Water Injection Information

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Water Injection Information

Post by Will66 »

This is a subject I've been looking into quite a bit, it appeals to part of me that once wanted to design mad race engines and looks to be very useful for Turboing in general and turboing rotaries in particular.

Rotaries are great motors, they’re tiny, they flow lots of air and they can be horrendously abused and still keep going. Even dying and in bits mine have always got me home. However they’re not without issues, fundamentally they don’t make as much power per unit volume of air as a piston motor, I believe poor volumetric efficiency is the technical term. However, they can flow loads of air, so the obvious solution is to give them more air to get decent, if not frankly astounding power.

Turbos force more air into the motor, positive pressure in the manifold and ultimately in the combustion chamber. More pressure at constant volume means more heat. Heat is bad, particularly if you’re trying to make your motor last.

We’re probably all aware that detonation in a rotary is a bad thing. It kills apex seals and does lots of damage to the engines. Detonation is caused by heat. It’s the petrol in the motor auto-igniting, that is burning without a spark plug igniting. Petrol does this at 257ºC even race fuel. So keeping your turbo rotary cool will bring big benefits in terms of reliability.

A lot of people think adding more petrol is the answer. Not always, to completely burn 1 gram of petrol you need 14.7 grams of air. That ratio, 14.7:1 is petrol’s stochiometric ratio and defines how much fuel you need for a given amount of airflow. Most engines run a bit richer than the stochiometric ratio under load although too rich and you’ll get problems, black smoke and carbon deposits particularly. Carbon deposits are bad, carbon in the motor creates hot spots which auto-ignite petrol when they get too hot, it also fouls up seals and leads to engine failure.

There is another way and it’s well known amongst those making big power turbo rotaries that run hard regularly. Water injection. Water obviously doesn’t burn, so it does not pre-ignite but it’s also an exceptional cooling medium. However, the coolest thing I think I’ve found about water is that a side effect of running water injection is that it effectively steam cleans the motor, removing carbon deposits. So not only does it cool the combustion process, helping prevent harmful detonation but it also removes carbon which can both cause detonation and gum up seals and kill bit of the motor.

It’s not without a few pitfalls, it does require serious ignition hardware if you’re going to tune up with it. That is run more boost and more water to keep things cool. And unless you make investment in systems that can vary injection with boost AND rpm you can end up running out of water injection as you’re getting to peak power which is less than cool. But it seems like WI offers too many benefits to be ignored by those serious about making big power from their forced induction rotary.

Rather than stand on the shoulders of giants and claim to be too much of a guru here are some of the stuff I've found useful, a lot of it is from rx7club.com in the US.

[urlw=http://www.rx7club.com/3rd-generation-s ... ix-806104/]This one is a doozy, it's FD based but it's rather enlightening as to the benefits of WI.[/urlw]

[urlw=http://www.rx7club.com/auxiliary-inject ... ng-888852/]This one has good information on injector sizing and fuel needs and the use of auxiliary injection of alcohol.[/urlw]

[urlw=http://www.riceracing.com.au/water-injection.htm]This one is from a guy called Peter Giljevic from Australia, he knows his onions when it comes to WI and has some excellent information.[/urlw] However he's one of the biggest keyboard commandos on the internet and posts some fairly reprehensible stuff about people who disagree with him, I say this as a warning to anyone of a delicate disposition who comes across him more regularly.

[urlw=http://www.rbracing-rsr.com/waterinjection.html]Lots of useful stuff here including a calculator for how much you need.[/urlw]

I'm going to keep adding to this thread/post as I find more stuff that will be useful but I think WI could be highly recommended for the RX8 particularly due to the issues with heat around the exhaust ports on the Renesis.
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Re: Water Injection Information

Post by warpc0il »

Funnily enough, one of my last jobs for Hawker Siddeley (BAe) was developing the water injection system for the Sea Harrier.

The GR3 Harrier had WI but the Sea Harrier had to be able to hover longer to match the speed on the mothership, before side-slipping to a landing (Always better to stop than land, rather than land then try and stop).

Anyway, as this was 1978, it goes to show that WI isn't new and has well documented advantages for internal combustion engines; even Pegasus gas turbines.
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Re: Water Injection Information

Post by Will66 »

Indeed, it was being used on the earliest F/I engines in fighters in WW2. I'm struggling to find a rotary drag car running on petrol in the UK that doesn't run it. The ones that don't seem to use methanol.

BTW methanol is generally outlawed for most track based motorsports due to the fact that it burns with an invisible flame.
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Re: Water Injection Information

Post by Soul »

Interesting stuff. So question 1) how much does it cost on top of a standard rebuild, and 2) at what levels of power is it worth going down this route?

If you're just going to low boost the engine to make 250-300hp, is it still something you should/have to do?
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Re: Water Injection Information

Post by Flameshades »

something i had a read over when i had the 13, might be of use (unless already seen..)
[urlw]http://www.turbomirage.com/water.html[/urlw]
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Re: Water Injection Information

Post by Will66 »

Soul wrote:Interesting stuff. So question 1) how much does it cost on top of a standard rebuild, and 2) at what levels of power is it worth going down this route?

