Trying to make sense of fuel efficiency formula

[JT A.]

The efficiency formula in the FSAE 2013 rules doesn't make any sense, but I think it's just a typo. So I looked at the FSG version of the rules (link here http://www.formulastudent.de/u...ules_2012_v1.1.0.pdf (http://www.formulastudent.de/uploads/media/FSC_Rules_2012_v1.1.0.pdf))

What I'm confused about is the EfficiencyFactorMin term. The efficiency factor is basically a measure of your speed:fuel economy ratio. Is this "EfficiencyFactorMin" actually the lowest efficiency factor of any of the cars that compete in endurance, or is it capped at some minimum?

If it is capped at some minimum(ie. Tmax is 1.45xTmin, and Vmax is whatever fuel consumption is the equivalent of 26L per 100km) then it makes the importance of the fuel event much more predictable for teams working on points analysis & strategy. If there is no minimum, some team could completely tank the event (ie burn 2 gallons of fuel and run half the speed of the fastest team) and it would really skew the distribution of points in the fuel event.

Here's 2 examples to show what I'm talking about (assuming I'm using the formula correctly)

Cap on EfficiencyFactorMin
If I had to guess, the cap would be a teams EfficiencyFactor if their endurance time was 1.45 x Tmin (the slowest time before DQ) and their fuel consumption was the equivalent of 26 Liters per 100km (the worst fuel consumption before penalties kick in under 2012 rules). This would result in a EfficiencyFactorMin of 0.3

Tmin for endurance is 1501s. Vmin is .673 gallons
Car A goes for a "balanced approach", runs an endurance time of 1580s and burns .8 gallons of fuel, and receives 92 points for fuel, 259 points for endurance.
Car B goes for all out speed, wins endurance with a time of 1501s, but burns 1.16 gallons of fuel, receiving 71 points and 300 points for endurance.

No cap on EfficiencyFactorMin
Lets say some team has some huge problems with their car and manages an Efficiency Factor of 0.1

Car A receives 98 points for fuel, and 259 points for endurance.
Car B receives 92 points for fuel, and 300 points for endurance.



So as you can see, if there is no cap in the minimum, 1 outlier team doing really bad in endurance/fuel can make a 21 point spread in fuel points turn into a 6 point spread in fuel points.

Can anybody clear this up for me? How does it work at FSG?

[BeunMan]

FSG has a 1.33 factor and not 1.45, which mostly negates this problem.

[Do-it-Guy]

I think given by the 300:100 weighting between Speed(Endurance-Score) and Fuel-Consumption (Fuel Event) there is no successful "balanced strategy" that results in a higher combined score Endurance+Fuel than the "race as fast as you can" strategy - independent from the fuel efficiency formula applied.

As an active teammember a few years ago i also tried to evaluate different race-strategies based on the given rules for the Fuel-Economy Score to find an optimum. Unfortunatelly i didn't have detailed Fuel-Consumption data of our car at different speeds, so i had to interpolate from the 3 Endurance results in this year from our car and different competitors. According to this, driving more slowly than you can to save fuel doesn't pay off. Having a more fuel efficient car than your equally fast competitor on the other hand does very much. (Just look at Delft former combustion cars).

If anyone has detailed data (realtime fuel consumption) of an FSAE-car at different race speed and is willing to share /publish , i would love to see them or being proved wrong.

On the Fuel-Efficiency-Formula:

In general, I think it is better to judge the effiency than the absolute amount of used fuel like in the old rules. The fact, that a possible slow car/team can "ruin" your possible advantage in Fuel-Score compared to an less efficient competitor is a bit strange but you have to deal with it. The 1.33 factor instead of 1.45 @FSG is the right way to go to limit this effect. Being depended on other cars in the field makes it even harder /impossible to calculate a perfect race strategy before the event, you would have to react on your competitors during the endurance..

[JT A.]

So cars that run slower than 1.33 x Tmin don't get factored into the fuel efficiency formula?

[TMichaels]

Originally posted by JT A.:
So cars that run slower than 1.33 x Tmin don't get factored into the fuel efficiency formula?
Correct.

[BeunMan]

As far as I heard (wasn't at Silverstone this year), TU Graz altered their strategy (someone please comment on this) to using less fuel and still trying to drive fast as possible as it would result in overall more points.

In the past (old formula) the difference of 2-4 seconds per lap with Stuttgart was canceled out by the Fuel scores for the Delft car, especially when the score went to 100pt. With the new score , the gap is less big and the car needs to be faster compared to the old score to get the same difference in 'efficiency' scoring. In my opinion it is a more fair system as it explicitly allows design decisions to take effect (e.g. balance fuel/speed).