Quote:
Originally Posted by pasadena_commut
Nitrogen could be used instead.
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Or, come to think of it, oxygen. This wouldn't save fuel as a retrofit in an existing motor. However, it could let a car with a very small motor produce bursts of energy, for acceleration or climbing hills, somewhat similar to a turbocharger. The atmosphere is 20% oxygen so adding 10% by volume pure oxygen to that would raise the oxygen level by nearly 50% (that is, to nearly 30%), which would let the motor burn 50% more fuel per cycle without changing the compression. (Ignoring for the moment complications such as the tendency for this high oxygen mix to ignite earlier.) Carrying around a tank of strong oxidizer would be a safety concern though, and the tank would have to be as far away from the gas as possible. If the oxygen tank ruptured in a crash, assuming the pressure related damage was contained by design, there would be a brief period of severe fire and explosion danger while the local oxygen levels are high, but this would dissipate quickly. It wouldn't be like a ruptured fuel tank, which leaves flamable liquid on the ground for a long time. Of course if both the oxygen and fuel tanks rupture at once, and there is any heat or sparks, it would be more boom than burn.
In theory a car could also be fitted with equipment to concentrate oxygen directly from the atmosphere while it drives. Depending on the amount of energy this takes, it might end up energetically favorable if the normally aspirated motor was enough for 95% of driving, and it used that time to top off a small oxygen tank. No idea which separation technology would be used though, because commercial oxygen separation is cryogenic and the equipment is very large - that technology is not likely to miniaturize well. In any case, the waste product of the separation is just the other normal atmospheric gases, so releasing them back into the air should not count as pollution. Hmm, carried to an extreme, where the car runs entirely on separated oxygen, there could be some substantial pollution related benefits - no Nitrogen to form NOx and on a lean burn the extra oxygen would convert any CO all the way to CO2. That could allow the elimination of the catalytic converter(s), which would recover some of the weight of the oxygen separating equipment. Or go whole hog and carry equivalent tanks of both fuel and oxidizer, both of which to be filled at the "gas" station. That would be one heck of a dangerous gas station though!