Overall Efficiency of Gasoline Powered Cars

22%.

Thanks!

Poor child,

Please don't think I have any real insight into the question. Any more than anyone else.

It's a guess!

My guess is as good as the next one.

Watch out for the HHO guys like onecraftydude who would have you believe that they can get 35%.

Engine? Transmission and engine? Body vehicle, engine, transmission? Apparently all of a sudden Kilowatt hours are applied to what is traditionally known for old brains as horsepower.

What electric motor is the 1 horsepower motor?

What 4 cycle gas cc displacement engine is 1 horsepower?

Last I knew great V8 engines were 25 percent efficient.

The definition of efficiency according to my understanding was that the machine was 100 percent efficient if all input produced equal output.

For regular people the machine is 100 percent if it gets them to work and back for less than walking, crawling, or public transportation.

Ok, I got suckered in...I thought someone just knew the answer and this would be easy, but thinking about it the 22% number is hugely high I'm sure. I'd be very surprised if the engine itself is that efficient.

As I said initially, it's going to depend on how economical the vehicle is for sure, but I really would like to figure out how efficient even the most economical car is in terms of total power throughput.

BTW, the reason they rate engines in kilowatts is simple...it allows direct conversion to electrical power. You can use millimeters or inches and still measure something physical. You're just calling it by a different name.

The 22% number is the efficiency number I learned in high school for a "modern" internal combustion gas engine.

The year was 1963!

Yes, 1963.

Good luck!

That is probably a correct figure for engine efficiency, but I was wanting to go further than that. As you know, you're lucky if a 300 HP engine delivers 75 to the wheels. I was actually looking for the overall efficiency, from energy in the tank to motive energy transferred to the road, and not just the portion that relates to the engine's efficiency.

I hope that makes sense...but I'm quite convinced that we'd be lucky to get 10% of the overall fuel energy content in actual usable power.

An easy way to imagine what I'm asking is to put a stick-shift car in gear and raise it on a hoist. Then using a torque wrench, turn the flywheel nut and think of how much oomph it's going to take to turn the wheels that way, through all the gearing from start to finish.

It's kind of an off-the-wall question, but I'd like to know the figure if someone has it.

I agree. 10% would be good. If you put it on the hoist, you are talking more about drive train efficiency, than system efficiency.

Too many variables come into play when you speak in the general terms.

Putting it on a lift takes away all mechanical drag, tires, running gear, wind resistance, altitude, relative humidity, temperature, rain, fluid viscosity vs temperature, etc. I'm sure there are other variables, too.

I think you would have to take a look at every friction point in the vehicle to come up with a ballpark figure. Test two "identical" vehicles and you will get different values.

I'm not smart enough to be of any real help.

You're right of course. None of that comes into play when the vehicle is on a lift, but I used it as a visual way of describing what I'd really like to know.

I suppose the figure I seek doesn't actually exist, since there are so many variables that could come into play, but even if we could agree on 10% as a working number it's pretty startling when you think that 90% of the energy value of every gallon of gas we burn is wasted!

22% should be pretty close. When I was in school about the same time as you the gasoline engine was said to be about 35% effecient. After the drive train, tires, etc and right at the road I can believe 22%

Google "Well to Wheel" and look for the publication in pdf format for a good discussion

well 25% is not that bad already, considering that much output goes into overcoming inertia and frictional forces.

friction would always be there, unless you use tyres that has less grip or reducing the inertia by making vehicles lighter.

both methods is a compromise to safety, which is not the way to go these days.

Thanks. That's what I was looking for.

It seems that if we're talking about a very high-mileage vehicle (36.7 mpg) we're still only at 12.5% overall. Without running the numbers, half that mileage, a more reasonable 18.3 mpg, should give half the overall, about 6.25%. That's in the range that I was expecting, frankly.

What does that imply to you for electric vehicles? We know their overall efficiency is far higher, probably around 80%, we could have some fun with numbers. To store the equivalent of 10 gallons of gasoline would mean 36.7 kwh*.0625*10, or 23 kwh total. To account for the electrical efficiency we'd have to have 23kwh/.8, or 28.75 kwh stored energy.

Does that sound reasonable?

If you are looking for a comparison between the efficiency of petrol engined cars and electric vehicles, there are some other parameters that come in to play. Electricity generated in an oil fired power station is much more efficient than a single internal combustion engine driving a single vehicle. There ar of course losses in transmission, but this can be equated in some measure to the delivery of fuel to the pump and additional refining. You also have to consider that the method of delivering torque via electric power (the torque curve) is totally different. There is in general no need for a gearbox which is in itself relatively inefficient, therefore the losses in the drive train tend to be lower for an electric vehicle. I did some rough figures on T.O.E. (Tonne Oil Equivalents) some years back, and reckoned that generating power by electric motor against internal combustion engine in a vehicle was almost three times as efficient. Around 10% for the I.C. against 30% for electric.

Careful when you compare figures. 1 UK gallon equals 4.54 litres whilst 1 US gallon is 3.8 litres. 1 ton equals 2240-lbs, 1 tonne equals 2204-lbs.

