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Post by GTCGreg on Jan 19, 2016 16:29:19 GMT
You wouldn't need a spark plug. Kind of like a diesel. but you don't want that happening outside the cylinder. No, that would be a bad thing. Carrying around enough O 2 in it's gaseous state is also not easy and LOX also has it's share of storage issues. Maybe some kind of atmospheric O 2 concentrator, but they usually don't do large volumes of gas too easily. |
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Post by the light works on Jan 19, 2016 16:41:57 GMT
but you don't want that happening outside the cylinder. No, that would be a bad thing. Carrying around enough O 2 in it's gaseous state is also not easy and LOX also has it's share of storage issues. Maybe some kind of atmospheric O 2 concentrator, but they usually don't do large volumes of gas too easily. right - and running pure oxygen as an oxidizer would tend to make the combustion rate much too fast for a piston engine using it to oxygenate an oxygen depleted gas mixture would be a much more plausible concept. |
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Post by c64 on Jan 19, 2016 19:51:57 GMT
Pure oxygen can't work. You need the nitrogen since the volume of CO₂ and especially liquid H₂O is a lot smaller than the same mass of pure oxygen and fuel.
The internal combustion engine depends on creating a pressure by creating heat from the combustion. It is basically the hot nitrogen which drives the pistons, the oxygen and fuel is required to heat it up real quick, pure oxygen and fuel doesn't create much pressure, just heat.
Hydrogen and oxygen is easier to calculate since common fuel for cars is a mixture of complex hydrocarbons of many different forms.
Burning hydrogen and oxygen is more simple:
2 g H₂+ 16 g O₂ = 18 g H₂O when accounting the masses. So the major mass of water is actually the oxygen. Lets ignore the hydrogen to simplify things:
1 kg of steam (the result of burning hydrogen) is 1673 liter,
1 kg of oxygen is ~740 liter.
So after burning the fuel, the result is only a bit more than twice as big so if there wouldn't be the heat, you would create roughly twice the atmospheric pressure, 2bar or 28 PSI which is what you create using a small bicycle pump.
Even worse, if the steam condenses, your 1kg oxygen turns into 1 liter of volume! So if the heat is gone, you actually have a very good vacuum!
It is the heat difference which creates a difference in volume which drives the pistons. And pure oxygen would generate a tremendous amount of heat expanding a small mass of gasses and you can't cool it down by too much or the steam would condense destroying all pressure. You could make a machine which could endure the heat and prevent condensation in order to work but that won't work like an internal combustion engine.
You need the nitrogen which actually does most of the energy conversion (heat to mechanical energy) so you still need the air.
Also pure nitrogen under pressure is highly reactive. That's why you may not grease treads of oxygen systems. The engine oil would combust and metals would corrode instantly under high pressure as in an IC engine.
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Post by GTCGreg on Jan 19, 2016 20:41:33 GMT
Pure oxygen can't work. You need the nitrogen since the volume of CO₂ and especially liquid H₂O is a lot smaller than the same mass of pure oxygen and fuel. The internal combustion engine depends on creating a pressure by creating heat from the combustion. It is basically the hot nitrogen which drives the pistons, the oxygen and fuel is required to heat it up real quick, pure oxygen and fuel doesn't create much pressure, just heat. Hydrogen and oxygen is easier to calculate since common fuel for cars is a mixture of complex hydrocarbons of many different forms. Burning hydrogen and oxygen is more simple: 2 g H₂+ 16 g O₂ = 18 g H₂O when accounting the masses. So the major mass of water is actually the oxygen. Lets ignore the hydrogen to simplify things: 1 kg of steam (the result of burning hydrogen) is 1673 liter, 1 kg of oxygen is ~740 liter. So after burning the fuel, the result is only a bit more than twice as big so if there wouldn't be the heat, you would create roughly twice the atmospheric pressure, 2bar or 28 PSI which is what you create using a small bicycle pump. Even worse, if the steam condenses, your 1kg oxygen turns into 1 liter of volume! So if the heat is gone, you actually have a very good vacuum! It is the heat difference which creates a difference in volume which drives the pistons. And pure oxygen would generate a tremendous amount of heat expanding a small mass of gasses and you can't cool it down by too much or the steam would condense destroying all pressure. You could make a machine which could endure the heat and prevent condensation in order to work but that won't work like an internal combustion engine. You need the nitrogen which actually does most of the energy conversion (heat to mechanical energy) so you still need the air. Also pure nitrogen under pressure is highly reactive. That's why you may not grease treads of oxygen systems. The engine oil would combust and metals would corrode instantly under high pressure as in an IC engine. How do you KNOW this stuff? I've taken thermodynamics classes in college and studied all the common thermal cycles and they never explained it as well as you do. |
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Post by the light works on Jan 19, 2016 20:53:24 GMT
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Post by GTCGreg on Jan 19, 2016 21:23:24 GMT
