h a l f b a k e r yYeah, I wish it made more sense too.
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My guess is this would already be in use if it worked. What I really want is to find out what the disadvantages are.
Portable oxygen concentrators for medical use simply pump air through a zeolite, which filters out the nitrogen. The output is ~90% pure O2. Dual tank concetrators give a steady flow
of 6 liters/minute, and they can't use much energy because they last fairly long on battery power.
If the purpose of turbos, superchargers, and NOS is to deliver more O2 to the cyclinder, why not use this to supplement the intake of a naturally aspirated engine? Is 6 L/min an insignificant amount?
I guess the first question I should ask is: if you replaced your NOS tank with oxygen, would it produce the same results? And if so, could an onboard oxygen concentrator provide enough O2 to be useful?
Hope I've made myself clear, and thanks for the feedback.
Power requirement for an oxygen concentrator (PDF)
http://www.thoracic...entOxygenDevice.pdf
40 watts portable (O2 as needed), 350-750 watts stationary (continuous--up to 10 L/min) [ldischler, Jun 19 2007]
[link]
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I'm interested in these medical oxygen concentrators - if the output is really 90% oxygen (up from 21% in air), then either the flow rate isn't very high, or you must be using quite a bit of power: this is fairly simple thermodynamics. |
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But actually, internal combustion engines don't really want too high an oxygen concentration: it's the expansion of nitrogen when it's heated as much as the expansion of the products of combustion that does the work. Heating nitrogen in the mixture also helps to keep the combustion temperature with the limits set by the materials the engine's made of. |
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The optimum ratio of oxygen:nitrogen, if we were in a position to choose, would probably be rather LOWER than the 1:4 of air, not higher. Real engines are designed for 1:4, and would perform worse if the ratio was changed in either direction - but I think you could build a more efficient engine to run in reduced oxygen, whereas one designed to run in increased oxygen would be less efficient (albeit more efficient than one designed to run in ordinary air, but actually running in increased oxygen). |
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The reason that increased nitrogen would allow a more efficient engine is this: more of the heat would be used heating the nitrogen going through the cylinders, where it actually does useful work, and less would be wasted heating air passing through the radiator. |
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I use supplemental oxygen... |
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//if we were in a position to choose, would probably be rather LOWER than the 1:4 of air, not higher// But that can't be, since cars that use nitrous oxide kits make significantly more power (albeit from using extra fuel) from the 33% oxygen in nitrous oxide, up from the 19% in air. |
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//Is 6 L/min an insignificant amount? |
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Yes. Consider a basic 2 liter engine. Every 2 rotations, the engine fills its entire displacement with fresh air, i.e. 2 liters. Therefore 6 liters of pure oxygen would run the engine for exactly 12 rotations, or approximately 0.008 seconds at 3000 rpm and wide-open throttle. If you stretched it out so the usage matched the consumption, you'd be putting just 0.001 liters of oxygen into the engine for each revolution. Given that air is 19% oxygen, the engine is already using .19 liters of oxygen every revolution, so you'll be adding roughly 0.6% more oxygen to the engine than it normally receives. |
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Assuming I didn't screw up my math somewhere. |
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[accurafan] There's no conflict between your statement and mine: the key being in that "extra fuel" thing. Higher oxygen levels could give you a better power:weight ratio (your statement), but at the cost of a lower efficiency (mine). |
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[absinthe] Indeed. Corrected. Brainslip... |
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[5th Earth] I'm not sure if you accounted for the fact that it takes 1 minute (60 seconds) for the 6 liters to be delivered. Unless you were assuming that the 6 liters of oxygen would be stored in a separate tank before it is released into the engine for a short burst of power, but if you did that then you could store more than 6 liters. |
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If this idea stored the oxygen before releasing it, then why not just use a pre-compressed oxygen tank. Or a bottle of liquid oxygen, but that has already been discussed on the halfbakery. |
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[5th Earth], I don't think you are accounting for the fact that due to intake resistance (throttle, intake valves) with respect to the tiny amount of time taken to complete an induction stroke, the cyclinder fills with air at a *very* low pressure. 2 litres of air in the cylinders is considerably fewer moles than 2 litres of atmospheric stuff. |
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/it's the expansion of nitrogen when it's heated as much as the expansion of the products of combustion that does the work./ |