Good luck, as I have been searching for a complete formula for years that takes in I.C., drive train, rolling road resistance, co-efficient of drag and all the other variables. If you find it (or you manage to steal it from GM, Ford or Chrysler or the like) let me know, as I will be very grateful.

I don't think this is correct. (1/2)(m)(V squared) is the kinetic energy of the moving car. That much energy must be applied to accelerate it to cruising speed, plus fricitionaly losses from the road and the airstream. However, at a constant cruising speed the kinetic energy remains constant, and thus zero output from the engine is required to maintain it in the absence of frictional losses.

The mass of the car does increase its the rolling friction. The higher the mass, the greater the road friction between the tires and the road. The higher the speed, the greater the wind resistance.

Consequently, the force required to maintian motion on level ground is only the amount required to counteract the retarding frictional forces (obviously, if it were a space ship in a vacuum, no force at all would be required to maintain speed and you would get millions of miles per gallon).

Consequently, knowing the frictional forces, the force applied through a distance is work. The rate of work is power. Thus, (F)(D)/(time) = Engine power output to the wheels where F is the retarding force and D is the distance traveled. F is in newtons, D in meters and time in seconds giving power in Joules (newton-meters per second). Knowing the amount of gasoline burned then allows you to calculate the overall efficiency of the engine and transmission and differential combination. You would need to know the losses due to the powertrain to be able to back track to the engine efficiency.

The effect of frictional forces on overall automobile efficiency is obvious. A sleek low resistance vehicle get much better gasoline mileage at higher speeds compared to a brick shaped vehicle even though the two vehicle are the same weight. It is also the reason that mileage improves by keeping your tires fully inflated.

Maintaining laminar flow over the vehicle minimizes drag. Turbulant flow is very bad because the velocity relationship moves to a higher relationship, squared relationship or even higher. This is related to shape, but not mass except to the extent that higher mass tends to lead to a higher coefficient of friction.

A sleek car can have a coefficient of fricition for air flow as low as 0.15 while a bus has a coefficient closer to 0.8 or 0.9, I think.

A good thumb rule for the thermal efficiency of a gasoling engine is 25% at the Crank Shaft, although approaching 30% is theoretically possible.

What I put in was an appoximation... which gives a good back of the envelope quick calculation. I think it provides an upper bound on the energy spent, thus a lower bound on the efficiency, but I would have to think more about that. Yes, Kinetic energy is the amount to accelerate to that speed.... but at 30m/s what % of the fuel is used to overcome friction/drag/losses in the drive chain etc? (trick question). While accelerating from rest then if acceleration is constant (otherwise you must integrate Fdx) then m*a*d=1/2mv^2. i.e for each placement of your foot on the accelerator (which equates to fuel consumption) you reach a terminal velocity (or KE) where you can no longer accelerate due to the sum of all the losses. So this should be an upper bound on energy in and thus a lower bound on car efficiency.

adonaldson@calbaptist.edu

Here is the link to a non math answer…

http://www.fueleconomy.gov/FEG/atv.shtml

They say for the typical car (whatever that means- after all it is a government site) the following is true:

100 units of energy from the fuel…

81.2 into the engine

62.4 is losses (engine friction, pumping air in and out, wasted heat)

17.2 is standby and idle

2.2 is accessories

18.2 goes into the driveline

5.6 is driveline losses

12.6 goes to moving the car

2.6 drag (goes up by the cube of the speed over 60mph)

4.2 wheel losses

5.8 inertia, braking

The bolded items are not present on the highway (if you assume constant speed) …hence efficiency goes up… but not the full amount since drag and wheel losses goes up with higher speeds on highway.

adonaldson@calbaptist.edu

Thanks for all the great recent responses from everyone. Since I started this discussion I feel some obligation to react, but I try to shut up unless I have something to add.

The site you linked to opened up with the answer to my question.

"Only about 15% of the energy from the fuel you put in your tank gets used to move your car down the road or run useful accessories, such as air conditioning. The rest of the energy is lost to engine and driveline inefficiencies and idling."

It's easy to see how huge advances in energy efficiency are at least theoretically possible if some technologies are abandoned while other new ones are developed and adopted.

My interest in this stems from a wholly new type of internal combustion engine that I'm working on which has only one moving part. Nothing like it has ever even been proposed before, and the potential fuel savings are just enormous. I can easily see 120-150 mpg with power equal to or exceeding most V-8 systems. What makes this unique is that even idling losses are greatly minimized or eliminated completely because the engine does not run in the conventional manner. The engine will spontaneously stop when no load is placed on it, and will spontaneously restart as power is required. It also is direct drive so there are no driveline losses to factor in.

I wanted to get some numbers that I could use to visualize overall power throughput from tank to destination, and while all the proposed numbers are subject to variation, it seems reasonable to use a number between 10-15% for those considerations.

In ref to bcmarshall posting. Just one moving part!? Well I cant imagine what kind of a new powerplant/gas engine this will be. Except perhaps something like a jet engine where the only moving part is the turbine blades. Not going to include the fuel pump etc for this discussion. I'd love to hear your response(s)

I can't really discuss it right now because of protection issues, but I guarantee you one thing. When it is finally disclosed you'll be slapping yourself on the forehead saying, "Why didn't I think of that?" It simple, intuitive, logical, and it can do nothing else but work.

