A request – 100 MPG Cars?

March 23rd, 2009

Posted by: admin

I’m responding to an off-topic request from one of the comment threads on a recent post.  For the record (and others can ding me if I get this wrong), you can put those kinds of requests into writing after clicking on the Ask link in the right-hand column.

At any rate, the request, paraphrased, asked me about whether or not we would see a 100-mpg car with the same kinds of features that we see in cars today.

I was (and am still) reluctant to answer this for a few reasons.

Ultimately, my answer is I don’t know, but I doubt that’s satisfactory to some.

I’m nowhere near a gearhead/petrolhead, as I never mastered a standard shift, and the bulk of my automotive knowledge comes from a combination of Car Talk, Top Gear and Wired’s Autopia.  While I minimize my driving, and try and maximize fuel efficiency as best I can while driving, I know I have more car than I need.

Even for those who aren’t gearheads but are interested in the issue, discussion of cars – especially in the States – can get particularly heated in a way resembling debates over sports teams.  That’s not particularly productive, and I don’t want to encourage it here.

Finally, I’m not sure that framing the question in terms of 100 mpg is really the best way to address the problems increased fuel efficiency is trying to solve.  Emissions can be reduced by driving less as well as driving more fuel-efficient (or non fossil fuel) vehicles, or some combination thereof.  The drop in miles driven in the United States, as well as the possible shuttering of makes and models that were on the lower end of the efficiency spectrum, can be as beneficial as increasing mileage.  Cost (both in money and emissions) per mile seem a better take on what the agitation in this area is aimed at reducing.

That said, I shall try and give an answer.  I think its possible that a 100 mpg car can be developed and sold successfully.  Given the embrace of good diesel and what amounts to a head start to 100 mpg (compacts in Europe can have an average MPG of at least twice the closest American equivalent – more if using diesel), I expect it to happen in Europe before it takes root in the U.S.  The efforts of Tesla and its electric sports car, as well as the Honda Clarity fuel cell car (both featured on the latest Top Gear episode to premiere in the U.S.), suggest that good, fast, and/or sporty alternatives to internal combustion are possible, but not yet ready for a consumer market.  Will they be the same as their internal combustion-based cousins?  No, but I have reason to think they will come close.

14 Responses to “A request – 100 MPG Cars?”

  1. Armin Says:

    As a European in the process of moving to the US, some comments.

    compacts in Europe can have an average MPG of at least twice the closest American equivalent – more if using diesel, however this is mostly due to teh fact that the definition of compact is extremely different. What the US calls a small car, is a standard size car in Europa. E.g. the Ford Focus is considered by more and more people a pretty big car. If you compensate by that, the difference between Europe and the US, is none, as the cars are the same. A Ford Fiesta (comming soon to the US) will not use less or more fuel depending on where it is sold :-)

    Using diesel can help Americans, however it will up the car-price as diesels engines are more expensive e.g. due to the standard mounting of a turbo or compressor to compensate for the lesser power. So MPG/CO2-based it will help, but whether it will help the wallet remains to be seen.

    Will 100MPG be feasible? Well, diesel contains about 38 MJ/L, which means in gallons 144 MJ/G. How far can we get from here? Well, if we would run in a vacuum, after getting to the initial speed, the answer would be infinity. The big problem is that we need to break and even if we regenerate energy this is not 100% return. Also there is air friction and tire friction. Just taking the air friction/resistance, already shows a problem. Air resistance increases more or less with the square of the speed. At high speeds therefore it is the dominant factor. Let us take 40 miles/hour or 18 m/s. Literature shows that if you want to get at 200 N resistance (air + roll) you are doing extremely well, even for light (roll friction) and streamed (air friction) cars. This means that you will run out of that gallon in 40000 seconds, which is about 450 miles at the given speed with that one gallon.

    Of course at 100% efficiency of the engine. Which means only about 23% is needed. So 100 MPG is actually not even that problematic. The problem is the starting-stopping-breaking and the fact you are using power for other things.

