Injecting prior to turbo comp' impellers

[Macabre]

Originally Posted by b_boy

For the sake of arguement let's say we could "recover" all the energy lost to heat at these near maximum speed. We could realize a 50% increase in compression with no heat loss. Effectively, our turbo would be 50% larger. That is a major accomplishment for the injection of a little water.

I've read through this thread, and this statement is really the crux of what's being discussed here. However, what I have not seen is any evidence or argument to suggest that this effect would be any different from the heat absorbtion that occurs when injecting water after the compressor. I.e., that it isn't accompanied by a proportional drop in pressure. I don't mean to be challenging, just looking for an explaination if there is one. It seems to me that there is a fairly large logic leap involved in the supposition that injecting water at the compressor inlet will increase the MASS at the compressor outlet (that is, a drop in temperature without a drop in pressure). It would be fairly easy to test. Anyone with a WRX + DeltaDash could gather this data from their MAF/MAP sensors. However the theory of why it would happen would be interesting as well. In order for the turbocharger to be "effectively" larger, it would need to flow a greater mass of air at a given PR with the same efficiency, and I cannot get my head around the logic of that.

[b_boy]

The data you seek do not exist for our little turbos, but for prop jets and turbine engines the evidence is ample. Look under "wet compression" of "fogging" or "overspray" or "swirl flash" and you'll find the papers and studies.

In addition we have the testimony (the word comes from if you lie, your testicles are lopped off) of HotRod and some others that you can improve the efficiency of compression itself.

The only advantages to injecting pre-turbo are 1) you want a bigger turbo but are not ready to role the dice, and 2) you have no intercooler, can't fit one, or don't want one, and 3) there may be a thermal advantage to not generating the heat early in the air flow (w/out heating the intake system).

To me number 1 is paramount the others. The quest for a greater dynamic range in turbos has been a long sought pursuit--variable vane turbos, twin turbos of differing size, larger turbos with less spool friction (i.e. ball bearing), external wastegates, and so on.

That said, water injection is still a marvelous means of increasing the density of the air, suppressing detonation, and permitting combustion with more power/push (leaner AFR), even if injectin post-turbo.

It's not the holy grail, but it's sure is fun thinking about, and pretty cool if you can make you 400 CFM compressor flow 500 CFM. Penny per HP it's a huge mod.

[Macabre]

#2 can be achieved with WI regardless. #1 is still dependant on the compressor flowing greater mass when water is introduced. I find this all very interesting, and may revise my plans for adding a second water jet pre-intercooler to adding it pre-compressor. I did find a good article based on your search terms that was very helpful - http://www.caldwellenergy.com/pdfs/WETCOM.PDF particularly "With compressor inter-cooling, the compressor discharge temperature is reduced considerably allowing more fuel to be burnt in the combustor. A secondary increase in power output is due to increase in mass flow rate." . It all sounds too good to be true but highly attractive if it works.

My second concern is how to calculate water usage for a given jet size given an assumption there will be a variable vacuum present at the compressor inlet. I suppose I could relocate my boost/vac gauge there for testing.

[Forum Admin]

Turbine's Power output is thrust related, the higher the mass on the intake regardless of either water molecules or air molecules, the higer the outout thrust.

Engine's output is mainly oxygen related, mass-increase as a whole in the intake may not yield extra oxygen available for combustion if a large portion of the mass is water molecule. This is an interesting topic to discuss if there is an actual oxygen increase.

If the engine can make more power by injecting a fine mist before the impeller, it can easily be verified on the dyno?

[Macabre]

Originally Posted by Forum Admin

Engine's output is mainly oxygen related, mass-increase as a whole in the intake may not yield extra oxygen available for combustion if a large portion of the mass is water molecule. This is an interesting topic to discuss if there is an actual oxygen increase.

Indeed.. this is why the data I would really like to see on the subject is output of the engine's MAFS compared to MAP and RPM. If no more air enters the vehicle intake, the turbocharger has not been made "effectively larger." It still feels like a big leap to me to state that water injected into the compressor will directly increase the efficiency of the compressor (vs. just reducing the outlet temperature). It may be that this is just a peculiarity of centrifugal compressors, or it may be that details that affect one type of system are being inappropriately applied to a combustion engine's turbocharger. Dyno results can be dubious on these issues.

[Richard L]

I think there is a bit more to it. The MAF is temperature compensated but wet air will give a different read on the hot wire type.

In order to verify the theory, we really need to find a relate simple method to get some result - it may not have to be vey accurate but the claimed 20%+ air flow increase should give some positive indications no matter how inaccurate.

I really like the idea behind the claim and I think it will work but may not be a much as 20% in oxygen increase. Any thing to reduce heat is a good thing especially on the turbo impeller.

Most turbo on the market is water cooled, some benifit for sure.

[slowMX5]

I have been watching this thread with some interest. I'm beginning to become inspired to do a little testing. Currently I am only using one of the TEC3r's (www.getfuelinjected.com) mapable outputs to map WI (using Aquamists 2C system), with 2 nozzles post IC. I have another spare mapable output - and I'm beginning to think that placing another HSV in a line supplying a pre-compressor nozzle might be a worthwhile experiment. This would enable me to play with the water delivery and compare results of varying switch on points and delivery amounts independently of water that is being delivered post IC.

The only thing making me think twice at present is I am running a Garrett Disco Potato turbo (GT28RS, 0.86 AR compressor 76 trim, 0.64 AR turbine 62 trim) - so it is if anything oversized for a 1.6L engine making 280bhp (sized for future plans).

Worth making the effort? I have full data logging software that will allow repeatable power/torque graphs to be plotted if using the same stretch of road.

[Richard L]

I can send you a HSV for that purpose?

[slowMX5]

Sounds like a plan. I'll post results here once I've got them.

[Macabre]

Originally Posted by Richard L

I think there is a bit more to it. The MAF is temperature compensated but wet air will give a different read on the hot wire type.

But the air at the MAFS should not be wet. The spray would still be well downstream of the MAFS (at least, on most engine types). The data I'd like to see would be whether this practice can affect a real efficiency improvement from the compressor. That is, at the same PR & flow, there's a greater mass of air in the charge. If more air-mass exits the compressor, it had to enter the compressor, and that should be suitably measurable by the MAFS. Or am I missing something?