Sorry I can't be more open about it.

What?! You've correctly calculated the kinetic energy of the moving car, but the "1 mile" is irrelevant to that number. When the car is in motion at that speed, that's its K.E. whether it's gone a mile or 1000 miles. Clearly, it gets that from the chemical energy in the gasoline, but it also gets energy to overcome aerodynamic drag, rolling resistance, etc. The car uses energy to move against a force (i.e., to do work). That force in a typical car is on the order of about 500 Nt at highway speed. So, moving one mile, or 1609 meters against 500 Nt accomplishes 804,500 Joules of work, and by the work-energy theorem this is equal to the energy converted. Thus it must be added to your 450,000 Joules.

So the energy in the gasoline serves two overall functions: adding kinetic energy by bringing the car to a give speed, and doing work against the forces resisting the vehicle's motion. A third, wherre applicable, would be to increase its potential energy by going up a hill. All of these are "useful" in terms of the vehicle's efficiency.

So you're seriously an engineering professor?

Great first post there, PA32. Welcome to CR4.

Thanks for the welcome. I got here via a Google search for "well to wheel efficiency electric gasoline" (or something close to that).

I actually have a post in my blog (the post is at: A potpourri of cluelessness) about misconceptions I've found in searching the tubes for information on energy and vehicle efficiency. I'll probably include the post from "Guest" in a follow up.

By the way, for anyone wishing to visit, my blog at Adventures in Fuel Economy, Energy Use, Physics, and Life is completely non-commercial and covers a variety of issues connected in various ways to the topics covered in the title.

I had heard something like 17%, average, explosion to wheel.

Many years years ago when I was thinking about buying a new 6 cyl pickup

The spec sheet on an american made truck with a 100 hp 6 cyclinder engine

stated the truck 100 hp engine developed 20 hp at the rear wheels (dyno tests)
and some import models at that time were only 10 hp at the rear wheels

One factor I see overlooked in many of the claims by electric propulsion advocates is the fact you still have all the drive train losses even if you did a substitution of an ICE to electric motor. Softer radial tires introduce lots of losses. Even just playing with the inflation pressure makes a difference. Hard riding narrow wheels like a bicycle style make for great milage. Just look at the solar racers in the Australian trans continental race. And automatic transmissions introduce approximately 3% - 5% losses. Otherwise why do they need a trans oil cooler. That excess heat is wasted energy. Every car enthusiast knows a manual gearbox gives better milage. but the emissions people won't allow them because it permits an engine to operate outside their designated parameters.

Weight is of course the other factor. By the time you add enough batteries to give decent fuel range on a full charge you eliminate one passenger or two from possible weight capacity.

To my knowledge there are direct-drive motor-to-wheel electric systems. If so, there is no need for a transmission.

I consider your comments about tires interesting, but irrelevant since those same options would affect the efficiency of the current gasoline powered vehicles. We've settled upon the tire configurations the world is now using, and we can't expect that to change simply because we're using a different propulsion system.

The real problem is battery capacity, the eternal problem of electric vehicles. Oil's energy density is tremendous, and there is only the time it takes to pump the fuel as downtime before you're back on the road. No doubt that oil is a phenomenal fuel strictly from an energy perspective.

However, the most gorgeous electric vehicle from Tesla Motors can get about 250 miles (400 km) on a charge. www.teslamotors.com They use laptop computer lithium-ion batteries.

That makes electric vehicles practical for all but the rarest of usages. The only time I personally exceed that range driving is on some long trip that I don't take frequently. I would guess 99% or more of my driving would fit within those limits.

While I am in agreement with all you say the practical limitations in the real world makes an al electric vehicle a tad more problematic that you might suppose.

At the moment we do not have a suitable infra structure to distribute electrical power to the car. When was the last time you saw a parking lot or service station where cars could plug in to be recharged? I know they exist in places like Edmonton and Winnipeg. But they are not designed for rapid charging of several cars at a time. Northern locations that do provide block heater plugs are still limited if several cars simultaneously plugged in to recharge thrie bateries.

My colleague drives a Prius and we work in a design office where we constantly get requests for electric drive diesel -electric or some other form of hybrid drive. The subject is not altogether unfamiliar to us.

You are right there are now some in-hub electric motors available. But for the most part electric drive vehicles are at the moment still using a drop in single electric motor as a replacement for an ICE.

The attitudes expressed so far exhibit a bias towards urban use and conditions. But expecting the rest of the world to conform is not realistic.

On the subject of ICE efficiency, my family has always driven Ford trucks. A long time ago we standardized on the venerable 300 CID engine. I now drive the latest fuel injected EPA compliant pollution controlled whatnot version of that same engine block. Strange as it may seem I still get almost the exact same milage. So that tells me that the EPA demanded changes negated all the improvements provided by fuel injection, electronic ignition, tuned intake manifold, exhaust etc. The F150 truck chassis hasn't changed much and neither has the overall vehicle weight. Certainly if you average out the variances from day to day and year to year it will not be a significant difference over a period of 35 years. I have been driving since 1962 and have held a driver's licence since 1964 when I turned 16 years old. I used to drive an average of 40,000 miles per year not counting driving for work. That gave me a fairly good feel of how to get good milage.

