm not sure how much we have in the car right now, but it is probably 30yd^2 at least.
If you want to make a beam, basically wrap C.F. around some foam (we use the pink house insulation).
As for the compression ratio, you are right. Regular gas would ignite. Hence we are provided with iso-octane, which will not pre-ignite. Hence an 18:1 ratio is possible. We don't actually have an engine that is 18:1, but there are some older engines that run at 14:1. The downside is that 100- octane gas is $200 per gallon. You could run 93 pump gas in the engines with the lower compression ratios with no loss in power. At $200/ gallon, the cost benefit doesn't exist anymore. The competition usualy gives away the extra fuel, which usually amounts to a gallon per year. We probably have ~8 gallons in storage. I hope the stuff doesn't go bad
![Tongue :P](https://www.fieldlines.com/Smileys/default/tongue.gif)
"3000 would be astounding!! "
I agree. A lot.
Hope I did it right...
3000MPG is (in US measurements) -
4 miles per teaspoon.
12 miles per tablespoon.
308 miles per (ghurd's) coffee mug.
and
NY, NY to LA, CA... with 61 teaspoons left in a 1 gallon tank.
We used about 30 grams of fuel last year I believe. If you go to the sae website, the 2007 year has data on the fuel used for each car to 5 significant figures. Last year we used about a film canister for 9.6 miles. I think my calculations were about 33 grams at 777 mpg, but that may be off by 10-20%.
best we could get was 105 mpg consistently, 3000 would be astounding!!
Cheers;
You have a drag coefficient of 0.7+, a bad engine, and bad tires.
I'm still working out the dynamics of the 18:1 compression ratio Grin
My MB 300TD is sitting nicely at 20:1 , I know it is supposed to be closer to 21:1, but with 177K on it and taxes coming due Undecided
Even ethanol auto-ignites around 15:1? not sure of that , never had the testicular fortitude to find out Shocked .
Having too much fun working with these numbers Cool
I'm not an expert in this field, but there are a lot of issue with the higher compression. A smaller bore diameter would definitely be required ( we have a block with a 50cc cylinder ).
I can't wait til we get the transmission in the car and we build the cooled seat. The transmission will be a single friction plate clutch. We may not have enough force on the plates, so we may have to add teeth to the plates. This would require some timing challenges between the clutch engagement, the tire rpm, the engine rpm, and the tire rpm.
If anyone was wondering about the bearings, we have 6 full ceramic bearings in the three tires. Using full ceramic bearings instead of steel bearings with seals helps a lot. We spun our tires by hand, and they rotated for 16 minutes! The steel bearings only rotate for about 30 seconds. The bearing resistance is only about 1% of the rolling resistance. Hence our car should roll for about 2 minutes while coasting from 20 mph to 10 mph on flat ground. In reality, most of the course is at about a -0.1% grade, so I have coasted for 0.8 miles while going from 34 mph to 4 mph
![Grin ;D](https://www.fieldlines.com/Smileys/default/grin.gif)
The back curve on the track is about a 1% grade, which is very noticeable in these cars. We would have to fire the engine twice to get up the hill.