Every month in the How It Works series, we pick one subject and take an in-depth look at how it functions, the physics behind it, and why you would or wouldn’t want to install it. This month, we decided to take a dive into water/methanol injection. Water/methanol injection isn’t new technology, but in the past decade it has really come to the forefront of the diesel industry as a safe performance enhancer.
Understanding The Chemical Side Of Things
Unfortunately, there is no standard chemical formula for diesel fuel mandated by the government yet. So, depending on the time of the year, who processed the oil and where it was processed, it will determine what the chemical formula of the diesel fuel you will have from the pump. Have you ever filled up and the truck felt a little doggish or more peppy than usual? More than likely this is because the cetane was different in that tank full than what was previously in there. At the pump you will find anything from C10H22 to C15H32, with the average or most common being C12H23.
Ever wonder what the ideal air/fuel ratio is for the maximum amount of power per given volume of fuel is? We put together three simplified balanced chemical equations. (Note: For reference (CxxHxx) is diesel, (O2) is air, (CO2) is Carbon Dioxide, and (H2O) is Water, etc.)
Average Diesel: 17.75:1 air fuel ratio
4[C12H23] + 71[O2] goes to 48[CO2] + 46[H2O]
Low Range of Cetane: 15.5:1 air fuel ratio
4[C10H22] + 62[O2] goes to 40[CO2] + 48[H2O]
High Range of Cetane: 23:1 air fuel ratio
[C15H32] + 23[O2] goes to 15[CO2] To 16[H2O]
What Is It?
Water/methanol injection is pretty much exactly what it sounds like. A combination ranging from 100% water to 50% water / 50% methanol is sprayed into the intake of an engine. As the liquid enters the intake, it absorbs heat energy from the surrounding air and travels along with the air. As the mixture enters the cylinder and as the intake valve closes, the liquid continues to absorb heat energy. When the piston starts to compress the mixture, it stays above what is called the saturation temperature (the temperature at which a liquid under goes a phase change converting into a gas, like boiling water, at a given temperature).
As the piston continues to compress the mixture, the liquid is able to absorb more and more heat energy. Then, once the fuel is injected into the cylinder and ignited, the temperature reaches the saturation point and the liquid becomes a vapor (or gas). During this phase change, the oxygen molecules from the water are able to interact with the fuel molecules to provide extra oxygen for combustion. While straight water doesn’t contribute to significant horsepower gains, this process does help to lower combustion temperatures. As the percentage of methanol that is introduced into this equation rises, more power is produced (thanks to the burning of the methanol).
So, Who Figured All This Out?
An engineer by the name of Sir Harry Ricardo is usually associated with being the first person to really start to use water injection in the early ’40s. He originally experimented with using water to increase the effective fuel octane ratings to allow for increased power on high boost spark ignition aircraft engine applications. This was usually used to aid in take offs during WWII. It was also used to help fighter aircrafts gain the upper hand in dogfights.
Even after WWII water injection was used but other advances in gasoline chemistry made this less and less needed. Most manufacturers preferred to build engines that are able to run at maximum output with the least external assistance needed (i.e. only adding fuel to the fuel tank).
Are There Benefits To Adding Water/Methanol?
Yes, there are quite a few benefits to water methanol. As the liquid is absorbing heat energy from the surrounding air, it is essentially reducing the intake temperature. As you may already be aware, air is denser at lower temperatures. So, by reducing intake temperatures, the cylinders are receiving more oxygen per unit volume. This helps to increase both horsepower and torque.
The effects are greater as boost pressures and intake air temperatures rise. The second effect of reducing intake temperatures is the reduction in exhaust temperature. If the air/fuel mixture is at a lower temperature before combustion, the resulting burn will be lower and thus, most of the time; an engine’s EGTs can be reduced with straight water. “Our testing indicates that high rates of 50/50% water-methanol injection increases EGTs under full load,” says Peter Treydte, Test Group Manager at Banks Power. This increase is due to the addition of a secondary fuel (methanol) into the combustion process.