Yes I have been following the Tesla development. I tell you that car would not last a month around here. Completely impractical?

We have to haul our garbage three kilometers to a transfer station. That car or any lik eit would get stuck and need a tow truck. The nearest tow truck is stationed 100 kilometers away. From here to the garbage transfer station involves driving up a mountain side with elevation changes of 800 feet.

And how long did you say a recharge takes? So now a shopping trip into town would involve staying overnight while the car recharged. I don't think so.

It really is pathetic that the overall efficiency that the entire world is running on is probably less than 10%. While we can never expect anything approaching 100%, I believe that 80% is reasonable with electric vehicles. So essentially the ratio of what energy value we utilize to what we could quite realistically accomplish with high efficiency electric vehicles is about 8:1. We could do everything we are doing now on about 12.5% of the energy we're currently using.

In memory of John Lennon...Imagine.

Imagine reducing your gasoline bill by 87.5% with no loss of convenience or comfort, and then imagine spending or saving that money as you see fit.

Imagine reducing the influence of oil companies by 87.5%.

Imagine the geopolitical advantages if the entire world's need for oil were reduced by 87.5%.

Imagine the environment with an 87.5% reduction in greenhouse gases.

What's intriguing is that this isn't science fiction. The physics don't lie, and in this case don't even protest what could be.

To go back to the efficiency calculations, let's very generously assume the average vehicle on the road gets 22 mpg (9.2 km/l). That 8:1 ratio implies that we realistically could be getting the equivalent of 22*8=176 mpg (9.2*8=73.6 km/l).

Imagine.

That fits with what I know about drive train efficiency. Only about 20-25% of the engine output is actually delivered to the wheels. If we assume the engine being 25% efficient, the overall efficiency would be 6.25%, or 1/16th of the fuel power being delivered to the wheels.

Does anyone disagree that a figure of 10% overall efficiency is a generous rule of thumb number that can at least be used for rough calculations?

That fits with what I know about drive train efficiency. Only about 20-25% of the engine output is actually delivered to the wheels.

Actually these figures are incorrect. Transmission losses are relatively small, with a modern transaxle loosing 10% or less (manual trans or locked torque converter). Even hypoid final drive gears (which favor quietness over efficiency) are at least 95% efficient and each loaded mesh in the gearbox proper is apt to be 97% efficient.

The Prius engine is 38% efficient at peak, and over 35% efficient over a fairly broad range, so in the Prius, it is not unusual to have efficiency to the rear wheels of over 30%. The tire losses are best considered separately, because they are relatively independent of speed and directly dependent on vehicle weight, with the Prius tires operating with rolling friction of about .008 x the cars weight. At low speeds, this is a major loss, whereas at high speeds the aero losses are much higher than rolling resistance.

The Prius electric motor is over 90% efficient much of the time (as is the electric motor in the Tesla). However, on average in the US, the generating and distribution efficiency for electricity is about 38%. So for a plug-in Prius (which are, so far, only available as conversions), the efficiency is nearly the same whether you power it with the grid mix (mainly coal) or with gasoline. The losses occur wherever the fuel is burned, with heat engines being fairly inefficient, in either case.

However, this is slowly changing, with newer power plants being 60% efficient (about 53% efficient to the plug). And electricity has the potential to be very clean, although the cleanest sources, wind and solar, are both very costly, and not free of environmental concerns associated with the equipment and its use.

My Progressive Insurance Automotive X Prize contender is a multimode hybrid, which can run on grid electricity alone, gasoline alone, or several combinations in different paths through the drive train. The efficiency when running on grid electricity (using the national mix) is about 38% (grid) x 95% (charging) x 95% discharge x 90% (motors) x 94% transmission to wheels = about 29%. In a direct drive cruise mode, it can do better than that: 34% engine x 94% transmission = about 32%. The fuel usage is pretty close either way, with coal, natural gas, and oil providing about 75% of the energy in one case and gasoline providing all the energy in the other.

No panaceas, but electricity is very likely the way things will go, because it frees us from foreign oil, and because eventually it can be produced cleanly.

Blink-

Your information tends to support my contention that the discussion focused on the efficiency of different power sources is misdirected, and should focus more on the efficiency of accomplishing the task at hand- it is far mor efficient to move less mass when going from point A to point B. A 2 ton Hummer is never going to be as efficient as a half-ton motorcycle for moving a single individual between home and office, or wherever. A small electric vehicle for travelling short distances is quite effective- we use electric golf carts quite effectively in the appropriate environments. But these would not do where distances are great and speed is an issue. The paradigm shift required is not electric vs. gasoline, but, rather, how much of our current practice with regards to general transportation is sustainable?

Charlie, your point is well made. Lighter vehicles would naturally use less fuel to move the same mass from poin tA to point B.

What is totally lacking in this discussion is not a technical issue but a social one. Widespread aceptance and adoption of light electric vehicles require some massive social engineering changes.

