Water Injection Myths
09-25-2005, 03:14 AM
#1
0.0 BAR
Thread Starter
Join Date: Feb 2003
Posts: 0
Water Injection Myths
Before I begin, I'd like to explain why I deal in Google search terms instead of URLs. I get absolutely zero work done when connected to the internet, so I got rid of my cable modem. Occaisionally, I hit a wireless AP at a coffeeshop, do an afternoon of strenuous downloading of various publications, and sift though it over the course of a few weeks on my laptop. I know you can search for the documents I refer to via google, I do it all the time.
Water Injection Myths:
1) Water injection displaces intake charge better occupied by fuel, or air mass.
Not true, for the casual user, injecting 25 to 50% water to fuel by volume. Running AFRs somewhat richer than stoich, leaves us liquid to air ratios in the 10.5:1 to 9.8:1 range, respectively. Not out of line with the liquid (fuel) to air ratios in OEM turbocharged vehicles (ie - Subaru, VW, et al) which are run at said ratios solely for reliability reasons.
NACA Memorandum E5H12, easily googled for as "naca-wr-e-264.pdf," is a paper entitled EFFECT OF WATER-ALCOHOL INJECTION AND MAXIMUM-ECONOMY SPARK ADVANCE ON KNOCK-LIMITED PERFORMANCE AND FUEL ECONOMY OF A LARGE AIR COOLED CYLINDER, by Jack E. Vandeman and Orville H. Heinicke. They were tuning for fuel efficiency AND power. The gist of it states that the knock-limited power increased as much as 88% by operating at a fuel-air ratio of 0.060 (16.6:1 AFR) and coolant-fuel ratio of 0.4 (40% water/diluent to fuel by volume). If we conservatively speculate the increase in knock limit, in a forced induction Honduh application, to be a mere 50% for a water-fuel ratio of 0.5 it renders some ineresting numbers. For D16, H22, and B18A/B with a knock limit of 350 whp on pump gas, with water injection 525 whp. For B18C with a 450 whp pump gas knock limit, 675 whp.
I've found other papers indicating a least possible increase of 41% for a water to fuel ratio of 0.6, but taking into account that most of these old papers dealt with an engine at or near it's torque peak makes me think the real world gains in the modern age will be much better. With the Honduh stuffs we try to bring the bulk of our boost in after the stock torque peak, which is where cylinder filling is most pronounced and detonation most likely, in order to keep the torque curve from dropping off so that mutant high rpms can generate power for us. Also, there's a LOT of variance between fuel types, and the nature of the tests taking place. The paper that lowballs the % gain in knock limit also equates injecting 0.6 ratio of water-fuel with an increase of 20 octane numbers, from 80 to 100 octane with the fuel used.
2) Water injection cools the intake charge.
Complete bullshit.
THE INDUCTION OF WATER TO THE INLET AIR AS A MEANS OF INTERNAL COOLING IN AIRCRAFT-ENGINE CYLINDERS by Addison M. Rothrock, Alois Krsek, Jr., and Anthony W. Jones (Google "naca_H2O.pdf") states that air mass increases only marginally as increasing amounts of water is injected. If any significant cooling of intake charge took place then there would be an increase in air mass draw into the engine, as cooler air is denser air. This means that water enters the engine as droplets, and does not vaporize/turn to wet steam until heated by the combustion reaction. Especially interesting to note this, since the test engine in question had IATs of 250 deg F! Over the boiling point of water. Large temperature differentials encourage thermal transfer, just like how the majority of heat transfer across an air-air intercooler happens in the first four inches the air travels + the rest of the intercooler's length just acts as a heatsink. The water is simply not atomized enough, nor the intake charge dense enough to carry any significant amount of thermal mass, to encourage any real thermal transfer in such a short exposure to the intake charge.
