Water Methanol Injection

How Diesel Water-Meth Injection Works

Water methanol injection is a performance enhancing solution to reducing high exhaust gas temperatures, such as those experienced during periods of high load. The process is often employed on diesel engines, which can encounter relatively high EGTs while towing. Additionally, water methanol injection is widely popular in performance engines found in various motorsports. In a traditional system, water and methanol (or pure water) is injected into the incoming air stream of a diesel engine, thereby reducing the temperature and increasing the density of the air prior to entering the combustion chamber.

Popular water-methanol system manufacturers include Snow Performance, Cooling Mist, and AEM Electronics.

Pure water is often favorable to a mixture of water and methanol as it eliminates the possibility of detonation. The diesel cycle, which relies on a relatively high compression ratio, is not intended to compress any fuel - air alone is drawn into and compressed in the cylinder, and fuel is injected at or near the top of the compression stroke where it instantaneously combusts. As such, the addition of methanol may have the propensity to detonate before the piston reaches top dead center of the compression stroke. The risk can, of course, be reduced by properly metering the flowrate of of the solution and reducing the concentration of methanol in the mixture.

Water methanol concentrations range from 50/50 (half water, half methanol by volume) to 100% water. Distilled water is preferred, as it reduces concerns with rust and mineral deposits forming in the intake of the engine. In theory, this risk is minimal as water does not typically "pool" in the intake and the conditions inhibit rapid oxidation. Additives can be added to the mixture to further reduce these concerns in applications that continuously or frequently rely on water/water methanol injection. Pure water injection is often favorable in high load scenarios, as the risk of detonation increases with engine load.

As water/water methanol is injected into the incoming air stream, it is finely atomized through the orifice of the injection nozzle. In the presence of hot, pressurized intake air the fine mist changes phase from a liquid to a gas, absorbing a significant amount of heat in the process. The process increases performance by 1) creating a denser intake air charge and therefore a greater amount of available oxygen in the combustion chamber and 2) by the addition of a supplementary fuel, the energy of which is extracted during combustion (not applicable to pure water injection systems).

A pure water mixture is favorable for maximum cooling, as the heat capacity of water is much greater than that of methanol. Methanol, however, also serves as an anti-freezing agent in mixtures, as its freezing point is considerably lower than that of water. In ambient temperatures greater than 32° F, there are no concerns with regards to the freezing of pure water systems. Winterized windshield washer fluid, which is typically on the order of 30% methanol and 70% water by volume, is commonly used both for its reasonable price and conservative mixture ratio. Owners can typically expect a 40-70 horsepower increase when a water-meth system is in operation and up to a 200° F reduction in exhaust gas temperatures (EGT). Actual results will vary considerably by application, mixture, etc. For the most part, water methanol injection is not compatible with naturally aspirated IDI engines.

A typically system includes a controller that meters the flowrate of water/water methanol into the intake based on various parameters. As such, activating the system does not initiate a fixed flow of injection - ideally, the rate of injection should correspond with engine load, speed, and turbo boost. Systems can also be staged to provide varying degrees of cooling and performance. A single stage, for example, which injects a small amount of water/water-methanol and a second stage that is activated upon a high load condition, such as pulling a long, steep grade.


Water Meth Injection Pros & Cons



Lower exhaust gas temperatures (EGT)

Must give up space to mount reservoir

Increased horsepower and torque

Will require frequent refilling if used often

On-demand system; use only when needed

Potential for rust formation

Inexpensive operating cost

Potential for detonation (concentrated methanol mixtures only)