The top ten greenest wheels

[stangguy 0]

The reason that the manufactureres haven't been able to greatly advance the fuel efficiency of the vehicles is because of the ####### and performance people want, the tougher crash safety standards, and the tougher emissions requirements. The first two have greatly increased the weight of cars while also making the engines biased towards more power over lower fuel consumption. The more stringent emissions standards also increases fuel consumption.

A big hindrance to reducing fuel consumption of engines is the restriction on NOx emmisions. You might have heard that 14.7 is the "ideal" air to fuel ratio for gasoline engines. It is actually far from ideal. It is actually the ratio of air mass to gasoline mass that theoretically allows all of the oxygen and gasoline to combine and be burnt and is more appropriately called the stoichiometric ratio. For the most power out of the engine you would want it to be close to 12, while for the most fuel efficient you want it around 18 or higher. An air fuel mixture with a higher than stoichiometeric ratio is called "lean". Because of emissions regulations almost all engines are designed to operate near the stoichiometric ratio.

For the same engine this could mean a decrease in fuel consumption of 18% or more at a given speed by running in a lean condition. Most automotive manufacturers have used some sort of "lean burn" technology in the past. The Civic VX is one of those older "lean burn" vehicles. However, a byproduct of burning things in a lean condition is the production of NOx compounds. With increased NOx restrictions "lean burn" engines have become more difficult to produce and require a more complex method of fuel and emissions control than regular fuel injected vehicles. Most of the "direct injection" gasoline engines are "lean burn" but can only operate in that area when engine is at a constant speed under low load because NOx emiisions increase when lean mixtures are burnt under high load. Also, most drivers want considerably more power when they push the pedal down becasue they are trying to get up to speed quickly, and the most effective way to do this is to increase the amount of fuel consumed by the engine.

You also need to be mindful that fuel economy measuring methods have changed twice, once in 1985 and again in 2008. Both times EPA mileage numbers for a given vehicle decreased. What this means is your 1995 Civic VX rated at 47/51 would now be rated at 39/46. It is still good but when you think about the other things that have changed it isn't great, especially when it is a specialty vehicle meant to get good fuel economy.

1995 Honda Civic VX

Curb Weight 2,100lbf

1.5l engine 92Hp

47mpg/51mpg (39mpg/46mpg EPA corrected values for pre-2008 vehicle)

1995 Honda Civic DX Sedan

Curb Weight 2,300lbf

1.5l engine 102Hp

34mpg/40mpg (29mpg/36mpg EPA corrected values for pre-2008 vehicle)

2009 Honda Civic Sedan

Curb Weight 2,600lbf

1.8l engine 140 Hp

26mpg/34mpg

If we adjust the power of the 2009 Civic down to the same power level as the 1995 Civic we can adjust the fuel consumption up by the same ratio and the engine size down. This is okay as an estimate because power output is inversely proportional to fuel consumption. You can also adust both fuel consumption and power by engine size because power and fuel consumption are directly proportional to engine size. Another though less accurate way to compare them would be to adjust the weight of the vehicle because during acceleration the amount of fuel required is directly proportion to vehicle weight. This is less acurate because only a portion of the EPA mileage test is done under acceleration. It will be even less accurate for the highway numbers because less of this test involves acceleration. The following adjustments were done to compare the 2009 Civic to the 1995 Civic DX. I did this because they have comparable technology in their engines with both being standard gasoline engines which makes the comparisons that I did more meaningful.