Per Andersson's thesis hosted on the Linkoping University website, regarding Poppet-valve EGR Systems in SI Engines, somewhere on or about page seven, mentions erroneous IAT readings when dealing with water injection. He refers to it as "wet thermometer syndrome," which is a well known thermodynamics problem. He links in his Bibliography to a entry level Thermodynamics textbook, whoopty! Droplets form, and linger on, the IAT sensor's probe and suck heat out of it. This is easier to do with a solid IAT probe, than with a thin gas like the intake charge.
It is also good to note that this paper also supports factoid 1). Over a variety of AFRs ranging from 14.9:1 to 11.1:1; and a variety of three water-fuel ratios of 0.2, 0.4, 0.6 ; an increase in "maximum indicated mean effective pressure," was realized of 13 to 71%. That bit in quotes translates into layman as the highest possible averaged usable combustion pressure before hitting knock limit. Yeah, that's a lot of words strung together. Kiss my ***, Seabiscuit.
3) Water injection cools the engine
Well, yeah, kinda. Not in the way you think.
Still referring to THE INDUCTION OF WATER TO THE INLET AIR AS A MEANS OF INTERNAL COOLING IN AIRCRAFT-ENGINE CYLINDERS by Addison M. Rothrock, Alois Krsek, Jr., and Anthony W. Jones. Literature says water injection substantially decreased engine temperatures EXCEPT across probes mounted on the exhaust valve guide. Water injection theory says that the droplets entering via the intake valves form droplets coating the combustion chamber, which vaporize/turn to wet steam when heated by combustion. The water grabs onto a large portion of the combustion heat and turns it to pressure a la steam turbine style, where normally it would pass across the chamber boundaries into the engine proper. The problem is, it drags all this heat right across the exhaust valve when it opens. Sure, the exhaust valve/exhaust valve guide temp is very slightly cooled by water injection, when compared to a non-water injection combustion chamber with the exact same indicated mean effective pressure (Seabiscuit!). When trying to increase specific output dramatically, leaving conventional pump gas knock limitations behind, the exhaust valve takes an assbeating by the increased thermal load. Sure, you are very slightly cooler, at the same power level, than a non-water injection setup, but it's not worth noting as a gain.
The rest of the engine near the chamber runs lots and lots cooler, especially the portion of the combustion chamber probed between the intake and exhaust valves. I'm going to project this cooling action onto the piston itself - not a big stretch of the imagination at all - which is a very critical area in a big power situation. A chunk of aluminum is half as strong at 600 deg F as it is at room temperature; at the temperatures seen during combustion it's getting pretty soft. I'm not getting into the differences in piston construction between an aftermarket forging meant for forced induction use versus a naturally aspirated stocker (ring lands, et al). But, from a simple thermal standpoint the significant drop in average piston temperature nets a nice bump in strength that should offset the lack of grain flow in an OEM casting. If you have forged pistons, oh my. Less loss of ring lands for the stock block turbo boys, but while theo-rectally there are no abrupt pressure waves from detonation since water injection has raised knock limit and dropped thermal load, the sleeves still see an uncomfortable amount of combustion pressure.
If you are a Mitsubishi ***, you just buy the $8/per sodium filled exhaust valves from the dealer that come in the Evo 8, and call it close enough fo rocket science. Aftermarket exhaust valves, with nice stiff springs meant for a turbo engine, and accepting that they will be high wear items, is what us Honduhboys have to live with. I'd guess that cam profile becomes crucial at some point if you want any longevity - I'm guessing best power profiles become compromised by needing the valve to stay closed a smidge longer to help with thermal transfer back into the head. I'm liking these short duration high lift cams more and more...
But, yeah, aside from that, water injection cools the engine. To the point that for OEM applications you can remove the radiator from your car, drain the coolant out of the block, and cool solely by water injection with 100% reliability. Sir Harry Ricardo did it 80 years or so back, for ***** and giggles.