But reading that article, it sounds like they do use it. But C64 is talking about it's ability to create pressure in a closed system, not the burn velocity. He's saying there isn't enough mass there to create sufficient pressure. Since E=1/2MV 2 higher velocity means a larger release of energy (squared term) than the mass contributes. In a rocket engine, it's the velocity of the escaping gas that propels the rocket forward. In an IC engine, it's the pressure on the piston that does the work. At least that's the way I interpret it, but then, I'm no rocket scientist. |
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Post by the light works on Jan 19, 2016 22:17:59 GMT
But reading that article, it sounds like they do use it. it seems your computer doesn't support the sarcasm font I agree with his conclusion, (won't work well) but not his reasons. you get a high coefficient of expansion out of burning liquefied or even compressed oxygen and hydrogen. - because of the very energetic combustion. but because of the very energetic combustion, you have an engine that will break itself if it is not built to withstand it - C64 is assuming the fuel and oxygen are ignited at atmospheric pressure, which is what makes his coefficient of expansion so low. atmospheric pressure engines can be made to function - I forget what the name of them is - but the traditional reciprocating engine is not an atmospheric pressure engine. it looks like the current highest performance engine runs at a compression ratio of 14:1. figure about 10:1 average. so instead of the oxygen/hydrogen mixture expanding to 2L in a 1L cylinder, it is expanding to 2L in a .1L cylinder. - assuming it is fed at atmospheric pressure with the piston down. let the cylinder purge at BDC, and inject hydrogen and oxygen at 10 atmospheres just before ignition and you have that plus whatever residual steam from the previous cycle superheating and expanding. add a water injection, and you're back to the question of how to hold the thing together. but then it comes back to the question of whether you are creating a high tech solution to a low tech problem. |
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Post by GTCGreg on Jan 19, 2016 22:36:31 GMT
But reading that article, it sounds like they do use it. it seems your computer doesn't support the sarcasm font I agree with his conclusion, (won't work well) but not his reasons. you get a high coefficient of expansion out of burning liquefied or even compressed oxygen and hydrogen. - because of the very energetic combustion. but because of the very energetic combustion, you have an engine that will break itself if it is not built to withstand it - C64 is assuming the fuel and oxygen are ignited at atmospheric pressure, which is what makes his coefficient of expansion so low. atmospheric pressure engines can be made to function - I forget what the name of them is - but the traditional reciprocating engine is not an atmospheric pressure engine. it looks like the current highest performance engine runs at a compression ratio of 14:1. figure about 10:1 average. so instead of the oxygen/hydrogen mixture expanding to 2L in a 1L cylinder, it is expanding to 2L in a .1L cylinder. - assuming it is fed at atmospheric pressure with the piston down. let the cylinder purge at BDC, and inject hydrogen and oxygen at 10 atmospheres just before ignition and you have that plus whatever residual steam from the previous cycle superheating and expanding. add a water injection, and you're back to the question of how to hold the thing together. but then it comes back to the question of whether you are creating a high tech solution to a low tech problem. You both seem to make sense, but I really don't know enough about this to debate it one way or the other. I'll just sit back and follow the discussion and hopefully learn something. |
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Post by c64 on Jan 19, 2016 22:51:18 GMT
But reading that article, it sounds like they do use it. But C64 is talking about it's ability to create pressure in a closed system, not the burn velocity. He's saying there isn't enough mass there to create sufficient pressure. Since E=1/2MV 2 higher velocity means a larger release of energy (squared term) than the mass contributes. In a rocket engine, it's the velocity of the escaping gas that propels the rocket forward. In an IC engine, it's the pressure on the piston that does the work. At least that's the way I interpret it, but then, I'm no rocket scientist. Correct. A rocket works by "actio and reactio". Sit on a swivel chair (with wheels) and toss away something heavy. You and the chair will move into the direction. The harder you toss, the faster you go backwards. Once the tossing is done, it doesn't matter what happens to the object you have tossed, it can change in any way possible or impossible. Only mass and the force you use to toss it matters, not the shape or physical condition. For a piston, only the pressure and the effective piston surface matters since this translates directly to pounds forcing the piston down. So for a rocket, it doesn't matter if the pressure is gone right behind the nozzle, all that matters is the force inside the nozzle and the mass it ejects per time while in an ICE, the pressure is all that matters. And what makes an ICE so horrible inefficient is that you can't spend all the pressure before you need to eject it. A 100% efficient engine wouldn't need a muffler since there is no pressure released out of a sudden. The rule of thumb is that a "perfect" ICE gives you 50% in efficiency. There are engines which are rated 60% or (slightly) better, but this is based on a technical rating system. Physically there is a lot more energy involved as accounted for. For example, inside a furnace, the heat of the flame is used as the reference. 100% is when all the heat of the flame is harvested. And this is impossible. A caloric value system can reach 120%. It also can't harvest all the heat of the flame - but burning hydrocarbons gives you steam as a waste product and by condensing steam, you get liquid water and energy which wasn't accounted for the flame itself. The technical rating ignores this and that is why a caloric value furnace has more than 100% efficiency and can cut your heating bill by 30% easily. 60% if you replace a simple classic furnace with a state of the art computer controlled caloric value one. |