    So why isn’t it already there? The answer is, they are almost there: Volkswagen has e.g. their 3L line (3 liter for 100km, which is around 78 mpg) and is now replaced by their BlueMotion Line. VW downed their ambitions as the technology used for the 3L line was way to expensive. But if they would use it today they easily exceed the current results for BlueMotion. Their 2010 Polo model is speced at 72 mpg (us gallons) without many of the expensive 3L stuff and being a class bigger (less small).

    Is it a normal car? You judge yourselve:

    100 mpg is on its way for sure. On both sides of the ocean.

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  3. Mark Bahner Says:

    I drive about 7 miles to work each day. And 7 miles back in the evening. And I probably don’t do more than 1 trip of over 20 miles in a typical week.

    With a plug-in hybrid, I could probably easily go the ~6000 miles I do every year on less than 60 gallons.

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  5. jae Says:

    It’s mostly about weight and cost. A 100-mpg car is simple, unless you want it to go over 40 and have a few comforts, like two seats, a roof, and some safety features. I wonder what the weight is of just the required safety features for an American car.

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  7. lgcarey Says:

    Sounds like a request for Amory Lovins concept of a composite bodied low weight crash-resistant ultra high mileage hybrid Hypercar SUV, which has been kicking around the last decade or so. http://www.rmi.org/images/PDFs/Transportation/T97-04_HypercarsFAQs.pdf

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  9. David Bruggeman Says:

    I have a couple of questions based on comments so far.

    Are European car safety features on par with U.S safety features? If so, I think the weight argument is undercut, if just a bit.

    Are diesel engines generally lighter, even with the turbo or compressor?

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  11. Mark Bahner Says:

    “Are diesel engines generally lighter, even with the turbo or compressor?”

    Diesel engines have higher compression ratios. That means they have to have more muscular connecting rods, crankshafts, and other engine parts. So I’d expect that a diesel of equal displacement to a gasoline engine would be somewhat heavier.

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  13. michel Says:

    Heating, air conditioning, size of vehicle. Lifestyle.

    No, you will never get 100mpg out of a large car driven in Phoenix at a comfortable temperature. Still less if it is stop start, but even if its being driven at 50 or 60 mph on a highway.

    You will get it out of a small, and this means Peugot/Citroen 105 or 205 sized, car, no air conditioning, driven mostly at constant speeds under 50.

    If you simultaneously with the takeup of such vehicles reduce the average mileage of them, you can make a big difference to total energy consumption on transport. You have to do both: improve mileage, and also reduce miles driven.

    Hybrids are just feelgoodery. They do not in fact, in driving which is typical of what people do, deliver any better mileage than economical non-hybrids. Specifically, smaller conventional cars always deliver better mileage than larger hybrids.

    What does this tell you? You really want to reduce gas consumption in the US, restructure the towns and suburbs so people do not have to drive fast and carry lots of shopping. Restructure them around public transport and local services and routes that are safe to walk or bike.

    You cannot maintain existing lifestyles of shopping, working and living, and existing layouts of roads houses and communities, and existing modes of transport, and still make large reductions in transport fuel consumption. People are going to have to travel by muscle power for shorter distances, and by public transport for longer ones, and that means restructuring of the physical environment.

    Or not doing it.

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  15. jae Says:

    The real gains are to be made in phasing out autos that only give 20 mpg or less. You get the same percentage increase in efficiency (50 %) in going from 20mpg to 30mpg as you do in going from 30 to 60. And we don’t need Big Brother BO to get this done; the free market has been doing this very well.