4) Water injection lowers EGTs
Not always. Note the thermal mass escaping past the exhaust valve in the previous explaination. Also, in some big power situations you'd have to run a LOT of water, two to three times the ratios discussed here, to cool EGTs significantly. This runs us into a problem. If the engine is overly cooled there is a very real potential for water that escapes into the crankcase forming sludge. Not from water injection, per se, because water is a normal product of combustion (two pounds of it formed for every pound of fuel burned) and is a normal inhabitant of the crankcase, but from engine oil temperature being taken below the boiling point of water. You don't get the engine hot enough, the water doesn't evaporate out of the engine.
This post is the product of my interactions with the following people over the course of a couple years. THANK YOU TO THE FOLLOWING:
Robert "Mean Gringo Bob" Harris for his mentorship, repeatedly repeating himself until I listened, explainations on how to use cutting edge technology called "search engines," and how to find elementary level books at the library because it seems they have - of all things - books at the library. Maybe it's just at my local library. I'll have to ask Bob.
Ben Strader for his $0.02 on the subject of water injection, intermixed with some hard won gems of engine theory. It's amazing what sort of things fall through the cracks when we forget to examine problems minutely, and ask the probing questions. Wish I'd had more sleep that day, asked a few more questions.
Lastly, thank you Jason "JDogg" Wadsworth, for being a miserable half-talent, supremely confident in his own ignorance. Can you hear me laughing?
Water Injection Myths:
1) Water injection displaces intake charge better occupied by fuel, or air mass.
Not true, for the casual user, injecting 25 to 50% water to fuel by volume. Running AFRs somewhat richer than stoich, leaves us liquid to air ratios in the 10.5:1 to 9.8:1 range, respectively. Not out of line with the liquid (fuel) to air ratios in OEM turbocharged vehicles (ie - Subaru, VW, et al) which are run at said ratios solely for reliability reasons.
NACA Memorandum E5H12, easily googled for as "naca-wr-e-264.pdf," is a paper entitled EFFECT OF WATER-ALCOHOL INJECTION AND MAXIMUM-ECONOMY SPARK ADVANCE ON KNOCK-LIMITED PERFORMANCE AND FUEL ECONOMY OF A LARGE AIR COOLED CYLINDER, by Jack E. Vandeman and Orville H. Heinicke. They were tuning for fuel efficiency AND power. The gist of it states that the knock-limited power increased as much as 88% by operating at a fuel-air ratio of 0.060 (16.6:1 AFR) and coolant-fuel ratio of 0.4 (40% water/diluent to fuel by volume). If we conservatively speculate the increase in knock limit, in a forced induction Honduh application, to be a mere 50% for a water-fuel ratio of 0.5 it renders some ineresting numbers. For D16, H22, and B18A/B with a knock limit of 350 whp on pump gas, with water injection 525 whp. For B18C with a 450 whp pump gas knock limit, 675 whp.
I've found other papers indicating a least possible increase of 41% for a water to fuel ratio of 0.6, but taking into account that most of these old papers dealt with an engine at or near it's torque peak makes me think the real world gains in the modern age will be much better. With the Honduh stuffs we try to bring the bulk of our boost in after the stock torque peak, which is where cylinder filling is most pronounced and detonation most likely, in order to keep the torque curve from dropping off so that mutant high rpms can generate power for us. Also, there's a LOT of variance between fuel types, and the nature of the tests taking place. The paper that lowballs the % gain in knock limit also equates injecting 0.6 ratio of water-fuel with an increase of 20 octane numbers, from 80 to 100 octane with the fuel used.
2) Water injection cools the intake charge.
Complete bullshit.
THE INDUCTION OF WATER TO THE INLET AIR AS A MEANS OF INTERNAL COOLING IN AIRCRAFT-ENGINE CYLINDERS by Addison M. Rothrock, Alois Krsek, Jr., and Anthony W. Jones (Google "naca_H2O.pdf") states that air mass increases only marginally as increasing amounts of water is injected. If any significant cooling of intake charge took place then there would be an increase in air mass draw into the engine, as cooler air is denser air. This means that water enters the engine as droplets, and does not vaporize/turn to wet steam until heated by the combustion reaction. Especially interesting to note this, since the test engine in question had IATs of 250 deg F! Over the boiling point of water. Large temperature differentials encourage thermal transfer, just like how the majority of heat transfer across an air-air intercooler happens in the first four inches the air travels + the rest of the intercooler's length just acts as a heatsink. The water is simply not atomized enough, nor the intake charge dense enough to carry any significant amount of thermal mass, to encourage any real thermal transfer in such a short exposure to the intake charge.