I have made a point of asking drivers of these large SUV why they would not use something smaller that uses less fuel. The answers are enlightening

I should also mention that in my area at least, most of the SUV are driven by women. Their reason for preferring an SUV as opposed to a Honda Civic is simple to understand. Most of them are terrified at having to drive part of their trip on a highway in close company of large trucks. When you then realize that in many cases these same women also pick up their kids from school and sometimes carpool for several other kids, it becomes easier to se why they cling to their SUV.

As to why these moms pick up their kids at school; another good reason emerges. Too many incidences of child napping and molestations have hit the public news. Even if the actual chances of a pervert operating in their neighborhood is small; their fear for their children is not. Couple this with school boards cutting back on bussing as a fiscal restraint and you get lots of SUV being driven by a single person for part of the day.

Before you see widespread acceptance of tiny, light weight cars for single occupants become a reality, several things have to take place. Traffic of heavy truck transport has to be segregated from light one passenger vehicles. Safe transportation of children to and from school must be universal. And an alternative to daytime school car pooling must be available. In many areas the family SUV is required after school to transport all the kids to their various extra curricular activities. Public transit is not always the answer since many attacks and molestations do take place in or near public transportation facilities. You can develop all the 1000 pound one person electric vehicles you like and even give them away, but it will not alter the need (percieved or real) for SUV type vehicles.

Excellent response, Elnav, and valuable information. It would be much more productive were attention focused on the issues you highlight.

Yes, I agree completely. And the line of thinking should extend to everything we do. A compact house consumes less in materials and energy than a large one, and is easier and less costly to clean and maintain. Etc.

After posting my last response, I had to go into town and paid especial attention to this subject while looking at how and who drove what vehicles. There are even a few of these "smart" cars around. You can see which factors were given emphasis by the designers. I'm a large guy and can no longer get out of a low slung aerodynamic car like a Tesla or a Volt. Arthritis and age is creping up at a gallop. Bear in mind America is facing a demographic trend of a graying population. My mobility problem will be shared by an increasing number of people. If it is a real struggle to climb UP from a low slung car you can bet it will not be popular with an ageing polulation no matter how energy efficient and economical it is.

One model does seem to adress this issue. It is very tall, quite narrow, and about 2 meter long. Sorry don't know who makes it. Either Mercedes or Huyndai. It probably could fit sideways into a normal parking space along the street. The owner happened by so I chatted a bit. He agreed it was great for in town but also said no way would he take it out on a surburban road or drive between this town and the next. In effect he is trapped and limited to driving in one town only. He said the vehicle is so tall and narrow it poses a handling problem in cross winds or side drafts from big trucks.

It is probably a perfect electric vehicle, as long as you never leave downtown. You would have to have a second vehicle if you ever wanted to get out of town on a week-end trip with the family.

OOPPS! He can't do that anyways. Provincial traffic act laws prohitbit having younger children in the front seat. In other words you cannot have children along if you only have a two seater. And that description seems to fit most of the latest small electric vehicles.

Om balance the Prius still seem a better all round fit for the mass market.

Your post was informative and well-reasoned, but when you looked at electric vehicle efficiency using the generating plant as the starting point I think you missed something.

We've been talking about the energy content of the fuel that goes into the tank. We haven't been considering how much energy it took to drill it, transport and refine the crude, and then transporting the refined product to retailers.

While the losses you refer to are real and must be considered when looking at a larger picture, in this case we have to compare apples with apples. The only fair consideration is what "goes into the tank", so to speak, what is actually delivered to the vechicle from your wall outlet.

Using your numbers without considering grid losses gives 95% (charging) x 95% discharge x 90% (motors) x 94% transmission to wheels = about 76%. Of course we have to factor in wind drag, rolling resistance, and the like, but to me it's far more informative to disregard them in both petroleum and electric vehicles, since one can assume that they're equal for both types. That allows a more direct comparison between the different motive systems.

The only fair consideration is what "goes into the tank", so to speak, what is actually delivered to the vechicle from your wall outlet.

Traditionally, in fuel economy contests in which different fuels are used, a well-to-wheels approach has been used compare energy usage among different fuels and energy sources. I argued in favor of this approach with the Automotive X Prize people, because it is the only way we can make informed decisions regarding the adoption of one form of energy over another, on a broad scale. (On an individual scale, we can simply fill up with whatever is cheap, if we don't care about our personal environmental impact.) The X Prize people advocated for measuring plug-to-wheels and pump-to-wheels because that is what the consumer is most concerned about, because it avoids possibly contentious debate over the well-to-wheel efficiency figures to use, and because promoting reductions in petroleum usage was a stated goal of the contest.

There is a knee-jerk response of some unthinking "environmentally-concerned" people that electricity is clean and good and that all hydrocarbon fuels are bad. These same people, however, advocate for the use of compact fluorescent bulbs because they reduce our carbon footprint (which is true in warm climates but not in cold climates, in which the "waste" heat from incandescent bulbs reduces heating load, making incandescent bulbs 100% efficient in providing heat and light). So for electric vehicles, they ignore the huge carbon footprint associated with charging, but they are aware of the very small carbon footprint associated with residential lighting. Seems duplicitous.