If you're just going to low boost the engine to make 250-300hp, is it still something you should/have to do?
W/I Kits cost up to £600 or so and I would think it's worthwhile even on a low boost engine.
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Re: Water Injection Information

Post by Soul »

The kit might be £600 or so but don't you then have to upgrade all the fuelling to counteract the water?
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Re: Water Injection Information

Post by Will66 »

No. You'd only need to upgrade the ignition if you're injecting lots of water, 700cc/minute plus. For a relatively low power build you'd only need 300cc a minute and a set of D585 coils would be fine with that.
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Re: Water Injection Information

Post by madder »

Rx8club thread 206956 gives some interesting insight into this. Yes w.I is a valuable tool for anti knock/detonation in aviation engines. However its valid use within the combustion housing I struggle with. Yes it can provide a degree of safety for our forced inductions. But will cause misfires and rob bhp.
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Re: Water Injection Information

Post by Dadiodude »

There were a lot of old systems that simply fed water vapour into the intake. You could buy a cheap kit for the Classic Scooby. The main advantage was raising intake oxygen levels. Whilst water doesn't burn it does expand at a hell of a rate so you have to be super careful when introducing it.
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Re: Water Injection Information

Post by Will66 »

It will only cause problems if you're injecting too much. If it is causing misfires you're injecting more than the ignition system can cope with.
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Re: Water Injection Information

Post by Dadiodude »

Of course. Engines put out more power on cool wet days and it makes sense to try to recreate those conditions.
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Re: Water Injection Information

Post by BIG-Mal »

On a not fi engine youll notice power loss, on a fi engine its recognised youd loose if I remember correcty 4psi of boost pressure due to the water injected (turbo cars increase there boost to compensate for the loss)
As mentioned above injecting too much water will cause issue, u could start with a simple aquamist 1s single nozzle setup which come in around 250-300 or cheaper these are good kits. Tuning isnt really required
Going for a ecu comtrolled wi system youd only really want that if your a serious driver/track drag driver. Having the system set up to operate from a certain inlet pressure is the basic arrangement. A 1lt tank would last quit abit unless your driving increadibly hard. From what ive had experience of running and read of running youd only really see benefits from running wi on forced induction engines.

Pound for pound theres also N2o aswell, ok this wouldnt last long if youve a lead foot but does cool the inlet temp, introduces more oxygen and gives added power.

For any car making sure youve a cool inlet temp will be beneficial
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Re: Water Injection Information

Post by SeanP »

So this WI -- is partially turning the engine in to a Steam Engine? :-k :-?
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Re: Water Injection Information

Post by Will66 »

Not sure why you'd lose boost pressure with water injection, you might with methanol as that cools the intake more (resulting in a pressure drop), water cools the combustion process.
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Re: Water Injection Information

Post by Flameshades »

has anyone looked into creating a kit for this (Will) i have been looking around and the pump they use seems to be for mobile homes / campers...
looks like the pump alone is about 70 quid?

just knowing the nozzles etc to run would be the harder part to find.

have had a look at some DIY kits and they seem to come in loads cheeper than the full kits,
also when they are working off pressure switches there is no need for controllers etc....
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Re: Water Injection Information

Post by Will66 »

Rice Racing's kit is pretty comprehensive and uses bleed pressure from the turbo to make it work. Aquamist do a complete kit too.
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Re: Water Injection Information

Post by BIG-Mal »

Trust me ive had water injection and know quite afew other ppl who have it. Boost pressure is reduced by the additions of the water vapour into the intake "It happens whatever engine u use" u do need to increase the boost to compensate
I was on 1.2bar low boost and 1.3/4 on high boost with water injection

Its not a bad thing its only a consequence from introducing the vapour. The only real issue is if you run out of water whilst still running that increased pressure as that could "ive known a couple of ppl this has happened to" kill your engine
Ie that led to a massively wide recognition that fitting a low water level sesnor & alarm/light is needed

Dont ask me how it effects none turbo ive no real idea "never had dealings with none turbo water injection... But ive read about ppl having it fitted"
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Re: Water Injection Information

Post by BIG-Mal »

Regarding meth "hmmm I like how that eats engine seals" including seals on the injection units

U could make a kit all u needs is a good pump
Aquamist for example theres a cheaper generic pump 'or was' found on fleabay. Pipework u can get from anywhere, inlet-man pressure sesnors simply buy the aqua ones and fit it to the pump, nozzles youd be good to use the smallest and next size up (off hand cant remember whilst writing this) any bigger youd prob find issues
"personnnaly I used 2 small nozzles to give a better coverage of spray

Ud have to be a Muppet to buy a controller, well unless u had a bloody huge engine spec and ran around a track in ur 8

Also if anyone was interested using a purge pump was quite handy... Some ppl bought direct units others opted for good flow rate washer pumps fitted just off the water tank
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