water injection systems
lodownlv
05-24-2005, 02:06 AM
was reading around about water injection. any pros or cons on this? and can it be used on high boost 7mgte's
lodownlv
05-24-2005, 02:09 AM
Turbo Water/alcohol Injection - The Theory
Water/alcohol injection relies on the fact that it takes much more energy to raise the temperature of water than it does to lower the temperature of air. The specific heat of a substance is a measure of the amount of energy (kJ) required to increase the temperature of a certain amount of it (kg) by a certain temperature (° C). The specific heat of water is 4.184 kJ/kg ° C. This means that it takes 4.184 kJ of energy to raise one kg of water 1° C in teperature. The specific heat of water is more than four times that of air, which ranges from 1.00 kJ/kg ° C to 1.05 kJ/kg ° C, for the temperatures we're concerned with.
Water/alcohol injection is dependent upon the relative humidity in the atmosphere. Lower humidity will increase the effectiveness of water/alcohol injection.
Advantages to Water/Alcohol Injection
Suppressing Engine Knock. Water/alcohol injection works to suppress engine knock in several ways. First, the water (and alcohol) reduces the temperature of the compressed air. When the exhaust gases are expelled from the combustion chamber, the cylinder, piston, and valve surfaces are at a very high temperature. The water entering the cylinder with the compressed air will work to cool these surfaces and any hot spots which might exist. It is in these hot spots that predetonation would typically occur. As the air is compressed in the cylinder, the water serves to reduce air to fuel contact, reducing the likelihood of auto-detonation. Lastly, if any alcohol is used, it serves to increase the octane of the fuel.
Increasing Intake Air Density. As previously mentioned, the water serves to decrease the temperature of the charged air. Since water/alcohol injection presents no additional flow restriction, this reduction in temperature can only be accompanied by in increase in air density. Also, when the water cools the metal surfaces in the combustion chamber during the intake stroke, this allows more air to enter the cylinder - effectively increasing the volumetric efficiency of the engine.
How Much Water and Alcohol?
Water to Alcohol Ratio. A 50/50 water/alcohol mix is recommended as the minimum, with 70/30 being quite common. In fact, many people use filtered windshield wiper fluid without any modification for a very cheap solution. For our analysis, we'll assume a 70/30 mix, which will have a specific heat of 3.66 kJ/kg ° C (the specific heat of ethanol is 2.43, and methanol is 2.51).
Water/Alcohol to Fuel Ratio. Most experts suggest a maximum water to fuel ratio of 25% and point to many tuning problems with rations this high. Typically, 10-15% water to fuel is a more manageable ratio.
Where to Inject Water
Theoretically, water/alcohol injection can happen anywhere between the air filter and the intake runners. However, injecting water before the turbocharger will damage the compressor wheel. On the other hand, injecting water after the turbocharger is made difficult by the need to increase the pressure under which the water is injected in order to overcome the additional pressure. Also needed is a check valve to inhibit compressed air from entering the water reservoir when water is not being injected, such as in low boost situations. The water should be injected as soon after the turbocharger as possible to allow time for the water to form small droplets. Often, people will inject perpendicular to the tubing to use impact with the back wall of the tubing to further break up the water drops. Alcohol also assists in creating smaller droplets. If water/alcohol injection is to be used in tandem with an intercooler, the water should be injected after the intercooler in order to maximize the temperature drop.
Water/alcohol injection relies on the fact that it takes much more energy to raise the temperature of water than it does to lower the temperature of air. The specific heat of a substance is a measure of the amount of energy (kJ) required to increase the temperature of a certain amount of it (kg) by a certain temperature (° C). The specific heat of water is 4.184 kJ/kg ° C. This means that it takes 4.184 kJ of energy to raise one kg of water 1° C in teperature. The specific heat of water is more than four times that of air, which ranges from 1.00 kJ/kg ° C to 1.05 kJ/kg ° C, for the temperatures we're concerned with.
Water/alcohol injection is dependent upon the relative humidity in the atmosphere. Lower humidity will increase the effectiveness of water/alcohol injection.
Advantages to Water/Alcohol Injection
Suppressing Engine Knock. Water/alcohol injection works to suppress engine knock in several ways. First, the water (and alcohol) reduces the temperature of the compressed air. When the exhaust gases are expelled from the combustion chamber, the cylinder, piston, and valve surfaces are at a very high temperature. The water entering the cylinder with the compressed air will work to cool these surfaces and any hot spots which might exist. It is in these hot spots that predetonation would typically occur. As the air is compressed in the cylinder, the water serves to reduce air to fuel contact, reducing the likelihood of auto-detonation. Lastly, if any alcohol is used, it serves to increase the octane of the fuel.
