CHEMICAL COOLING
WATER… AU NATURALLE !
WHY ON THIS GREEN EARTH would anyone think that putting water into an engine could be a good idea? Could this be anything but a mistake? At the very least, you will rust the engine from the inside out, correct?
SNAKE OIL AND WATER DON’T MIX
Terms like “Nitrous”, “Super-Charging”, “Wastegate” and countless other hormone inspired phrases, leave the topic of “Watermisting” a little… dry, uninspiring to say the least. Water is not a fuel. By itself, water does NOT burn, dissociate, or otherwise directly increase engine power or fuel economy. But perhaps water DOES increase engine efficiency AND fuel economy when it is used to eliminate or reduce the waste heat processes, processes that convert otherwise useful engine power, to non-useful heat. Trust that this heat, wherever it is created, has pump fuel as its origin energy source; this is fuel wasted that could otherwise go to propulsion.
Whatever can be done to reduce heat manufacture during turbo compression results in better economy and lower EGT. No snake oil claims here, just simple thermodynamic facts of life. This is a FACTBASED article on the merits of pre-turbo “water injection” as a “preemptive” cooling mechanism, a means to rid those waste heat mechanisms, before they happen, and direct that energy to the wheels.
BUT IT’S A DRY HEAT
Your body is an engine: an organic power plant. How quickly a large room goes up in temperature when a crowd of people pile in. And water is our coolant. If we couldn’t perspire, our temperature would never be held down to 98.6 F. Water is essential to all life and living things for heat control. So how about applying this to an overworked engine.
One day I was towing an 8% grade, headed for a rain shaft. I was listening to my fan roar and watching my coolant temperatures rise. It lasted only about 30 seconds. But 15 seconds into this, I noticed a funny thing. My fan quit running and my temperatures were near normal. Sure enough as I exited the shower, it all began again. There is no question that this was effective. Something similar happened to me without the truck.
With its’8% humidity, Outdoor desert activity at 112 F is lip blistering. Heat stress can quickly turn into fatal heat stroke as quickly as 4 hours after the onset of heat stress symptoms. On non-monsoon days I pedal through 8% humidity, and 112 F, and I do it in a white absorbent cotton long sleeve shirt. I carry 2 liters of water on my back, and on a normal 112 degree day, I can go through most of it in 2 hours. At the first sign of nausea or weakness, I get wet, no delay. “Air Conditioning” on the fly, and it is amazingly effective.
I was deep into the Sonoran Desert on my mountain bike, 108 degrees, when a monsoon storm came in from the East. In the distance, a wall of dirt could be seen advancing toward South Mountain, and the breeze was whipping up. “This should be a treat”, I thought to myself. I had seen it many times, but usually from the radar display. This time I was caught out. Soon, wind driven dust filled my eyes, which gave way eventually to rain. The rain came down so hard it hurt. I circumnavigated the lower “dry” washes, which were filling up fast, and narrowly escaped being stranded, getting across the main wash before it flooded. By the time I drove through the final mile of water crossings, the storm had nearly passed. When I left, it was 112 F, intolerable. And now it is 86 degrees, and I am shivering: 26 degrees cooler in an hour, but why? Prideful and tattered, I arrived home to see my neighbors looking skyward from safely inside their open garages.
“But it’s a dry heat!” I yelled, with arms spread like a stage win at the Tour de France. “Experimenting with the meds again?” they replied.
Elsewhere, a fireman pulls up to the scene, sweat dripping as he struggles to unfold the same flat line he has carefully stowed a hundred times. Finally the engineer turns a wheel or 2 and the line quickly goes round, revealing a high pressure projectile stream spewing 150 feet before hitting the target. And then, in an act of defiance, 90% of this water collects under the fire and runs right off the sight and into the sewer. There must be a better way.
PROPOSITION
Here is a thought. Our vehicle is, at best, 35% efficient. Typically, for every 3 gallons of fuel burned, only 1 gallon actually turns your wheels. The other 2 gallons, 65%, is wasted. Much of that goes out the exhaust as heat. However, some of it is heat energy wasted in nonpropulsion heat processes. Imagine if we could redirect even 10% of that 2 gallons back to the wheels. That would mean that our 35% efficiency could go to 45%. In theory, that would represent a 30% increase to fuel economy, 45/35=1.30. In other words, anywhere we can find and eliminate a waste heat process, our effort should reward 3-fold. Who doesn’t like driving with a constant tailwind?
The biggest waste heat process we find in any forced induction vehicle is in the turbocharger compression process. More specifically, the more you try to squeeze out of it, the more parasitic and heat producing it becomes. When you are making 400 HP with the help of an inefficient turbo, at high elevation it will manufacture 475,000 BTU/hr of heat from the compressor. This is only slightly less than the needs of our cooling system, and is the wheel power equivalent of 200 HP!!! That is the power experienced by the turbo shaft, albeit with very low torque and very high (140,000) rpm. Still, that “power” has to come from somewhere. It comes from the conversion of exhaust heat, to mechanical turbine work.
For a better explanation, see Thermal Feedback explanations in former works.
PUTTING OUT THE FIRE
THIS is where water injection gets exciting…extreme turbo shaft activity.
From…Aircraft Gas Turbine Powerplants Handbook:
“The injection of water into the gas path causes heat transfer. When the fluid evaporates, heat in the air will be transferred into the fluid droplets, cooling the air and making the gas flow more dense. Water injection in a gas turbine engine is then a means of augmenting engine thrust. Augmentation can be thought of as occurring in two ways. First, addition of water to air in the compressor increases compression and mass flow. second, water cools the combustion gases which allows additional fuel to be used without exceeding maximum temperature limits during takeoff. Increases in these three engine parameters results in a thrust increase in the range of 10 to 15 per cent.”
