Supercharged car...
- Do I need a different Aquamist system to the turbo kit?
If you intend to install the water jet after the throttle plate, a 1-bar check valve must be purchased along with the kit (system1s only). This is due to the presence of vacuum, water can be siphoned pass the water pump under vacuum conditions.
Normally aspirated car...
I have a normally aspirated car, would water injection help me to obtain more power?
No, in general. Unless you decided to increase the compression ratio, more advance ignition or run lower fuel grade than recommended by the manufacturer.
How do I advance the ignition timing?
Cars manufactured with knock sensor will automatically run more advance timing in the absence of knock. It is difficult to advance the timing on car without a knock sensor built-in.
My normally aspirated car suffers with sever detonation problem under heavy load such as towing, would water injection cure my detonation problem?
Yes, water injection will minimise the onset of detonation or even totally eliminates it, but you don't necessarily need to use the Aquamist system as high water pressure is not required, a ten-dollar washer pump and a water jet will work jet as well. Pay careful attention to prevent water from siphoning through the water pump during idle, a similar inline checkvalve will do the job.
Would water injection help to improve the economy of my normally aspirated car, ie more mpg?
Water injection will enable you to run more ignition advance so you can achieve MBT timing (Maximum brake torque) thus improve the efficiency of the engine, mpg will increase as a result but you need to carry a lot of water on board !
Turbo Diesel car...
Is water injection effective on turbo diesels ?
Yes, Water injection can improve the torque output of the diesel engine, simply due to extra cylinder pressure during the evaporation of water. Further information links can be found on the "design/reference" section on this site.
Do you have any practical example of a water injected vehicle ?
Not exactly, the only example we have encountered was a 11.5 litre, boost pressure of 4.6 bars (absolute) !!! The Skoda truck was run by a very dedicated team from Czech Republic, and they are currently running the European truck Championship.
Common Scepticism
- Is water injection really necessary or it is just a new gimmick?
Well, yes and no. For the old fashioned traditional engine tuners with fixed ideas and blinkered outlook, water injection is regarded as an utter nonsense and a complete waste of time. Engines are designed to consume FUEL and not WATER.
On the other side of the coin, engineers such as Sir Harry Ricardo (1930s) and bunch of aeronautic engineers (German, English and American) during the WWII (1940s) has found the positive side of injecting water into their supercharged fighter-plane engines. So the traditional has begun, Formula 1 engines (1980s) used it. SAAB 9-5 supplied as an OE part and now World Rally cars use it (1995 onwards). We leave you to decide ...
Whenever a problem is discovered, there is always a tendency to solving it, that is human nature. Old problems just keep re-surfacing, detonation, fuel quality, harmful emissions etc just won't go away, despite the advancement of Electronics and Engineering materials available.
So what is the problem facing the performance orientated enthusiast today?
Monetary and Regulation constriant is the biggest hurdle. Works racing teams with big budgets has to obey constraints set down on the rule book, whereas street machine has no rules but limited by cost as well as legacy left by the original engine manufactures; Stringent emission legislation has pushed the engine manufacturers to come up with cleaner and more efficient engines. That means low compression engine out and fuel efficient, high compression engine in. Unfortunately fuel quality hasn't caught up, in fact it is getting worse.
What is the solution then?
Aquamist (1998 on) is putting forward one of the many solutions to solving cooling and detonation problems, it is not intended to replace good engineering and other cooling systems it just broaden the choice and gives people an alternative to intercooler upgrade, fuel dumping, low compression pistons and fitting ignition timing retardation devices.
Is the Aquamist water injection idea based on scientific facts ?
Yes, we will try to explain the whole concept right from the beginning, starting with the basic engine dynamics. Please bear with us for the next few paragraphs before we get to the point.
Lets for example look at the properties of a naturally aspirated 2-litre engine when it is turboed or supercharged, we shall see how the airflow characteristics changes and how it is eventually translated into horsepower and the reasons for water injection.
We first look at the intake cycle of a four-stroke engine, all results are calculated.
The red dot on this chart shows a 2-litre naturally aspirated engine at 6000 rpm consuming a massive 5.76Kg/minute of air !
To obtain more power without increasing the engine size means that some form of force induced system has to be used.
Why isn't there more force induced engines around ?
Unfortunately there are a few drawbacks. Excess heat is one of the biggest problems, it has haunted the turbo/supercharging systems for decades. Without heat problems, we can run higher compression ratio or lower octane fuel, no need for intercoolers or chargecoolers, no Aquamist, no heat stresses on engine components and most importantly, no heat-induced detonation problems.
Where does the heat come from ?
Two main source of heat: when air is compressed, it just heats up naturally, compressor efficiency is the other, it can contribute over half of the total heat produced.
Examining the heat source in details ...
Chart shows the calculated compressor exit temperatures under different boost pressures. At 25 C ambient, compressing the air to 0.5 bar will raise the charge temperature to 61 C (39C rise) at 100% adiabatic efficiency.