Mike Ryan doing a little testing and tuning before his almost record setting run up Pike’s Peak in the rain and snow. He is sure to smash the record in 2014.
What Are The Disadvantages?
Not everything is without some risk. The most common issue that we at Diesel Army have seen is rust. As the water is being injected into the intake, it is being sprayed into a fine mist. Companies like Banks Power have spent hundreds of hours perfecting the shape of the cone and volume of water being injected to reduce this issue, but this mist does go everywhere and there is a potential for uncoated parts to rust. There are some additives that can be added to the water methanol mix that can help prevent this.
For example, Banks PowerBlend includes about 0.5% corrosion inhibiting oil. Also, depending on the type of engine, this may not be much of an issue. Many of the newer engines use a lot of aluminum parts, which aren’t susceptible to rust.
Another issue that can arise comes from people who have set up their trucks to “need” water to cool everything down. The common problem can be burning up internal engine components if the water runs out. This is usually only an issue for competition vehicles, but there are some vehicles that run more boost than they should without an intercooler and rely on water to keep the temperatures down. Outside of that, most other issues are hypothetical, this could happen if… scenarios, which are rarely ever seen, much less proven.
My Buddy Was Telling Me…
We all have those friends who are experts on every subject and can tell you about “everything wrong with everything.” There are some rumors that adding water methanol will advance the timing of the engine and create a spike in cylinder pressure before Top Dead Center (TDC). This would cause unwanted stress on rods and other components and if large enough, could actually damage components. What is actually happening is that the water/methanol mixture is cooling the air inside of the cylinder, which means that there is less heat energy available to start the combustion process.
While a person cannot feel the difference in ignition (it’s in milliseconds), the fact is that ignition actually happens slightly after when it normally would or another way of describing it would be that the ignition seems like it’s retarded. The second side of this equation is the methanol. After much research, you’ll find that methanol has a lower cetane number, which means it has a higher auto ignition point than diesel. This means that the diesel ignites before the methanol and thus is what ignites the methanol.
Because the cooler charge temperature is retarding the timing, by the time methanol actually starts to add power, it is after TDC and the increased pressure caused from the expansion of the methanol being burned is met by a retreating piston. The increased pressure is what most would call “safe” pressure. Meaning it is going the same direction as the assembly and not against it, (much less likely to harm anything).
Why Do Most Manufactures Recommend No More Than A 50/50 Ratio?
“The 50/50 mix keeps the methanol from being flammable, which allows it to not be characterized as a fuel. If we move beyond 50/50, we increase the flammability of the fluid, reducing the safety of fluid handling. This would mean that we would need to design the injection system as a fuel system at much greater cost and with additional safety measures,” says Treydte.
Where Does The Mixture Get Injected?
Inject post intercooler / pre intake
Depending on where the mixture is injected into the system will depend on how all of this interaction takes place. The most common place to inject the water or mix is somewhere on an intake elbow leading into the intake manifold. According to Gale Banks, the intake elbow offers one of the best locations to inject the water.
One extremely innovative thing Banks Power did with their new nozzles was to develop a nozzle that sprays different size droplets. The smaller droplets undergo the phase change sooner while the larger droplets are able to remove more heat from the system before they undergo a phase change.
Banks designed their nozzles with a 100 degree, full-cone spray pattern to fully take advantage of the increased velocity in the center of the tube. As the water is being injected into the intake, it has a chance to interact with the surrounding air. This helps to reduce the air temperature and is the process described in the “What Is It” section above. This is the same process that a non-intercooled vehicle undergoes.
Having a single injection point on a street vehicle works fine, but for racing this may not be the best design. With larger amounts of water being injected into the system, there becomes a greater chance of the liquid not being dispersed evenly between cylinders, which could lead to lot of issues.
