(Water injection system)
Billet alloy components * Stunning anodised finish *
Centrifugal constant output pump
Water injection is not a new idea, being first used in the 1930s, yet the principles remain the same today and are popular with the rallying fraternity, and it is now common knowledge that in the recent past, the factory rally teams of Peugeot and Renault, as well as the Volvo Touring Car teams have used water injection and you'll also find them fitted to the first Escort Cosworths and even the latest turbo'd Saab road cars are fitted with water injection as standard.
It is a well known fact that water does not burn but it is an efficient coolant (why else would most engines be water rather than air cooled), so it makes good sense to use it to reduce peak combustion and inlet air temperatures. This is achieved due to water having a high specific heat capacity and latent heat of evaporation, or in English, it's excellent at absorbing heat. It can therefore be used to control induction temperatures on high performance normally aspirated and turbo'd engines. Also water injection can be used to reduce high air temperatures making the air denser. If you get more air into the engine you can add more fuel and gain power.
The combustion process mixes air and fuel which is burnt to create energy, once you have an efficient fuel metering system the power output is governed by the amount of air that the engine can draw into its cylinders. With intake restriction removed, a normally aspirated engine is limited by atmospheric pressure, unless you add a turbo or supercharger. These devices compress the air as they force it into the engine at a greater pressure, known as boost pressure. Water injection is just another device for increasing the amount of air drawn into the engine as cooling the air makes it denser so there's more to mix with fuel.
You should notice that your car performs better in cool, damp weather conditions and this is because the air is denser which means more fuel will be burnt with the extra air and the resulting air/fuel ratio will be neater to optimum(assuming the engine is jetted correctly normally in cold conditions). By adding a water injection system to your vehicle it is possible to artificially simulating these conditions and adjusting the turbo boost level or advancing the timing it is possible to achieve an increased power and fuel economy, whilst suppressing detonation and producing less harmful emissions, cleaner pistons, valves and plugs.
A simple way of testing this theory is to measure acceleration on two
days with opposite weather conditions.
With turbo charged cars, there is an uncontrollable temptation by the
vehicle owners to keep winding up the boost a little more, or add a
turbo upgrade, both of which pressurise and heat the gases even more
than the increased levels that the initial turbo set up achieves. Adding
an up rated inter cooler in an attempt to combat the temperatures will
certainly help, but temperatures are still bound to rise uncontrollably
above acceptable levels. lf the temperatures and pressures rise too
high, detonation occurs, with the fuel auto igniting before the spark
plug should be doing its job. It's the same as running massive amounts
of ignition advance, and ends the same by melting piston crowns. The aim
of water injection is to get the inlet temperature down to the optimum
temperature of, as above this temperature the risk of detonation
increases. Intake air at a turbo outlet is capable of reaching 120C at a
boost of I bar and as high as 165C at 1.5 bar, so you can see why there
is a problem. A standard inter cooler will normally fail to cool
effectively, and a 50% increase in inter cooler size will only reduce
temperatures by 60 - 75C, depending on boost pressure and vehicle
specification. Water can prevent these temperature rises when injected
into the air intake stream by reducing the inlet charge temperature,
giving rise to improved volumetric efficiency of the engine.
Additionally the evaporating water reduces the charge temperature prior
to ignition, reducing the possibility of pre-ignition due to hot spots
in the cylinder head. Water is the best choice for intake charge cooling
because it's readily available, cheap and can be stored under the bonnet
in a suitable reservoir, plus it absorbs heat better than most other
Lets see how good water is as a coolant, by passing air at 120C
through a tube at a rate of 5kg per minute. At the center of that tube,
we sprayed 50gms per minute of water at 25C. and found the final air
temperature was 95C. a large reduction. For l00g of water per minute,
the final air temperature was 70C, a reduction of 43% in temperature,
while 200g reduced air temperature to 25C an 80% reduction. In other
words, a flow of 200g of water per minute injected into the air stream,
totally absorbed all of the heat in the air. Obviously modified engines
will benefit most due to their higher pre-combustion pressures and
temperatures (usually caused by higher compression ratios)
On a test car which had an induction air temperature at the butterfly of 70C at full boost a 43% reduction was needed to reach the optimum of 40C. The equations indicated 100g/min of water would be required to achieve the desired temperature drop. Several tests at different induction temperature levels were carried out to see if performance was affected. The tests started with 100 to 150g per minute and revealed that slightly more cooling was needed, the jet was changed accordingly and brought the charge temperature at the butterfly from 70C right down to 43C. Another series of tests were carried out, when the ignition was advanced and boost increased progressively to show the benefits of water injection. With the timing at 15 degrees and 12psi boost there was no difference in power with the water injection operated. As the boost was increased however, some big power gains were achieved. An average RS Turbo engine with standard compression would normally run about 11 degrees advance and detonation would occur at about 14 psi of boost. With an unusually advanced 15degrees of timing it would knock above 13 psi, but the tests showed it was possible to ignore timing and boost limitations and find 210 bhp and 233 lb-ft without any sign of detonation. An added bonus was driving the car on the road, the improved smoothness of the engine at high revs was very noticeable. The potential of water injection for anyone wanting to run high boost safely is obvious and it's also applicable to engines that run lots of advance and suffer detonation. With water injection you get peace of mind even if you don't go for more power.
Whilst the results of these tests are good it is possible to make the induction air temperature too cold and it is vitally important to inject the correct amount of water as at some point the volume of water needed to correct the temperature can be too much for correct combustion and power is lost. If the temperature drops below 40C, "fuel dropout" can occur, a phenomena where fuel vapours turn into droplets which won't burn as efficiently and can cause a weak mixture which can ultimately have the same catastrophic consequences as high inlet temperatures.
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