Per Andersson's thesis hosted on the Linkoping University website, regarding Poppet-valve EGR Systems in SI Engines, somewhere on or about page seven, mentions erroneous IAT readings when dealing with water injection. He refers to it as "wet thermometer syndrome," which is a well known thermodynamics problem. He links in his Bibliography to a entry level Thermodynamics textbook, whoopty! Droplets form, and linger on, the IAT sensor's probe and suck heat out of it. This is easier to do with a solid IAT probe, than with a thin gas like the intake charge.
It is also good to note that this paper also supports factoid 1). Over a variety of AFRs ranging from 14.9:1 to 11.1:1; and a variety of three water-fuel ratios of 0.2, 0.4, 0.6 ; an increase in "maximum indicated mean effective pressure," was realized of 13 to 71%. That bit in quotes translates into layman as the highest possible averaged usable combustion pressure before hitting knock limit. Yeah, that's a lot of words strung together. Kiss my ***, Seabiscuit.
3) Water injection cools the engine
Well, yeah, kinda. Not in the way you think.
Still referring to THE INDUCTION OF WATER TO THE INLET AIR AS A MEANS OF INTERNAL COOLING IN AIRCRAFT-ENGINE CYLINDERS by Addison M. Rothrock, Alois Krsek, Jr., and Anthony W. Jones. Literature says water injection substantially decreased engine temperatures EXCEPT across probes mounted on the exhaust valve guide. Water injection theory says that the droplets entering via the intake valves form droplets coating the combustion chamber, which vaporize/turn to wet steam when heated by combustion. The water grabs onto a large portion of the combustion heat and turns it to pressure a la steam turbine style, where normally it would pass across the chamber boundaries into the engine proper. The problem is, it drags all this heat right across the exhaust valve when it opens. Sure, the exhaust valve/exhaust valve guide temp is very slightly cooled by water injection, when compared to a non-water injection combustion chamber with the exact same indicated mean effective pressure (Seabiscuit!). When trying to increase specific output dramatically, leaving conventional pump gas knock limitations behind, the exhaust valve takes an assbeating by the increased thermal load. Sure, you are very slightly cooler, at the same power level, than a non-water injection setup, but it's not worth noting as a gain.
The rest of the engine near the chamber runs lots and lots cooler, especially the portion of the combustion chamber probed between the intake and exhaust valves. I'm going to project this cooling action onto the piston itself - not a big stretch of the imagination at all - which is a very critical area in a big power situation. A chunk of aluminum is half as strong at 600 deg F as it is at room temperature; at the temperatures seen during combustion it's getting pretty soft. I'm not getting into the differences in piston construction between an aftermarket forging meant for forced induction use versus a naturally aspirated stocker (ring lands, et al). But, from a simple thermal standpoint the significant drop in average piston temperature nets a nice bump in strength that should offset the lack of grain flow in an OEM casting. If you have forged pistons, oh my. Less loss of ring lands for the stock block turbo boys, but while theo-rectally there are no abrupt pressure waves from detonation since water injection has raised knock limit and dropped thermal load, the sleeves still see an uncomfortable amount of combustion pressure.
If you are a Mitsubishi ***, you just buy the $8/per sodium filled exhaust valves from the dealer that come in the Evo 8, and call it close enough fo rocket science. Aftermarket exhaust valves, with nice stiff springs meant for a turbo engine, and accepting that they will be high wear items, is what us Honduhboys have to live with. I'd guess that cam profile becomes crucial at some point if you want any longevity - I'm guessing best power profiles become compromised by needing the valve to stay closed a smidge longer to help with thermal transfer back into the head. I'm liking these short duration high lift cams more and more...
