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Originally Posted by bobkoure
Hmmm... where to start...?
First, in a diesel engine (and to a lesser extent non diesel IC) the fuel/air mixture that's combusting is typically surrounded by just air. If you were going to go in the adiabatic direction, you'd have to design your combustion chamber to reduce turbulence so as to have essentially an "air jacket" around the combustion process. Have a look at the way ported 2 stroke engines control gas flow.
The reason to (at least attempt to) go with a fuel cell over a hydrogen-driven IC is to reduce NOX. I'd be surprised if the exhaust from that BMW was much if any cleaner than that of a comparable, fuel injected, catalytic cleaned, gas powered model - particularly if you include the pollution produced to produce the fuel to drive the two vehicles the same distance. Maybe we'll get to cheap clean hydrogen, but it doesn't seem to be either yet. The only places in the world where electrolysis looks to be a viable option are places with lots of excess hydropower - like New Zealand - and they currently export most of their excess hydropower as aluminum (primary component being electricity to smelt bauxite).
Finally, just slapping a turbo on a Prius doesn't seem like a good idea at all. That's a modified miller cycle engine in there. So you replace the pistons and cams (and maybe shim the deck) - you've still got an engine that's turned on and off a lot and the engine management is not expecting to have to deal with the additional gas inertia involved with a turbo.
Back to carbon nanotubes...
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I assume your talking about stratified (areas of fuel surrounded by air) engines (not commonly used as there are problems with NOx, most modern (SI - spark ignition) engines don’t work like this (although a lot of older ones claim too)
Increasing turbulence is an engine design goal. Engines contain some of the most turbulent flows that you will ever find. The reason is your typical flame has a combustion speed of 0.6m/s (ideal speed) however this is not fast enough to allow good combustion (7000rpm do the math on cylinder sizes). To increase this engine designers increase turbulence and use swirl (rotating air caused by opening one valve more than the other, which is why two inlet valves are common) and tumble (air falling over it self to get in to the engine). Creating an air jacket in a situation like this is near enough impossible, you’ve got a flame moving at 3m/s its going to fill a cylinder. Also by your reasoning your going to need a thick thermal boundary layer about the cylinder head which is not going to happen.
Your right about NOx but you have to consider that fuel cell bi products (the catalyst) are nasty stuff as well and that hydrogen powered IC is more efficient (if I’m reading things right twice as efficient, due to higher energy density of hydrogen and faster flame speed). Also replacing although electric motors and servicing them is a big hassle.
If your going to industrially make hydrogen you use a shift reactor, basically you burn (heat a lot more like) hydrocarbons in little air to produce carbon monoxide this can then be reacted with water to make carbon dioxide and hydrogen. This produces a little power as well so you can do it for power plants. This is a current plan with clean coal technologies which burn coal this way and then burn the hydrogen. The CO2 can then be disposed if you want by basically piping it underground (into old oil fields) meaning you’ve got zero emission oil.
Nanotubes arent commericalised yet, personally im still waiting for space stations i can visit that spin.