Started a new thread on this because it's slightly tangential to the other WI thread running.

Basically I'm interested in knowing how those who use water injection then tune the engine. If you use a dyno and 4-gas exclusively then this is not an issue, however for those of us who tweek things by driving around with a mate on the lap top using WB-02 then there are some problems.

Without going into the in-depth theory, when you add water it acts as a dilutent to the partial pressures of the gas that the nernst cell is sensitive to. Other way of putting it is that it gives the wrong reading. Very few of the WB systems out there are calibrated for this.

So how does one approach this?

 

Bill, I was using a 50/50 mix of water and methenol on my Impreza, and mapped the engine to use it for safety.

Dan

 

Bill

Interesting?

Firstly I suggest that people stick to topic before replying to this thread..... I don't want to see any BS "why are you running that sh*t" "you don't need it"

Now...

I have not noticed the effect on my WB (I use an Autronic Model A) when I dynoed my car I used a PLM Motec meter and the results seemed consistent. I infact have not been running without WI for a number of years and hence cannot comment on the differences between running it and not running it and it's effect on the accuracy of the WB meter, I am always running the system so whatever number it punches out I go with.

Are you saying with your comment that the accuracy will vary depending on how much humidity is in the air as well on any given day?

 

I've often wondered this too...

The O2 sensor senses the differing partial pressures of oxygen in the atomoshpere vs the exhaust, as per the bosch catalogue.

Then something like WI should liberate more o2 in the exhaust right? If so then the mixture would read leaner than what it is?

Also with different combustion chanbers...ie radically different engines, say a rotary VS a 4 valve engine.You'd expect the combustion effeciency to differ hence the free oxygen content of the exhaust to differ. Once again a 11.0 AR might be different on these 2 engines...comments?

 

Maybe a little more depth

However let me start with a caveat. The first being that a fool with a tool is still a fool; or to invert it some of the best tuners I have met rely very little on the measurements and a lot on their knowledge. There are many ways to skin a cat. So please no posts on how EGT is better than 4-gas etc.

Back to the oxygen sensor. When running rich there is no oxygen, but various other ions which the nernst cell is sensitive to. The transfer curve for the sensors is calculated for regular pump gas. So if you run propane, methanol or some other wonder concoction then you need to recal the sensor slightly.

When you introduce water it reduces the partial pressure of the other gasses, so the meter will read leaner than you actually are. Same is true of Nox. How much leaner I am still researching. Unfortunately the last person outside of NTK to work this out wouldn't tell and had a heart attack. NB Nos will have the same effect.

More bad news: the sensor is also sensitive to temperature and pressure. This is only normally a problem if you are running the sensor pre-turbo.


But before anyone starts panicing. The errors are calculable, its just they are not published. A friend of mine was working on them so I'll check with him and get back. It's only a concern for people who 'must' hit a particular AFR come what may and they are usually asking for trouble.

I'll get back when I have some data

Bill

 

Re: combustion efficiencies. This is a very interesting topic and fraught with difficulties. To really answer that you need a 5-gas so you can measure all the soup in your exhaust. However if you don't know what you are looking for, it won't help. With pump gas the WB will give a pretty good indication of what you have though.

Remember with tuning for economy you want to use up all the fuel, with power you want to use up all the oxygen. The books say 13.5:1 for that. Allow 10% worse with a rotary and you get to 13.2:1 Any more fuel than that is for cooling purposes only (NB I've not got my engineers hat on at the moment so I'm not going to bother going into the minutae of cooling vs knock prevention) so you might as well use something cheaper than fuel, like water.

As an aside one of these days I want to test some theories that the aviation boys came up with, that you can run seriously lean at cruise with a 13B with no ill effects as there are no valves to burn out. Nox goes through the roof and cats burn out, but I don't have a cat so don't care.

 

going by what I have been told in the past. NA models can run on type of pump fuel. Doesnt matter if its low or high octane. Only once you start producing boost do you want high grade fuel. The higher the better, and as the US can get 91 octane from normal pumps, our (UK) highest is 88/89 depending on where you go, you would be well advised to use either some form of additive, or WI.

How much of this is crap I dont know, but I am watching and learning, as I want to get my WI/WS installed on my FD.

Dan

 

Well,

I am interested in this thread for 3 reasons:
1) I tune alot and need to keep learning
2) I have played with other substances being injected into the "mix" and how to tune with / against it ...need to test more here too
3) I plan on installing, testing, running a WI system on at least 2-3 cars by start of fall

The question I have to myself is do I tune WITH the WI, or without it.

Scenario 1 is that I run the WI system 100% (while needed, engaged to come online where targeted...while I have H20 available) and reap the rewards in daily driving where ever that maybe. Street or strip. I tune the car for this...runing WI when needed at higher boost/temps lets say.

Scenario 2 is that I run this system on demand...say in high boost or at the track. But don't tune against. Use it as an "extra" buffer.

