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Hydrogen and Internal Combustion (IC) engines

In response to Josh's question in episode 798, and maybe saving Molly a little research work (I guess my email last Friday didn't get through), there actually is research being done on running internal combustion engines on hydrogen gas. According to the latest research, such an engine can be as efficient as the best diesel engines. It's also thought that a hybrid car with a hydrogen-powered IC engine would have the same mileage as a hydrogen fuel cell car, but at a fraction of the cost (see http://www.abc.net.au/science/articles/2008/06/16/2273538.htm )

There were also several papers presented on storing and using hydrogen in IC engines at the recent 17th World Hydrogen Energy Conference. Of course, the problem of safely storing hydrogen in a car for use in an IC engine is exactly the same problem as storing hydrogen for use in a fuel cell car. See http://www.whec2008.com

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BMW H2R

In reply to: Hydrogen and Internal Combustion (IC) engines

BMW developed a super sleek race car that runs completely on liquid hydrogen. Under the hood is a 6.0-liter, V-12, 232 hp hydrogen-powered engine. This slightly modified gas engine can propel the car to 187 mph. Hydrogen has a few advantages over gas.

1. Hydrogen is very abundant
2. Hydrogen burns clean, when it burns it is combines with oxygen to produce H20 or water, this water can be reused to make hydrogen again.
3. Hydrogen weighs less than gas and produces more power.
4. Hydrogen burns faster and cooler than gas.

The BMW H2R set 9 international speed records

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OK here's the scoop on hydrogen

In reply to: Hydrogen and Internal Combustion (IC) engines

Hydrogen is a pretty decent fuel but it has some annoying problems. First of all you can't just pump it up out of the ground- you have to make it. Which means it is not a prime-mover. It is more like a kind of battery that you charge up with some other prime mover- like oil, gas, sunshine or wind. But in any event you have to make it and that is an inefficiency that has to be overcome.

Hydrogen is of course a gas- and a really light one. Really light- and this means you have to store it at elevated pressures or liquify it. It takes a ton of energy to compress it and move it around. Liquifying it is even more energy intensive. So storing it is a real problem. Even when liquified it has a density of only 4.4 lbm/cubic foot. This is like a tenth of gasoline- so even as a liquid it is more like a gas. So to store a set amount of energy it takes a pretty big, more complex, more costly fuel tank.

If you choose the high pressure route we are talking about grandma handling a 4000 psig hose at the gas station- a damaged hose or refueling interface and you could start a really nice fire almost by accident. Also since we are talking about gas it takes a long time to fill the tank- it is like filling a SCUBA tank and that is not a 2 minute job. The act of filling the car's tank will cause it to become very hot- it resists the further inflow of gas and you have to do work to push that gas in there. Moving gas around like this turns out to be very inefficient. If you want to slam-fill a tank it will also have to be designed to take the high peak temps - making it much heavier. The material of choice for such tanks is graphite fiber composite and it doesn't want to be at 400F! Even if you did cram the fuel in it and had a tank that could handle the heat the density of the H2 in the tank would be low- when it cooled down you would see that the tank was only half full or so.

Also, hydrogen doesn't like being confined. Its itty bitty molecules will just go through materials that can otherwise contain gases. In other words it leaks when there is no leak. This diffusion is a problem when you want to use thin, light vessels to contain it. Or use ordinary seals at joints in your plumbing. In some (many) materials it gets into them and the hydrogen molecules make the metal very brittle- like a glass. This is a particular problem at high pressures. These issues make it a relatively high safety concern since leakage is very likely and it could be in a confined space. Hydrogen will burn over a range of mixture ratios that other fuels won't- meaning it can catch fire at only a 5% concentration or up to 95%. And you don't need a classic ignition source like a big spark. It can light due to catalytic effects with some metals or even small electrical discharges-like nearly invisible ones. So it is easy to light. And unlike carbon-bearing fuels it burns invisibly in the infrared- you can't see the flame normally. There would be a color though when you walked into the flame. This makes refueling a big problem- far more dangerous than even volatile F1 fuel. You could never fuel an F1 car with H2 in the 6 seconds they do now. Unless you replace the storage vessel too.

As an IC engine fuel it could work but H2 has a high flame temperature and we are still talking about burning it with air- which has nitrogen in it. This means that at these elevated temps you can form oxides of nitrogen which are classical pollutants. You have to mitigate this- which you don't have to do with a fuel cell. But of course right now fuel cells are expensive- though they can be unbelievably simple when you see one- like a stack of pancakes bolted together. Eventually we'll get them but it will be a while.

So take it from someone who designs with H2 on a daily basis- don't do it unless it confers a huge advantage. For example the use of hydrogen on a booster rocket- the stage that lights on the ground- is not a benefit as compared to kerosene. This is one of the lessons of Shuttle- though you would never know it listening to NASA. Hydrogen only really shines as an upper stage fuel.

BTW I am a huge F1 fan and would love to see them push more widely useful technologies- but H2 is not really a great choice.

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