F1technical.net

Much as I don't like using Wiki, it say s this..I was told the water gives up it's oxygen, but I'll defer to you experts.

In internal combustion engines, water injection, also known as anti-detonant injection, is spraying water into the cylinder or incoming fuel-air mixture to cool the combustion chambers of the engine, allowing for greater compression ratios and largely eliminating the problem of engine knocking (detonation). This effectively increases the octane rating of the fuel, meaning that performance gains can be obtained when used in conjunction with a supercharger, turbocharger, altered spark ignition timing, and other modifications. Increasing the octane rating allows for a higher compression ratio which increases the power output and efficiency of the engine. Depending on the engine, improvements in power and fuel efficiency can also be obtained solely by injecting water. Water injection may also be used to reduce NOx or carbon monoxide emissions.

Water injection is also used in some jet turbine engines and in some shaft turbine engines, when a momentary high-thrust setting is needed to increase power and fuel efficiency.

Many water injection systems use a mixture of water and alcohol (approximately 50/50), with trace amounts of water-soluble oil. The water provides the primary cooling effect due to its great density and high heat absorption properties. The alcohol is combustible, and also serves as an antifreeze for the water. The purpose of the oil is to prevent corrosion of water injection and fuel system components. Because the alcohol mixed into the injection solution is often methanol (CH3OH), the system is known as methanol-water injection, or MW50. In the United States, the system is commonly referred to as anti-detonant injection, or ADI.

In a piston engine, the initial injection of water cools the fuel-air mixture significantly, which increases its density and hence the amount of mixture that enters the cylinder. The water (if in small liquid droplets) may absorb heat (and lower the pressure) as the charge is compressed, thus reducing compression work.[1] An additional effect comes later during combustion when the water absorbs large amounts of heat as it vaporizes, reducing peak temperature and resultant NOx formation, and reducing the amount of heat energy absorbed into the cylinder walls. This also converts part of combustion energy from the form of heat to the form of pressure. As the water droplets vaporize by absorbing heat, it turns to high pressure steam (water vapor or steam mainly resulted from combustion chemical reaction). The alcohol in the mixture burns, but is also much more resistant to detonation than gasoline. The net result is a higher octane charge that will support very high compression ratios or significant forced induction pressures before onset of detonation.

strad wrote:I understand that..but when they first started running turbos in the USA a hot rodder trick when running high boost/compression was water injection and the reason offered was that it not only cooled but added oxygen.

it added oxygen by increasing the density of the air charge due to the rapid cooling effect water has. Be careful listening to hodroders, mechanics and the like who work with certain aspects and sound knowledgeable but actually have just taken something and twisted to suit their need to understand, often erroneously.

Water injection in Otto cycle engines raises MON (motor octane number) but not so much RON (research octane number). It was used for highly tuned engines and only at WOT (because of the MON benefit)

In a constant pressure engine the effect is purely charge density related with alcohol addition as an anti freeze)

There is no disassociation of hydrogen from Oxygen. Water participates as water and only changes phase, and is exhausted as water (steam) and water droplets.
Not great for longevity of any engine hence only used in racing engines that willl be rebuilt often and military gas turbine applications where TBO (time between Overhaul) is very short

The temperature of dissociation for water is just about achievable in an internal combustion engine, but of course all that happens is that as things cool down it recombines. So it might knock the edge off the peak temperatures away from the walls of the chamber, but any measurable effect of water injection is due to the other (good) things it does rather than this rather slight one.

strad wrote:Much as I don't like using Wiki, it say s this..I was told the water gives up it's oxygen, but I'll defer to you experts.

The wiki you quoted says nothing about water giving O2. It is just a cooling agent. Water is very effective in cooling because of its high heat capacitance.

As others noted, the WI used in supercharged recip aeroengines was to reduce the intake charge temps at conditions of low altitude, high ambient temperatures, high manifold pressures, and high engine loads, such as those existing during take-off. The WI reduced charge temperatures by its latent heat of evaporation. And it also further reduced peak combustion temperatures by the water vapor acting as an inert gas, absorbing heat from combustion without contributing any energy to the process.

With aircraft applications, a small amount of methanol would be mixed with the water to prevent freezing when the aircraft operated at high altitudes. Some of the unlimited air racers that use hot-rodded recip engines use water sprays over the intake charge cooler cores to increase their heat transfer rates without increasing their frontal area and drag.

