Paul Young asked:
Is there an optimum level to which you should fill your car's petrol tank so it doesn't just use the excess energy simply to carry the petrol around? Do vehicle manufacturers make the capacity of the petrol tank the perfect size with this in mind?
Thanks for the great show
We put this to James Painter, from Bloodhound SSC...
James - Hello, I'm James Painter. I'm one of the engineering leads on the Bloodhound land speed record project. We’re at the moment designing and developing a vehicle to set a new land speed record and we’re targeting 1,000 miles an hour.
Well that's an interesting question. I mean really, once you're carrying around more fuel than you actually need to get from A to B or to your next petrol station, you're carrying around more fuel, essentially, than you need. So, I suppose essentially non optimum, but certainly, it does depend on how far you want to go, how quickly you want to get there and how much you enjoy sweating when the low fuel light comes on.
Certainly in terms of vehicles and automotive manufacturers are a lot of family size fuel tanks tend to 40 to 60 litres and really, that's driven by giving vehicles a reasonable range. And also, in terms of the packaging space that the manufacturer has got to play with in terms of getting the fuel tank located. So when you are carrying around this additional fuel, certainly starting and stopping, accelerating and breaking that fuel is a bit more of a penalty within town driving, rather than when you're on the way to way and you're actually doing at a constant speed on the motor way.
Diana - So it’s best to only fill up what you need but this could lead to hundreds of visits to the petrol station which might be out of the way and therefore add extra mileage.
if warm humid air finds its way into the colder petrol, condensation can occur= water in the pet roll.
Gasoline weighs about 750g per liter, so carrying 80 liters of petrol has about the same effect as hauling around an additional 60kg person. If you spend most of your driving time on the motorway with properly inflated tyres, then this shouldn't affect your mileage in a noticeable way -- your car's efficiency is set mostly by drag, which isn't greatly affected in that case by how much weight is in the car. If you spend most of your driving time in town, you will spend some extra petrol accelerating the petrol in the tank -- but if you have a very small, light car that (including you) has a mass of ~600kg and a 40 liter petrol tank, you are looking at (at most) a 5% effect on mileage when your tank is full compared to when it is empty.
Tanks tend to be sized so that a person can get about 200 to 400 miles per tankful. My little Fiat has a 5 gallon tank.
Properly inflated tyres will do more for fuel consumption, along with driving as if there is a raw egg between your foot and the pedal. Driving and anticipating conditions ahead to minimise harsh acceleration or braking will do more than what having a variable amount of fuel in the tank.
wont an overinflated tire give better gas mileage? at the expense of uneven wear CZARCAR, Thu, 19th May 2011
It all depends on the fuel efficiency of the vehicle to start out with, and the actual improvement.
There are discussions about biodiesel and vegetable oil being able to leach out zinc from anything that is galvanized. I'm not quite sure why an oil would be able to do that. Perhaps they aren't 100% neutral, especially if not a commercial product.
re: Michelin tires saving fuel
Biodiesel is not exactly an oil, though it looks like one and burns very similar to one. It is more like a soap, being made from long chains joined together, formed from an acid- base reaction, and being a organic salt. It is quite hygroscopic, and will tend to absorb water from the air, which causes it to break down with time, releasing the acid component.
The Tank should never be below 25% or quarter of a tank for reason of the fuel acts as a coolant for the fuel pump. If it runs at a lower level you have chances of air being sucked up and temporary lapse of lubrication to the fuel pump, over heating of pump and possible drawing of the sediments at the bottom of the tank into the fuel system. The fuel savings from driving with a lower amount of fuel doesn't out weigh the cost of a fuel pump ($300-1000 Cnd) Ton, Sun, 29th May 2011
I have another reason for keeping as lttle petrol as possible in my car.