SX water injection

[adam quantrill]

Calling all SX owners. I've been toying with the idea of adding water injection and talked to Dennis Priddle a few weeks ago who reckoned it was a good idea (he fits it himself now). Also a chap from Ford at BBWF 05 thought it was a good wheeze. The recent hot weather must leave you all with disappointing acceleration, mine is certainly down on top end.

So the plan is to spray in water upstream of the Sprintex. This will also help seal the vanes and increase compression slightly.

Dennis says to do so on fairly large throttle openings only, so I will build a small comparator circuit to run off the throttle pot and feed 12V to a washer pump. I'm putting in a seperate reservoir (ebay - £3 - complete with pump!) under the bonnet expressly for this - with no screenwash or detergent in it.

I'll probably also run the washer motor with an adjustable speed so I don't "flood the engine" as it were.

Let me know if you're interested - I can put together some kits if need be.

If anyone has supercharger experience - and wants to chip in - please do.

Incidentally Dennis also says there are some compact water-cooled charge coolers available now, which should fit.

[deetes]

I toyed with this idea just to cool down the inlet on my 390, but it was as expensive as a really expensive thing. Most of the systems available were for turbo motors and required a managment sytem to operate them.
Just thinking, would it be possible to use the cold start injector for this?

[rev-erend]

Adam - I've seen the kits for sale.

The pump looks like it would deliver a lot more water than a washer pump..

Althought they could be just making it 'look' like a simple solution would not work.

Have you tried one of Magna Parva's plenum insulators yet - that might solve most of your problems anyway..

[dickymint]

rev-erend said:

Have you tried one of Magna Parva's plenum insulators yet - that might solve most of your problems anyway..

Or indeed one of Wedg1e's insulators (cheaper)

[adam quantrill]

No point - because the charge temperature is determined by Boyle's law, and so the plenum would probably be better off not insulated, as it would conduct heat away from the incoming gas.

Back of a fag packet - incoming at say 300K, increase pressure by a factor of 1.5, temperature becomes 450K - eek! That's 180 degrees C. Someone tell me I'm wrong...

I can't see the point of using much more than a powerful washer pump, because I'd be stopping for water every 5 miles (unless I had one of those water scoops like the old steam locos used to have).

See here: www.procharger.com/intercooled.shtml looks like I'm about right.

Edited by adam quantrill on Wednesday 9th August 16:11

[GreenV8S]

I think that you need to atomise it if you want it to evaporate at any significant rate within the intake pipe - and you need it to evaporate to give any benefit, of course. Unfortunately this requires high pressure and carefully designed jets, which means you need the likes of Aquamist parts - and they aren't cheap. Whether you use Aquamist or not, you can still use the same approach of triggering the WI off a pressure switch.

[rev-erend]

Adam - I think it's worth a try but they is plenty of 'theory' around on EFI .. stuff like - they use EFI injectors aimed at the back of the inlet valve - because fuel at low speed drops out of suspension and ends up puddled at the bottom on the inlet tract in the low speed air flow.. and must there for get used up when the air speed goes up.. big over richment.

So - to apply this to your water.. if your water is not atomised enough then it is not cooling anything and could well puddle up and just get burnt up as steam..

Doing nothing..

My guess but no doubt Pete or Matt will be along to set me straight

[jchase]

I can lend you my steam tables if you want to figure out the wetness ratio of your steam engine... you could use the water to cool the inlet charge by having a steam generating intercooler...and you could have a little chimney and a whistle out the bonnet too...he he he

[adam quantrill]

Yeah - I could make a cup of tea as well - who wants a ride on the footplate?

As I'll be squirting the water into the Sprintex I'm sure there will be plenty of opportunity for it to bw atomised, vaporised and pulverised by the gnashing vanes spinning around at high speed.

[phart]

Certainly on a turbo engine, its VERY VERY important to make sure you have a good vaporisation before hitting the turbines, because at that velocity it wears the vanes out, a lot of people mix methanol with the spray too to make up for the marginal loss of combustion - good to stop it freezing in the winter too.
Another important note is that the water tank is well below the height of the inlet jet, nasty stories of water syphoning out into the bores, while standing still, then bang when you try and crank over!
An alternative I used on my saab 9-3 was an adjustable pressure switch from RS triggering a spray directly over the outside of the intercooler, used a washer pump and jets, was very effective and I figured a lot safer than putting water into the engine without an expensive kit!
Having said that a mate runs an aquamist system and loves it.

[leorest]

Judging by the size of cables used on a mates Aquamist setup(on a 300bhp MR2 turbo nutter machine) it's not just a flash looking washer bottle pump its got some serious oomph to it! I imagine it's high pressure rather than high volume for best atomisation.
I think some people put ice in the water tank for extra cooling but I doubt it makes much difference.
Leo

[GreenV8S]

The aquamist system is a serious bit of kit. When you turn it on you don't get a spray, the air just goes foggy. It's a very high pressure low flow system, and it doesn't use a huge amount of water, I was running far too much water on mine and also had it set to come on far sooner than it needed to and it was still only using something like 1 gallon of water to ten gallons of petrol.

