Car fuel consumption spreadsheet

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
It's an old Dos Borland Quattro format which is what I've used for donkey's years for spreadsheet work cos I'm too set in my ways to use newfangled windows spreadsheets but they should be able to recognise it without any problem.
Play with the numbers and you'll see what your actual car ought to be giving in mpg terms. If I enter the data for my Focus (3000 lbs, 0.013 RR, 22 sq ft, 0.33 Cd) I get 38 mpg at 70 mph which is what it actually does. You can then alter those numbers to see how easily we could all be driving small, single user 100 mpg cars if the will were there or if fuel prices went up enough.
We don't need hybrids, regenerative braking or any other unusual tactic (not that I'm decrying them) to achieve this. Just common sense, efficient diesel engines, low weight, size and drag.
In no more than 5 minutes I could sketch out a small streamlined car that could carry two people and luggage and get them from London to Aberdeen on 5 gallons of fuel for 25 quid. My Focus needs three times that. If you want to move house it won't be the ideal vehicle for you but as most cars only have one person in them for 99% of the time it would do for most of us for general use and commuting.
--
Dave Baker



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On Wed, 28 Jan 2009 12:47:52 -0000, Dave Baker wrote:

The trouble is that although I may only need to move myself for commuting, I need to transport myself, the wife and kids at other times, trolley(s), diy bits and pieces, shopping, bulky items, etc., so I'd end up having to own two cars. Most people - even singles - sometimes carry a carful and so cars generally need to be big enough for the reasonably common occurences.
SteveW
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Steve Walker wrote:

The microcar concept was done to death in britain, they were popular for many decades, but no more. The passenger question isnt really an issue, one can build cars for any number of people far smaller than what we have on the road today.
The biggest issue that kills microcars is safety. This could be solved by using them on separate roadways, protected by steel barriers from the big cars/trucks. Fuel efficiency is just one of several advantages - purchase cost, road congestion gone, far fewer pedestrian fatalities, parking space problems solved, etc. And greater safety and much lower cost means more people could afford them, leading to more job and business opportunities etc. They're a win win win win win option as long as theyre kept away from the big cars.
Re Cd, no sane person would drive a microcar at high speed. But 40mph max is more than enough to go round towns & cities.
NT
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snipped-for-privacy@care2.com gurgled happily, sounding much like they were saying:

Not at all. You seem to be completely forgetting about things like the Smart and various superminis.
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Bu**ered if I'd have one nothing quite like a good Six feet of metal in front of U;)
--
Tony Sayer




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The microcar concept is a million miles from what I'm contemplating here. Making cars very small and very short is counterproductive in most respects. Safety, luggage capacity and very importantly it makes it impossible to generate a low drag shape.
It's nice to have low weight but it's not the major issue, or at least not worth taking to extremes, especially if you have regenerative braking (RB). The main issues are frontal area and Cd. So what we need are low, long, narrow streamlined cars where's still plenty of metal between the passengers and whatever they might hit at each end.
The Prius actually has many things close to right. It has a very low Cd by virtue of length and careful streamlining. What it doesn't have right is frontal area and weight although the RB counteracts much of the downside of the latter. But, and it's a big but, if the car is heavy the performance is crap unless the engine is large and that kills low speed consumption because the engine isn't working efficiently and has high internal friction.
2000 lbs is not an extreme weight reduction measure. As I said it was a perfectly normal weight before cars got bloated with safety features. With modern materials that's plenty to build a decent sized car with but it must have a lower frontal area than normal to get best consumption.
My target as I said was 2000 lbs, 17 sq ft and Cd of 0.26. That frontal area only means the car being about 10% narrower and 10% lower than a Prius. Just a few inches in each dimension. 21 x 0.9 x 0.9 = 17
Now you leave it comparitively long, say normal saloon car length, to preserve luggage and passenger capacity and help with streamlining. It would look a little unusual in its proportions but not unduly so. I can easily conceive of a car weighing much less than 2000 lbs with modern materials but it's not necessary to go that far.
Packaging could perhaps be a driver in the front with luggage space to his left, two passengers behind him, maybe two child seats behind those as an option and the boot space behind that with the spare seats easily removeable to create a van/estate car. More innovative would be to have the drivetrain to the left of the driver and more luggage space in the long streamlined nose/crumple zone as well as in the rear.
Engine could be something like a 70 bhp diesel which would give adequate if not sparkling performance due to the low weight. 0-60 mph in 12 seconds. A 90 bhp engine would drop that to 9 seconds which is starting to get reasonably nippy.
This not a city car concept. It's an open road tourer capable of going long distances with very low fuel consumption. Travel in cities is best dealt with by other means - electric cars, small cars with RB and public transport. Top speed would be about 110 mph, a five gallon tank would take you from London to Aberdeen.
--
Dave Baker