Pilots, whose lives depended on it, have seen it first hand. WWII fighters used ADI (anti detonation injection — the common term in the aircraft world for WI ) to improve performance, permitting escape to higher altitude. Water injection helped launch B-52G Bombers with 200,000 lb weapon loads into Vietnam.
“The injection of water droplets into compressor inlet ducting is now commonly used as a means of boosting the output from industrial gas turbines. The chief mechanisms responsible for the increase in power are the reduction in compressor work per unit flow and the increase in mass flow rate, both of which are achieved by evaporative cooling upstream of and within the compressor…Consideration is also given to the efficiency of the compression process”…J. Eng. Gas Turbines Power — October 2004 — Volume 126, Issue 4, 748
In the case of an 8 engine B-52, you get more thrust. With your truck, more torque.
FIREMETRICS
We monitor an important heat stress indicator…EGT, exhaust gas temperature. It must be controlled or things melt. When the engine has to work harder (to fund waste heat processes), EGT is unnecessarily high, a longevity concern. Factory tuning usually insures it will be sufficiently low. When we get brave and decide to up the power, we introduce more fuel, hence higher EGT. It can easily go from 1200 F to 1400 F, even higher in an aggressive tune. Much like dessert survival, water can be used the same way here to stay within limits. By breaking the bonds that hold water molecules together, the surrounding temperatures (EGT) will lower. This breaking of water molecule bonds is called evaporation.
SO WHAT IS 1000 BTU OF HEAT?
1 BTU is the amount of heat required to change the temperature of 1 Lb. (2 cups) of water, 1º F. BUT, for each pound of water converted to vapor, 1000 BTU’s are required (970 to be exact). In other words, evaporating water uses the same amount of energy as it takes to heat it 1000 degrees. That 1000 BTU’s consumed during evaporation is known as the Latent Heat of Evaporation. Water has one of the highest on the planet. Since water is cheap, and stable at atmospheric pressure, it is the perfect substance for internal cooling, for your body, AND for your engine.
-A 40 gallon bathtub requires 8000 BTU of heating in your water heater, yet only one of those gallons needs to evaporate to cool it all the way back to room temperature.
-Five 60W light bulbs consume 1000 BTU in one hour.
-To burn 1000 BTU anatomically, you have to exercise aerobically for 2 hours
-1000 BTU is 1 oz of diesel fuel burned, or to produce 300 HP for 5 seconds
The amount of energy absorbing potential available in 2 un-evaporated gallons of water is enough energy to run a marathon. The cooling needs of an 8 cylinder turbo-diesel at 70 mph can be met in the energy absorbed from evaporating just 1 cup of water every minute.
Maybe the best analogy: If your clothing was soaked with water on a 60 degree, no humidity day, with a 20 mph wind, by the time the 2 cups of water evaporated (1000 BTU) off your clothing, about 20 minutes, you would be left fighting for life with a dangerously hypothermic 92 degree core temperature. Evaporation is that effective.
With water such an affordable and plentiful material, it would seem foolish to forget to take advantage of it to help meet our power and efficiency requirements. Yet, there is so much confusion and ignorance surrounding this concept, for one main reason: there is no real understanding about how it works, thus how to make it work better, safer.
Most kits are applied to spark ignition vehicles. The main improvements to these vehicles is that the water droplets that enter the combustion chamber, lower the combustion temps, inhibiting the automatic knock/detonation timing retard that occurs in closed loop ECU timing control. Since the vehicle can then maintain more advanced timing, more power is produced. These protection mechanisms do not exist on the diesel PCM software, so this type of misting has less merit. All that “detonation suppression” and “computer timing retard” yada yada, is not relevant to a diesel. There is no IATknock timing retard algorithm, so if you are accustomed to gasoline knock and octane concepts, fuel-water ratio, etc, dump these concepts and forget everything you have been taught.
MYTH 1: “Water Injection creates a condition where hydrogen and oxygen are liberated in the combustion process, thus making more power”
Truth: I came across this claim by a prominent Diesel performance manufacturer. Presumably we are left to believe that the dissociated hydrogen and oxygen are responsible for the power boost…and this is a blatant lie. The energy required to split the components of water, is unimaginable. If it was this easy to do with heat, we would all have water in our fuel tanks! Oxygen gas is not created from water.
MYTH 2: “When water is evaporated, it creates steam which displaces air, so less oxygen is available for combustion.”
Truth: When water goes to gas state, the resulting air flow rate, and oxygen density, increases with the cooling effect. This will be proven later.
MYTH 3: “I live with high humidity, I would not benefit from water injection. “
Truth: No matter the ambient humidity, the relative humidity of the same parcel, after compression, is much lower. In fact, it can lower to only a tenth of ambient humidity, permitting more water to be evaporated. Also, in elevated areas, seldom is humidity greater than 20%. Why do I bring this up? Because induction cooling is needed most at high altitude where compression heating is at its worst. Naturally occurring low humidity at these elevations plays right into our hands.
MYTH 4: “Water injection will destroy my compressor”
Truth: No question, poor application can erode the compressor, but it is also true that 99% of pre-compressor misting is done improperly. If you follow all the bad historic examples so prevalent in this hack industry, yours too can be damaged. Yet, it is not understood when the turbo explodes from a 36 psi overspeed, that water could have prevented it.
MYTH 5: “The evaporated water will re-condense in the CAC, posing a pooling and hydro lock threat to the motor”
Truth: This one you will see on every internet forum that discusses W/I. I could go to the psychrometric chart to demonstrate, but let’s just rely on just a little common sense here. At max power and air flow, air is running through the CAC at over 100 mph and in a temperature range of 200-500 F. Is it possible for anything to pool in this environment? Of course not. However, if water flow occurred at idle, because of siphoning, or worse, engine off, due to a malfunction, there’s a problem. The mixture that enters the cylinder must remain compressible. If too much liquid water enters in the intake stroke, it becomes an incompressible obstacle preventing the piston from reaching a fully compressed state, with subsequent catastrophic rod bending stress. Precautions must be used to prevent this solitary danger.