[adam quantrill]

phart said:

Certainly on a turbo engine, its VERY VERY important to make sure you have a good vaporisation before hitting the turbines, because at that velocity it wears the vanes out

Yeah. this doesn't seem to be an issue with the Sprintex as far as I know. As I mentioned earlier, the wetting of the vanes helps with the seal. In fact I was thinking that it's better to have the vapourisation happen at or just after the supercharger, because

a) that's where the air is hottest

b) it cools the supercharger

c) the expansion accompanied by the vapourisation is after the supercharger and forces the air towards the engine

d) the air and droplet mix entering the supercharger is at its densest, as oppoased to air and vapour which is less dense than air.

[GreenV8S]

It's a common myth that water evaporation displaces air.

The volume of air displaced by the water vapour is utterly negligeable compared to the density increase you get from the cooling that occurs. The problem is that there is a limit to how much water you can evaporate, so ultimately the choice comes down to where abouts within the induction system or the cylinder do you want to 'spend' this cooling effect?

[Jasper Gilder]

As probably the only other SX owner out there I'm going to watch with interest. As mine is the only one owner car in the world, I'm going to keep a watching brief as I want to keep my car original, but you're right, there is a power variation which is affected by ambient temperature and on days like that it seems to help to keep the supercharger spinning, so no laziness and relying on the torque

By the way, does the green V8S run now?

[adam quantrill]

GreenV8S said:

It's a common myth that water evaporation displaces air.

It's a myth that is perpetuated in my mate's aeronautics course. Wet air is less dense than dry air at the same temperature and pressure. (That's why clouds float - except in Ireland and Wales). It would be interesting to work out whether dry air with water droplets is denser (on average) than wet air where the same quantity of water has evaporated, hence cooling the air. Of major concern is the 02 density - obviously as you add H20 the 02 density is diluted.

I'm going to look into the latent heat of vaporisation figure for water (40kJ/mol) - a quick calculation implies that for each 1% increase in specific humidity there's a temperature drop of 10 degrees (K or C), which sounds quite promising. I should see significant cooling for quite modest amounts of water input. The 'evaporative intercooler' idea of Jim's is starting to look quite attractive, too...

Edited by adam quantrill on Thursday 10th August 09:44

Edited by adam quantrill on Thursday 10th August 10:01

[leorest]

"The 'evaporative intercooler' idea of Jim's is starting to look quite attractive, too... " I agree nice low tech, cheap, and because of that, elegant. But as it's working through a heat exchanger (efficiency must be less than 100%) it will require more water to be as effective.
Hypothetical question to get you thinking a bit… If you froze the intercooler in a block of ice would this, initially, be more or less effective than a water injection system which was properly implemented and optimised? I recon the latter.
This one made me laugh… Someone once suggested connecting up the air conditioning to cool the water injection reservoir. Cant help thinking this is a bit like trying to charge your battery from your cigarette lighter socket.
Leo

[adam quantrill]

Don't forget heat capacities as well as heat flow. So, for example, if you could cool an intercooler down to freezing point dring cruising, it would take a while to warm it up if it had a large heat capacity. This is still useful for a sprint to blow someone away, though power would drop off at sustained high speeds.

[350matt]

adam quantrill said:

No point - because the charge temperature is determined by Boyle's law, and so the plenum would probably be better off not insulated, as it would conduct heat away from the incoming gas.

Thats only true if the plenum is at a lower temperature than the incoming air, which on yours Adam it may not be as its not uncommon to see 80° on turbo exits, whereas on most normally aspirated cars the plenum is hotter than the incoming air and so heats it up


Water injection does work but the more you can atomise it before it goes into the cylinder the better results you'll get.

Using the supercharger itself to atomise it will work up to a point and for the cost of what you're proposing you might as well give it a go, just don't go to mad on the flow rate you can only get away with a small amount before you start running into combustion problems



Best of luck

Matt

PS I should point out with the MP insulator there is no need to machine trumpet bases ( with costs incurred here)as its only 2mm thick but it still reduces inlet temps by 15° as measured on the data logger in my old wedge.

Edited by 350matt on Thursday 10th August 12:45

[GreenV8S]

adam quantrill said:

GreenV8S said:

It's a common myth that water evaporation displaces air.

It's a myth that is perpetuated in my mate's aeronautics course.

You're missing the point. There's no doubt that the water vapour takes up some space, the point is that the temperature drop caused by the evaporation increases the density, and this is a far greater effect than the tiny space taken by the water vapour. The evaporation increases the air density.