2009 Honda Civic (numbers adjusted to match engine power of 1995 Civic DX)

1.3l engine 102Hp

36mpg/47mpg

2009 Honda Civic (numbers adjusted to match engine size of 1995 Civic DX)

1.5l engine 117Hp

31mpg/41mpg

2009 Honda Civic (numbers adjusted to match highway fuel economy of 1995 Civic DX)

1.7l engine 132Hp

28mpg/36mpg

2009 Honda Civic (numbers adjusted to match weight of 1995 Civic DX)

Curb Weight 2,300 lbf

124Hp

29mpg/38mpg

What these comparisons show is that efficiency has increased since 1995. If we look at engine size the Civic has increased its fuel economy by 7% city and 14% highway while increasing power by 15%. This is notable because it means they are producing more power while consuming less fuel; a double bounus. If we look at engine power the Civic has increased its fuel economy by 24% city and 31% highway while decreasing engine size by 13%. If you look at the numbers adjusted for weight it shows a potential bias towards more power. I would have liked to find acceleration times because that would give us a definitive idea of whether the extra power output was for quicker acceleration or to overcome the heavier weight and increased electrical power requirements of the newer car. However, I doubt the extra power is purely for overcoming weight and additional electronics because the weight change was minimal and most cars from the mid 90's have similar electrical systems to those made now.

For those wondering, I have a bachelor's degree in Mechanical Engineering. I focused on thermal/fluid systems which is the core background for those designing engines and other energy conversion devices. During my last two years in University I worked on the engine for a student designed and built race car, studiying a lot of the intricacies that make a more powerful engine and those same things can also make a more fuel efficient engine. Even though I wasn't fortunate enough to go into the automotive field after graduation, I keep track of current developments in the field because it is soemthing that I really enjoy.

[Niels Bohr 72]

Great breifing Stangguy!

[Niels Bohr 72]

I'll also add to that Honda Civic....The Sedan is lighter than the Coupe. Therefore, the Seden is more fuel efficient.

[NickD 202]

1. 2010 Toyota Prius | 50 mpg (51 city, 48 highway)
2. 2010 Honda Insight | 41 mpg (40 city, 43 highway)
3. 2010 Ford Fusion Hybrid | 39 mpg (41 city, 36 highway)
4. 2009 VW Jetta SportWagen TDI | 34 mpg (30 city, 41 hwy)
5. 2009 MINI Cooper | 32 mpg (28 city, 37 highway)
6. 2009 Ford Escape Hybrid | 32 mpg (34 city, 31 highway)
7. 2009 Honda Fit | 31 mpg (28 city, 34 highway)
8. 2009 BMW 335d | 27 mpg (23 city/36 highway)
9. 2009 Toyota Highlander Hybrid | 26 mpg (27 city, 25 highway)
10. 2009 Chevrolet Silverado Hybrid | 21 mpg (21 city, 22 hwy)

My old 1984 five speed Honda Accord would fit nicely in there, 46 mpg on the highway, and 33 in the city, not a poker either with 0-60 times in ten seconds. 2004 five speed Cavalier ain't half bad either with 42 mpg on the highway, but drops to 30 mpg in normal city driving. Won't count the Dan Ryan in Chicago when you creep at 2-3 mph with constant stop and go driving, EPA should do their mileage tests on that road. Especially with hybrids, those batteries would be dead weight with that kind of driving.

They should also specify the kind of gas they are using in their test, I lose 5-7 mpg with that stupid ethanol ####### and even more with so-called oxygenated winter gas where I was paying $4.30 per gallon for 20% air added to the gas. The old gas use to be 120,000 BTU per US gallon, that has dropped down to as far as 91,000 BTU's.

It's all BS with our energy evaluation with our government and they should toss in the maintenance cost if your batteries go dead, Toyota lists out the battery pack in the Prius at $7,000.00 but has been known only to charge their customers $3,000.00 as a good will policy. Plus all of the additional electrical problems you can run into and the added initial cost of these vehicles.

Then you have to learn how to drive these hybrids, if you see a stop sign a mile ahead, time to take your foot off the gas and use the dynamic braking to charge up the battery so you conserved about 50% of that braking energy to take off again. If you do this on a highway, may have a semi parked in your exhaust pipe. But 99% of the drivers fly up to a stop sign and slam on the brakes, no gains there. And absolutely impossible to drive this way in the city, 50 zillion horns would be blasting your ears off and talk about the getting the finger.

A more effective means would be to get rid of the traffic lights and the stop signs, our roads have not been kept up with the ever increasing traffic demands.

