water injection and then some (long!)

[H Villemure]

Chris,

are there any other side effects to water injection? Like corrosion, oil
contamination in case of less-than-perfect blowby? Would you use a set
of spare injectors to the manifold (say below at 180°) to inject water?

Also, this would be an absolutely great solution to the problem of
detonation, but wouldn't you have to re-calculate the efforts in the
connecting rods and wrist pins to account for the increased momentary
pressure? I am not sure that all stock rods (especially Honda's, heh)
could take that?.. I will go back to the open-system analysis and try to
figure a few orders of magnitude. I do not find it so obvious to figure
it with forced induction.

Thanks for the great input,

Chris Conlon wrote:
> 
> Hi everyone,
> 
> The following is all sliced together from various posts. I'm mainly
> replying to Barry, but have quoted many other people too in here. It's
> long and long winded... consider yourselves warned. :)
> 
> > > Water flow at 50% of the fuel flow rate (mass/mass) is the number I
> > > keep hearing, not to say that other numbers can't work.
> >
> > This is what I am not sure of.  Seems to me the kits I have seen are much
> > much lower than 50%.  I am wondering what range should be considered usable.
> > I read one study that worked with 5-15% based on mass.  Also the nozzles
> > that come with a number of the kits I have seen would be limited to more in
> > the 10-15% range, but I dunno.  This is something I need to determine.  I'd
> > prefer to not use trial and error to get into the ballpark.  Do you recall
> > where you got the 50% number?
> 
> Ok, I have to apologize for using lazy science in this one. Basically I
> have just seen a bunch of people running 25%-50% water:fuel on various
> engines, and similar numbers in papers that people have quoted (but which
> I have not read). I fully believe Bruce's value of 50% max, and apologize
> for being imprecise and unreferenced. ;)
> 
> Yes a bunch of commercial kits seem to run way less than that. Another
> imprecise, unreferenced impression is that the quantity of water is not
> very critical, and can vary over a wide-ish range. I plan to use trial
> and error and EGT to get into the ballpark. Sorry, I know this is kinda
> vague.
> 
> > I am thinking an el cheapo PIC 16C84 will do the trick since there is not
> > much work to be done and a very small amount of code to write.  I will need
> > ADC for the MAP but I could use a chip for that if I get lazy.
> >
> > Next on the gadget list is to come up with a good algorithm for an
> > intelligent self-learning boost controller coupled with an intelligent
> > blow-off valve.  Then I could tie the water injection controller into the
> 
> At least some of the PICs have 8 bit A/D, IIRC. I was going to use one
> before I went 68hc11.
> 
> <cranky rant>
> As for the boost control: Have a small dedicated air pump and a solenoid
> valve to actuate the wastegate. Keep the wastegate FULLY CLOSED at ALL
> TIMES except when the turbo nears overspeed. (Yes you need a turbine RPM
> measuring setup.) For boost control, get a fly-by-wire throttle, put it
> *before* the turbo, and have the throttle follow the driver's foot except
> when boost is too high. (Thus putting boost control where it should be
> IMHO, but without burdening the driver.)
> </cranky rant>
> 
> > > If non intercooled, and your looking to help cool the intake air charge,
> > > then I'd go with the finer the mist the better.
> >
> > Okay.  I am intercooled using factory air-air exchangers so they are "okay"
> > but will become soaked withing 20-30 mins of hard use like on a road course.
> > Maximum peak boost will be between 21-25 psi with 21+ psi sustained.
> 
> If I might suggest, stop for a moment and ask why exactly you're using water
> injection? It sounds like the answer is "to run higher boost without
> detonation". Cooling the intake charge is great, but not at the expense of
> *displacing* large amounts of that intake charge with inert steam. Ideally
> you want the water to enter the cylinder just under the boiling point,
> but still as liquid. This is because the main power increase due to water
> injection (assuming constant boost) is not due to cooler charge but due
> to the large increase in cylinder pressure as a small volume of water
> flashes into a large volume of steam. Also the anti-detonation effect is
> largely due to the heat of vaporization. (Not entirely - in humid air the
> water is already fully vaporized, but even though there is no heat of
> vaporization to overcome, there is still some slight anti-detonant effect.)
> 
> Now you may notice that here I took my supposed answer to why *you* want
> to run water injection, and sort of ignored it anyway. This is because it
> can give power increases even on NA engines, by making use of more of the
> heat of combustion, while still having the anti-detonation effect.
> 
> Water injection on a boosted motor is IMHO a great thing. It lets you run
> more boost (if you want), but even if you don't it still lets you extract
> more power from the motor. Essentially it's recovering heat energy that
> would have gone into high EGTs, and turning it into hot steam which does
> extra work pushing on your pistons. *And* while displacing only a small %
> of the intake charge, as long as the water stays as liquid. This is why
> Greg is so insistent that the water be injected near the valve, and timed