Increasing Intake Air Density. As previously mentioned, the water serves to decrease the temperature of the charged air. Since water/alcohol injection presents no additional flow restriction, this reduction in temperature can only be accompanied by in increase in air density. Also, when the water cools the metal surfaces in the combustion chamber during the intake stroke, this allows more air to enter the cylinder - effectively increasing the volumetric efficiency of the engine.
How Much Water and Alcohol?
Water to Alcohol Ratio. A 50/50 water/alcohol mix is recommended as the minimum, with 70/30 being quite common. In fact, many people use filtered windshield wiper fluid without any modification for a very cheap solution. For our analysis, we'll assume a 70/30 mix, which will have a specific heat of 3.66 kJ/kg ° C (the specific heat of ethanol is 2.43, and methanol is 2.51).
Water/Alcohol to Fuel Ratio. Most experts suggest a maximum water to fuel ratio of 25% and point to many tuning problems with rations this high. Typically, 10-15% water to fuel is a more manageable ratio.
Where to Inject Water
Theoretically, water/alcohol injection can happen anywhere between the air filter and the intake runners. However, injecting water before the turbocharger will damage the compressor wheel. On the other hand, injecting water after the turbocharger is made difficult by the need to increase the pressure under which the water is injected in order to overcome the additional pressure. Also needed is a check valve to inhibit compressed air from entering the water reservoir when water is not being injected, such as in low boost situations. The water should be injected as soon after the turbocharger as possible to allow time for the water to form small droplets. Often, people will inject perpendicular to the tubing to use impact with the back wall of the tubing to further break up the water drops. Alcohol also assists in creating smaller droplets. If water/alcohol injection is to be used in tandem with an intercooler, the water should be injected after the intercooler in order to maximize the temperature drop.
Brian R.
05-30-2005, 10:35 PM
When you copy an article, you should provide a link or citation to the original so that the original author get credit for the thinking.
The author is not correct in many ways.
He is incorrect when he states that the cooling effect of the specific heat difference between water vapor and air is the main reason for using water injection to cool the charge. The main reason for using water injection is because of the heat absorbed from the air by the water during evaporation of the water from the liquid state to the gas state is very high and causes alot of cooling of the incoming charge. The heat of vaporization of water is 2260 kJ/kg. Sucks up alot of heat going from liquid water to water vapor.
The auther cites the specific heat of water as 4.184 kJ/kg °C. This is not a valid number for water vapor (as is found in an intake and is what is relevant to his context), only liquid water.
It is obvious that the cooling effect of water vaporization is much more important than the effect of the increased heat capacity of the water vapor/air mixture vs air.
The author also stated that the water needs to be allowed time to form small droplets after injection. This is also incorrect. The water evaporates as it is injected and only needs time to totally evaporate and mix with the rest of the charge in the vapor phase to more evenly cool it. Maybe this is what he meant, but it's not what he said.
Also, he states that "As the air is compressed in the cylinder, the water serves to reduce air to fuel contact, reducing the likelihood of auto-detonation". This is pure BS. There is no way water could reduce air-to-fuel contact. You would not want to reduce this, even if you could. Maximum fuel/air mixing is critical for even burning and maximum efficiency.
To answer the original post, water injection can be used with any engine.
The author is not correct in many ways.
He is incorrect when he states that the cooling effect of the specific heat difference between water vapor and air is the main reason for using water injection to cool the charge. The main reason for using water injection is because of the heat absorbed from the air by the water during evaporation of the water from the liquid state to the gas state is very high and causes alot of cooling of the incoming charge. The heat of vaporization of water is 2260 kJ/kg. Sucks up alot of heat going from liquid water to water vapor.
The auther cites the specific heat of water as 4.184 kJ/kg °C. This is not a valid number for water vapor (as is found in an intake and is what is relevant to his context), only liquid water.
It is obvious that the cooling effect of water vaporization is much more important than the effect of the increased heat capacity of the water vapor/air mixture vs air.
The author also stated that the water needs to be allowed time to form small droplets after injection. This is also incorrect. The water evaporates as it is injected and only needs time to totally evaporate and mix with the rest of the charge in the vapor phase to more evenly cool it. Maybe this is what he meant, but it's not what he said.
Also, he states that "As the air is compressed in the cylinder, the water serves to reduce air to fuel contact, reducing the likelihood of auto-detonation". This is pure BS. There is no way water could reduce air-to-fuel contact. You would not want to reduce this, even if you could. Maximum fuel/air mixing is critical for even burning and maximum efficiency.