[stangguy 0]

1. 2010 Toyota Prius | 50 mpg (51 city, 48 highway)
2. 2010 Honda Insight | 41 mpg (40 city, 43 highway)
3. 2010 Ford Fusion Hybrid | 39 mpg (41 city, 36 highway)
4. 2009 VW Jetta SportWagen TDI | 34 mpg (30 city, 41 hwy)
5. 2009 MINI Cooper | 32 mpg (28 city, 37 highway)
6. 2009 Ford Escape Hybrid | 32 mpg (34 city, 31 highway)
7. 2009 Honda Fit | 31 mpg (28 city, 34 highway)
8. 2009 BMW 335d | 27 mpg (23 city/36 highway)
9. 2009 Toyota Highlander Hybrid | 26 mpg (27 city, 25 highway)
10. 2009 Chevrolet Silverado Hybrid | 21 mpg (21 city, 22 hwy)

My old 1984 five speed Honda Accord would fit nicely in there, 46 mpg on the highway, and 33 in the city, not a poker either with 0-60 times in ten seconds. 2004 five speed Cavalier ain't half bad either with 42 mpg on the highway, but drops to 30 mpg in normal city driving. Won't count the Dan Ryan in Chicago when you creep at 2-3 mph with constant stop and go driving, EPA should do their mileage tests on that road. Especially with hybrids, those batteries would be dead weight with that kind of driving.

They should also specify the kind of gas they are using in their test, I lose 5-7 mpg with that stupid ethanol ####### and even more with so-called oxygenated winter gas where I was paying $4.30 per gallon for 20% air added to the gas. The old gas use to be 120,000 BTU per US gallon, that has dropped down to as far as 91,000 BTU's.

It's all BS with our energy evaluation with our government and they should toss in the maintenance cost if your batteries go dead, Toyota lists out the battery pack in the Prius at $7,000.00 but has been known only to charge their customers $3,000.00 as a good will policy. Plus all of the additional electrical problems you can run into and the added initial cost of these vehicles.

Then you have to learn how to drive these hybrids, if you see a stop sign a mile ahead, time to take your foot off the gas and use the dynamic braking to charge up the battery so you conserved about 50% of that braking energy to take off again. If you do this on a highway, may have a semi parked in your exhaust pipe. But 99% of the drivers fly up to a stop sign and slam on the brakes, no gains there. And absolutely impossible to drive this way in the city, 50 zillion horns would be blasting your ears off and talk about the getting the finger.

A more effective means would be to get rid of the traffic lights and the stop signs, our roads have not been kept up with the ever increasing traffic demands.

I'm not sure where you got your values for the new engergy of gasoline, but an E15 mix, or gasoline that is 15% by weight ethanol should have an energy content of about 110,000 BTU per US gallon. Pure Ethanol has an energy content of 84,000 BTU per US gallon.

The fuel economy change that you list is a bit high, but if it is for your 1984 Accord it is believable because it would have a very poor engine control system that could not adjust for the use of blended fuels. Most modern vehicles should see closer to a 7% loss in economy because their engine management can better adjust for strange fuel mixtures and air conditions. As far as oxygenated winter mix gasoline, I'm not sure what is required in the midwest. But recently on the west coast all winter mix gasoline is E15 so it is pretty much the same year round energy wise. This is because MTBE was banned in California and mixing batches with MTBE for the other states isn't cost effective so all stations now have to use ethanol as the oxygenate because it is the only one available.

Driving methods do make a big difference in fuel economy and that is why the EPA adjusted their measurment methods in 2008. Also, the method that gets the best efficiency out of a hybrid will also get the best efficiency out of a non-hybrid. Also, you will still see benefits from a hybrid when making sudden stops because there is still the same amount of energy to be recovered. But a quick start will instantly require the use of the gasoline engine and quickly uses up the stored energy from the batteries.

[Scott & Lai 12]

The reason that the manufactureres haven't been able to greatly advance the fuel efficiency of the vehicles is because of the ####### and performance people want, the tougher crash safety standards, and the tougher emissions requirements.

The nerve people have, wanting to survive an accident