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Low drag is completely irrelevant when driving at town speeds.
No-one is suggesting that a microcar is suitable for anything other than low speed, short distance use.
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You have just designed a Vauxhall Astra. 8-)
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Oh my God!!!!!
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On Wed, 28 Jan 2009 07:28:10 -0800 (PST), snipped-for-privacy@care2.com wrote:

eh? They were around in the 50's and 60's, mainly abominations and they were hardly popular.

If the Smart 2 seater isn't a practical, safe, microcar then what is?
I know I'd sooner be in a crash in one of those than in a 1960's Mini or anything of the same era and size produced by Fiat or Renault or Citroen.
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I wonder what dennis drives ...
--
geoff

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wrote:

Astra 1.7 CDT, Corsa 1.2 or a smart depending on what I am doing and who got there first. The Astra always goes first and I spend a lot of time in the Smart. It uses more fuel than the Astra BTW.
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They were fairly popular with those wanting to 'upgrade' from a motorbike who couldn't afford a proper car. They were very much cheaper new than a new small car - unlike the Smart.

No worse than a motorbike.

Indeed.
--
*Santa's helpers are subordinate clauses*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Exactly...
I'd rather not be in a Smart at all.
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I agree we don't need Hybrids .. what we need is an escalation by HMgov to roll out Hydrogen fuel refill points. The Hydrogen fuelled car with no batteries is the single most important invention for the automotive industry. http://automobiles.honda.com/fcx-clarity/how-fcx-works.aspx
Honda has it in production and the sooner it reaches UK the better .... ZERO emissions .... fuel produced by simple electrolysis of water - which can be easy & cheap, no expensive & heavy batteries to run out.
If the tree huggers want to be really good, via wind wave or whatever.
I'd be happy with it coming form a Nuclear Plant.
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The Honda is a hybrid. Where do we get the hydrogen? Where do we store the stuff? The reliability of the fuel cell? OK that can be overcome in time. The idea I like but it is the fuel that is the problem.

Production? Where can we buy one?

It has a large battery set as it is electric drive. There is nothing so simple as an all EV car. And when supercapacitors improve more, then they will sing.
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Hybrid? Depends how you define that I guess - it certainly doesn't use any petrol.

Same argument for LPG - it'll become common I suspect

Much like lpg... storage of hydrogen isn't a really a problem

Not sure that's a major issue... how reliable are batteries in a prius?

Southern California IIRC
IMO, hybrids are a bodge - fuel cells seem radical enough change that they might just be the answer...
Darren
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snipped-for-privacy@ukc.ac.uk (dmc) gurgled happily, sounding much like they were saying:

Fine. So it's not a petrol-electric hybrid.
What it IS is a bit more difficult to classify - since the hydrogen's being used as an electricity storage medium alone, it's probably fair to refer to it as an electric-only vehicle.
Mind you, it's a thoroughly one when you look at the plug-to-motion efficiency...

<splutter> It certainly is.
Look at BMW's 7-series hydrogen concept of a few years ago. The boot was full of hydrogen tank, giving it a range of about 100 miles - which had to be used within a week else it all escaped.
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Well, ok - maybe it's not *quite* that simple :-). It still seems to me the most promising way of getting away from petrol/diesel in the near(ish) future.
Someone just needs to work out a way of producing and distributing hydrogen slush like they use on the shuttle :-)
Darren
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snipped-for-privacy@ukc.ac.uk (dmc) wrote:

Currently hydrogen is produced using electricity, over 80% of which is generated by burning fossil fuels - therefore generating lots of CO2.
It is difficult to think of anything more pointless at this time than a hydrogen fuel cell powered car. That will change when we have a lot more power generated by nuclear and renewables. But that won't be for at least another 15 years.
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