To answer the original post, water injection can be used with any engine.
lodownlv
06-01-2005, 05:11 AM
the information was gatherd from http://www.turbocalculator.com/alcohol-injection.html
i also asked if i could use it so i did not plagiarize it :-)
my question is who do i believe? and whould it be to mine or anyones benefit? please explaine further on your theory and how you gathered your information and hypothesis. finally if you have information on my other thread on the megasqurt? since you sound prity intelligent. :-)
i also asked if i could use it so i did not plagiarize it :-)
my question is who do i believe? and whould it be to mine or anyones benefit? please explaine further on your theory and how you gathered your information and hypothesis. finally if you have information on my other thread on the megasqurt? since you sound prity intelligent. :-)
Brian R.
06-01-2005, 08:43 AM
It doesn't really matter whom you believe. I was just being informative. The physical chemistry is really irrelevant to the application unless you want to do something novel with the water injection system and need to predict the results of changes you want to make. The author of the article you copied should have confined himself to recommendations for the application (which is all that anyone really considers relevant anyway) and not delve into the physical chemistry of why water injection does what it does.
I am qualified to talk about physical properties of water and associated physical processes since I am a Ph.D chemist (having taken upwards of 10 semesters of physical chemistry) with an industrial engineering background. The author is obviously not a chemist at all. To paraphrase a deputy in "The Unforgiven", he may be a hell of a mechanic, but he just ain't no chemist.
There are some facts that relate to this system and they are irrefutable facts.
One is that water evaporation will occur in the intake system with water injection since the water is sprayed in as a fine mist and the intake air is hot (particularly after the turbo) and in turbulent motion.
The second is that the heat of vaporization of water (liquid to gas) is 2260 kJ/kg. That is alot of cooling capability. Water has one of the highest heats of vaporization of any substance and this vaporization (evaporation) will occur in the intake.
Third - Any effect that is dependent on the relative heat capacities of water/air vs air as he speculates is going to be unpredictable because it will not only depend on the amount of water injected, but the flow rate of the air/water mixture through the intake. The higher the flow rate (higher the rpm) the less heat transfer can occur to influence the change in temperature. I think he must be referring to a N/A system with this argument since the air from the turbo can only cool down and a higher heat capacity, as in a water/air mixture, would only inhibit the cooling of the water/air mixture by heat transfer from the walls of the intake (or intercooler).
On the other hand, the cooling effect of water evaporation is independent of the rpm and only depends on the amount of water injected (up to a certain point), for cooling of a predictable and constant magnitude to occur.
Take it for what it's worth.
As far as a specific water injection system goes, get recommendations from people with a similar setup to yours and go with it.
I am qualified to talk about physical properties of water and associated physical processes since I am a Ph.D chemist (having taken upwards of 10 semesters of physical chemistry) with an industrial engineering background. The author is obviously not a chemist at all. To paraphrase a deputy in "The Unforgiven", he may be a hell of a mechanic, but he just ain't no chemist.
There are some facts that relate to this system and they are irrefutable facts.
One is that water evaporation will occur in the intake system with water injection since the water is sprayed in as a fine mist and the intake air is hot (particularly after the turbo) and in turbulent motion.
The second is that the heat of vaporization of water (liquid to gas) is 2260 kJ/kg. That is alot of cooling capability. Water has one of the highest heats of vaporization of any substance and this vaporization (evaporation) will occur in the intake.
Third - Any effect that is dependent on the relative heat capacities of water/air vs air as he speculates is going to be unpredictable because it will not only depend on the amount of water injected, but the flow rate of the air/water mixture through the intake. The higher the flow rate (higher the rpm) the less heat transfer can occur to influence the change in temperature. I think he must be referring to a N/A system with this argument since the air from the turbo can only cool down and a higher heat capacity, as in a water/air mixture, would only inhibit the cooling of the water/air mixture by heat transfer from the walls of the intake (or intercooler).
On the other hand, the cooling effect of water evaporation is independent of the rpm and only depends on the amount of water injected (up to a certain point), for cooling of a predictable and constant magnitude to occur.
Take it for what it's worth.
As far as a specific water injection system goes, get recommendations from people with a similar setup to yours and go with it.
lodownlv
06-04-2005, 04:39 PM
i think im just going to inject nos instead
Brian R.
06-06-2005, 08:31 AM
Why give up on the WI? Much cheaper to run than NOS.
lodownlv
06-10-2005, 07:09 AM
well ive ben getting mixed things about water injection. dosnt nos sound better? :-)
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