MYTH 6: “Water will corrode the aluminum CAC from the inside out”
Truth: If so, intercoolers in foggy low lying areas all need to be replaced. Done in moderation, liquid water need never see the inside of a CAC more than that experienced on a cold wet morning. Water is typically actuated less than 1% of total operation, and even then it is under high heat conditions, any moisture wetting the CAC in this short duration spray is gone within seconds of the end of spray. It would take days or weeks of constant exposure to water for oxidation to be significant. Typical spray duration exposes the CAC to much less water than operation in wet humid environments, by far. Methanol mixtures are no worse.
MYTH 7: “For w/i to work well, the water should be cold”
Truth: Widely misunderstood. The energy absorbed to evaporate a pound of 80 degree water is 700% more than required to heat (or cool) that same water by 100 degrees. Cooling the water first is too much trouble for too little benefit.
MYTH 8: “For w/i to work well, the water must be hot, closer to its boiling point”
Truth: Water evaporates at all temperatures. If it didn’t, puddles would never dry, little Johnny would always be soiling the carpet with muddy feet, and the kitchen floor would be perpetually wet following mopping. It does evaporate quicker near its BP, but this point is a minor one.
And my favorite:
MYTH 9: “Pre-compressor WI reduces the efficiency of the intercooler”
Truth: It is not a myth. This is a physical fact… and …so what? Seriously, so what? It is irrelevant. The idea here is that CAC efficiency, by definition, is dependent on the inlet temperature conditions being as large as possible…Subtract ambient air temperature from Compressor Outlet Temp (COT), a larger number means higher CAC efficiency. So lowering COT means the CAC is less utilized. A bad thing? In the end, what is important is charge temperatures and density entering the cylinder. The opponent usually argues that it is better to let the CAC do it’s job, THEN apply evaporative cooling. I don’t agree. This completely disregards 2 very important known observations.
1. It ignores all the other benefits of PCWI to the (parasitic, heat creating) turbo compression process itself, which handily outweigh this small point, and
2. There is no practical way to evaporate significant amounts of water after the compressor, making for a mute argument, one without any legs.
Because of these myths, and poor application, pre-compressor water injection has a bad reputation. I say that this is because it is rarely ever implemented intelligently.
WALKING ON WATER
In liquid water, the individual water molecules are all held together in a 3-dimensional lattice by the hydrogen-oxygen attraction. HHO–HOH– OHH…Each is simply H2O, with different alignments. They are bonded together, hydrogen to oxygen, with hydrogen bonds, represented by the red arrows.
A TINY droplet of water-note that evaporation can only occur at the water-air interface. This surface area limits how quickly evaporation can progress
Inside this drop of water, a few molecules away from the surface, each molecule is engaged in a tug of war with its neighbors on every side. For every “up” pull there is a ”down” pull, and for every “left” pull there is a “right” pull, and so on, so that any given molecule feels zero net force. At the surface, things are different. With only air above, there are no neighbors above to pull on it, thus the net force on the surface molecule is directed into the liquid. This force asymmetry causes the water surface to bend and ultimately form the shape of a sphere…rain “drops”. This “stretchy skin” net-like effect is called surface tension, the fire crew’s enemy. It is the property of a fluid that “pulls” it together, to collect and pool, instead of disperse. It readily forms streams, ponds and runs downhill.
The same stuff that helps water to clean clothing, also helps water to put out petroleum fires. Since the key to extinguishing fires is coverage, a barrier between the fuel and the oxygen is . With petroleum fires, pure water is heavier than the fuel, sinking and pooling beneath petroleum on contact. So water must be treated with a foaming agent. The foaming agent (surfactant) forms bubbles in the water, giving it the lightweight floating property to stay on top and suffocate the petroleum fire.
With surface tension, if you fill a glass with water, you will be able to add water slightly above the rim of the glass without spilling over. Similarly, these 2 water bugs are enjoying natural procreation on a water bed under tension … they have legs that are like a freshly waxed hood, or a ducks feathers.
A drop of dish detergent would spoil all this fun, and this marriage would sink, as would the paperclip. Surface tension may make it possible to play away from predators, but it plays a deterrent role in evaporation.
Before birth, in preparation to breath our atmosphere, surfactants are created in-utero. They break down the liquid “film” that interferes with oxygen uptake, increasing interface surface area and aiding in the absorption of oxygen into the blood stream. Since they are produced late in the 9 month gestation period, for premature births, these surfactants have to be artificially administered.
BREAKING THE TIES THAT BOND
Relative Humidity, a variable property of air, is the measure of how much water vapor is in the air, in comparison to how much total water that the air can hold. It is expressed as a %. If we expose dry air to liquid H2O, the air will absorb water gas molecules as they evaporate, each water molecule setting up residence between oxygen and nitrogen air components. Only so many H2O molecules can fit. When one more gas (vapor) molecule can no longer fit among the air components, that is known as saturation, or 100% humidity. At that point, water added just stays liquid water. Once the air mass is saturated, there is a simple way to put more water in it: heat it. If you heat it up, the mass expands and allows more room for more water molecules. Now it will take on more water. (if you are getting ahead of me, you already realize this is what happens under hood.)
STEAM ME UP
I said I would explain where the energy comes from for evaporation. Each H2O molecule can have 4 bonds to others. In order for just one surface water molecule to evaporate, all 4 of these H-O bonds must be broken. This takes energy. You can deliver this energy in the form of heat, like when heating it on the stovetop. OR, to a lesser extent, evaporation will occur spontaneously and invisibly at lower temperatures. The energy for this comes from the air and water itself… the “surroundings”, in turn lowering its temperature. This “latent” heat removal is commonly called “evaporative cooling”, the main crux of this article.