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Post by c64 on Jan 19, 2016 22:54:52 GMT
But reading that article, it sounds like they do use it. it seems your computer doesn't support the sarcasm font I agree with his conclusion, (won't work well) but not his reasons. you get a high coefficient of expansion out of burning liquefied or even compressed oxygen and hydrogen. - because of the very energetic combustion. but because of the very energetic combustion, you have an engine that will break itself if it is not built to withstand it - C64 is assuming the fuel and oxygen are ignited at atmospheric pressure, which is what makes his coefficient of expansion so low. atmospheric pressure engines can be made to function - I forget what the name of them is - but the traditional reciprocating engine is not an atmospheric pressure engine. it looks like the current highest performance engine runs at a compression ratio of 14:1. figure about 10:1 average. so instead of the oxygen/hydrogen mixture expanding to 2L in a 1L cylinder, it is expanding to 2L in a .1L cylinder. - assuming it is fed at atmospheric pressure with the piston down. let the cylinder purge at BDC, and inject hydrogen and oxygen at 10 atmospheres just before ignition and you have that plus whatever residual steam from the previous cycle superheating and expanding. add a water injection, and you're back to the question of how to hold the thing together. but then it comes back to the question of whether you are creating a high tech solution to a low tech problem. It doesn't matter at which pressure you operate if you step back and look at the entire system. You start with atmospheric pressure and you eject the exhaust to atmospheric pressure. |
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Post by the light works on Jan 20, 2016 1:34:45 GMT
it seems your computer doesn't support the sarcasm font I agree with his conclusion, (won't work well) but not his reasons. you get a high coefficient of expansion out of burning liquefied or even compressed oxygen and hydrogen. - because of the very energetic combustion. but because of the very energetic combustion, you have an engine that will break itself if it is not built to withstand it - C64 is assuming the fuel and oxygen are ignited at atmospheric pressure, which is what makes his coefficient of expansion so low. atmospheric pressure engines can be made to function - I forget what the name of them is - but the traditional reciprocating engine is not an atmospheric pressure engine. it looks like the current highest performance engine runs at a compression ratio of 14:1. figure about 10:1 average. so instead of the oxygen/hydrogen mixture expanding to 2L in a 1L cylinder, it is expanding to 2L in a .1L cylinder. - assuming it is fed at atmospheric pressure with the piston down. let the cylinder purge at BDC, and inject hydrogen and oxygen at 10 atmospheres just before ignition and you have that plus whatever residual steam from the previous cycle superheating and expanding. add a water injection, and you're back to the question of how to hold the thing together. but then it comes back to the question of whether you are creating a high tech solution to a low tech problem. It doesn't matter at which pressure you operate if you step back and look at the entire system. You start with atmospheric pressure and you eject the exhaust to atmospheric pressure. and that is why they don't bother to put turbochargers on engines. [/sarcasm] |
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Post by GTCGreg on Jan 20, 2016 1:51:12 GMT
It doesn't matter at which pressure you operate if you step back and look at the entire system. You start with atmospheric pressure and you eject the exhaust to atmospheric pressure. and that is why they don't bother to put turbochargers on engines. [/sarcasm] If you're injecting both the O and the H directly into the engine, what are you going to super charge? I thought the whole idea was to operate without any air intake at all. Or am I entirely misunderstanding the concept? |
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Post by the light works on Jan 20, 2016 4:35:26 GMT
and that is why they don't bother to put turbochargers on engines. [/sarcasm] If you're injecting both the O and the H directly into the engine, what are you going to super charge? I thought the whole idea was to operate without any air intake at all. Or am I entirely misunderstanding the concept? you are. c64 is saying engines feed from atmospheric pressure. the fact that supercharging is effective enough that they actually use it demonstrates that it is not a rule that engines must start from atmospheric pressure. if you are injecting fuel and oxygen, you can inject it at whatever pressure you want to. |