Now go back and substitue WATER with another substance that is known to affect combustion/performance and does the answer change?

I guess what I am saying is that it depends on what the goal is. Run low grade gas at high performance levels? Run high boost and high grade gas and lower risk? A mix?

 

Fish: Actually regular UK gas is nearer 90 and optimax is 92 by the R+M/2 method.

Or 66 will deliver 110 octane race gas to you door at $10 a gallon.

Badog: short answer is that, whatever you add that is not regular gas will change the answer. I've downloaded the notes and will look at them as soon as my chores are finished. I have to strip off an elford turbo to sell to pay for hoses to get my dry sump plumbed etc :-)

 

Next time I'm out with the wideband I'll make two runs at low boost (below my normal WI trigger point) & record the first w/o WI and manually actuate the WI on the second. Stay tuned.

 

Hmmm now i'm confused...

I know that at stoich all the O2 molecules are nicely paired off....but i thought in the 'real' world that there was some o2 left, even if very small, and thats how the sensor operated? obviously not...

can you give us a bit mroe detail please?

 

You're getting more into the realm of WHEN the oxygen is used up. In the combustion chamber a stoich mix, due to atomisation, localised cooling etc will not burn in a timely manner. However, as it comes flying out the exhaust the remaining free oxygen will be consumed, so that what you see at the sensor is no oxygen.

But yet calling them oxygen sensors is only valid in the lean regime. When rich they are sensitive to the other ions in the end gasses.

http://not2fast.wryday.com/thermo/wa.../opt_mass.html

http://not2fast.wryday.com/thermo/wa...injection.html

Couple of links for those interested whilst I fight with the combustion products tables I haven't looked at since I was 19. The first explains the cooling and charge density effects of WI and most importantly how much water is enough to reach equilibrium. At another stage I'll try and explain why more water can be beneficial IF you inject it after the intake closes. If anyone has worked out how to fit an injector in the place of the oil injection ports on top of the rotor housings please let me know :-)

Second link goes into the thermodynamics behind the first link. And this is where we are at. The combustion products are well known and have been since about 1935. The calculations will be simple once I relearn all my college thermo.

nother link:

http://not2fast.wryday.com/turbo/glo...rbo_calc.shtml

This is a lot of fun. You can get any answer you want if you declutch your brain, but used sensibly is a very useful tool for playing around with turbo specs. It is also good for showing that, with sensible WI you can run a car without an intercooler, if you are that way inclined.

If you are impatient, then remember that the rule of thumb, found by Sir Harry Ricardo playing with supercharged aero engines before most of us were born is that you can replace up to 50% of the MASS of fuel with water for the same power and detonation resistance.

http://not2fast.wryday.com/efi/EFI_Calcs.xls

Shows you how to work that in injector flow. So you could tune without WI to say 11:1 and then (a bit at a time) reduce fuel and add water until you are at around 13:1 AFR (about 20% reduction in fuel consumption). Personally I wouldn't go leaner than that unless I was on an engine dyno and had a budget to find the limit.

Right back to that table

Bill

 

Holy Smoke there's some good info there....i'll have to try and wade thru it now

 

Hey Bill you wrote:


Injecting the water where the oil injectors are in the centre plate will not be injecting water after the intake is closed but i suspect you know that...were you meaning to do it there so the water has least chance to vapourise b4 the intake is closed?

 

Well, looking at a display 6-port you have a good 30-40 degrees between inlet closing and the apex seal crossing the oil injection port. Unless that jobby on top of a rotor housing on post 86 engines isn't the oil injection port. Whatever it is, if you time the injection of (water/nos/propane etc) it gets in after the inlet has closed and so doesn't reduce charge volume.

(NB my experience is entirely with older engines and homebrew injection systems in non-mazda installs so I am not au fait with the majority of the factory systems. As my Westfield is visible smoke only for emissions I can take an ignorance is bliss attitude)

 

"Not a good idea" Max saturation for a methanol / water mixture is 80% Meth / 20% H2O. Even at this ratio it will start to separate. Like oil and vinegar. It probably GO BOOM SOON. I would suggest running straight H2O. H2O is a great pre-detonate. If you live in a hard water area, use purified water or your injectors will clog in time. Just my $.02

 

This tread just got dug up -

https://www.rx7club.com/forum/showth...threadid=32303

 

Er...No. I read that other thread and purposefully started this one as a discussion on the actual tuning process pertinent to the fact that both WB-02 and EGT tuning methods will require some recalibration due to the effects of water.

It can be done by a roundabout method, but it would be far nicer to have a little spreadsheet that allows you to compare reported AFR vs actual for WI conditions.

 

Bill - I should have read farther before my response. I only read the first tread and replied. Got a phone call then turned off my computer. Very interesting discussion so far. Lots of info to absorb. Please post with further up-dates