Watch a drop of water sitting on a freshly waxed hood. This compact spherical shape is a big deterrent to air stream evaporation…. It is the perfect shape for minimizing surface area, the air-water interface area. This same drop will be gone in moments if it is spread across a chamois (or cotton shirt), a larger surface area. To get a good evaporation rate for decent cooling, we need a way to increase the surface area of the water you wish to evaporate. Swamp coolers do this by soaking a wicking cloth in water and passing the air through it. Another common method is fogging: the water is forced through a small orifice at extremely high pressure, creating billions of micron sized (area-conserving) droplets which evaporate quickly because of the shear number, and small volumes. This is the premise for water injection.
CLEARED FOR TAKEOFF
“Water injection” is the process of using water to cool the (surrounding) air charge. This process has been used in countless applications dating back at least 100 years.
GE uses fogging to increase electrical output by 20% and decrease fuel consumption in thousands of its power generating turbines. This is particularly profitable during peak consumption periods, as it permits fewer turbines to meet the electrical needs: lowering staffing and maintenance costs as well. A B-52G uses 10,000 lbs of water to shorten takeoff roll for heavy takeoffs. An extra 8000 lb of thrust is created, lasting 140 seconds. This “wet” thrust can be felt, and shortens takeoff run by hundreds of feet. The drier the ambient condition, the higher the thrust benefit.
“To take the concept of evaporative cooling a step further, spraying water into the compressor of the combustion turbine, CT, is a viable and now proven technology for increasing turbine power output by up to 25%. This method of power augmentation is referred to as wet compression, overspray, super saturation, high fogging and many other names…” Caldwell Energy Company
THE 10 TOP REASONS TO DO THIS WITH YOUR VEHICLE?
1. Variable intercooling: On demand, you can switch on the water to cool charge air further under high heat conditions. This reduces CAC heat soak that occurs under sustained high load conditions.
2. Overheat protection: cooling the CAC, in turn, aids radiator cooling.
3. Timing benefits: The increase in humidity to an otherwise dry charge, improves combustion quality, more positive torque is produced and less detonation occurs.
4. Turbo Longevity: Compression becomes quasi-isothermal, reducing the heat expansion impact. This compression efficiency increase results in reduced turbo RPM and extended longevity.
5. Slows air charge velocity: the denser, slower charge creates less frictional loss of boost in the related plumbing.
6. Increased Air Uptake: for the same turbo rpm, pre-compressor cooling keeps the compressed air cooler, thus denser… Higher MAF and more oxygen density.
7. Internal Wash: nothing is worse for carbon buildup than hot dry air. Humidifying it reduces this, and when utilized beyond saturation, has a steam cleaning effect.
8. Poor mans turbo upsize: when injected pre-compressor, the turbo acts as if it is a size bigger, without any of the disadvantages of larger turbos.
9. Potential for EGT control, 250 F reductions are typical, 350 F reductions are possible.
10. And one for the environmentalists, a 60% reduction in poisonous NOX emissions.
Imagine if every time you accelerated to 70 mph, a 40 mph tailwind whipped up to help. Wet compression is such a tailwind in the thermodynamic world.
“Wet compression is a process in which water droplets are injected into the compressor inlet air and allowed to be carried into the compressor. As the water droplets evaporate in the front stages of the compressor, it reduces the air temperature and therefore reduces the amount of work that must be done by the compressor …The net effect is reduction in compressor work. … Wet compression also results in a significant reduction in the compressor discharge temperature…There is no other technology that offers so many benefits and yet is so economical.…” WET COMPRESSION by Sanjeev Jolly, P.E.
TIME IS NOT ON OUR SIDE
Our biggest challenge in accomplishing what we want is TIME. Air travels from airbox to cylinder, sometimes, in under a second. A typical 60 micron droplet requires 10-15 seconds to evaporate when adrift, though it varies depending on air humidity, temperature, as well as motion. If air stagnates around the drop then the air layer immediately adjacent to it will become saturated. Getting the air and water droplet to interact more leads to quicker evaporation. This causes that adjacent saturated layer to be continuously replaced with dry air. This is why hypothermia is accelerated with wind.
Our droplet needs a “breeze”: A 600 mph, 400 F breeze? Even better!
The 120,000 rpm compressor is a blender with incredible cyclonic effectiveness. Small droplets that hit the compressor are immediately pulverized into thousands of smaller microscopic foglets as they are swept through this storm. The total surface area of water exposed to air is instantly 1000-fold that of the best post-CAC installations. These sub micron sized droplets, mixing with air at 600 mph, are then flash vaporized in the 400 F degree compressed air environment.
RIVER WILD-EROSION
Once upon a time, somebody decided to place a misting nozzle such that it shot across a tube. In fact, every dealer of these systems make the exact… same… mistake! A single high volume nozzle is positioned such that it is aimed at the opposite wall of the tube. The mist shoots out at 100 mph, and 100 micron diameters, 20 times larger and 50 times heavier than fog. Most of the droplets immediately collide on contact with the walls surface, and recombine (surface tension!), just like our fire hose example. The resulting re- formed steady stream of liquid then gets dragged along the wall and into the fastest part of the compressor, the tips. These blade tips are bombarded and eventually emerge…eroded, at the tips naturally where the stream meets the blade. If you see how this happens, it is easy to avoid.
