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#11
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In article , Bryan Martin
wrote: Lets see. You take energy from the electrical system to crack water into H2 and O2. Then you pipe the H2 into the engine with the gasoline where it will combine with oxygen to form water. The article I read doesn't say what you do with the O2, I guess you just vent that to the atmosphere. Seeing as how conversion of water into H2 and O2 is not 100% efficient due to losses in the wiring and such and seeing as how burning H2 with air is also not 100% efficient, there is no possible way to get a net energy gain out of this system. In fact this system will result in a net loss and lower fuel economy since the electrical energy to drive the electrolysis must come eventually from the alternator which is driven by the engine. That's the Second Law of Thermodynamics: in ANY energy conversion scheme there is inefficiency and therefore loss. The only way to get any kind of gain out of this is to inject the water itself into the engine. This might give some power gain in the short term but pumping salt water into your fuel system and engine will certainly do them no good in the long run. The article specifically mentioned putting water and an electrolyte (salt) into the booster tank. Agree on the salt. Water injection only works to increase power if you increase engine compression. The higher compression ratio gets you more power, the water injection cools the charge and acts like an octane booster. Just don't run out of water... If you run water without increasing compression ratio, you will get a little due to the density increase of the air, but it's not major. -- Harry Andreas Engineering raconteur |
#12
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Harry Andreas wrote: In article , Bryan Martin wrote: ... The only way to get any kind of gain out of this is to inject the water itself into the engine. This might give some power gain in the short term but pumping salt water into your fuel system and engine will certainly do them no good in the long run. The article specifically mentioned putting water and an electrolyte (salt) into the booster tank. Agree on the salt. Someone else wrote that it was KOH that was added, not a salt. Dunno why, if it was just a water injection system. Would the KOH help to control NOx emmissions? Could the KOH be threre for boiling point elevation? Water injection only works to increase power if you increase engine compression. The higher compression ratio gets you more power, the water injection cools the charge and acts like an octane booster. Just don't run out of water... If you are injecting atomized (e.g. liquid) water into the cylinders then during the power stroke the water will evaporate. That evaporation converts heat to pressure at constant temperature. You get a higher compression raio without a higher temperature. Does THAT help to control NOx, in addition to giving you more power? If you run water without increasing compression ratio, you will get a little due to the density increase of the air, but it's not major. IIUC, adding the water will increase the compression ratio due to the phase change of the water. Water injection increases the compression ratio without changing the geometry of the cylinder and piston, right? -- FF |
#13
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#14
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Water can reduce the charge termperature as it evaporates in the cylinder
which can increase the charge mass a little, but mostly it improves knock resistance by cooling the charge and increasing the specific heat of the charge mass. But to really take advantage you have to either increase the compression ratio or boost. NOx is recduced somewhat since the peak temperatures are reduced. If you are trying to change the fuel chemestry to get more energy out - you have to put energy in. Lose - lose. If you are trying to make the fuel burn "better" to make it "all" burn - gasoline burns just fine. Unburned fuel in the exhaust comes from three primary sources - mixture that is pushed into the crevices around the piston / sparkplug / etc. where it can't burn (it comes out of the crevices during the exhaust stroke), mixture that is quenched at the cylinder walls due to heat loss. And excess fuel from running rich. The bulk of the charge mass burns just fine. Cow magnets, magic additives, whatever aren't going to change any of that. If making the fuel burn "better" made it burn faster - Well, if it really worked all you would do is destroy the engine because the faster combustion would result in detonation. -- Geoff the sea hawk at wow way d0t com remove spaces and make the obvious substitutions to reply by mail Spell checking is left as an excercise for the reader. |
#15
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In article , "Capt. Geoffry
