Thoughts on MPGe
Tuesday, July 13, 2010 at 06:41AMOur #97 mainstream 4-seat Very Light Car achieved 101.4 MPGe in the combined EPA cycle at the X Prize Knockout.
An interesting side note to this accomplishment is that the engine we are using is a 250 cc, one-cylinder internal combustion engine from a Yamaha WR 250R. This small motorcycle weighs 300 lbs and gets 70 MPG, and does not have to meet tough emissions standards.
Our Very Light Car weighs over 700 lbs and gets over 100 MPGe. – while exceeding the stringent 2014 emissions standards, including cold start. How does this leap in mileage occur? Mainly two ways: the extreme platform efficiency of the Very Light Car, and improvements made to the engine. The Very Light Car adds a turbocharger, increases compression, uses extensive exhaust gas recirculation and reengineered internal parts and runs on E85. A similarly efficient gasoline engine we considered doable but would have taken longer, especially the emissions system.
The Very Light Car is not the only entry remaining in the X Prize that can be compared to an existing car’s mileage. Tata’s Indica Vista EV X (a production 4-passenger car, entered in the Alternative 2-passenger Side-by-Side class, presumably to avoid the mainstream 200-mile range requirement) gets 33 – 40 MPGe as a production car, but in the X Prize achieved much more: a combined 134.3 MPGe while running as an electric vehicle.
What explains the much greater efficiency of the X Prize Tata? No doubt it partly reflects the efficiency of the electric motor, properly applied. But this achievement is also a function of the underlying method of measuring energy use in an electric vehicle.
Energy use in an internal combustion engine is straightforward: measure an amount of gas, drive, and measure again. For the X Prize the cars have standardized gas tanks that are removed and weighed.
Electricity use is similarly measured at the X Prize. Batteries are refilled at charging stations and metered for energy consumption: a “plug-to-wheels” formula, that accounts for losses in the charger, in the battery, and energy used by the engine to move the car. Certainly a more accurate representation than measuring the energy use motor-to-wheels, which leads to results all over the map, including some very high mileage numbers.
A problem is that electricity is only an energy carrier and thermal conversion of energy is not considered in this calculation. In the real world for every BTU put into the American power grid for the production of electricity only 52% makes it to the plug. This 48% loss (from energy conversion and distribution) is not accounted for in the plug-to-wheel calculation.
This plug-to-wheel calculation is important as there are many good reasons to shift toward an electric transportation future, such as new options, existing capacity, energy independence and remote emissions. However, a more accurate number for the Tata efficiency would be 40 mpg on gasoline and (134MPGe x .52) 70 mpg as an electric.
This is a more efficient vehicle as an electric but the efficiency comes with costs: battery expense, range restriction and issues like grid capacity and resource allocation. Certainly a path worth pursuing, especially as the electric grid moves away from coal towards renewable sources of energy.
Very complicated issues – what about the efficiency of distributing gasoline or ethanol? - and the X Prize is to be commended for adopting a clear, understandable standard in MPGe.
But the fact remains: our Very Light Car – the most efficient automotive platform ever built – has crossed the 100 MPGe threshold.
Reader Comments (19)
Clearly, the opposite logic is also true. Forcing cars to carry all their energy in batteries instead of in the road itself is left-over from obsolete gasoline service station days. (After all, we don't charge big batteries at power plants and truck the charged batteries to our houses.) We can get another order of magnitude efficiency in our transportation system with a power grid that accommodates the needs of electric vehicles as they roll. After all, nobody has suggested that gasoline deliveries be constricted to wire-sized tubes for fairness sake, have they?
The X-prize rule-makers basically designed your Edison2 cars. Since most American highway vehicles carry a single occupant, those same X-prize rule-makers excluded America's greatest transportation need: single occupant vehicles. Why? Perhaps to make things easier on themselves. Perhaps they did not want to infringe or marginalize Shell's low speed fuel economy contests. Maybe their reducing the usefulness of their prize to human civilization was of secondary consideration to American market automobile demand patterns? Clearly their goals were entirely short term. Hopefully the next iteration will be a REAL challenge, like 1000 mpge.
