water injection

[Carl]

I forgot to mention the cooling of the intake charge temp by water injection too, as it would mean that a denser mixture is going into the engine so more charge means more power too.
Kind regards
Carl

[bill shurvinton]

Hi Carl,

Partly. You also have to factor in that the latent heat of vapourisation of water is much higher than petrol, so during the compression stroke more cooling of the intake charge will occur for the same mass of liquid injected. So you get a double benefit of more air getting in AND less work done in the compression stroke.

Added to that there is the knock supression as you rightly say.

Then there is the improved combstion efficiency.

haven\'t got my text books to hand so can\'t check if the superheated steam adds anything significant to the BMEP.

Oh and your EGTs are lower. If used correctly this can become a benefit as you can setup your turbo so that it spools up early, but use the Wi to prevent melting your blades at the top end.

OR we can just say WI is very good.

[20B_boy]

Originally posted by bill shurvinton
OR we can just say WI is very good.

That\'s me sold then  

R.

[tsh]

Bill,

What magic number do I need to change to make that turbo calc. look like a rotary? If I put in 1.3l, then it makes about 100bhp, not 200+. Very interesting thread btw...

Sean

[bill shurvinton]

Carl,

you beat me to it. I was typing whilst you were posting :-)

Sean. I tend to set it to 2.3 litres as that works well as this is the effective air injested over 720 degrees.

Please not that the calculator requires you to be thinking. It won\'t stop you putting an AFR of 2:1 in and getting huge HP.

Bill

[maximtaylor]

Nice explanation lads

OK, so:

1) We tend to run rich, as part of reason for this is to help cooling combustion, therefore more steady flame front etc.

2) Without water injection, I tend to run about 11:1 air/fuel ratio.

3) The water injection kit I have is solely boost activated (10 psi kick in). And will inject the same quantity of water whether running 4k revs, or 6k revs. But more air will be flowing at 6k revs, so the ratio of water to air will drop....

Follow so far?

Now:

a) what a/f should I be aiming for with water injection, bearing in mind that water / fuel ratio will vary at different revs because of 3) above!!!!

b) The aquamist advice says aim for about 10% water to fuel quantity used, but I have read that up to 30% water to fuel can be used - this would mean HUGE water injectors!!

Should I just tune on the basis that w/i is not fitted, ie 11:1 a/f ratio, then use w/i solely as a preventative measure? Or lean off to about 12:1, or more?

I think I should be cautious.........

Anyone fancy sponsoring my engine

Regards

Max

[Fish]

Dont know about most of what you have just put up, as I need to learn it myself.

I would map on the basis of NO W.I. then add it for some safety.

Dan

[DRAGON]

Originally posted by Carl
I forgot to mention the cooling of the intake charge temp by water injection too, as it would mean that a denser mixture is going into the engine so more charge means more power too.
Kind regards
Carl

This wont actually happen. The reason water injection increases power is because it allows you to run more boost, leaner A/F ratios and more advanced timing. if you put water ona a car and dont change anything it will not be more powerful, it will proberly be abit slower.

[Carl]

Ross,
Notice that this comment I made was in addition to my previous comment.
Hope that this makes more sense with that in the frame.
Kind regards
Carl

[bill shurvinton]

No Carl is dead right. If you look at it from a thermodynamic perspective, a water mist WILL increase the density going into the chamber allowing more charge in. But it must be finely atomised, which is why injection at the compressor itself is the best way to do it.

All the theory behind this was worked out some 65 years ago by the likes of Sir Harry Ricardo.

Its the same reason some cars love damp air and run best just after a rain shower (when traction is at its lowest). can\'t win em all.

Bill

[DRAGON]

No I have to disagree, WATER INJECTION ALONE WILL NOT INCREASE POWER. Even Aquamist admit it, and they make a living form selling the kits! This is a quote straight off their site- "1. My turbo car runs standard boost, would water injection increase the power output ?
Water injection will not increase the power normally."
I have also read something about the water obviously taking up space that would have otherwise been fuel therefore this cancels out the benefit, unless increasing boost etc.

[Fish]

I agree in heart with this statement Ross, but most cars dont see the intake temps that the rotary does.

I fitted up today my gauges, and was watching the intake temps on the way home.

Cruise was between 35-40 when making progressionit went up to around 65-70. So by making the intake temps cooler, could only help with this.

Dan

[bill shurvinton]

If you want to believe the aquamist website fine. Aquamist make fine pumps.

However, the ideal gas law and the works of Ricardo, Glassman, Heywood, taylor, NASA and the other \'greats\' of internal combustion research do not agree.

I\'ve done the sums and, when I finally get around to building up a turbo engine, I won\'t be using an air/air intercooler. However, like most things I do in the automotive area it will be pretty much a one off, as the aftermarket doesn\'t cater for the way I like to do things. But I wouldn\'t recommend this to anyone without a good grounding in the associated thermodynamics.

Bill

[DRAGON]

Aquamist make a living from water injection, they would be the first ones to admit it if it increased as it would increase sales.

I view water injection as heat absorber rather than an charge cooling tool.

[bill shurvinton]

Absorbing heat IS charge cooling, so I fail to see how the distinction matters to the incoming air.

As for Aquamist they have to tread a careful line. they cannot afford bad publicity so they are using a conservative approach and targeting a specific market for high boost turbos, who will pay a high premium for something that can be built for under £100.

WI has been proven to work very nicely on NA engines, and there are technical papers to prove it, but you won\'t get aquamist saying that on their website, and they certainly don\'t have engine research facilities along the lines that MIT have.

Still sceptical? Load up the turbo calculator and play around with different positions for WI and see how the maths drops out. All my comments are based upon sound and proven physics.