Water and methanol injection does the same job in different ways, they both perform in-cylinder cooling and knock suppression well. Since water has a higher latent heat value than methanol, you need to inject twice the amount of methanol by mass to extract the same amount of heat during combustion. This is why all pure alcohol injection systems require a bigger jet, you need to inject 2.5 times by volume more than water. This makes little difference in practice except you need to find a bigger container.
Effect on knock suppression is totally different:
Water suppresses knock by quenching peak flame front temperatures hence regulating the frame propagation speed ? (too fast burn promotes knock). In-perfect charge distribution produces lean and rich pockets. Lean pockets burn at a higher temperature (oxygen-rich = faster) compared to fuel-rich pockets (excess CO slows down burn speed).
Alcohol suppresses detonation by increasing the knock threshold value of a given fuel grade. Since large amount of alcohol is required to control in-cylinder temperatures, air/fuel ratio will be affected significantly. Some fuel has to be removed to avoid over-rich mixture.
Power producing potentials:
In theory, more power will be produced if more charge is jammed into the combustion chamber, resulting in higher cylinder pressure and temperature. In practice, the associated components such as pistons, turbo turbine, etc has a finite operating temperature constraint. This is normally reflected by the EGT. The general accepted EGT figure is about 900C.
Power is basically a force exerted onto the piston per unit of time. Force (pressure) is generated with heated air in a confined space. If cylinder pressure can continue to increase without temperature rise, we have the ultimate power plant. Water injection and alcohol injection will be a good tool to perform this work, lets examine this in more details how each concept can help achieving this.
POWER TUNING:
(Assuming we have a powerful ignition system, a strong engine and unlimited supply of air and fuel).
For water: the task is relatively simple. First generate as much heat as possible by adding more boost and fuel. Water is then injected to absorb the excess heat until EGT is within a permitted safe level. Overall BMEP (Brake Mean Effective Pressure) is now increased due to the vaporized water. The amount of BMEP increase will depend on the mechanical strength of the engine structure. Water?s ability to push the power capability is almost unlimited.
For methanol: First consider using methanol as a fuel instead of Gasoline. Methanol?s ability to increase power is confined to the knock threshold, and available heat to increase the BMEP of an engine. Methanol has only about half of the energy content of gasoline, so twice as much methanol has to be injected to produce the same power. As twice the amount of liquid has to be injected, the cooling effect is huge, resulting in over-cooled combustion chamber, limiting the BMEP. A 100% methanol engine has to use multi-spark ignition system to ensure the mixture is constantly being re-ignited due to the cold combustion chamber. Within those constraints, there is still huge potential of power increase.
A good compromise to inject a percentage of injected into a gasoline engine. This will ensure good inlet and in-cylinder cooling effect, but how much? From reading many results form various forums, it appeared to be between 10-30% to fuel. Unfortunately, the results were not consistent, some got excellent power increase, some experienced engine knock, some misfires and some with very low EGT. Why?
4-5 years ago, AI system was very basic, at a certain manifold pressure, the pump starts and deliver a fixed amount of alcohol into the engine. In those days, results have always been very consistent and yield excellent power increase. But for the past few years, the results have been a mix bag. I could only put this down on the availability of the 2-dimensional AI controller. They are termed as an electronic progressive AI controller. Method of delivery is very similar to the mechanical rising-rate fuel pressure regulator. The flow is governed by the pump speed, the controller reads the manifold pressure via a MAP sensor, translates to a PWM drive signal to the delivery pump.
Lucky for some, the availability of stand-alone, piggyback type of engine controllers give user a high degree of control, changing fuel and ignition timing is a merely rapping a few keys on the laptop. In my view, I think this is the reason for the inconsistent result ? user?s interpretation of quite a complex ratio of methanol and fuel. Taking fuel out of the factory ECU to accommodate a methanol delivery system that has no reference to RPM, is a tall order. There are a few guys on this forum have managed it, I take my hat off to them.
My personal view on this relatively new concept requires a great deal of patience, dyno result means very little compared to logged data. Dyno-graphs always cause argument. I would really hope to see more logged graphs with AFR, Methanol flow rate, and EGT. If possibly the log should include a second to fourth gear run-up so we can spot the afr change due to Methanol. For those who has just embarked on the WAI, tune with 100% water - W50:M50 - 100% methanol and lastly 100% for ultimate power.
Need to clarify, get to experiment with water first and then add alcohol to until you are running 100% methanol. Lastly, you need to go a bit mad with crazy power, 100% water will be best. Some examples below with water only:
http://www.aquamist.co.uk/dieselmax
http://www.i-club.com/forums/showthr...&highlight=wrc
Water Injection, what mix/ratio of methanol should be used?
Linear Mode