Thorpe" The Sea Hawk at wow way d0t com wrote: Water can reduce the charge termperature as it evaporates in the cylinder which can increase the charge mass a little, but mostly it improves knock resistance by cooling the charge and increasing the specific heat of the charge mass. But to really take advantage you have to either increase the compression ratio or boost. NOx is recduced somewhat since the peak temperatures are reduced. If you are trying to change the fuel chemestry to get more energy out - you have to put energy in. Lose - lose. If you are trying to make the fuel burn "better" to make it "all" burn - gasoline burns just fine. Unburned fuel in the exhaust comes from three primary sources - mixture that is pushed into the crevices around the piston / sparkplug / etc. where it can't burn (it comes out of the crevices during the exhaust stroke), mixture that is quenched at the cylinder walls due to heat loss. And excess fuel from running rich. The bulk of the charge mass burns just fine. Cow magnets, magic additives, whatever aren't going to change any of that. Actually, ( I was trying to make it simple ) either compression or boost can be expressed as as BMEP, which takes both into account. As BMEP rises you get better combustion of any unburned fuel from being too rich (not a factor in today's autos) , but the higher pressure also suppresses the boundary layer at the cylinder wall, giving better combustion there also and lower unburned hydrocarbons as a result. Using water injection, as you say, allows you to increase BMEP without risking knock because it cools the intake charge, acting (as I said) like an octane improver. -- Harry Andreas Engineering raconteur |
#17
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Capt. Geoffry Thorpe wrote: Water can reduce the charge termperature as it evaporates in the cylinder which can increase the charge mass a little, but mostly it improves knock resistance by cooling the charge and increasing the specific heat of the charge mass. But to really take advantage you have to either increase the compression ratio or boost. NOx is recduced somewhat since the peak temperatures are reduced. If you are trying to change the fuel chemestry to get more energy out - you have to put energy in. Lose - lose. If you are trying to make the fuel burn "better" to make it "all" burn - gasoline burns just fine. Unburned fuel in the exhaust comes from three primary sources - mixture that is pushed into the crevices around the piston / sparkplug / etc. where it can't burn (it comes out of the crevices during the exhaust stroke), mixture that is quenched at the cylinder walls due to heat loss. And excess fuel from running rich. The bulk of the charge mass burns just fine. Cow magnets, magic additives, whatever aren't going to change any of that. Ah but the thermodynamic efficiency of a heat engine increases as the compression ratio or temperature ratio increases. The issue is not how to get more heat out of the fuel, it is how to convert more of the heat to mechanical energy. -- FF |
#18
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Peter Skelton wrote: On 20 Sep 2005 10:25:08 -0700, wrote: ... Someone else wrote that it was KOH that was added, not a salt. Dunno why, if it was just a water injection system. Would the KOH help to control NOx emmissions? Could the KOH be threre for boiling point elevation? Freezing point depression. Like to prevent carburator icing, or just so the water tank doesn't freeze in the winter time? The refernced article seems to have expired, is the engine in question fuel injected? -- FF |
#19
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Water injection does not increase efficiency, it lowers it. The water goes
in as a liquid and goes out as a gas. The energy to do that comes from burning fuel. It will always take more fuel to produce a given amount of power with water injection than without. Water injection does allow higher MP or higher compression so the engine can produce more power. Piston engine fighters used it for more peak horsepower and some turbines use it for the same purpose but it definately come at the price of higher fuel burn per horsepower. Mike "Jeff" wrote in message ... Some fellow is claiming he has a small device that will boost combustion efficiency and save drivers lots of money, while reducing emissions. Obviously, plenty of claims have been made before, so I'm asking -- does this sound on the level? Water injection has been around for a long time, both for internal combustion and aircraft jet engines, it does improve efficiency, reduce temperatures and reduce some emissions. It depends what is being claimed for the actual device. Regards Jeff |
#20
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"Mike Rapoport" wrote in message ink.net... Water injection does not increase efficiency, it lowers it. The water goes in as a liquid and goes out as a gas. The energy to do that comes from burning fuel. It will always take more fuel to produce a given amount of power with water injection than without. Water injection does allow higher MP or higher compression so the engine can produce more power. Piston engine fighters used it for more peak horsepower and some turbines use it for the same purpose but it definately come at the price of higher fuel burn per horsepower. Mike Hmm, consulting my ancient copy of Ricardo's "High Speed Internal Combustion Engines", Sir Harry said that water injection can be substituted for any excess fuel consumed for the purpose of reducing cylinder temperature and/or increasing detonation margin. Further, evaporation of the water reduces the intake charge temperature so as to reduce pumping losses. He goes on to say that, while there is energy lost to evaporating the water droplets, the overall fuel economy of an aircraft engine at max power setting will be improved by use of water injection particularly if the compression ratio has been increased to take advantage of the increased detonation margin. Bill Daniels |
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