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Medical oxygen supplies often have an inline water source to add water vapor. As discussed elsewhere, perhaps the huge expansion of liquid to gaseous H20 might subsitute for the missing nitrogen used by the engine. This idea then converges on the hydrogen peroxide injection idea which gets the best of both worlds. |
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OK, I looked for that water injection idea and cannot find it to link It has a good discussion. Help, please? |
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[BJS], I repeat, with a minor correction: If you stretched it out so the PRODUCTION matched the consumption, you'd be putting just 0.001 liters of oxygen into the engine for each revolution. Given that air is 19% oxygen, the engine is already using .19 liters of oxygen every revolution, so you'll be adding roughly 0.6% more oxygen to the engine than it normally receives. |
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In other words, if you are producing oxygen at 6 liters per minute, that's exactly the same as a 6 liter tank being emptied in one minute. At that rate of production/consumption, the enrichment will only be 0.6% over normal atmospheric levels, at my example of 3000 RPM and fully open throttle. |
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But then, this is with my initial assumptions. As [Texticle] pointed out, the air density in the engine is lower than atmospheric density. How much lower, I don't know. |
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Ok, then. I didn't understand what you meant exactly. |
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Each litre of gasoline uses 1848 litres of oxygen to fully combust. (from a quick internet search) |
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So if your car consumes 6/1848 litres of gasoline per minute (approximately 0.003 litres per minute), then this invention might be useful. |
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I'd estimate an efficient car uses 0.1 litres per minute. |
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This would become interesting if you start thinking in terms of injecting the oxygen (leaving questions of production aside for the moment) instead of using intake valves. All kinds of possibilities, however theoretical, open up. |
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[bungston] You can indeed use water instead of nitrogen as the additional working medium over and above the combustion products - indeed an engine with water injection (in addition to atmospheric nitrogen, not instead of it) has been demonstrated, with slightly better efficiency than a standard IC engine (in line with my statement that a slightly higher percentage of nitrogen would allow more efficient engines). The efficiency gain from water injection is small, and isn't sufficient to justify the extra complexity or the need for a water supply - especially since the engine would have to run on reduced throttle (or risk overheating) if the water supply ran out. |
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[5th Earth] At wide open throttle and middling revs, air density in the cylinders just before ignition is typically around 0.3 bar in a normally aspirated engine. In a turbocharged engine, it can be as much as 1 bar, possibly even more than that. Your analysis is pretty nearly correct - the error is a small factor, not nearly enough to upset your argument, which is absolutely correct. |
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[Cosh i Pi], surely you mean bdc just before the compression stroke starts? What you're saying is 30% volumetric efficiency is typical (or are you saying that around 4% volumetric efficiency is typical?) |
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That air at +/- 30% atmospheric is then compressed. With an 8:1 compression ratio the pressure just before ignition should be around 2.4 bar. If the figure of 30% is correct, that would be the sort of pressure range you aim for with SI engines running on conventional petrol/gasoline, regardless of whether they are supercharged or not. |
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The aim of supercharging is not a greater pressure just before ignition, but a greater mass of charge at the same pressure as with a naturally aspirated engine. That, rather than any consideration of durability or physical strength, is why supercharged engines require lower static compression ratios. Nor do engine-driven superchargers "waste" more power per unit of charge mass than the pistons do during the intake and compression strokes. |
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[ned] Indeed, that's exactly what I meant (bdc that is). Brainslip - it's something to do with age... :( ... that's my excuse, and I'm sticking to it...until I can think of a better one... |
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One of the key points about turbocharged engines is that they can maintain high pressures at higher revs - by 3000 rpm, normally aspirated engines are having difficulty getting as much air into the cylinders as you want. |
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Electrolysis. That's what we need. Splitting water into oxygen & hydrogen, storing it up in a tank and unleashing the lot when a boost is desired. Probably squirting some un-split water in for cooling purposes too. |
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All powered by a solar panel on the roof to keep hippies happy... |
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Ozone - oxygen's violent cousin. Much better to add to the mix:O) |
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