fuel tank capacity

[shanchan]

How to decide on the fuel tank capacity.
And what inputs we must have to do those calculations.

[Moreboost]

depends on the location of the moon on day you conceived the idea that a fuel tank is necessary.

[MCoach]

Calculations vary.

How accurate are you looking to get?

[shanchan]

Originally posted by MCoach:
Calculations vary.

How accurate are you looking to get?

Just to get general idea

[Racer-X]

If you already have a car you should run some laps and see how much fuel you use. Then add a little extra capacity so you're sure you won't run out in Enduro.

If you're a new team you should just make it huge. Look at the most amount of fuel any team used at Michigan and add a bit onto that.

[TMichaels]

... or go create a fuel consumption map of your engine on the dyno over load and rpm, then develop a working lap time simulation and run it on the endurance track of the competition you will be attending. Fill the calculated load and rpm values into you fuel consumption map, add some extra amounts of fuel for modelling errors and the fact that you will not get the last ml out of the tank and you are done and have learned lots of things and a good story to tell in design.

[MCoach]

Originally posted by TMichaels:
... or go create a fuel consumption map of your engine on the dyno over load and rpm, then develop a working lap time simulation and run it on the endurance track of the competition you will be attending. Fill the calculated load and rpm values into you fuel consumption map, add some extra amounts of fuel for modelling errors and the fact that you will not get the last ml out of the tank and you are done and have learned lots of things and a good story to tell in design.


If you have the time, this.

[Markus]

Wow, that's what I would call "over-engineering" Tobias...

Just make it big enough. Say 7-10 liters. 7 liters should already be plenty but the point sensitivity of fuel tank size is so minor that play it safe. Weight is around ~1kg/l when taking tank material into account and excluding fuel pump, losing that 5kg's to "top teams" will not make a difference. Packaging and size will be your biggest constraint.

Plus there are benefits from bigger tank: longer testing time - less fuel heat problems.

But if you want a ballpark, a "top team" with 600cc inline four would be around 4-5 liters in tank size and use around 3-3,5 litres of fuel during endurance.

PS. Tobias, if we go by the intent of this competition that should yield bad design score: a weekend autocrosser that has a tank capacity designed for a certain lap amount of certain track somewhere in the world, in simulated environment, would not be something I would appreciate as an amateur hobbydriver...

[TMichaels]

Wow, that's what I would call "over-engineering" Tobias...
Everyone has the right of having a personal opinion http://fsae.com/groupee_common/emoticons/icon_smile.gif

I call it thoroughly engineered.


PS. Tobias, if we go by the intent of this competition that should yield bad design score: a weekend autocrosser that has a tank capacity designed for a certain lap amount of certain track somewhere in the world, in simulated environment, would not be something I would appreciate as an amateur hobbydriver...

You know as well as I do that this rule is not enforced at any competition. I am not judging whether this is good or bad, just mentioning it. And thus it becomes part of the requirements you are engineering the car for.

[Warpspeed]

Originally posted by shanchan:
How to decide on the fuel tank capacity.
And what inputs we must have to do those calculations.
At the initial design stage there are going to be many unknowns, and fuel consumption will definitely be one of those. There just are not enough reliable engineering inputs to be accurate. All you can do is guess...
The first consideration should be to be able to use every last drop of available fuel without sucking air bubbles while driving the car to it's max.
How about a small tall skinny tank to feed the engine from directly, and a second much larger main tank to keep the small tank topped right up with a second fuel pump ?
No rule says you have to fill the main tank to the brim.
Experience will tell you what the fuel efficiency will be under various driving conditions once the car is built and tested, and how much fuel is needed to compete.
So basically make the main tank fairly generous as other posters have already suggested.
There is no real penalty in an over large main tank only half full.

[Markus]

Originally posted by TMichaels:
Everyone has the right of having a personal opinion http://fsae.com/groupee_common/emoticons/icon_smile.gif

I call it thoroughly engineered.
For thoroughly engineered you have to add a fuel tank splash simulation verified with a jig and a heat analysis of the fuel pump on endurance simulation... http://fsae.com/groupee_common/emoticons/icon_razz.gif

With certain pump, tank location, tank size combination that is a real problem as pumps are fuel cooled and actually capable of heating themselves to death if the fuel loop is too short and / or abrupt.



You know as well as I do that this rule is not enforced at any competition. I am not judging whether this is good or bad, just mentioning it. And thus it becomes part of the requirements you are engineering the car for.

Yes I know, just wanted to throw some "Zee" in there... http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Warpspeed]

Not all electric fuel pumps run fuel cooled wet motors.

The high pressure EFI pumps always do, and the EFI fuel pump and injectors must never see any air bubbles under normal running if you wish to avoid engine stutters and misfirings.

But a low pressure high volume fuel transfer pump is a very different beast.
It could be a dry electric motor "carburettor" type fuel pump, that is designed be run intermittently dry without issues.

A well designed two tank, two pump fuel system has the advantage of always supplying solid fuel flow under high "G" loadings right up until the fuel is all totally gone.