Electricity is not "consumed" in any real sense -- it is an energy carrier, not an energy source. The resource being consumed is out of sight of the typical consumer, and the typical consumer is unaware of the pollution associated with generating electricity. If consumers were informed and engaged, however, they would be asking, "Is it environmentally better to drive an electric car or a diesel car or an ethanol car or a hydrogen car?"

Today, the most environmentally egregious car is probably the BMW 7 series hydrogen-fueled car. It burns hydrogen in a spark-ignition ICE that can also burn gasoline. The hydrogen comes from methane (natural gas), the source for 95% of all hydrogen distributed. So we start with all the losses of extracting, compressing, transporting, (etc) the natural gas, then add the losses in reforming it into H2 and CO2... and then add the losses of compressing the H2 and refrigerating it and liquefying it. Once in the BMW's tank, 50% is lost to boiling off in 9 days: as the super-insulated tank warms, it must be vented to avoid explosion from over-pressure. (In the BMW the vented H2 goes through a catalytic burner, so at least your garage does not fill with H2). If the original methane were burned in a diesel BMW, the overall process efficiency would be perhaps 6 times as high -- yet BMW spins this vehicle as being environmentally sound. If the population at large were asking the right questions, BMW would have to think long and hard about the wisdom of promoting this environmentally egregious vehicle as "green." Only with a woefully uneducated population can such greenwashing fly -- fortunately for BMW, that is what we have.

Measuring from well-to-wheels is not easy, but it is essential to avoid the oversimplifications that lead to bad policy. Fortunately, much of the difficult work has been done, and the results are available in the Argonne Labs GREET spreadsheets. From these spreadsheets, we can see that gasoline is distributed to the pump at better than twice the efficiency at which electricity is distributed to the wall outlet.

We should think about vehicle energy usage in much the same way that we think about energy to heat our homes. It is widely acknowledged that heating with electricity is expensive -- just as you would expect, because you've burned the fuel miles away at medium to low efficiency. Even though electric heating elements are 100% efficient, that level of efficiency in the home is not enough to overcome the generating inefficiencies outside the home. Viewed either economically or environmentally, it is better to heat with natural gas.

The only fair consideration is what "goes into the tank", so to speak, what is actually delivered to the vechicle from your wall outlet.

I'd counter that the only fair consideration is the actual resource usage. The plug or pump is only a proxy for the real energy resource consumption. To compare apples to apples, you have to look at the whole life cycle. Without doing so, we would have people running cars on corn ethanol while thinking that they were being "green," not realizing that (according to at least Pimental's study) the petroleum consumption in producing corn ethanol alone exceeds the ethanol's energy value.

Excellent points Blink. However, your comments about the pollution inherent with electricity generation needs clarification. Not all electricity is generated equally. Here in BC we have an over abundance of hydraulic generated electricity from big power dams. If our government would permit micro scale hydro generated power; it would be even greater. For such areas, electric vehicles charged from a wall plug makes sense.

That same vehicle in the Mid west would require power generated from goal or natural gas powered generators. The pollution at source is much greater than from a hydro dam. So it is not as good a choice theere. (Se also below on Methane)

Solar power such as the giant Spanish installation using sunlight focussed by a field of mirrors is also great; ... in Spain and other southern latitudees with little cloud cover. But not if the area has frequent cloud cover or seasonal monsoons.

Quite aside from the capital cost investment required; this is possibly the least polluting generating source available. But with solar, power generation coincides with peak demand. Hydro is 24/7 in most cases. Recharging overnight requires tapping into baseload. Much depends on what is available to the various local power utilities. This is going to be a huge variable which will influence the final cost to consumer as far as cost of electric versus petroleum.

You mentioned hydrogen being generated from methane. The Midwest and other areas with huge dairy herds or even bird flock farming has the raw material for methane digesters that could produce a substantial amount of fuel from manure. Federally funded experiments were conducted and proved to be viable. Yet we do not see this being done commercially on a large scale. Why? Instead we see food crops being diverted to produce ethanol which has its own problems.

Is it a case of some one or some group insisting on a one solution must fit all? Right now farming on an industrial scale has a disposal problem for the manure from the herds. The technology is already there to convert this waste stream into a fuel source. Only congress knows why this development is not being encouraged.

Gasoline and diesel may continue to be the best fuel choice for some regions. Other regions can benefit from locally availabel resources. The debate is not just gasoline vesus electric.

But if you're going to discuss drilling, refining, etc. of the gasoline then you must also discuss mining and transporting the coal (typically for base load energy) to the generating station. I haven't seen this calculation, but the mining, in particular, must be energy intensive (and burns fossil fuels). The transportation to the generating facility may not be so bad - per ton mile rail transort efficiencies are quite good on full trains.

All that said, in my opinion electric will without question be the main transportation power source of the future. It can be produced sustainably and reliably in large quantities, given the social will. The biggest road block I see at the moment is the transmission infrastructure but perhaps that can be mitigated with distributed generation of some type.

PA32R wrote: in my opinion electric will without question be the main transportation power source of the future. It can be produced sustainably and reliably in large quantities, given the social will.

REPLY

I recall reading ( during the sixties) in Popular Mechanix or maybe in Popular Science that we would all be driving nuclear powered cars by the nineties. Yeah sure!!

