On Board Energy Storage - Reason Automobile Engineers Chose (Choose) Fossil Fuel
My name is Rod Adams. I am addicted to my fossil fuel powered vehicles. (The accompanying photo was taken in July 1986.)
I thought it might be worth taking a few minutes to remember that people who developed internal combustion engines were not people focused on selling fossil fuels, they were people interested in solving a very real challenge - energy storage and delivery on a moving vehicle. When all factors are taken into account, fossil fuels provide a compact, lightweight form of energy that can be readily converted to power in device that is moving - sometimes very rapidly and without any connection to the earth.
There are certainly times in all of our lives when we feel like the big oil companies have us over a barrel, but their dominance came as a result of the high performance that their product gave to automobiles, trains, trucks, ships and aircraft. By many measures, their product remains the best technical choice available.
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The high performance results from chemistry and thermodynamics. Both carbon and hydrogen - the two main components of the hydrocarbon fossil fuels - will combine with oxygen in an exothermic - heat generating - reaction. In an environment with an excess of oxygen the reaction will result in a rather benign exhaust of carbon dioxide and water vapor plus a good quantity of heat.
When you look at the products of the reaction in a balanced equation - where all of the input elements are accounted for in the outputs - you will discover that the products weigh about 4.5 - 5 times as much as the hydrogen and carbon input.
The rest of the weight comes from oxygen. Here is the chemical equation often used to describe gasoline combustion (gasoline is actually a complex combination of various hydrocarbons each with different numbers of carbon and hydrogen atoms, but C8H18 is representative of them all.)
C8H18 + 12.5 O2 –> 8 CO2 + 9 H2O
By mass, only 114 units out of 514 units are in the gasoline, while the rest is in the oxygen. This is important for vehicles because oxygen does not need to be carried - it can be sucked in as needed. There is also no technical requirement - in the absence of new regulations - to capture and store the waste products and carry them around.
The people who developed the internal combustion engines were seeking a way to eliminate the weight of the water, piping and pressure vessels that limited the portability of steam engines. They figured out that they could use the hot products from combustion to directly move pistons and turbines as long as the input fuel did not have too many contaminants that could damage the engine parts. Coal and wood contain a lot of contaminants and both of those solid materials cannot be moved with pumps.
Batteries have to contain all of the chemicals on both sides of their energy releasing equation. The very best batteries available today can store about 0.4 MJ/kg (0.05 kw-hr/lb) including the cases and safety systems. In contrast, gasoline carries about 46 MJ/kg (5.7 kw-hrs/lb).
Even with a 20% efficient IC engine, a gasoline tank stores 20 times as much energy as a battery of equal weight. As the vehicle is moving it gets rid of some of that weight. Battery powered vehicles must carry the full weight of their energy source.
The energy density difference also plays a key role in the time that it takes to put more energy back on the vehicle once a fuel load is consumed. A two minute fill-up of a 12 gallon tank puts the equivalent of 87 kilowatt-hours into the vehicle, again, taking into account the 20% thermal efficiency.
87 kilowatt-hours in 2 minutes works out to 2.6 MegaWatts. Even with a 220 volt connection, that would require about 11,800 amperes of current. Just imagine the size of the electric cables for that current.
There are certainly places and applications where electric vehicles have a role, but it is worth remembering that at least five or six generations of engineers have looked very hard at trying to meet transportation needs and they keep coming back to the same fact - when you want to move a vehicle, you need power, (energy per unit time).
The more energy you can store on board the vehicle, the longer the power will be available. The more weight per unit energy that you need to add, the quicker you get to the diminishing returns where more and more of the energy is being used to drag the energy itself around. The quicker you can refill the tank, the more use you can get out of the vehicle and the more freedom and independence you can have.
After all, those are the truly valuable service provided by vehicles of all kinds - freedom and independence of movement.
Photo credit - Adams Family car circa 1986 - taken by the mom who is not in the photo.
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Great article Rod! It’s important for us to remember the sort of scale that we are all talking about.
I don’t see things a bleakly however. You are dead on about the disadvantage of weight in battery powered vehicles, but your calculation assumes energy only comes into the vehicle when plugged in, not when breaking (this still isn’t going to get past 12kA thought) and that the rest of the car’s weight stays the same.
What amazes me about auto design over the last few decades is how average fuel economy has gone down rather than up. Comparing energy requirements for current gas vehicles to the all-electric ones we need is comparing apples to oranges. With the bloated, steel framed gas cars we have now, only 1% of the gas energy actually accelerates the driver. THIS is the number that needs to change for your calculations change the way we think about cars.
I agree in that maybe when engineers first tried to resolved the transportations problems the best solution was combustion engines.
But i disagree in that thats remains the same through the time, since we have much more advancements and we became more and more aware of the problems of gas emissions. We have, as humankind the knowledge and the capacity to resolve most transportation problems without using fossil fuels. Just if we wanted to.
The storage technology is far advanced that a few years ago, and the storage weights can be compensated by electric cars engines.