The only modern jet aircraft that uses WI is the Harrier and its Rolls-Royce Pegasus engine. The aircraft has a 90 second supply of water that is injected into the engine's compressor to prevent overheating of the HP turbine during a hover and vertical landing.

richard_leeds wrote:Out of interest, what were the lap times for testing and quali at Barcelona?

Interestingly, the fastest time in testing was 1.22.030 by Raikkonen on the last day, while in May Hamilton managed a 1.21.707 in Q3 (only to be moved back in the grid). I believe this was not the case other years? People normally compare this year's winter testing with last year's race. But then this year with the Pirelli lottery, morphing Coanda exhausts and DRS (not much of that in winter testing), who knows how the times from Winter testing and the more refined cars for the European season should be compared.

jamsbong wrote:

strad wrote:Much as I don't like using Wiki, it say s this..I was told the water gives up it's oxygen, but I'll defer to you experts.

The wiki you quoted says nothing about water giving O2. It is just a cooling agent. Water is very effective in cooling because of its high heat capacitance.

Actually the major cooling is from evaporation, i.e. phase change or the latent heat.

olefud..I did not quote Wiki for that reason

Measured loads can change Massive with weather even in a single day. Take huge pains to control wind tunnel atmosphere and using CAS not IAS or ground speed for on car testing. Think about the desert in autumn. Dry lakes are ideal test conditions save that.

olefud wrote:

jamsbong wrote:

strad wrote:Much as I don't like using Wiki, it say s this..I was told the water gives up it's oxygen, but I'll defer to you experts.

The wiki you quoted says nothing about water giving O2. It is just a cooling agent. Water is very effective in cooling because of its high heat capacitance.

Actually the major cooling is from evaporation, i.e. phase change or the latent heat.

not to mention the steam acts like a de-greaser which keeps the combustion chamber cleaner than without.

The water also leaves the cylinders prone to rapid rusting if you dont clear the system with pure petrol after running with water injection.
It would also condense the water on cooling and risk engine damage from hydraulicing.
A term little used today but well known to the users of high performance aero engines especialy WI radials where the bottom cylinders could easily fill up with fuel and water when turned off. Bent con rods were common.

continuing the off thread excursion .....
most Shackletons used WI on takeoff every time, so many of us have seen this unknowingly (about the only British use of it)
the 28 cyl Corsairs used WI to give 3000 hp for 5 min War Emergency
Cook Cleland carried 700 lb of the mixture in his Corsair enabling 4500hp for 70 min to win big races

importantly, all radials (and inverted inline engines) with or without WI are assumed able to leak oil into the low cylinders and lock
some are doing it right now
it's a vital check even today

autogyro wrote:The water also leaves the cylinders prone to rapid rusting if you dont clear the system with pure petrol after running with water injection.
It would also condense the water on cooling and risk engine damage from hydraulicing.
A term little used today but well known to the users of high performance aero engines especialy WI radials where the bottom cylinders could easily fill up with fuel and water when turned off. Bent con rods were common.

Since water is about half of the combustion end gas of hydrocarbon fuel it wouldn’t seem that adding a bit more would be much of a rust problem. Hydraulicing is more a result of a stuck float or, in radial, oil leaking into the bottom cylinder.

NA race cars will lose power because of the reduction in atmospheric air density with height and with temperature
they will also lose power with (absolute) humidity, but AH decreases with height
most of the power loss with humidity is due to displacement of induction air by water vapour, the rest is density loss with humidity

the power loss is/was about 30% at Mexico City, and about 20% at Kyalami (humidity has a negligible effect at these altitudes)

about 5% in Singapore (2/3 from humidity) and about 7% at the Hungaroring (1/3 from humidity)
about 14% at Interlagos (1/3 from humidity)

these are calculated by the SAE method J1349 for correcting measured power according to atmospheric conditions
this seems pessimistic (it disregards the benefits of lower exhaust pressure with lower atmospheric pressure ?)
without humidity its Interlagos figure is 11.5%, Renaults figure was 8%

the 2014 F1 engines will not have significant power loss as above
the turbocharging pressure will be adjustable to compensate for density reduction in the atmosphere, and for water vapour content

5.14.2 Other than engine sump breather gases, exhaust gas recirculation, and fuel for the normal purpose of combustion in the engine, the spraying of any substance into the engine intake air is forbidden.

I reckon that covers water injection as TC already posted.