And remember the Chrysler turbine car? You can join an emminent group of world renouned scientists that made firm declarations and predictions of what would and would not be posible in the near future (at that time) Every one of them was proved wrong by subsequent events. Cars driven by compressed air show just as much promise as electric cars.

Possibly true - I'm no expert, but how is the air to be compressed? Any movement further from the "prime mover" involves losses.

Nearly everyone forgets about the cost of replacement batteries in electric vehicles, and maybe disposal of the old batteries. A replacement car set of batteries probably cost more than a whole petrol powered car. Cost efficiences must come into it as well. Thank you.

My colleague who drives a Prius tells me it will cost him $9000 to replace the battery pack which is expected to last 7 to 9 years. So now we have a situation where these ecologically approved Prius cars comes up for trade in after seven years. Maybe less.

Who is going to buy a used car knowing it will cost them $9000 on top of the purchase price to get it back to normal running condition. Even if you gave them the car free. How many people are willing to pay $9000 for a used vehicle that still requires service and maintenance on running gear, tires, brakes and what have you.

Even brushless electric motors have shaft bearings that eventually needs replacement. How many miles on an electric vehicle does it require to wear out such a shaft bearing. We simply do not have a track record to know.

I am familiar with working on high voltage switch gear etc. But even I would have second thoughts about working on the 800 Volt Battery system in a Prius. with dealers charging over $100 per shop hour even routine service work rapidly gets too expensive for the average joe. From everything I have read about other electric vehicles they also run at high voltages to get the power without using huge electric cables frm battery to motor. I would love to have one for testing but the reality is, electric vehicles still seem to have some real service issues that would be objectionable to the general public. I am also aware of a few fire Department / Emergency Responder departments with Jaws of Life equipment being trained how to deal with electric cars without killing themselves. If you cut through the power cables it could be fatal.

I don't know what fuel injected vehicles have done to efficiency, but in 1980 a carburetor engine was slightly less than 5% efficient. That is to say: The majority of gasoline used is for engine and manifold/exhaust system cooling, another large amount is wasted in frictional engine heating which is counteracted with radiators and fans, and the remainder is lost to drive train friction and the "operator factor". Oddly enough, most drivers transfer 5% or more of their gasoline into brake pad heat when driving in town.

Terrific post.

I was simply wondering if you took an old Ford Falcon, and the same year Mustang, and ran them, you might discover a gestalt.

Far as I understood they were essentially the same car, with only different bodies.

To get a REAL handle on efficiency, you should consider the work you want to accomplish. Take your weight, figure out how far you want to move it in what period of time, and this is the work you want to accomplish. Figure out how much energy is available in the fuel you are using, and how much you will burn in the allotted time. This is how much you are putting in to the system. Don't count the weight of the car unless your goal is simply to relocate the car. Otherwise, all of the energy used to move the car is wasted. All that should count is what is required to accomplish your primary purpose.

In the case of a car, for most people their primary purpose is to get to work, but the car can't get you there without getting itself there, so it seems impossible to ignore that.

Just as with fuel economy, which is based on a combination of driving factors, efficiency must sort of level out at some average value. In your suggestion I'd need to make hundreds of measurements at various speeds and conditions and then average them all together to get more than a snapshot, which is what a vehicle's mileage really represents.

In opening this discussion I was a bit naïve to believe that there was an "answer", one that could just be plugged happily into some equation to show us what we're losing and to make a real comparison with other technologies.

The only disagreement I have with what you said is that it isn't real-world. It's ideal, and hell, who wouldn't agree with the ideal picture you paint? I mean, if we turned this forum into a search for the urban utopia, we could probably come up with some cool stuff.

I don't mean to disparage what you said. I'm simply looking at what is now, and not what should be. I'm seeking the closest thing I can find to a real-world answer to a real-world question.

Many would convert the the different fuels into BTU equivalents.

This could also be done for battery or electrical enery to BTU equivalents

At the following web site an battery car is calculated to have an efficiency of 275 mpge (equivalent)

click on http://www.futurevehicletechnologies.com/

Hope this gives some insight !!! Gary

That car is cool! Thanks.

They've got a three-wheeled electric car with an onboard generator that gives it unlimited range if you surpass its 135 mile (216 km) battery range, with a full recharge in about an hour of generator time, or three hours at home plugged into the wall. Awesome.

They're giving a fuel equivalence of up to 325 mpg (137 km/l), so we can certainly take that back to my original question.

This is a 1,200 lb (545 kg) vehicle, and we'd expect a similar gasoline vehicle to be high mileage, perhaps 35 mpg (15 km/l), so the 8:1 ratio I surmised earlier doesn't seem too far off the mark. In this case it's 9.2:1, so the 8:1 number may actually be low. That's the kind of figure that I've been seeking, something that puts into concrete terms just how much energy we're wasting, or conversely, how much more we could do with what we have.