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  17. Armin Says:

    David, European car safety features are usually a bit ahead on the US due to regulations. Note, before all you Americans get all patriotic on me :-) – this is about brands and models, not companies. Due to various market-conditions the US markets favours things like leather seats, automatic and stronger engines. The Europe market has more technology on-board per car. I work for an automotive company and new features are on average sometimes even two years earlier available in mainstream models in Europe than the US and Japan. Again, brands and models not companies, as US companies like Ford en GM (e.g. Opel in Europe) do the same thing. Although this doesn’t limit itself to, this also included safety technology. This doesn’t offset however weight-wise the difference in size.

    I must admit, I’d prefer a bigger car with less electronics and more leather though :-)

    And diesel engines are generally more heavy, as is – as Mark explained – but even more due to the the turbo or compressor. Also more expensive in buying price. But diesel is inherently more efficient by physics (diesel vs otto efficiency) and by energy per liter/gallon. It will make up for that.

    The problem with diesel environmentaly seen however is in its small particles (cancer), sulfur (acidification) and NOx (lungs and acidification). You need high grade diesel, and a NOx-kat and small particle filter to get the same cleanness as a modern petrol engine. See e.e. Mercedes E class BlueTec. Sofar California is the only place where these things are mandatory (indirectely by emision regulations). In diesel loving Europe this will in effect only happen when the EU euro 6 regulations kick in. This will up the price of dieselcars …

    So CO2 wise diesel is a good thing to look at, but price wise and in terms of other emisions it has its own set of problems. We tend to define environment to much a CO2 today and forget about the rest. Personally I rather have CO2 emmisons in my backyard than any of the other nasty stuff …

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  19. Jon Frum Says:

    It’s good to see Armin mention diesel pollution in he second post. We don’t have many diesel cars in the US becuase of restrictive air pollution legislation. Europeans have been happy to kill a certain small fraction of their population for the pleasure of using diesel fuel.

    As pointed out above, 100 mpg is not about cruising efficiency, it’s about starting and stopping losses. A car is far more fuel efficient cruising at 60 mph on the highway than averaging 15-20 mpg in stop and go traffic.

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  21. Mark Bahner Says:

    “The problem with diesel environmentaly seen however is in its small particles (cancer), sulfur (acidification) and NOx (lungs and acidification).”

    This is also the issue of small particles (global warming). Diesels emit much more black carbon (soot) per unit distance traveled than gasoline engines.

    The IPCC may minimize black carbon as a source of global warming (and also as a source of melting ice in the Arctic), but that doesn’t mean the IPCC is correct:


    In fact, it has been argued that diesels are greater contributors to global warming than gasoline engines (at least over the first decade after emissions):


    P.S. Over the next 2-3 decades, black carbon emissions from diesel engines in Europe should decrease dramatically (by as much as 90 percent). Unlike with CO2, any climate impacts (e.g. on Arctic ice melt rates) should be closely timed to the reductions in emissions; there will be no need to wait many decades to see if there is an effect, as with reductions in CO2 emissions.

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  23. maxlybbert Says:

    If the question is “will we *ever* see a 100 mpg car with the kind of features current cars have?” I would say the answer is “yes, especially if you count accounting gimmicks like plug-in hybrids” (the plug-in hybrid doesn’t get all of its energy from gasoline, so it’s easily possible that one could go more than 100 miles on a gallon of gas if it starts with a fully-charged battery).

    If the question is “will we see such cars in the next five years?” I would have to say “don’t bet on it.”

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  25. bverheggen Says:

    It is worth noting that the average mileage of cars hasn’t improved in decades, but that is mostly due to there not being an incentive.

    I blogged about past and future cars here: http://ourchangingclimate.wordpress.com/2008/10/02/the-car-of-past/

    Here’s an example of a ICE car which gets 100 mpg (still in an experimental phase I believe):

    On a test bench you can get still much better than that, but stop and go and going uphill will start to be difficult: the opel P1 experimental car got >350 mpg. Needless to say, it won’t have the same features as the cars you generally see on the road. But it may show that large improvements over today’s mileage are possible.


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  27. jae Says:

    The trial lawyers will probably make it impossible for us to ever get a decent 100-mpg car.