For example (i love Tesla motors concept) Tesla has made an electric engine from the very idea that electrics engines are different, and should be different…
I recommend to read this:
http://www.teslamotors.com/efficiency/how_it_works.php
http://www.teslamotors.com/performance/electric_power.php
This is silly, according to the logic of this post we might as well all run our cars on liquefied propane or hydrogen which contain about 50 and 140 MJ/kg compared to pure gasoline at about 47. Why don’t we? Duh, it’s the price. The Ford Model T was designed to be run on ethanol, later it was changed to run on gasoline because it was so cheap. It’s all about the price, which (in the long term) is going to keep getting more expensive.
The 20% efficiency is also BS. That’s the efficiency of the engine by itself. After you include the transmission, rolling resistance, idling, AC, stereo, etc., the efficiency goes way down, estimates are as low as 5%.
Rod-
This is a little off-topic, but I like the VW van!
Mike:
I happen to like my air conditioning and stereo. Electric cars will also have rolling resistance that is exactly the same as a similar gasoline or diesel powered vehicle.
HMGD:
Tesla motor cars are wildly impractical for solving the problem of moving people from place to place, unless you happen to be a childless rich person with the ability to write a check for more than $100,000.
My current automobile is a Jetta TDI that gets and average of 41 MPG in combined city and highway driving. It has a tank that provides more than 500 miles between fill-ups. Many days it is carrying three or four people to work. It can also carry enough luggage for a week’s trip. (As an aside - my TDI used to get 47 MPG until the fuel switchover. Have any other diesel drivers noticed a reduction in fuel economy with the ultra low sulfur diesel?)
Justin:
There are two big and one minor reason why fuel economy for many cars has decreased. 1. They have gotten fat and need a weight reduction program. I remember what the original Altima, Civic, Jetta and Accord looked like. Today’s models are much bigger. 2. Increasing emissions standards have added fuel consuming equipment. 3. The measurement standards have changed so that they are more realistic, causing the stickers to show a lower number.
Also - braking is not an energy source. You can recover some of the energy instead of wasting it with frictional heat generation, but the energy providing the motion in the first place came from the gasoline or battery.
Tim - I liked it too. One of the reasons I chose that photo for this is to show the enormous box that we used to carry our stuff when the kids were growing up. Though we only had two children, the van was often full of swimmers, softball players, cheerleaders, or students.
This might be an over simplification, but I have noticed that a lot of electric car fans have not been parents and do not understand the needs of many of the people who use cars.
Oops - I forgot to address one more of Mike’s issues.
Though my comparison focused on energy density in terms of units of mass, there is also an important measure in terms of units of volume.
Hydrogen is a gas, so it takes up a lot more room per unit mass. In a volume the size of a typical gasoline tank you can store less than 1/3 of the energy of gasoline even with a 10,000 PSI storage system.
In fact, propane and natural gas are good candidates as vehicle fuels in certain markets where the prices are right.
I certainly agree there - price does matter and the price of gases varies much more around the globe than the price of liquid fuels.
I only mentioned Tesla Motor just to illustrate the advancements in electric car technology. But i more than aware that the Tesla Roadster itself is not the solution for everyone, and not for even most of us.
Now, the concept of Tesla engine its right and it seems to me that is quite impressive, because we are talking about a sport car type. Now imagine that concept in a sedan car. First it wont require all the power that a sport car does, and it can focus in range, and more mobility so it can transport 4 persons and get them farther…
So i for one, as the CEO of Volkswagen and many others said, i believe that the future does belongs to the electric car, and near future also.
Because overall electrics cars are becoming a better solution than fossil fuel based cars. Environmentally, economically, and in terms of efficients.
Just have in mind this, no one can denied that more than ever before electrics cars are been seen more and more feasible, and car production leaders are just beginning to join this revolution, many projects has just started to develop better storage solutions. Big projects in fact.
And for me its just a matter of adaptability if we wanted and we built the platform for electric transportation it will become a reality soon…
I´m just glad to know that there are plug in projects around USA.
Cya…
HMGD:
As you say “many projects has just started to develop better storage solutions”. I wish the projects good luck, but please understand that there are not going to be any big chemically based breakthroughs.
Desire for a solution is one thing, chemistry is another. I would also suggest that well publicized projects often have motives other than building production systems.
Hydrogen would work as well but no one wants to build that infrastructure. Biofuel could help but that is years away. Electricity could be of some use but there is no generation capacity for 20 million + electric autos.
Our best bet is to move to town, buy our food from other countries, just sit on our colective arsses and keep bombing some poor children in another country because they have “our” oil.
Just watching:
How would you store the hydrogen on board a car? Even if the supply was available, tanks pressurized to a rather extraordinary pressure of 10,000 psi or an amazingly cold −423.17 °F would contain only a fraction of the total energy available in a 20 gallon, atmospheric pressure and temperature fuel tank.
Biofuels work and are available today in similar energy densities as fossil fuel, but the total quantity of energy available is far less than the 80 million barrels of oil per day currently used. (I cannot recall the numbers exactly, but I think that the world’s total food production converted to biofuels would provide about 20% of the energy currently produced by the oil industry. That is not very sustainable - who wants a world full of cars without any drivers?)