Excuse me Bubba Nicholson, but in what way is 100 mpg for a car not a challenge? Why didn't you build a car if it was so easy? According to you it would have been an easy $10 million in the bag. Just one problem with your theory of running cars like slot cars, how is anyone that's driving a car going to change lanes or park? The reason nobody has ever suggested gasoline being piped in tiny wire size tubes is because nobody ever had to consider that a more efficient possibility.
Well, if you haven't noticed, other countries already have much more fuel efficient cars in production. VW and their polo blue motion diesel of 74 mpg. Why not sell it to Americans? They say it won't sell here in the states. This is the paradigm that the X-prize is trying to break. Car makers say people aren't buying our more fuel efficient vehicle models, QED nobody wants to buy something more efficient. People are saying they do. So the goal of the x prize is to shift the current paradigm. And by the way, are you or me currently getting over a mere 50 mpg? I didn't think so. Clearly the X prize is doing a lot more about the future than any car company I have seen.
Could this engine be used with methanol? Methanol can be produced today without subsides relatively cheaply, from natural gas for $1 a gallon.
I dont have much hope for economic cellulosic ethanol. Maybe ethanol produced from gasified biomass but methanol can be produced easily that way too. Fermented corn ethanol is just awful, its expensive and bad for the environment, and theres not enough corn or sugarcane ethanol for everyone.
I've heard methanol is toxic but is it worse than gasoline?
Well guys at Edison2 I hate to say it, but if the other teams' performance numbers are true from the x prize's website, the reason that the x-prize has not and will not account for that calculation is because a lot, if not all of your other competitor's cars would fail on meeting the 100 mpge calculation. Of course if you think about it, 100 miles per gallon is really challenging thermodynamically. A bicyclist couldn't go 100 miles per gallon of milk alone. So if all of the other teams fail, it would look bad on the x prize foundation. I at one time considered entering the x prize with an old go-kart tandem chassis I had previously built and contemplated the power source. What drew me away from hybrid is the fact that you are always stuck with transporting 2 propulsion units, and in the end they both draw from the same source for energy. That one seems like a "duh" to me. Electric power would have been way too heavy after reading in a text book about how 10 milliliters of gasoline holds the same energy as the best fully charged 15 kilogram (33 lbs) lead acid battery. Of course there, the thermodynamic equation needs to be reversed, because the gasoline is only potential energy, ok so, 20 milliliters, fine. So maybe the ball got rolling too quick for electric, and only a few people are asking, "Hey wait a second, can we think about this in real efficiency first?" Of course that's my German heritage speaking. I would have used the diesel engine from vw from their polo blue motion diesel and applied it to my go-kart since it's the only diesel engine small enough that is using a common rail injection system. I wish other diesel manufacturers like Kohler or Kubota would consider a small engine for common rail injection.
Anyway, that's my thoughts on MPGe, I wish you guys the best success.
52% thermal efficiency for electric generation by power plants in the USA is incorrect. It is more like 40% for natural gas, but this varies depending on how much comes from combined cycle plants and how much comes from peaking plants, and a lot of other stuff in between. For coal, the thermal efficiency is 32%. Both types take a hit for distribution efficiency which is 93%.
Only the coal efficiency matters, since this is by far the least expensive fuel used in electricity generation, and there is abundant reserve capacity. Some would have us believe that this can be fixed by cap and trade or tax legislation. Yes, there can be pressure to use more natural gas, but this will take a very heavy hand laid on the coal users, and remember, what would be required at the current price differential will have to be much strengthened as the natural gas price increases in response to a doubling or tripling of the rate it is used.
Only when renewables provide sufficient reserve capacity that coal is no longer needed, then there will be a change.
If we agree that coal is the basis on which the MPGe should be calculated, the electric car mileage should be about 30% of the XPrize reported numbers.
