Water injection (sometimes combined with alcohol) is used for cooling the intake charge (see InterCoolers?). Some efficiency and power can be gained. Issues are
- water tank freezing
- somewhat advanced ignition needed
- maybe it effects WideBandO?2 readings too?
See WaterInjection/Links for sites and pages dedicated to the topic.
See WaterInjection/Hardware? for notes about recommended components and their sources.
There is a forum on it, info should probably go there
I have brainstormed about this a little bit.I have already used it on a Lancia Delta HF Turbo 1.6 .So what I say is based on it.
The longer and more boost you make, the hotter the engine gets. Also, the temperature of the air going into the engine is hot. You can run better and more expensive fuels, pull the timing back, and you will still get to a point where it still detonates, no matter how much fuel you put in. The problem is the heat. Some have used water injection and it will effectively raise the octane and lower the combustion temps. Problem is controlling the water injection. Most methods just turn it on or off. Also pumps, and solenoids are very expensive. But actually the Bosch fuel pumps, fuel pressure regulators, and FuelInjectors? (are you sure?) will tolerate alcohols. I would not recommend leaving methanol (or any kind of alc.) in the system for more than a few days because methanol is corrosive and will chew on everything that is not stainless steel or compatible with it. If you rinse, or "Pickle" the methanol system when it is not in use or storage, you will not have any problems. (When methanol sits in a tank, it will absorb moisture out of the air, and will turn into a green jelly and other nasty things you don't want to mess with). Alcohols do 3 things for us. First, they have BTU's. There is energy in them as compared to water. Water converts to steam and absorbs heat, which works great, but you do get a bigger yield out of a fuel that burns cooler. (The heat from the Gas helps light off the alcohol better, and the alky cools the combustion temps, but not as cold as 100% alcohol would. Also note that you shouldn't mix two different liquids with two different specific gravity's. They are being mixed as an atomized spray in the intake airflow, and then homogenizing together in the combustion chamber). Second, they burn slower in the combustion chamber and have a cooler flame front. This stabilizes the combustion and because of the slower burning, you don't have to pull your timing back. Third, by adding a injector up stream of the air flow, alcohol will "Flash" or evaporate quickly and act just like a big expensive intercooler. By using this, you don't spend the big bucks on an intercooler, don't have the weight and all the plumbing, and you gain throttle response by not having long pathways to the engine or the volume tank effect. It is just one injector (MarcellGal? plans to use 2 or 3 different size on/off solenoids controlled from the same pressurized rail to get 3..7 steps of flowrate. This requires measuring the response of the valve turnon, and some advanced control from firmware, but otherwise should be good) as close to the output of the turbo as possible so it will have time to cool the airflow. You want a 'Stand Alone' water injection system, that controls "How Much" the injector is turned on at a certain boost pressure. You only put it in under boost. The fuel pumps which can be used (worked for me) are the big Bosch units, out of the VW Rabbits/Golfs. As far as mixing 1/2 water with 1/2 methanol goes, it should work just fine as a boost enrichment detonation control, but, I would at no time want to see what happens to my fuel injectors if water goes through them, let alone the pump! The problem with water injection is the pumps and solenoids. So if it's enough for your application, you can simply use windshield washer pumps (maybe two inline), and some kind of electric solenoid, with a properly sized carb jet, as injectors.This way, it's a lot cheaper.With the addition of some alcohol, freezing won't be a problem.And affects on the O2 sensor readings would interest me too...
Tons and tons of NACA papers related to detonation and water injection:
I think there is a very informative post from the DIY-DFI board that is listed on the above link. It outlines the part that water takes in combustion aside from the cooling effects. It appears this is the real reason that water prevents detonation---Chris G.
Here is the post:
From: Robert Harris <email@example.com>
Subject: Water and its effect on combustion.
Date: Mon, 10 Jul 2000 10:24:08 -0700
Let us take a quick look at ignition. Those who have a Heywood can look it up - mines on loan so going by memory. The first thing that happens is a plasma cloud is formed by the arc consisting of super heated electron stripped atoms. When this cloud "explodes" a ball of high energy particles is shot outward.
The highest energy particles are the hydrogen atoms - and they penetrate the charge about 5 times as far as the rest of the particles. As they lose energy and return to normal temps - about 5000 k - they begin to react chemically with any surrounding fuel and oxygen particles. The effectiveness of spark ignition is directly related to the availability of free hydrogen. Molecules containing tightly bound hydrogen such as methanol, nitromethane, and methane are far more difficult to ignite than those with less bonds.
During combustion - water - H2O ( present and formed ) is extremely active in the oxidation of the hydrocarbon. The predominate reaction is the following:
OH + H ==> H2O
H2O + O ==> H2O2
H2O2 ==> OH + OH
Loop to top and repeat.
The OH radical is the most effective at stripping hydrogen from the HC molecule in most ranges of combustion temperature.
Another predominate process is the HOO radical. It is more active at lower temperatures and is competitive with the H2O2 at higher temps.
OO + H ==> HOO
HOO + H ==> H2O2
H2O2 ==> OH + OH
This mechanism is very active at both stripping hydrogen from the HC and for getting O2 into usable combustion reactions.
Next consider the combustion of CO. Virtually no C ==> CO2. Its a two step process. C+O ==> CO. CO virtually drops out of early mid combustion as the OH reactions are significantly faster and effectively compete for the available oxygen.
Then consider that pure CO and pure O2 burns very slowly if at all. Virtually the only mechanism to complete the oxidization ( Glassman - Combustion Third Edition ) of CO ==> CO2 is the "water method".
CO + OH ==> CO2 + H
H + OH ==> H20
H2O + O ==> H2O2
H2O2 ==> OH + OH
go to top and repeat.
This simple reaction accounts for 99% + of the conversion of CO to CO2. It is important in that fully two thirds of the energy of carbon combustion is released in the CO ==> CO2 process and that this process occurs slow and late in the combustion of the fuel. Excess water can and does speed this conversion - by actively entering into the conversion process thru the above mechanism.
The peak flame temperature is determined by three factors alone - the energy present and released, the total atomic mass, and the atomic ratio - commonly called CHON for Carbon, Hydrogen, Oxygen, and Nitrogen. The chemical reactions in combustion leading to peak temperature are supremely indifferent to pressure. The temperatures and rates of normal IC combustion are
sufficient to cause most of the fuel and water present to be dissociated and enter into the flame.
As can be seen above, water is most definitily not only not inert but is a very active and important player in the combustion of hydrocarbon fuel. Ricardo and others have documented that under certain conditions ( normally
supercharged ) water can replace fuel up to about 50% and develop the same power output, or that the power output can be increased by up to 50% addition of water. This conditions were investigated by NACA and others for piston aircraft engines. It is important to note that these improvements came at the upper end of the power range where sufficient fuel and air was available to have an excess of energy that could not be converted to usable pressure in a timely manner.
As a side note - Volvo recently released some SAE papers documenting the use of cooled EGR to both reduce detonation and return to a stoic mixture under boost in the 15 psi range - while maintaining approximately the same power output. Notice - they reduced fuel and still get the same power output.
When you consider that EGR consists primarily of nitrogen, CO2, and water ( to the tune of about two gallons formed from each gallon of water burned ), you might draw the conclusion that it also was not "inert". They peaked their tests at about 18% cooled EGR - which would work out to about 36% water injection and got about the same results under similar conditions that the early NACA research got.
See also: FuelInjectors?