By the way, I found an absolutely great fuel energy conversion website. It allows you to convert virtually any fuel to virtually any equivalence. It's where I got the numbers posted in the original question. Mark this one in your favorites, boys.

http://www.shec-labs.com/calc/fuel_energy_equivalence.php

For those of us who do need trucks here is a great vehicle that looks suitable for conversion to somethine like the electric vehicle.

http://www.rockymountainminitrucks.net/

Only slightly bigger than a quad. They can even be fitted with pad tracks for driving off the paved roads. Even with options this rig sells for less than $10,000.

Okay it isn't aerodynamic but it has much greater payload. And herabouts you simply do not drive fast, not if you want to stay connected with the road.

This is EXACTLY the sort of alternative we ought to be pursuing. Although this vehicle will not replace a pickup truck needed to haul trash over backwood trails, it makes a whole lot of sense to replace that 2 ton gas guzzler with a 1200 lb vehicle for local transport. Less energy to accomplish the same task. It doesn't matter so much what the source of energy is- the idea should be to use LESS energy overall...Where appropriate. And without sacrificing safety.

Here is another website for the conversions to mpg-equivalent

http://en.wikipedia.org/wiki/MPGE#Energy_conversions

Cheers Gary

One topic that has not been discussed is that the mpg reading is very dependent on how it is measured. The EPA ratings are averages over a specified driving cycle containing accelleration, braking a small amount of cruising and idling (during which time it obviously consumes fuel and goes nowhere for a 0 mpg component).

Google "brake specific fuel consumption" and look at the mpg vs speed curves. They fluctuate all over the place (depending mostly on the gearing). One of the sites gives mpg vs speed for a BMW 325i (transmission and gearing not specified). What is interesting to me is that both the EPA highway and EPA city numbers fall on a straight line that represents tankful averages while the instantaneous numbers represent the upper bound of what is possible by careful and informed driving. These numbers are 30-50% apart (depending on the number used for reference) and this is for the same vehicle.

As far as efficient vehicles go remember that in 1955 when Road and Track tested the Lotus 7 (in those day available as a kit car for about $ 750.00) it measured 55 mpg at 55 mph. We haven't come very far in 54 years. I haven't been able to dig up that road test to see what engine was in the test car, but it probably has a performance camshaft and carburetors, meaning that the engine probably didn't deliver very good specific fuel consumption numbers in the low power end of the operating range.

Does anyone have access to that road test?

Since we've had a lot of talk about electric vehicles, an email I got from Tesla Motors just blew me away.

They've got a 5 passenger sedan, which has a 300 mile all-electric range and a 45 Minute quick charge. http://www.teslamotors.com/models/index.php

This is what I want! Anybody got an extra 50 grand they'd be willing to contribute...in the interests of science, of course!

I really think your best chance would be to try a mainstream auto magazine such as www.hotrod.com . They have excellent tech articles and often respond to tech-mail that they view as reader worthy. Believe it or not any serious gear head is just as much about fuel efficiency as your local Prius owner. More efficiency equals more usable horsepower.

Good luck.

no it cannot be equated

A 300 HP engine gives on the flywheel 300 HP at the max rated speed, with a tolerance, let us say plus minus 3%.

The efficiency of the engine can reach up to 40 % that is of 100 brute power input, 60% is lost, as thermodynamic efficiency, as friction, heat transfer to the cooling water, heat transfer to the exhaust pipe, ancillary equipment, etc. This data are well known for each given engine, in terms of fuel consumption in g/CV hour at a given speed and power output.

Grosso modo, we could take 85 % the efficiency of the transmission (manual gearbox and differential gear assembly) and 90 % for the wheels and other equipment.

That gives 0,765 (76,5 %) the efficiency at max speed, that is, 229,50 HP at the wheels, more or less.

A 300HP engine needs an energy input of 300 / 0,40 =750 HP, and the global efficiency would be:

229,50 HP / 750 HP = 0,306, that is 30,6 % Global efficiency from the energy/time of the fuel in hp to the power at the wheels.

For a given vehicle, it is possible to calculate with very narrow tolerances the thrust at the wheels compared with the energy of the fuel / time.

A real example:

A small diesel traction engine, 60 CV at 4000 rpm, consumes, 230g / CV hour of fuel, that is:

0,230Kg /CV hour x 60 CV=13,8 Kg of fuel per hour is the brute input in one hour, to obtain 60 CV at the flywheel, at 4000 rpm.

The conversion of 13,8 Kg of fuel ( diesel ) / hour to CV is as follows:

13,8 Kg / hour x 10500 Kcal / Kg = 144900 Kcal / hour

144900 K cal / hour x 60 minutes /hour=2415 K cal / minute

2415 k cal / minute x 9,351 /100=225,82 CV

225,82 CV is the brute power input from the fuel tank to obtain 60 CV at the flywheel, at 4000 rpm.

Then, the global efficiency is:

60 / 225,82 =0,2656 that is 26,56 % global efficiency at 4000 rpm, at full power output of 60 CV.

At max torque output, the global efficiency is greater, maybe of 35 %. I have not calculated it.

A bigger engine would have a better global efficiency of about 30 % at maximum rpm an at max power output.

Conversion coefficients:

Kilogram- cal /minute x 0,09351= power in HP

1 CV x 0,986777= 1 HP

1HP x 1,0134 = 1 CV

For a gasoline powered engine the calculus is similar.

Arturo