water injection for BPU?

[a98pmalcolm]

is it worth i for a BPU+ supra?

 

Im running around the 420ish BHP mark

 

What kinda gains can be expected?

 

Thanks

 

Paul

[Terminator]

Forget gains and think protection.

[Chris Wilson]

Water injection serves 2 closely related functions on a turbo engined

car. Firstly it cools the charge air temperature by utilising an effect

known as the latent heat of evaporation. This property can be self

demonstrated very easily. If you pour something that evaporates quickly

like petrol on your hand it feels very cold. This is the rapidly

vaporising spirit removing heat from your skin and bloodstream by the

aforementioned process. By spraying a very finely atomised mist of water

into the inlet of a turbo engine when under boost conditions the

evaporation of the water into steam causes a temperature reduction in the air and

fuel intake charge. A cold charge is less likely to be subject to

detonation than a hot charge. A cool charge is also denser, able to

carry more air and fuel mix per unit of volume. These 2 properties of

water injection allow either less chance of detonation at a given boost,

maybe allowing lower octane fuel to be used, or to allow a rise in boost

pressure usage without detonation. These are very desirable goals for

any modifier of a turbo engine, or one using an engine mapped to run

on a higher octane fuel than generally available in the UK. Japanese

import turbo cars for example.

 

People ask whether squirting water into an engine causes corrosion. In

fact this is not a problem, the combustion temperatures under boost

ensure the water is turned instantly to steam and is ejected out of the

exhaust. The water mist is injected only when high boost is sensed via

a supplied pressure sensor switch. The basic combustion process of

hydrocarbon fuels causes LOTS of water to be generated anyway, which is why cars

not driven on regular long journeys will rust out a mild steel exhaust

system from the INSIDE out. If water is added in the correct volume, via

the supplied, calibrated jets, this is not a problem.

 

Even when used alongside a larger or more efficient intercooler, or

indeed when an intercooler is used in an application where one was not

present as standard, water injection can and does increase charge cooling

still further. Water can be stored either in the existing windscreen

washer bottle or in a separate, dedicated, container. In cold conditions

it is essential to add an anti freeze additive to the water to stop pump

damage through freezing. Windscreen washer additive serves this purpose

fine and the engine won't mind ingesting this solution at all. Or you

can add neat methanol, which is usually the anti freeze additive in

washer fluid anyway. Using a 50 / 50 percent by volume water / methanol

mix will actually help increase the octane of the intake charge, as an

added benefit. As a yet further advantage the latent heat of evaporation

of methanol is extremely high. A win / win situation. It is not however

obligatory to use methanol as an additive. All components of the water

injection kit that are in contact with the fluid are stainless steel or

able to tolerate water and methanol or screen washer additive without

degradation. A properly set up system does not use a vast amount of

water, in fact a modern car sized screen washer bottle used also for the

water injection reservoir will suffice admirably. A water filter is

included to keep any sludge out of the pump or jet. This should be

checked regularly for contamination and blown out if residue is

apparent within.

 

A more technical explanation:

 

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 O

H 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

goto 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.

[Steve]

Chris, can you supply water injection kits?

[Kirk]

thats 1 HELL of an answer..... Edited September 28, 2009 by Kirk (see edit history)

[Chris Wilson]

Yes, but only ERL Aquamist or Bosch ones. I doubt anyone will want a Bosch one, as they are silly money unless you have a specific need for port injected water. I recommend the basic Aquamist 1S kit for 90% of road car set ups, the programmable one adds a lot of complexity that's pretty needless on a dual purpose engine used on road and track.

[Chris Wilson]

The "more technical" section is plagiarised

[Kirk]

im guessing these would be pretty pointless on an NA track car?

[Steve]

Yes, but only ERL Aquamist or Bosch ones. I doubt anyone will want a Bosch one, as they are silly money unless you have a specific need for port injected water. I recommend the basic Aquamist 1S kit for 90% of road car set ups, the programmable one adds a lot of complexity that's pretty needless on a dual purpose engine used on road and track.

 

Email sent

[JamieP]

im guessing these would be pretty pointless on an NA track car?

 

Id not bother on a NA, TT or single, never use mine and its been fine.

[bignum]

Mine gave around 5bhp on the dyno on a warm day, i just run it for the added protection, it could be more worthwile on a bpu car as it will help stop det as the 2nd turbo comes on.

[Kirk]

what is yours running si? the official figures?

[Chingy]

I run mine just for added protection

[magictorch]

Im fitting one on my bpu soon hopefully

Edited December 14, 2009 by magictorch (see edit history)

[nigelboyne]

great thread lets know how you get on magictorch

[merckx]

thats 1 HELL of an answer.....