REALITY CHECK
An interesting study found w/i to be quite safe in axial compression where peak tip velocities are similar to what we would subject a turbo compressor to:
“Prior experience with wet compression systems that have operated on other large frame industrial combustion turbines has shown that most erosion occurs on the leading edge of the row 1 compressor blade producing a slight change in chord length (approximately 1mm) over 24,000 hours of wet compression system operation. However, this wear was not extensive enough to require blade replacement at that interval. Stationary compressor vanes are expected to see some loss of coatings and roughening of the surfaces that are wetted, but have not shown a change in chord length. Downstream stages of rotating compressor blades will also show signs of erosion in the tip region over time, as the water droplets are centrifugally forced outward. This continues until the water is fully evaporated around the 5th or 6th compressor stage. “…Caldwell Energy.
The fogging methods in these plants involve large ducted tunnels full of nozzle arrays, an important detail to mention. We don’t have the luxury of all this room. However, GE uses fog augmentation on hundreds of power producing CT’s, and does it 24/7!
CT Humidification (FOG) Room
DEFINE IRONY
My favorite definition comes from Steve Buscemi’s in the movie CON AIR, referring to the criminals, with a Lynyrd Skynyrd song playing on a boom box. “…a bunch of idiots dancing on a plane, to a song made famous by a band, that died in a plane crash.” Then I started thinking how blade erosion got its bad rap, and how the typical installation seems to be a product of criminal IQ.
During normal use, a vehicle would rack up just 30 minutes of injection over 10,000 miles, less than 2 hrs for those that tow frequently. So while a crude injection system might be relatively tortuous to a blade tip, the shear minimalist use serves to rationalize its practicality. SAAB (“born from jets”) believed this in implementing a factory preturbo misting. They reaped 15-20 HP (over 10%) on water alone with a 2 L displacement. You can do the math for your own application. These turbo’s were inspected in a test program and guess what? … It caused compressor blade erosion. Yup, after 100,000 miles, and with the aid of a 10 power lense, there was enough erosion to predict a useful life of only…200,000 miles, boo hoo. Returned to service, without any performance degradation. What is most impressive is that these same turbochargers, formerly capable of only 20 psi, could output 24-26 psi with water. Fair tradeoff? At these overspeed levels, the useful life of the same turbo without the benefit of this cooling, was only 60,000 miles. Am I starting to make sense?
Define Irony: “Condemning pre-C injection for it’s one inherent con, when it doubles the overall life of your turbo as a unit.” If you are going to grenade your turbo in overspeed self-destruction, why would you ever worry about slow `erosion to an affordable and replaceable part, in a process that is proven to increase longevity of your turbo at these levels?
HEAT FROM?
A wedge of air is ingested between each adjacent pair of compressor blades. When spinning at 100,000+ rpm the air is subjected to huge centrifugal forces as it moves from the center of the impeller and toward the blade tips, compression. Consequently, the molecules are forced closer together as it gets near the volute exit where T2 is measured. A lot of internal friction occurs in this process. Near the tips of the compressor, air approaches sonic speed. The resultant frictional heating makes the air try to expand, which increases the pressure. This resists what we are trying to accomplish, the outward movement of the air. Eventually a balance is struck between the centrifugal forces trying to throw the air out of the impeller and the backpressure build up due to the compression and from heating. The whole process takes a millisecond.
The addition of water, with its enormous latent energy absorption potential, removes a large fraction of the heat induced pressure gain. Frictional heating and expansion is reduced and T2 above is also reduced. As a result more air can exit the impeller over a given period of time, and more of the pressure gain is real compression instead of waste heat. With this cooling (contraction), the lower air velocity lessens the resistance losses in the entire tract.
TECHNICALLY…
Have you ever noticed that your vehicle runs stronger, cooler, and more responsive when running through a fog? When I lived in northern California, my twin turbo loved the cool mist mornings. In thermodynamic speak, what happens in fog is the result is a more isothermal (constant temperature) compression which is more efficient than adiabatic compression. The work of compression is:
W(c) = m Cp (T2 – T1)
Lowering T2 (exit temp) through evaporative cooling from fog reduces the effort (work) that is required to turn the compressor. In other words, it will turn slower, while producing the same boost, only cooler, denser. Or you can apply the same turbine work and get more compression (boost).
Boost production has the highest heat consequences at higher elevations, where air is almost always dry, and never foggy, the humidity paradox. So you need to bring the fog to your turbo. But how much?
LOOK IT UP
The “psychrometric” chart , although kind of busy, is useful; it describes the physical and thermal relationships of moist air. It will let us predict how much water to use, without any formulas.
Consider an air parcel that is heated, it expands, it becomes less dense…. The air molecules get further apart, allowing more room for water molecules to fit. “Relative” humidity decreases, even though actual water content stays the same. Then as more water is introduced through evaporative cooling, the temperature comes back down, shrinking the air parcel. The evolving water molecules inhabit quickly shrinking (cooling) real estate, and soon it saturates again. Track this process in a simple problem.
Problem 1: On an 80 F day, RH is 60%. Under hood, the air is heated up 40 F before it reaches the compressor. Plot the humidification of this air assuming enough water to reach 100% saturation.
For anyone towing in high elevations, 60% RH is very conservative, 10-20% is a more average number. If you live in the Desert Southwest, as I do, 60% happens about 3 times a year, so it will be very conservative.
1. Plot our initial conditions: an 80 degree day with 60% humidity. Note, some of the properties of this air. The specific volume, the inverse of density, is 13.9 ft^3/lb. A lower number represents increased dry air density, exactly what we are after.
2. 80 F is the ambient condition. But because of engine heating and radiation, actual intake air box temperature is usually higher. Let’s say it is heated up 40F, to 120 F. This is typical. (besides, ☺ this chart doesn’t go higher than 120 F). So move to the right to 120F, now our specific volume is 14.9 ft^3/lb, density reduced. BUT NOTE, humidity has dropped from 60% to 17%.