But, yeah, aside from that, water injection cools the engine. To the point that for OEM applications you can remove the radiator from your car, drain the coolant out of the block, and cool solely by water injection with 100% reliability. Sir Harry Ricardo did it 80 years or so back, for ***** and giggles.
4) Water injection lowers EGTs
Not always. Note the thermal mass escaping past the exhaust valve in the previous explaination. Also, in some big power situations you'd have to run a LOT of water, two to three times the ratios discussed here, to cool EGTs significantly. This runs us into a problem. If the engine is overly cooled there is a very real potential for water that escapes into the crankcase forming sludge. Not from water injection, per se, because water is a normal product of combustion (two pounds of it formed for every pound of fuel burned) and is a normal inhabitant of the crankcase, but from engine oil temperature being taken below the boiling point of water. You don't get the engine hot enough, the water doesn't evaporate out of the engine.
This post is the product of my interactions with the following people over the course of a couple years. THANK YOU TO THE FOLLOWING:
Robert "Mean Gringo Bob" Harris for his mentorship, repeatedly repeating himself until I listened, explainations on how to use cutting edge technology called "search engines," and how to find elementary level books at the library because it seems they have - of all things - books at the library. Maybe it's just at my local library. I'll have to ask Bob.
Ben Strader for his $0.02 on the subject of water injection, intermixed with some hard won gems of engine theory. It's amazing what sort of things fall through the cracks when we forget to examine problems minutely, and ask the probing questions. Wish I'd had more sleep that day, asked a few more questions.
Lastly, thank you Jason "JDogg" Wadsworth, for being a miserable half-talent, supremely confident in his own ignorance. Can you hear me laughing?
09-26-2005, 08:59 AM
#3
3.0 BAR
Join Date: Jul 2003
Posts: 6,449
Re: Water Injection Myths
Originally Posted by Joseph Davis
But, yeah, aside from that, water injection cools the engine. To the point that for OEM applications you can remove the radiator from your car, drain the coolant out of the block, and cool solely by water injection with 100% reliability. Sir Harry Ricardo did it 80 years or so back, for ***** and giggles.
Pimp juice JD. I plan on giving this all a shot next year at some point...I may have to fly you up to see if the above is true.
Now my question is...when tuning water injection, how does the A/F reading on your wideband differ? Water takes up more space in the combustion chamber, after combustion, seems there will be more O2 in the air, correct...or will it just be water still, coupled with the H20 and CO2 produced by combustion and the same amount of left over O2 will be present in the exhast stream to be measured by the wideband...
09-26-2005, 12:55 PM
#4
0.0 BAR
Thread Starter
Join Date: Feb 2003
Posts: 0
Re: Water Injection Myths
Originally Posted by xenocron
Now my question is...when tuning water injection, how does the A/F reading on your wideband differ?
That was going to be myth 5), but frankly I don;t know the subject enough to speculate. What I WANT to say, but may be partially to wholly incorrect, is:
- In ideal combustion, H20 and CO2 is the end result. In real world combustion we have minute traces of contaminants: HCs (unburnt from being too rich), NOx (from running too hot), CO (chamber temps were too cool or too unpressurized to completely burn CO, which is a fuel - google "producer gas"), and a buncha other trace crap. You get two pounds of water formed for every pound of pump gas injected, more or less.
- H2O is stable until ~ 1700 deg F, at which point it decomposes into hydrogen and oxygen. At those temps, they can't seek out each other to make water, so they seek out aluminum and iron. Combustion pressures above 1700 deg F fall off because there is a strong argument for wet steam being the motive force for the internal combustion engine. We spend millions to make nuclear power plants to heat water and run steam turbines because it really doesn't get any better.
? Now, here's the problem. There are a LOT of minute sub-reactions taking place before the end result of CO2 and H2O. Does water act as an oxidizer (it is normally very corrosive) to a significant amount during the combustion cycle, especially with a good jot of heat and pressure to act as catalysts?