Unfortunately most modern compressors operate between 60% to 70% efficiency. At 65%, the actual outlet temperature is 81C (56C rise) !. If this sounds bad, a Roots-type blower has only 45% efficiency, you can just imagine what the exit temperature will be at those efficiency.
Worse still, higher pressure produces even higher outlet temperatures as seen on the chart.
We will base the rest of the section on 65% compressor efficiency unless otherwise stated.
- What does it all mean?
Temperature rise affects air density. When the air is hot the density decreases and vice-versa when the air is cold. The proportion of the two densities is called density ratio
As you can see, doubling the pressure only yield 53% increase of air density. In order to double your engine power, you need to run a pressure ratio of over three or 2.1 bar boost, compressor exit temperature approaching 200 C (392F)!
How much density increase if I were able to cool the charge air? Amazingly large increases, Chart shows the density increase as charge air is being cooled. This will apply to compressor exit temperature right up to 300 C.
If you manage to drop the temperature by 75C, you will get a density gain of 33.6%. A 300bhp engine will have a theoretical power increase of 100 BHP !!!.
What is the current method of cooling the charge air?
Air/air Intercooler, Water/air chargecooler is the most established way of cooling the charge air.
Water injection is recently re-introduced, It has been implemented on F1 car (1980s) and currently used by all the World Rally Championship Cars.
Which is the best method?
Having been kept waiting for so long. we'll be brief - Water injection of course! we are biased.
Before waving your arms in the air, lets be scientific and drop the hypes and hearsay and work it out mathematically...
There is just one more simple calculation to be made- the Mass Air Flow...
Chart shows a Mass Air consumption by a two litre engine up to 2 bar (pressure ratio of 3) boost.
From the mass, we can calculate the efficiency of all three methods.
We shall see the effectiveness of an intercooler.
The efficiency of a intercooler relies on the following factors:
1) Frontal area.
2) Pressure drop across the cores
(external and internal).
3) Road speed.
4) Air temperature differentials-
(external and internal).
To simplify the calculations, given that there are so many variations in size and efficiency. We start with an intercooler with 50% efficiency.
We will calculate how much heat is being removed for a given mass airflow based on a boost pressure ratio of 2 at 6000 rpm, using the same 2-litre engine. The result will be used to compare against a water injection system
Ambient air temperature is 25°C and the compressor exit temperature is 124°C. At 50% intercooler efficiency (reasonable assumption as both the engine and intercooler is operating close to their peak flow limits), the temperature drop across the inter-cooler should be:
(124°C - 25°C)/2=49.5°C
The final air temperature entering the engine is 74.5°C.
- We shall see the intercooling properties of water injection.
Water temperature is 25°C and the compressor exit temperature is 124°C and Water flow rate of 250cc per minute.
In the region we are working in the partial pressure of water vapour in the mixture is very low.
We can assume that the enthalpy is a function of temperature alone within reasonable accuracy (e.g. for 250g /min of water and 8.64Kg/min of air, the partial pressure of water in about 0.06 bar).
Consequently the final temperature is an inverse linear function of water proportional as nearest makes no difference.
The calculation and results:
At 200cc/min: 66.09°C
At 250cc/min: 50.88°C
At 300cc/min: 36.27°C
So there we are, we have proved our point, water is just as effective as an intercooler.
We decided to calculate a few more water flow rates so that a chart can be plotted, useful for visual prediction.
Even at a modest flow rate of 200cc per minute, water is a better cooler than a 50% efficient intercooler by a long way.
Notice at 350cc/minute of water, the final temperature dropped below the ambient of 25°C !!! there just isn't a 110% efficiency intercooler around yet ...
- Summarising the comparison...
Before rushing out to buy an intercooler or make a water injection, please beware of the short comings of both systems, we listed a few here.
Water injection will only be effective if it is injected in a form of mist, the droplet size is the key to a successful water injection system.
Small droplet size increases the overall surface area, essential for good intercooling property. This is the reason why Aquamist uses line pressure over 7 bars.
Would water rust up my engine?
In our view, no more than average on a wet day. Lets put things in perspective, water is around us all the time whether you like it or not. It either exists as vapour or as puddles on the ground. Depends on the air temperature, the proportion changes, once the air can no longer absorb water, it forms minute droplets and eventually into liquid.
The term "Relative Humidity" expresses that equilibrium, it spans between 0%-100% typically.
How wet is a rainy day or country with high humidity level then?
In rainy days, the relative humidity (RH) is over 90%, in the tropics (not raining) is often in the 80%.
So what is the amount of water being ingested by an engine on a wet and rainy day?
Chart shows the amount of water a 2-litre engine consumes on a typical 45% RH day, at 6000rpm, it draws in 150cc/minute of water.
On average, the engine drinks more water in its life time from the atmosphere than water injection at near WOT, unless of course you live in the desert.
Lastly, the burned air/fuel mixture contains approximately 50% water vapour and 50% Carbon dioxide, so 250cc/min of water from water injection only accounts for less than 1.6% the total output from the exhaust.
If your engine is prone to rust and seizure during a wet season, then water injection is not for you, All engines should function normally under these conditions.