> with the valve opening. Water evaporating outside the cylinder = big lose.
> Think of it as accidental EGR.  I can't manage to build that kind of setup
> just yet; my approach is ceramic coatings on the intake ports and valves.
> Hopefully this will at least help keep more of the fuel and water in the
> liquid phase til they pass the intake valve.
> 
> > If the droplets are small enough however, won't this effectively be the same
> > deal?  Clearly we don't want puddling, and we need "vapor" (small airborn
> > droplets) that can take heat from the air charge to allow more fuel to be
> > dumped in (but not so much that the water displaces required fuel).
> 
> In case I was unclear above, IMHO a slight err on the side of larger
> droplets and too many droplets will probably net you more power than too
> fine a mist or too little water (which will more easily flash to vapor).
> Generally you'll have enough heat of combustion to vaporize everything
> and then some. One of ERL's suggestions, which I like, is monitoring
> EGTs.
> 
> > >A last thought on evaporation.  The evaporation rate of water is very low
> > >below its boiling point 100c stp.
> >
> > Suggest reading a steam table. It all depends on temperature and PRESSURE.
> 
> Water and/or methanol will produce significant vapor pressure well below
> boiling. Temperature is a measurement of *average* molecular energy, the
> peak of a bell curve. This is why a swamp cooler can cool air below
> ambient, why wind chill happens, and so forth.
> 
> > Simply atomizing water will not cause it to change from a liquid to a
> > vapor - it takes 100c STP to accomplish that.
> 
> Nope. And atomizing it will greatly speed the process. Finely divided
> materials dissolve and react more quickly. Consider how gasoline mist
> burns compared to a pool of liquid gasoline.
> 
> ...
> 
> Now if water/methanol formed a more stable azeotrope, in some ratio,
> that might give a higher heat of vaporization than either one alone.
> I think it's the other way round, though. Does anyone know offhand,
> if you mix a bunch of water and methanol, do they get hotter or
> colder? If they get colder, the heat of vap should be higher.
> Otherwise the addition of methanol is mainly as antifreeze.
> 
> > Yippee.  I understand more or less.  A side benefit of doing this is that it
> > reduces NOx emmissions.  Neat huh.
> 
> Ok, now you're in for it. You came close enough to one of my pet ideas
> to trigger off another rant. Faint hearts, bail out now. ;)
> 
> The main reason water inj reduces detonation is that the high heat of
> vap sucks up "excess" heat energy, and thus reduces the formation of
> various oxygen radical species. These radicals are essential for flame
> propagation, but if the mixture has a high enough energy density, it
> can cross over into detonation. Lowered combustion temps reduce the
> formation of O radicals. O radicals and NOx are intimately related,
> since the same conditions, lean mixtures and hot mixtures, favor the
> formation of both. In fact NOx are formed mainly through O radicals
> bumping into N2. When the mixture is rich, O radicals (and NOx) are
> more likely to "bump into" some fuel molecules, and keep the fire
> going. When there's lots of spare O2, heat and N2, lots of "leftover"
> O radicals end up bumping into N2, which then hangs around. Oppositely,
> rich mixtures tend to "sop up" O radicals more aggressively, which
> keeps the mixture burn rate from accelerating enough to detonate.
> 
> Water vapor ("humidity") also slightly reduces detonation. IMO this is
> in part because water is a modest spin trap, and can convert some O
> radicals into slightly less reactive species. This has the effect of
> slowing combustion slightly, or rather, preventing it from making the
> 1000x speedup it would need to make to turn into detonation. It's no
> accident that many of your higher octane fuels (most things with an
> aryl group for instance) are decent spin traps as well.
> 
> ...
> 
> One of my pet ideas for when I hit the lottery is a *high* compression
> NA engine, with full ceramic coatings and almost full-time water
> injection, that runs slightly lean mixtures, on pump gas. And produces
> very low emissions even without a cat.
> 
> The thinking went like:
> High compression - to get a higher efficency
> Ceramic coatings - ditto, plus keeping the fuel and water from boiling
>   off in the intake ports.
> Water injection - above maybe 25% throttle, to prevent detonation and
>   reduce NOx, which would otherwise be sky high.
> Lean mixture - to reduce CO and HC, which would be sent sky high by
>   the water injection.
> 
> High compression (+ coatings) would also help get the lean, wet mix
> hot enough to ignite reliably.
> 
> Can all this be made to work? I dunno... comments welcomed.
> 
> > If you were "whacky", you might consider adding steam after the throttle at
> > *** PART THROTTLE ***.   This would greatly reduce the pumping work and
> > recover some waste heat.  At less than wot, this would not cause a loss of
> 
> Hmm I'll have to think about this. :)  My idea has been focused on WOT
> power, not part throttle BSFC, but I'm not against upping BSFC if it
> doesn't hurt max power.
> 
> Ok, it's way too late, as should be evident from the foregoing. Thank
> you all for your kind indulgence.
> 
>    Chris C.

-- 
Helene V.
___________________
"If it ain't broke, make it faster"
Celica Supra 1982 & 1983
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