You don't get to dump on the electric cars' MPGe based on lack of including 'production to plug' losses until you include the 'well to pump' costs for gas or ethanol.
Somehow that part is never mentioned when people compare gas to electric.
How much energy is used to pump, transport and refine the oil?
Then how much is used to transport it to your local gas station and how much to run the gas station itself?
One other question. The X-prize Edison2 is built of carbon fiber. The web site says production models will be made of aluminum and steel. What is the increased weight for equivalent strength and what then will be the MPGe? If less than 100, the whole X-prize thing is a sham as I thought the idea was to reward designs that can be made in quantity for sale to 'regular people' for their daily drivers AND get 100 MPGe minimum.
Bruce Alvarez,
Of course you are right about including well to pump losses for gasoline or ethanol. But then you also need to include the transportation cost for coal, which might be about the same. About 80% seems to be reasonable for efficiency of either process.
I tend to think it is reasonable to start at the input to the heat engine which is the point where the big losses occur in any fuel based system. That will get you a reasonable comparison. Compared to the losses in heat engines, the other losses become quite insignificant and tend to balance out.
The real problem here is that the favoritism given to the electric drive systems is huge; so much so that it is an easy thing to achieve 100 MPGe under the Xprize rules and a nearly impossible thing to achieve that goal for cars that carry their own heat engines.
The failure to understand the basic energy relationships in energy conversion means that the
Xprize will hugely distort the competition.
I have argued that this will be of significant harm to the public since it will lead to much misguided effort to make cars electric. This is a major national disaster. This spill of intellectual garbage seems to pervade the entire developed world, and is threatening China and India as well.
If we implement good hybrid technology we will improve both the oil usage and the CO2 emissions situation. If we take the next step and convert these to plug-in operation, the world will depend less on oil. But the other big crisis of CO2 emissions will be made worse. And the false impression that electrification has accomplished something will poison the market for real progress.
The Edison2 work is an example of real progress. But it will be very hard to sell to a complacent public that is happily driving around on coal power.
Bruce Alvarez,
You make a good point about the 'production' status rules. I would not call it a sham, but it does show a real problem with the way the Xprize folks fail to comprehend the realities of the advance development process.
Of course, when they started they were working on the belief that the 100 mpg would be an easy game for electric cars, so there could be focus on getting production type features in place, and adding design cuteness to the package.
For cars that carried their own heat engines, some real engineering development was required. And the reality is that where real engineering development takes place there always are difficult issues and trade-offs. Fortunately the Xprize folks did not get into the qualities of the engine regarding suitability for mass production. That might make our friends here sweat a bit, since getting that little Yamaha engine to be super efficient, jacked up with the supercharger and other new stuff, could bring some longevity issues. I am not criticizing; this is the kind of struggle that any real development must undergo.
That is an example of how the burden is made unfair by the favoritism to electric vehicles. Nobody is out in the coal fire power plants trying to jack up those furnaces so the electric cars will get the required 100 mpge.
Moving the heat engine off the car and into a central location is a good thing. As it's significantly easier to add greater efficiencies in on central plant than several million smaller plants.
Work is being done to make the grid more efficient, superconducting wires, etc. And coal is a current problem but given proper impetus and demand Nuclear can provide a happy and *safer* solution to the problem. We just need to get the bureaucrats to extract their heads from where the sun doesn't shine.
