Dave Baker wrote:
Rather than it get lost in the pointless drivel (dribble?) in the Petrol v
Diesel (Prius) squabble I'll start this new thread.
One of the many programs I've written over the years to help me in my
automotive related business is a spreadsheet which calculates the power and
fuel useage a car requires to travel at a given speed. It takes the weight,
rolling resistance, frontal area and drag coefficient, works out the wheel
bhp and flywheel bhp required at each speed from these and then applies
average BSFC (brake specific fuel consumption) data for both petrol and
diesel engines to calculate the fuel requirement and mpg. You can also enter
the price per litre of each fuel and it will calculate the pence per mile
fuel use.
You can also alter the speed in any of the calculation rows to a new value
and it'll tell you how much power you'll need to achieve that top speed and
what the fuel consumption would then be.
By playing with the car weight and drag data you can find out very quickly
what factors affect power requirement and fuel consumption. Basically weight
affects rolling resistance which is a big factor at low speed but not at
high speed and aerodynamic drag is the reverse. For good economy at low
speed you want a low weight vehicle and at high speed a low drag one.
Using it you can easily see what is needed to design a genuine 100 mpg car.
Low weight, low drag, efficient diesel engine. A 2000 lb car with low
rolling resistance tyres, 17 sq ft frontal area, 0.26 Cd drag (same as a
Prius) should do 110 mpg at 60 mph and 90 mpg at 70 mph with an efficient
diesel engine. For a one or two occupant vehicle this is not a difficult
concept to realise. The average hatchback in the 80s weighed less than that
and many cars such as the Mini have been much lighter.
This morning I've tweaked the program to be more user friendly and added
some guidelines for the data inputs for various cars. It's hosted here.
http://www.mediafire.com/?zk0mkoj41jx
well after a minute of 100% CPU use when I hit that page, and still
unable to download, I think I'll give it a miss, thanks
I take it its some 'green' site designed to burn CPU cycles instead of
carbon?