3. When we fog the air and evaporate water to saturation, this is a process where enthalpy (diagonally on the chart) is held constant since we are not adding or removing (total) energy from it. The energy supplied to the water for evaporation is taken from the air surroundings. So following the dashed constant enthalpy line, it arrives at 80 F, and density increases to 14.0 ft^3/lb dry air, a 6-7% increase in dry air (and oxygen) density. This air density is almost what it was before being heated under hood. This is a key point. This shows that with even modest amounts of air charge heating, high humidity quickly becomes low humidity, which can be cooled more. Myth #2 busted.
Problem 2: Using the plotted chart, how much injected water is necessary for saturation?
Go to the right side axis. Our 60% humidity air starts out at .013 lb moisture per lb of air. At full saturation, moisture content has increased to .022 lb/lb. .022-.013=.009 lb of water must be injected for every lb of air, to obtain 100% humidity. Our turbo-diesel typically uses 50 lb/min of air. So we need to mist 50 x .009 = 0.45 lb (8 oz) of water, each minute. Keep in mind, this is a high humidity example. In the high Rockies, rarely is humidity over 10%, just like my desert. If you run this chart again, you will see that saturation comes with 16-24 oz/min, and additional temp reduction (increased density), real important in this rarified environment. If you run higher boost in your tune, there is more air flow, so 30 oz/minute might be required.
A 40% reduction in humidity occurred with just a mere 40 F under hood temp increase. And this is on just the cold side of the turbo compressor, before compression heating. Now imagine what happens to humidity after 20 psi of compression, and the resultant 300 F temperature increase. With full boost, temperatures routinely exceeds 400 F…for you racers who are maxing out small stock turbochargers, or if towing heavy in high altitudes… easily 500F! I have logged 590 F…near sea level. That is basically 0% relative humitity.
100% outdoor humidity becomes a bone dry 3% at 400 F, it will absorb LOTS of evaporated water. This makes precompressor fogging the single best location to begin conditioning the air. It is your one shot at massive chemical intercooling using latent heat affects.
We are compressing air up to 30 psig in the turbocharger. Exiting the compressor at this pressure, on a hot day, COT is 500 F. We want/need that air to be as cool as possible before entering the cylinder. The typical heat soaked CAC will bring it down to 250-300 F on a hot day. Water can cool it down to 300 degrees… if enough water can be evaporated. To bring it to 300 F, our 200 degree desired reduction, we have the usual heat balance equation:
Q=m*Cp*deltaT
Q=70 lb/min*0.25 BTU/lb/F*200F=3500 BTU/minute= 210,000 BTU/hr
To do this by evaporating water, at 1000 btu/lb, we need to evaporate water at the rate of 210lb/hr, or 3 lb/minute, around 1-2 liter per minute.
But in reality, as the air is cooled, it quickly saturates well before that much water can be evaporated. That might impose a limitation, hypothetically 100,000 BTU/HR on how much evaporative cooling is possible with water. How do we get around this limit?
IT ONLY WORKS IF YOU WORK IT
So far, everything we have discussed centers on water alone. As the world’s universal solvent and almost cost-free element, it deserves the lion’s share of the practical discussion. But what happens when I mix another “solvent” in, like alcohol? How will that affect cooling? Will it interfere with water evaporation? What’s this talk about “fuel value”?
Other solvents have independent properties. Alcohols, for example, boil at lower temperatures (aromatic) than water, so they evaporate quicker, a good thing for cooling.
Alcohol, when mixed with water, has no idea what the humidity is, and it doesn’t care. It evaporates on its own alcohol saturation schedule with little regard for the adjacent water molecule. As far as the alcohol sees, air with 100% humidity is irrelevant. Alcohol gas will saturate the air parcel separately, on its own, independent gas saturation mechanism. So if you mix water with methanol, 50/50, you should now be able to evaporate double the amount of mixture: since only half of it is water. There is a huge additional temperature drop opportunity also, up to another 100 F, some prior to the compressor.
In other words, if one gallon per hour of pure water was calculated, then 2 gallon per hour of 50/50 water/methanol will evaporate just as readily, with a large increase in the cooling effect, compared to water alone. Get some rubbing alcohol and give yourself a sponge bath with it under a ceiling fan, you will get the idea.
An added plus with some solvents is that the surface tension of the water-based mixture is often reduced. Just 10% methanol, for example, drops the evaporation inhibiting surface tension 30%, viscosity also, and this means a higher nozzle flow rate, smaller droplets, less agglomeration, and increased evaporation rate. More surface area… more evaporation… multiple evaporation mechanisms…multi-solvent evaporative cooling.
PLUS it is a fuel adding to our power requirements. Nothing else does this with so little operational cost. But does this mean that it is safe?
FUELING SPECULATION
Rudolph Diesel designed our combustion cycle based on chemical-free air being compressed in the cylinder, and thus heated, this heat auto-ignites the ensuing spray of diesel fuel near maximum compression. “Auto ignition” is the spontaneous, yet predictable firing of the air fuel mixture from the heat developed by the cylinder compression itself.
The inherent ignition delays built into this cycle are important, and must not be overly compromised. I assert a simple philosophy here that originates from nothing more than an intuitive reality. In my mind, being unfaithful to this detail may cost you your motor.
IGNITION MUST REMAIN UNDER THE CONTROL OF YOUR ECU
OEM timing algorithms assume that just air is used, not ignitable gases like methanol vapor. The moment you introduce flammables and combustibles into the charge air stream of a diesel, you have potentially compromised the inherent safety net of a cycle that relies on the ingenious simplicity of pure air (oxidizer only). Simply put, if the air charge (with vapor fuel mixed in) ignites before diesel auto-ignition, ignition timing will be advanced to a point that can cause premature and massive cylinder pressure, you can inadvertently bend rods or less serious, convert your head gaskets into mush. But as long as the ECU-controlled, diesel auto-ignition mechanism is the ignition source for your charge fuel, there will be no problems. Don’t let the tail wag the dog.