Yep, there are some really big problems out there that we face. The most real solution, is without question getting better efficiency first. The reason an electric car can go 100 miles or more is because it was very light before getting thousands of pounds of batteries strapped on. Try to imagine most Americans here in the South East region. The majority of vehicles here are either sedans or SUVs. The Toyota Sequoia weighs in at 3 tons (5,800 lbs). If it were electric, being extremely optimistic since the Tango has "only" a 1 ton battery, a Toyota Sequoia would need at least a 2 ton battery. Now ask yourself, is a battery electric car really that energy efficient if it takes over 5 tons (10,000 lbs.) to transport 4 people 100 miles? The truth is that it requires on all of our part a minimum sacrifice. If everyone payed close attention to the road as they did when they took their driver's license test, people could relax a little more about how heavy their car has to be to avoid being squashed like a bug from other idiot drivers that are: smoking, talking on the cell phone, texting messages on facebook, putting on make-up, looking at passengers while communicating to them in the car while they're driving a big ass 3 ton killing machine. But it's ok because they're not going to die, you will unless you protect yourself with more weight. Or we could all just actually drive our cars. I really liked one of the "Top Gear" episodes I saw where the "Stig" was driving a Caterham R-500 and the presenters are saying "Yeah it has no stability control, a manual transmission, no air bags, no gps, no stereo, no traction control, not even ABS." The other one says "Yeah that's a car you actually have to drive."
biologist111
One way to look at it is to force 'gallons' to actually be involved. That could be done by insisting that the central power plant is powered by a diesel engine. The thermal efficiency of this kind of engine roughly matches that efficiency of the average US power plant. The electric car MPG numbers would all go down to one third of the presently stated Xprize numbers.
Hey Jim!
Well I have to agree with you. Making calculations is very good to do, but ultimately, real numbers like gallons have to be applied in real world energy efficiency. After all, nobody will ever buy mpgE, they will always buy gallons or some other form of standard measurement, KWhr, for example. Rudolph Diesel is one awesome inventor for making the diesel engine. It does to me seem like the most efficient engine design. Especially with all of the latest technology in common rail injection. Although, it seems like a shame that it gets such an ordinary name. Although, for power "creation", one thing I've become more interested in is the new designs on sterling engine solar collector generators.
About hybrids, as I said, two power plants, ultimately getting there energy from the same place, seems a bit ridiculous to assume that it would be more efficient, than one really well engineered power plant (for a car).
Now with why I'm still not a huge battery fan yet (maybe one day) is for multiple reasons.
First, the charging time seems to take a long time, and I've run plenty of radio controlled cars, and they don't take but 15 minutes. I could easily give up ten extra minutes to charge up, but not hours.
The second is that I'm all about energy conservation, but not if it costs the environment more in the end. Basically, I know from experience that batteries wear out. When I would build and run RC cars, I had the best batteries. The amount of run time was much better, but the longevity wasn't any better. I ran them hard everyday after school for years. So, in difference to laptop batteries, I exposed mine to the same outside conditions a car will face. So, if the batteries wear out they get thrown away, and if that happens more often than an engine needs re-building it's not the least bit cost effective. Cost effective by the way, is also another form of efficiency.
The third reason is that battery cars lose efficiency drastically when temperatures drop, and if they drop low enough they will permanently have their range, and longevity reduced. The same is also true as temperatures get really high, and in lithium ion's case they blow up. Not a good solution for a car with a replaceable battery lasting a long time.
The fourth reason is the weight. Cars in my mind have gotten way too heavy over the years. By definition it's not energy efficient to have heavy cars having 3 tons+ of mass, just to transport 4 people, and usually only one. To me it's not acceptable to say, "screw everyone else as long as I'm ok." The only way the system will work well, is if the people in it stick it out to make it work well for all people that have to live in it. It takes realizing that you're not alone in your problems, and a desire for a tiny bit of safety sacrifice if it means it would contribute to the greater good.
So for right now, a more efficient vehicle first, and as battery technology improves in all of those areas, eventually there will come a meeting point. Meaning, light vehicles, and long lasting, efficient, lighter batteries will come together naturally, because the light cars won't need heavy bolstering, and heavier chassis to accept the batteries.
Just one more note to add. If it only takes, say 30 or 40 hp from a ICE to keep a car going at 60mph. What about having a super capacitor driven motor to accelerate the car up to speed. Most people don't do racing, they do one sprint up to speed. Capacitors are much lighter than batteries, much quicker to charge. Have it integrated to the transmission with a one way bearing. So maybe a hybrid would work if you had a late rpm turbo diesel engine, and capacitor motor(s) for the low end immediate torque.
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