By: Haitham Alhumsi
One of the things that have changed over the last 10 years is the availability (and proliferation of knowledge) about available alternative fuels or octane boosters. Two such options are:
1- E85 fuel which is comprised of 85% Ethanol which has an octane rating of about 100 to 105 octane vs the typical 87 to 93 octane pump gasoline.
2- Water / methanol injection systems that can be used either as supplemental fueling system (based on the methanol content which carries an octane rating of 110 octane or higher) or can be used for in cylinder cooling when the water vapor injected with the methanol transforms into steam inside the combustion chamber, thus extracting lots heat out of the combustion chamber, and thus slowing down the speed of travel of the combustion flame front simulating the effects similar to those of a higher octane gasoline.
With the availability of these octane increasing or octane simulating concoctions, it has become more accessible of recent for the performance enthusiast to build more powerful supercharger systems, especially when space limitations dictate the inability to use an intercooler.
The use of a higher octane fuel by definition means that the air fuel mixture is more resilient to auto-ignition and detonation. Furthermore, in the event of a pre-mature ignition, the higher octane fuel creates a slower traveling flame front which gives the piston more time to travel upwards in the cylinder bore (Closer to top dead center) before meeting the flame front and this reduces the time that the piston surface is improperly pressurized and overheated reducing the possibility of catastrophic failure.
Last but not least, the use a water / methanol injection mix includes two phase-change events:
1- The injected methanol changes from a liquid state to a vapor state at its boiling point of 65*C, i.e. as soon as it hits the compressed air mixture coming from the supercharger outlet. This phase change absorbs a lot of the heat out of the air and methanol mixture reducing inlet air temperatures even before the mixture reaches the combustion chamber and starts to get compressed. This temperature reduction goes a long way towards eliminating or highly reducing the possibility of detonation.
2- The injected water, changes from a liquid state to a vapor state at its boiling point of 100*C which depending on the availability of an intercooler in the system, my occur in the intake plumbing before reaching the combustion chamber, or may not occur until the mixture is ignited. Either way, when the temperature is high enough, the water mist injected in the air stream will flash vaporize into steam also absorbing a generous amount of the heat created in the combustion.
Why is this important for cooling ?
“The first-order phase transitions are those that involve a latent heat. During such a transition, a system either absorbs or releases a fixed (and typically large) amount of energy. During this process, the temperature of the system will stay constant as heat is added.” … read more
Which means that the water or methanol will try to keep the air / fuel mixture at a fixed temperature of 65*C for the methanol phase change, and 100*C for the water phase change, for a long time (until the entire fuel has changed state) while absorbing a very large amount of heat energy out of the compressed air.
Since the air entering into the water/methanol spray’s path (especially with a lack of an intercooler) can be as high as 100*C above ambient (so with an ambient temperature of about 40*C for under hood temps we’re talking about an air inlet temperature of around 140*C in the intake piping).
Once this 140*C air meets the water & methanol mixture both the water and methanol will attempt to bring down the air / fuel mixture down to 100*C (the boiling point of water) and if all the water has vaporized into steam, then further down to 65*C the boiling point of methanol. If both operations are successful then the final temperature of our mixture is 65*C or 25*C above ambient which is great for any intercooler, and even more impressive for a higher octane non-intercooled system like ours relying on water methanol injection.
Now there are two possible applications for water / methanol injection:
1- The typical added cooling application:
a. In this setup, the water / methanol mix is usually mixed in a 50/50 mix of water and methanol.
b. The jetting is usually about 10-15% the total fuel flow of the system:
For example a 300hp four cylinder car needs four 450cc/min fuel injectors to produce that power figure. Our total fuel flow at peak power is 450cc/min 4 = 1800cc/min or 1.8 liters per minute of fuel.
1 gallon is four liters and 1 hour is sixty minutes so our total fuel consumption is equivalent to 27 gallons per hour of fuel (if you were able to stay at peak hp and rpm for a whole hour).
The reason we’re doing this math is that water / methanol jets are rated in gallons per hour.
So 10 to 15% of 27 gallons per hour = 2.7 to 4.05 GPH injection nozzle.
Now remember that 50% of our mixture is methanol, which is a high octane gasoline. So when injection 15% water methanol mixture with 50% of that being methanol, then our final air fuel ration will be richer by 7% or about 1 AFR point. This means that to reach optimum power again and our optimum air fuel ration we need to either increase boost pressure or retune our car to optimize it for the added high octane fuel.
2- Using methanol as a fuel
In light of what we just mentioned about methanol being a fuel, you could possibly use water /methanol injection as a supplementary stand alone high octane fuel system. The trick here is to keep in mind that the amount of water you spray in the system must be controlled to prevent the engine from hydro lock.
So in using water / methanol as a supplemental fuel as well as a cooling agent, limit the water content to 5 to 7% of your fuel injector flow, and compensate for your added fuel demands with methanol.
Here’s an example:
We have a car that produces 300 hp and has 450cc/min injectors installed.
At this power level the fuel injectors are already maxed out.
We want to raise the boost pressure on this car to reach a target of 360hp for example using methanol (rather than 93 octane fuel) as our fuel, and using some water injection for cooling as well.
450 (cc/min) * 4 (injectors) / 1000 (cc per liter) * 60 (minutes per hour) / 4 (liters per gallon) * 7% = 1.89 gallons per hour of water.
We want to spray enough methanol to cover our added 60hp worth of fuel.
60 hp requires four 90cc/min injectors
So our total gasoline requirement = 90*4/1000*60/4 =5.4 gallons per hour of gasoline.
One thing to note about gasoline is that you need double the volume of methanol as you would gasoline to reach a target lambda of 1 (ideal combustion) or what in gasoline would be an air fuel ratio of 14.7 parts air to 1 part gasoline.
So our total methanol requirement = total gasoline requirement * 2
Our total methanol requirement = 10.8 gallons per hour of methanol.
Now here are the final numbers:
Water / Methanol nozzle size = 10.8 (methanol) + 1.89 (water) = 12.69 Gallons per hour
Water / Methanol mixture = 1.89 / (12.69) : 10.8 / 12.69 = 15% water to 85% methanol
So how can I pull this off?
Obviously if you go ahead and get a single stage water methanol injection system spraying 60hp worth of fuel, and you activate it at 3000 RPM’s your car will bog down horribly and you may even cause catastrophic damage by washing the oil right off your cylinder walls with that much unneeded fuel.
To pull this system off successfully you need to use a progressive injection system with an appropriate injection duty cycle controller, tuned to ramp up the delivery of your water/methanol injection as the engine demand increases (based on RPM, MAS voltage, Boost pressure or a combination of these factors).
There are now several 1 dimensional and 2 dimensional water/methanol injection controllers, here are some examples:
Painless performance integrated 1 dimensional progressive water injection kit:
FJO racing has a two dimensional computer controlled progressive injection kit:
|Aquamist provides a simplified multidimentional system that tracks and follows your fuel injector duty cycle controlled by your factory ECU. The factory ECU adjust for throttle, boost pressure, airflow readings, temperature corrections, gear selection…etc and the acquamist simply takes the output of all that complex processing and follows it.|
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