Right before the cylinder in the intake runner (1 nozzle per cylinder)
Another option is if the water is being injected into the intake right before the valves (like the individual runners), then the majority of this process is taking place in the combustion chamber, not in the intake manifold and the charge air cooler (CAC) tubes, giving less “mixing” time for the liquid mixture to extract heat from the charge air. This means that the inlet air temperature (and resultant air density) going into the cylinder isn’t much different than without the liquid.
Therefore, the majority of the heat energy absorbed by the liquid will be directly from this air in the cylinder, yielding potentially a greater exhaust gas temperature drop per volume of water. This does increase the risk of over-injecting the charge and inhibiting the combustion process in-cylinder.
When too much liquid is present in-cylinder, too much heat can be absorbed during the compression cycle, at best causing power loss (reduced heat and reduced pressure equals less work done on the piston), and at worst, inhibiting the diesel auto-ignition process. “Bottom line, port injection can improve cylinder to cylinder distribution of an injected fluid, but allows less time for said fluid to evaporate and increase air charge density per-intake valve and can decrease power and inhibit the diesel combustion process when injecting large quantities,” says Treydte.
Inject post turbo, pre intercooler
If the water is being injected after the turbocharger, but before the intercooler, the process is basically the same but there are some issues/concerns. The water/methanol injection now must travel through the intercooler. Some of this mixture may not make its way all the way through the intercooler and standing liquid may be an issue inside of the intercooler. Thus, less of the mixture will make its way through the system and less will be available for combustion. This should be considered a last resort.
The supercharger on this setup is highly compressing the inlet air, causing high air temperatures. To manage this, Banks Power employs a single stage shot of water.
“It can be done, but it isn’t recommended if injecting large quantities, as even very fine water droplets impacting the edge of the turbocharger compressor wheel turning near the speed of sound will eventually cause erosion of the wheel – think water jet machining. It will function to reduce the charge air temp out of a compressor, but it is an additional mass the compressor must process, which reduces the unit’s total throughput potential. We only recommended if the charger outlet temperatures are extremely high. We use it on the high pressure ratio screw supercharger on the Pike’s Peak Freightliner for this very reason,” says Treydte. In addition to these concerns, the same issues above with spraying pre intercooler, also factors into this.
The Injection System Is Hooked Up, Now What?
Mike Ryan’s Freightliner uses multiple stages of water methanol injection to control the temperature, density and power.
With the mechanicals hooked up, the last things to really focus on are the electronics. Water injection needs to be turned on and off. It is not a system that remains on during all conditions. This is where the majority of the differences between manufacturers of injection systems come into play.
Companies like Banks Power, have created a control strategy that properly matches fluid delivery to engine demand. When the engine is experiencing a situation where the water methanol can be of great benefit, it will automatically come on. This leaves the driver focused on driving and not playing around with finding a switch or pushing a button to turn on the pump. In addition, many of these systems will illuminate a light or let you know when the system is low on fluid.
Where Do I get Methanol From?
There are a few options here. Straight water can be used (distilled water), also a lot of people run windshield washer fluid. The issues here are inconsistency in mixture percentages. A really broad average is that typically washer fluids run about 30% methanol. To get a consistent product that you can count on with the right ratios, the best bet is to always purchase from manufacturers like Banks that sell a premixed fluid at 49% methanol, 51% water (Banks calls it PowerBlend), that can be easily shipped via UPS (another advantage of it being lower than a 50% methanol mix).
So, Who Really Needs It?
With water methanol injection being a safe power adder most people looking to increase their horsepower and torque should look into adding a system to their vehicle. Also, anyone looking to just reduce EGTs when towing heavy load or regularly going up long grades. While injecting liquid into an engine that has the potential to hydro lock can be scary, in today’s world, with everything being electronic, water injection can be a safe enhancer and also, a safety device to extend the life of the engine when installed and used properly with the proper components.
Stay tuned as we dive a little deeper with a complete install and dyno testing of a water methanol system.