Di-ethyl Ether (starting fluid) is an example of this with the 320 F number in the table below. It will ignite as soon as it hits a live glo-plug. Even if they are de-energized, if you were to feed ether into the air supply of a warm diesel, it will ignite well before TDC causing the piston to try to turn the motor backwards. If a large amount is sprayed, you will have severe damage to fix. Find the starter fluid can in the garage, and the warning on the can that reads something like, “Never use this product on a warm motor”.
Ironically, diesel fuel is another example with a low auto-ignition temperature, about 450-480 F… by design. If diesel were in the cylinder on the compression stroke, it too would ignite prematurely. I met someone who decided to prove just that, by putting diesel vapor in the air tract: it lasted a few seconds. He eventually replaced his injectors with larger ones, sometime after the $3000 overhaul, amusing.
ALL ABOUT METHANOL (pure, undiluted)
If we are going to use it, we need to understand it. The last thing I want to do, is pretend that it is harmless. Some diligent prevention here can potentially save a lot of facial hair.
General Description: A colorless, fairly volatile and FLAMMABLE liquid with a faintly sweet pungent odor like that of ethyl alcohol. …The vapors are slightly heavier than air and may travel some distance to a source of ignition and flash back. Any accumulation of vapors in confined spaces, such as buildings or sewers, may explode if ignited. Used to make chemicals, to remove water from automotive and aviation fuels, as a solvent for paints and plastics, and as an ingredient in a wide variety of products. (NOAA Reactivity 2007)
-Flash Point- The lowest temperature at which a liquid gives off enough vapor to be ignited at its surface: 52 deg F
-Lower Explosive Limit Or lower flammability limit. LEL. Lowest concentration of a flammable vapor in air at which explosion or combustion can occur: 6%
-Upper Explosive Limit Or Upper flammability limit. UEL. Highest concentration of a flammable vapor in air at which explosion or combustion can occur: 36.5%
-Auto-Ignition Temperature: the lowest temperature where the component ignites without any ignition source.867.0 ° F (USCG, 1999)
-Vapor Pressure: 100.0 mm Hg at 70.2 ° F ; 237.87 mm Hg at 100° F (NTP, 1992)
-Specific Gravity: 0.792 at 68.0 ° F (USCG, 1999)
-Boiling Point: 148.3 ° F at 760 mm Hg (NTP, 1992)
-Molecular Weight: 32.04 (NTP, 1992)
AUTO-IGNITION
This color chart helps characterize the risk for your diesel when introduced in the charge air stream. Yellow fuels need careful scrutiny. Red fuels, like ether, are a surefire way to run over your crank.
Auto-ignition temp (F)
850-1100 F
550-850 F
0-550 F
The yellow zone represents compounds that must be carefully administered. That means that to use them in the charge air stream, the temperature of the charge stream must be closely controlled, because if these compounds become too warm before cylinder compression, they can take on the auto-ignition dangers of red compounds when compressed. A 550 F compound must be used more carefully than a 850 F compound.
AUTO-IGNITION POINTS OF VARIOUS FUELS
As compression occurs, the new fuel impregnated, combustible air charge, gets heated to 900-1000 F at TDC, the exact number depends on the compression ratio and the cylinder inlet air temperature, IAT, then subtracting our evaporative temperature drop. The question that needs answering is when will it combust, compared to diesel ignition? How do we relieve our concerns?
“USE ONLY UNDER THE SUPERVION OF AN ADULT”
Is methanol safe to handle? I admit that when I have to visit the emergency room, I almost always find that I am not at my best, usually in a bad mood, barking at someone who is trying hard not to tell me in a tactful way, how dumb I was. For ego’s sake, I prefer to avoid this whole scene, and I have become good at it. Thus, idiot-proofing our effort is a primary consideration-safety first. Many will tell you to use good ole windshield washer fluid for its convenience and cost. I like that idea myself, but will never assume that just because we use it to smear bug guts on glass, that it is safe to use in or near a combustion environment. I have seen enough racing mishaps to know that this kind of blind faith is a BIG mistake.
What we typically do with methanol is buffer it. We add water (see chart) which helps slow combustion, The right proportions of fuel-water, about 10-20% methanol, allow you to use it with zero net timing change requirement, while water alone tends to leave timing over-retarded.
The flash point of a chemical is the lowest temperature where it will evaporate enough fluid to form a combustible concentration of gas. The flash point is an indication of how easy a chemical may burn when exposed to a flame. Materials with higher flash points are less flammable than materials with lower flash points. Clearly then, adding water to methanol reduces its flammability danger, the chart indicates this.
What the chart is saying, for example, is when your ambient temperature is 75 F or higher, a 50% mixture can be ignited with a flame or spark. If it is winter, and 32 degrees, you can’t ignite pure (100%) methanol at all, you need at least 54 degrees.
For commercial purposes, and normal material handling, the industry publishes these guidelines about methanol:
“Class 1B flammable liquid. Burns with a clear, almost invisible flame, especially hard to see in strong sunlight. Methanol-water mixtures with 25% or more methanol are flammable. Avoid water streams which may splash and spread flaming liquid. Vapors are heavier than air and may flow along surfaces to distant ignition sources and flash back.”… MATERIAL SAFETY DATA SHEET, FIRE AND EXPLOSION HAZARDS ALDON ® CORPORATION
In other words, please, …don’t fog methanol near your open-pilot gas water heater in your garage, unless you want people to toast marshmallows over your remains. Ask me how I know this.
Recognize that windshield washer fluid comes in many concentrations of methanol, from 0% to 40%, depending on the freeze rating. By and large, fire incidents with methanol mixtures are not common, we owe that to the high auto-ignition temps, and dilution. But by way of disclaimer, if after reading this, you receive treatment for burns to your face, while installing a system with a cigarette in your mouth, thank the Darwinian God of fertility that he made you ugly enough to keep you from seeding the world with offspring that also lack good judgment. (You typically don’t find the woman of your dreams in the burn unit.) As I said, I have an aversion to emergency rooms. You can do what you will.
