Conservative Limits for Injectorants

Barry Bordes · 06-05-2012, 06:39 AM

First a little story of my water injection history that you may find interesting.

In 1974 I bought a used 72 Alfa 2000 GTV with all the early emission controls.
The cars at that time were very slow. I decided a turbo might help.

The problem was at that time everyone up to then used suck-through
carbs to limit boost and I was going to try to blow-through the mechanical injection.
I put a .84 AR turbine housing on a Corvair turbocharger.
( I think it had a something like a 1.3 AR housing stock, also to limit boost).

It was my first turbo kit .... followed by making my first waste-gate…
then my first blow off valve ( I called it a “surge and lag pressure relief” because
I didn’t know that they existed).
I even fooled the Spica 400 psi mechanical injection rack to give its full flow,
but it was not enough. It had reached the fuel enrichment limit and I proceeded
to blow the lands off of my forged Mahle pistons...... Detonation!

My dad came to the rescue. He told me about the studies done in WWII which
enabled our bombers and fighters to achieve high boost using water injection.
(He was a lead mechanic on the engine line for B-24s in Ann Arbor at the Willow Run Ford Plant).

Water Injection transformed this car. This allowed performance exceeding a
911S, the fastest car at the time.

Back to the present..... this is one of the papers I used as reference.

If you study Report No. 815 under NACA papers from WWII
the tests show the limits of the different injected coolants on a
CFR test engine (which features an adjustable compression ratio).
The report is very long but this chart summarizes it best for me.

The chart's limits were established with a conservative pressure
safety margin of 7% (backed off from incipient knock pressure).

Indicated Mean Effective Pressure (IMEP) is listed on the left column
and I added boost in in.HgA and PSI on the right hand side.

They also used Fuel-Air Ratio so I converted it to AFR for our
convienence (some may prefere Lambda).

Knock limit for rich fuel- IMEP 285 lb/sq in. (about 14 psi)
For water IMEP 325 lb/sq in. (about 18 psi)
For water/meth- IMEP 460 lb/sq in. (about 30 psi)
My tests so far show that Rotaries behave similarly.

Barry Bordes · 06-05-2012, 06:40 AM

Notice the amount of fluid they were using for the test.

1/2 pound fluid for one pound fuel. So add 50% to your injected weight of fuel.

We seem to run the bare minimum and sometimes we get away with it.

The scary part is that they could run the meth/water to 22 AFR at 35 pounds of boost!

Barry Bordes · 06-05-2012, 06:43 AM

In another study (NACA Report No. 756) a comparison of different percentages of just water was done, namely 0, 20, 40, and 60%.

This shows that on average we are not running enough injectorant.
Or put another way, we should run as much as our ignition can handle.

Barry

Barry Bordes · 06-05-2012, 06:49 AM

Compare the knock limit pressures when the inlet air temp goes from 150*F to 250*F.

Water stays about the same but the the meth/water curve drops below water when lean.

Remember this when designing safe guards to cut boost if the injectorant pressure is lost.

Also consider the consequences of not running a cold air inlet!

Barry

06-05-2012, 06:39 AM	#1
Barry Bordes Rotary Fanatic Join Date: Feb 2008 Location: Slidell, LA iTrader: (0) Posts: 191 Rep Power: 17	Conservative Limits for Injectorants First a little story of my water injection history that you may find interesting. In 1974 I bought a used 72 Alfa 2000 GTV with all the early emission controls. The cars at that time were very slow. I decided a turbo might help. The problem was at that time everyone up to then used suck-through carbs to limit boost and I was going to try to blow-through the mechanical injection. I put a .84 AR turbine housing on a Corvair turbocharger. ( I think it had a something like a 1.3 AR housing stock, also to limit boost). It was my first turbo kit .... followed by making my first waste-gate… then my first blow off valve ( I called it a “surge and lag pressure relief” because I didn’t know that they existed). I even fooled the Spica 400 psi mechanical injection rack to give its full flow, but it was not enough. It had reached the fuel enrichment limit and I proceeded to blow the lands off of my forged Mahle pistons...... Detonation! My dad came to the rescue. He told me about the studies done in WWII which enabled our bombers and fighters to achieve high boost using water injection. (He was a lead mechanic on the engine line for B-24s in Ann Arbor at the Willow Run Ford Plant). Water Injection transformed this car. This allowed performance exceeding a 911S, the fastest car at the time. Back to the present..... this is one of the papers I used as reference. If you study Report No. 815 under NACA papers from WWII the tests show the limits of the different injected coolants on a CFR test engine (which features an adjustable compression ratio). The report is very long but this chart summarizes it best for me. The chart's limits were established with a conservative pressure safety margin of 7% (backed off from incipient knock pressure). Indicated Mean Effective Pressure (IMEP) is listed on the left column and I added boost in in.HgA and PSI on the right hand side. They also used Fuel-Air Ratio so I converted it to AFR for our convienence (some may prefere Lambda). Knock limit for rich fuel- IMEP 285 lb/sq in. (about 14 psi) For water IMEP 325 lb/sq in. (about 18 psi) For water/meth- IMEP 460 lb/sq in. (about 30 psi) My tests so far show that Rotaries behave similarly.

06-05-2012, 06:40 AM	#2
Barry Bordes Rotary Fanatic Join Date: Feb 2008 Location: Slidell, LA iTrader: (0) Posts: 191 Rep Power: 17	Notice the amount of fluid they were using for the test. 1/2 pound fluid for one pound fuel. So add 50% to your injected weight of fuel. We seem to run the bare minimum and sometimes we get away with it. The scary part is that they could run the meth/water to 22 AFR at 35 pounds of boost!

06-05-2012, 06:43 AM	#3
Barry Bordes Rotary Fanatic Join Date: Feb 2008 Location: Slidell, LA iTrader: (0) Posts: 191 Rep Power: 17	In another study (NACA Report No. 756) a comparison of different percentages of just water was done, namely 0, 20, 40, and 60%. This shows that on average we are not running enough injectorant. Or put another way, we should run as much as our ignition can handle. Barry

06-05-2012, 06:49 AM	#4
Barry Bordes Rotary Fanatic Join Date: Feb 2008 Location: Slidell, LA iTrader: (0) Posts: 191 Rep Power: 17	Compare the knock limit pressures when the inlet air temp goes from 150F to 250F. Water stays about the same but the the meth/water curve drops below water when lean. Remember this when designing safe guards to cut boost if the injectorant pressure is lost. Also consider the consequences of not running a cold air inlet! Barry