Water Injection for NA Engines, any benefit? 6

[zimbali]

Hi,

Could anybody let me know if water injection can help to reduce the intake air temperature significantly in NA engines? I heard that it is mostly used in Turbocharged engines.

And if it is useful Practically, is there any way to make a DIY version on a low budget?

Engine: 1.6L, 112 BhP, compression ratio: 10.5



Cheers


You can live in your car, but you can't drive your House!

 

[bbyron]

What is the expansion rate for steam how many varibles such as pressure or temp or volumn of water any general formulas

 

[patprimmer]

bbyron

If you do a site search, you will find it has already been discussed, calculated and explained

Regards

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[CCycle]

How much water is included with the 10% ethanol we now have in fuel?
When they switched to reformulated fuel I was driving a 2.5 L, na, TBI, sensor/catalyst 9:1 cr engine. It was getting 40 mpg routinely. Upon the switch to reformulated fuel it got 32 mpg. We also had a three cylinder 1.0 L that was getting 50 mpg. Upon the fuel switch, mileage dropped to 42 mpg. This mileage drop seems greater than can be accounted for by adding 10% anhydrous ethanol.

I am not necessarily a proponent of water injection but here are a couple of observations;
Water does more than just cool charge. It tends to take carbon deposits out. Back in the days when I was racing boats we would occasionally get a leak in intercooler or intake manifold. We could tell which cylinder(s) were getting the water. They would be clean of deposits. Also, I used to work in a refinery. We would clean carbon off catalyst beds by hitting them with superheated steam. They called it the water gas reaction where highly superheated steam would disassociate enough to change any carbon around to CO2.

 

[crysta1c1ear]

I see this thread has come up again.
When I did some calculations, I couldn't connect to eng-tips. Now that I'm reminded about it, I don't have the calculations handy. But from fire fighting and other websites, you can discover that a litre (equals a kilogram) of water boils to 1700 litres of steam.

If in a confined space, like an engine, the pressure would rise rather than the volume, but in PV energy terms it would still be 1700 litre atmospheres. (Pressure units are mass^1 * length^-1 * time^-2. Energy is mass^1 * length^2 * time^-2, famous example E = M c squared. So a pressure times a volume is an energy.)

I took the latent heat of vapourization of water etc and worked out the energy required to boil a kilogram of water. I compared that with the energy you hope to get back - the 1700 litre atmospheres of PV work - converted into more convetional units like Joules.

As people have stated above, vapourizing water, is very inefficient use of the energy in petrol. The 1700 litres atmospheres of PV work you hope to get back are very small compared to the amount of petrol energy needed to create them.

If I find my figures, I may post them here for completeness, as they provide a sort of evidence to support what pat said:

Water injection does increase power on an NA engine IF, AND ONLY IF, THE COMPRESSION RATIO IS TO HIGH FOR Available FUELS, as it reduces the tendency to detonate and allows optimum spark advance.

(I never doubted Pat. I did however want to quantify the inefficiency of using steam to provide pressure.)

 

[bbyron]

patprimer

Search everywhere, no discussion found just need to know if steam expands fast enough to keep up with increased engine rpm

 

[mattsooty]

The problem is this: -

In an NA engine, with optimised gas exchange at that given speed/load, the addition of any dilutent (be it EGR, water injection, fuel/H2O emulsifiers etc etc) will result in the amount of free O2 being the limiting factor.

Put simply, the amount of ignition advance towards theoretical MBT (and past the knock threshold) will not free up much in the way of torque. This can easily be explained by the fact that by adding additional dilutent/working fluid you are simply slowing the burn rate.

You may initiate combustion earlier but the centroid of pV diagram will be retarded (or at least roughly static).

Nett effect = nothing

If, however, one increases the dynamic CR then there will be some gains. However these will be very marginal...Until you find a way of increasing Patm

MS

 

[globi5]

If you had a naturally aspirated engine with a compression ratio of 17, and inject 0.2% (Vol) water, the energy required to compress air adiabatically would just be sufficient to heat the water to 100C and transfer it to steam (if it originally was at 20C).

Of course this would require that the water is evenly dispersed and the individual droplets are small enough that they can evaporate in that short time. But if you were able to do this, couldn't this be a recipe to make a highly efficient gasoline engine? Or is there a reason why you wouldn't go up to a compression ratio of 17 even if you can keep the temperatures down during the compression cycle?

 

[globi5]

Apparently OEM water injection is applied in large turbocharged diesel engines to reduce NOx:

http://www.wartsila.com/Wartsila/do...ications/brochures/product/engines/w46_tr.pdf

 

[alochin]

Water injection increase gas mileage and engine response (power or torque?) only if you retune your engine, mainly leaner AFR and avanced timing.
Improvments are more noticeable at low rpm and low to medium throttle. That is what I noticed on my vehicles.

The expansion into steam does not contribute, as the combustion of the same amount of gasoline will produce more expansion.

Water injection also removes carbon deposit. Old engines will like it a lot!

LEAD was very beneficial in term of performance, I don't think it increased combustion (I bet it retarded it as well).

By keeping exhaust temperature low, water injection will prevent the production of NOx without the need for enrichment through an EGR system, which polutes (just less noxious than NOx) and reduces gas mileage.

Water injection has several effects. Looking at just one effect (like steam expansion) let you draw the wrong conclusion.

The only drawbacks are added servitude to the user (2nd tank to fill up) and potential engine damage if the WI system fails, or run out of water. A leaned off timing engine won't resist long.

A modern ingnition box like the MSD DIS has a timing retard input (designed for NOS, but can be used for anything) that allows to set timing back to stock if WI system fails.
Leaning the AFR by adding a voltage offset to the O2 sensor can also be easily disabled.

So it is possible to design a safe and efficient WI system.

Andre.

 

[patprimmer]

I just searched water injection and got 34 hits

Try thread71-72284

You will see a contributor called SBBlue.

Click on his name and look up his contributions. He has done all the math and it was accepted by the professionals on the site.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.