APPLICATIONS
How you structure water cooling really depends on your goals. Performance junkies prefer the term “drugs” to describe chemical fuels used in the charge airstream, mainly for shorts bursts of high power. Haulers have a very different need, mainly dealing with heat soak and thermally protecting their equipment, with “longevity” higher up on the short list. Even large intercoolers are subject to efficiency erosion from heat soak. This happens when we stand on the pedal for longer than a few seconds (towing). The 500 degree heat from compression quickly consumes the heat storage capacity of the metal cooler, going from being 150 F to 250 F in 30 seconds. There is going to be more value in augmented cooling after this heat soak sets in.
TOWING:
Earlier I mentioned how fighter pilots used water to power turbo-charged flight to higher altitudes. Higher altitude? Going where the enemy can’t chase you is a nice advantage. The limitation to flight at higher altitudes is oxygen content, and relying on the turbocharger to provide it after it has reached the rpm limit of its performance. At higher altitudes, this rpm (choke) limit is reached sooner for a given desired air flow. The water cooling allows the turbo to compress more air at that rpm limit…this provides the added power necessary to get higher, doing so also with less heat manufacture.
Elevation towing is a special opportunity to exploit water misting for a very similar result. Grade performance loss is, in large part because the turbo loses efficiency, and everything gets hotter and hotter as the pull progresses uphill to thinning atmospheric conditions. Soon, so much heat is produced that the radiator can no longer function correctly behind the CAC. This is the condition loathed by all heavy haulers, especially a few LLY owners.
Excess heat advances ignition. If monitoring cylinder pressure, what happens is that the location of peak pressure pulls back toward TDC, an over-advance timing condition, and torque begins to drop off while cylinder pressure increases, a double negative, and bad for torque production.
Having this system at the end of your finger is the single handed cure-all for these symptoms of thermal feedback. Actuating water injection, increases MAF, reduces the harmful heat production, and puts LPP back where it needs to be, restoring torque optimization very quickly.
SMART CIRCUITS-DOSING
If you see this as I do, having paid money for my WW fluid, then I am inclined to set up the injection scheduling such that it only occurs when it will make a difference. By avoiding spraying until conditions require it most, can reduce fluid consumption by 75% easily. Consumption occurs when thermal conditions will put it to the best possible use. The “Mist-Miser” mode, let’s call it.
PERFORMANCE: There is not much point in injecting when the heat is not being created, so fogging will be set up for high airflow production only (this is when the compressor is heating the most). In essence it will be used to extend top end full throttle performance.
A “performance” algorithm might be, boost > 25 psi, AND throttle > 95%, AND intercooler outlet temps > 150 F (or some tweaked variation of this). We know this condition is creating a LOT of induction heat for the engine. These conditions insure also that injection does not occur when conditions would be favorable for pooling and hydro lock…a failsafe.
ECT CONTROL: Another user might be using this to help keep ECT under control. In this case he might use, ECT > 235 AND Boost > 15 AND TPS > 70%. Again, meeting ALL conditions will insure prudent consumption, knowing that added cooling is not necessary once you unload, even if ECT is still high. Slow cooling is better for the truck anyway. The specific parameters you use should address all your specific concerns for safety, as well as imprudent use.
After 2 years, here is the patent pending result of being obstinate.
I-FOG Shown installed on the LMM mouthpiece
Working around the limitation of time and solid boundaries, means you have to use multiple, smaller capacity nozzles, perhaps locate them axially to the air stream, all flowing concentrically with the air stream, to reduce agglomeration, then make it easy and affordable to install. All from a single point feed, and NOT introduce excess parasitic airflow resistance?
I-FOG addresses every challenge.
1. 8 Concentrically aligned, small capacity nozzles eliminates coarse mist, reduces agglomeration.
2. Supplies a variable amount of finely atomized fog, with capacity up to 2 liter/minute.
3. Uses multiple nozzles (up to 8), BUT only requires a single connection. The plumbing is all internal, no snake pit of tubes to hide or maintain.
4. Flow rate easily adjustable with various nozzle ratings.
5. Invisible to airflow-has no appreciable plumbing resistance due to its huge 4.75” size and aerodynamic low drag profile.
6. Fits all LBZ/LMM and all LLY with Induction Overhaul Kit.
7. Can also be used to supply Nitrous Oxide or alternative airborn fuels, propane, etc…even in combination with each other.
RESULTS:
To make a significant difference to the cooling system and potential load capacity, a 60,000 BTU/hr is necessary. This has been demonstrated in past cooling system efforts. This unit is capable of 180,000 BTU/HR, which is enough cooling to air condition several of the homes on my street. This change alone can reduce your 375,000 BTU/HR induction related heat, to 195,000. That is enough to silence the fan and reverse any heating tendency of your turbo-diesel, with just about ANY load you can find. The resulting power improvement through parasitic fan elimination, improved ignition quality, and increased compressor efficiency, when combined with the fuel value of 40% methanol, provides an on-grade benefit of 100 HP minimum. Add nitrous to one of the convenient tapped npt ports, and the latent cooling can be increased further.
This is the perfect option to counter the influence of thermal feedback power erosion, which I have dedicated myself to over the last few years. I have created this spreadsheet to help with determining just how much cooling and power to expect. There is a separate tab dedicated to water- methanol cooling.
Up to:
-180,000 BTU/hr with water/methanol
-100,000 BTU/hr with water only
-100 HP increase (40% methanol)
-350 F EGT reduction
-Added cooling equivalent of a radiator and electric fan off of a 1500.
-10-15% increase in mass air flow