http://www.aquamist.co.uk/rescr/rescr.html

28. 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.

29. 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)!

30. 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 !!!.

31. 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.

32. 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...

33. 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.

34. 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.

35. 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 ...

36. 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.

37. 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.

38. 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.

 

You got PM

 

uh huh. basic engineering now throw that in a simulink simulation and you gots yourself a wonderful little tool for knowing exactly what changes will do what with the click of a button.

 

isnt there a locating pin in the compressor halfs that only allow the turbo to be put together with the outlet facing down? I took a viii turbo apart in 2005....

 

who needs locating pins?? come to think of it, the turbos (IHI turbos) on our race car had pins to. we just ground them off. i would imagine you can do the same with the mitsu turbo.

 

Wow,

Very impressive use of engineering to validate this project.........although I think my brain hurts a little now .

Keep us posted. I think that you should run straight methanol and then inject high pressure water into the inlet stream. Would make an outstanding (and responsive) drag racing combination.

Paul

 

In actuality, yes. As indicated on a wideband meter, no.



As for this projects, I have my doubts as to its real world performance equalling theoreticals for a number of reasons, but good luck with it nonetheless.

 

good luck

let us know how this turns out

 

TedB: you mind sharing some of your doubts?

 

Hi Paul, i do not have anymore space for a dual injectant system......

Abner

 

i think the whole tuning industry should use lambda...this afr thing is even confusing a well known tuner here

~0.85 lambda is the ideal burn........

 

i think your right on, running without the intercooler, i think people overrate the intercoolers or dont understand alky, i barely do but know it freezes the air nice

 

i think the key to make this thing work is atomization........smallest mist size, highest surface area, lightest mist one can generate

 

i love engineers that put their knowledge to cool stuff. I work with way to many of them that suck

That pin can be grounded off, or in my case broken off
then drilled out

 

If i were to try this on my car, I would clock the compressor to point up instead of down...run the charge pipe to the TB and plumb the alky or meth as close to the turbo as possible...then spend alot of time on the dyno