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Post by GTCGreg on Jan 20, 2016 5:14:24 GMT
If you're injecting both the O and the H directly into the engine, what are you going to super charge? I thought the whole idea was to operate without any air intake at all. Or am I entirely misunderstanding the concept? you are. c64 is saying engines feed from atmospheric pressure. the fact that supercharging is effective enough that they actually use it demonstrates that it is not a rule that engines must start from atmospheric pressure. if you are injecting fuel and oxygen, you can inject it at whatever pressure you want to. I understand that you can inject at any pressure you want. I think what you are saying is that if you inject enough volume, and hence pressure, of H and O, the burning of the fuel will produce enough pressure on the piston that the engine will operate properly. I think what C is saying is that it will melt first. Again, I'm not arguing one way or the other. I honestly don't know. |
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Post by the light works on Jan 20, 2016 5:39:06 GMT
you are. c64 is saying engines feed from atmospheric pressure. the fact that supercharging is effective enough that they actually use it demonstrates that it is not a rule that engines must start from atmospheric pressure. if you are injecting fuel and oxygen, you can inject it at whatever pressure you want to. I understand that you can inject at any pressure you want. I think what you are saying is that if you inject enough volume, and hence pressure, of H and O, the burning of the fuel will produce enough pressure on the piston that the engine will operate properly. I think what C is saying is that it will melt first. Again, I'm not arguing one way or the other. I honestly don't know. vice versa, C is saying it won't develop enough pressure to push the piston, I'm saying you can use enough to push the piston, but if you try it with a standard gasoline engine, you will probably have to go look for the cylinder heads after you try it. |
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Post by GTCGreg on Jan 20, 2016 6:21:51 GMT
I understand that you can inject at any pressure you want. I think what you are saying is that if you inject enough volume, and hence pressure, of H and O, the burning of the fuel will produce enough pressure on the piston that the engine will operate properly. I think what C is saying is that it will melt first. Again, I'm not arguing one way or the other. I honestly don't know. vice versa, C is saying it won't develop enough pressure to push the piston, I'm saying you can use enough to push the piston, but if you try it with a standard gasoline engine, you will probably have to go look for the cylinder heads after you try it. Too bad SR-Racing doesn't come around anymore. He's probably tried it. |
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Post by silverdragon on Jan 20, 2016 8:41:52 GMT
[edit this post written before I read this page in full, so thats before I read that some of you may have reached the same ideas....]
Scrap the above LOX/Hydrogen fuel idea, I just watched a thing on testing the booster rockets for the space shuttle, when you know what temp a bottle of LOX or Hydrogen "freezes" at, you may want to think cooling on an infernal combustion engine, as it the temp change from LOX to Burnt would create all kinds of problems for the pipes supplying the LOX to the engine, and then the cooling of the LOX expanding may even freeze the vehicle and anyone near it.
When I say the bottle of lox freezes, I dont mean the Lox freezing, I mean anything else near it, its a sort of cryogenic type freezing temp. it will effectively freeze the air around it.
The space shuttle rocket nozzle is kept from melting up when the engine is running by pumping liquid oxygen through vent pipes on the outside of the combustion chamber..... otherwise the whole engine would have just melted....
Going from LOX to burn fuel would therefore cause all kinds of thermal shock problems for the whole engine.
I aint saying it cant be done, just that we aint NASA here, and maybe we cant try this at home.
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Post by GTCGreg on Jan 20, 2016 10:02:42 GMT
What a party pooper. You mean I have to put all these parts away?
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Post by the light works on Jan 20, 2016 14:47:12 GMT
the nickname "ice cube" gets applied to any firefighter who comes out of a fire with ice on his regulator from sucking down his bottle too fast.
looking at the idea of a rebreather system that used the oxygen to oxygenate the exhaust gas (using the exhaust for filler to have a 10% oxygen mix) might still work out.
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Post by c64 on Jan 20, 2016 21:47:36 GMT
It doesn't matter at which pressure you operate if you step back and look at the entire system. You start with atmospheric pressure and you eject the exhaust to atmospheric pressure. and that is why they don't bother to put turbochargers on engines. [/sarcasm] Except accelerating the combustion somewhat, all a turbo charger does is to increase the effective engine displacement so a small, lightweight engine can have the power of a much bigger one while staying mostly as agile as a small engine. Also you can run the engine without turbo for small power throughputs so you use less fuel for driving slow or idling compared to an engine with the large displacement the turbo simulates when you need a lot of power. |
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