I think the (or just speculative) answer may lie with paying close attention to alcohol's combustion. Unlike gasoline, which produces water later in the combustion reaction, alcohol immediately produces water. BUT, alcohol produces less contaminants in real world combustion, so I'm ASSuming there are less sub-reactions and less possible ways for water present to skew AFRs.
What I plan on doing is dyno at some point, and deduce amount of air entering engine from power output. Easy at that point to deduce injector pulsewidth at X spot needed to produce Y AFR. Also need a dyno to get a firm hand on the ignition tables.
09-26-2005, 02:12 PM
#5
3.0 BAR
Join Date: Dec 2004
Posts: 2,133
Re: Water Injection Myths
good explaination. This helps me better understand what you were rambling about that time in walmart 
jk. Nice post jo. Chris asked a very good question. I would love to see some afr's during tuning of the water injection.
how do you plan to regulate the pulse of injection on your setup? are you tying the water injectors in with the fuel injectors to pulse at the same time? Can that be done effectively? Sorry if this brings it off topic, but this is REALLY interesting.
jk. Nice post jo. Chris asked a very good question. I would love to see some afr's during tuning of the water injection. how do you plan to regulate the pulse of injection on your setup? are you tying the water injectors in with the fuel injectors to pulse at the same time? Can that be done effectively? Sorry if this brings it off topic, but this is REALLY interesting.
09-26-2005, 02:52 PM
#6
0.0 BAR
Thread Starter
Join Date: Feb 2003
Posts: 0
Re: Water Injection Myths
Originally Posted by B16CRXT
how do you plan to regulate the pulse of injection on your setup? are you tying the water injectors in with the fuel injectors to pulse at the same time? Can that be done effectively? Sorry if this brings it off topic, but this is REALLY interesting.
Dan Nicoson sent me a prototype to play with last week. Above is a picture of the driver board, although mine is only configured for one injector + is not intended for in car use. The unit is slaved off of fuel injector pulsewidth, currently gain fire but final working unit will be true sequential. There's also a control head that allows me to select secondary injection scale (I can modify pulsewidth from a factor of 0.2 to 2.0) and delay (how much of the fuel pulsewidth to ignore before starting secondary water pulse). He also sent me a signal generator to mimic a variety of duty cycles at a variety of rpms. Pimp ----.
There's a 1001 stumbling blocks in the way right now. If you hit 100% duty cycle on the fuel injectors, it cuts off the water injection because the driver only monitors trigger signal; needs modified to monitor trailing edge of the primary pulse, so if it doesn't come the water injection keps working. Most OEM fuel pumps and injectors appear to be stainless internals, and deal well with water run to them, but the two OEM FPR tried so far like to rust shut; you can get them freed up, but that corrosion will evenually result in failure and aftermarket SS FPRs are $$$. Ultimately planning to control water pressure at the pump motor by PWM of the voltage sent to it, but that's a good bit off and in the meantime you NEED a reliable FPR.
As soon as Caveman gets the Y8 intake manifold to me, I'll demonstrate how to drill + tap the manifold for secondary injectors on the cheap. Dan used a Bridgeport mill, I'll use a block of wood and $20 Walmart drill.
09-26-2005, 03:33 PM
#7
3.0 BAR
Join Date: Jul 2003
Posts: 6,449
Re: Water Injection Myths
Originally Posted by Joseph Davis
Jebus, you would have to ask that question, wouldn't you?
A wideband reads the measured amount of 02 left over from the combustion process. But does it measure the actual molecules or the parts of O2 vs. the parts of the rest of the air.
Air is what? 20% O2, 67 % NO & 13% CO2 (been a LONG time sense chem 101) LOL
Whatever those ratios are...after the combustion process, there will be less O2 parts compared to the rest of the parts of air because you forced in some water, so maybe it will be a leaner reading?
I dont know...I have a major headache, work blows. I need to get to my chiropractor
)
