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  #21  
Old 30-09-2004, 09:17 PM
b_boy b_boy is offline
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This is fascinating stuff!

I'm a biologist so my understanding can only go so far, but the physics is not so great that I can appreciate the content.

So, back to tuning.

HotRod suggests something that I've wondered for some time, that is, that fine tuning the water injection can permit an optimal balance between fuel, air , and power. This idea suggests a method of tuning quite different than is ordinarily taken. Whether the "angle", or the rate of burn, or the speed of the flame front is slowed by water injection is slowed, the effect with respect to tuning is the same: ignition needs to be retarded to achieve MBT.

We have a number effects happening in close succession: cooling of the charge, cooling of the cylinder, slowing of the rate/flame, and augmentation of the combustion itself. Most of these variables will affect ignition timing, not fuel. While WI permits more boost, thus more air, and a denser air, also more air, these WI effects are occuring pre-cylinder. The remainder are in cylinder effects.

Why is this important?

Well fueling is going to hover at a near constant ration of 12.5 to one. Thus from a tuning stand point fuel addition is constant value with respect to air mass. When tuning, fuel can be pulled back to this empirically derived minimum and left there.

Once fuel is set, the tuner has a choice: retard timing or reduce water injection. From the above discussion, I would say that reducing water is the first choice, finding a level that still permits 12.5 AFR and no knock. If the ignition advance (set by tuning with WI off) is still too little for peak power, advance can be further retarded to increase power.

In the end, a tuner will have achieved higher boost, cooler charge temp, elimination of knock, minimal water usage, and maximum power.

Now back to fuel

Is 12.5 AFR the goal for most power? I will suggest a way that this might be determined. If we use gas of differing octane, does the AFR of maximum power change? The octane rating everyone knows is a misnomer. It should be anti-knock rating, and the chemical composition of different octane fuels is different. While the maximum fuel efficiency occurs at around 14.5:1 AFR, I can see that "waiting" for the final stochiometric combustion products to form would be a detrimate to power production. The time associated with "waiting" for the final byproducts would probably hover close to a percentage of fuel left incompletely burned, no matter what the octane number.

Above is the perspective of engineer or scientist. In the real world of tuning another perspective holds. More fuel, means more power. While the 12.5:1 AFR may produce the most power per unit fuel, adding additional fuel may produce more engine power per unit time. My anecdotal observation is that no tuner tunes to greater than 12:1 AFR, usually 11.6-11.8:1 even with huge intercoolers and race gas.

Please comment on the difference.

Next I'd like to do another 1,2,3...tuning method revised to incorporate all of this discussion.
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  #22  
Old 30-09-2004, 09:59 PM
hotrod hotrod is offline
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Default AFR and WI

As you can see below the relationship between rich / lean mixtures and power output is not a simple one.

If they had used different ignition timing they would have gotten much different curve shapes. My guess is the dip in power under WI in the lean mixture area is due to the (inappropriate) fixed 30 deg BTC ignition timing for the injection rate/AFR.
When they went lean enough they got enormous power output nearly 2x the non-WI max power.

NACA report 812 ( Feb 1944) They ran tests on several "internal coolants" and charted their imep vs Fuel Air ratio ( .08 FAR = 12.5:1 AFR )

Code:
Figure 6 inlet air temp 250 deg F
With no WI (smoothed values read off chart)
Knock limited imep........ FAR .................. AFR    
260 ----------------------- 0.12 -------------- 8.33
265 (peak)----------------- 0.11 -------------- 9.09
240 ----------------------- 0.10 -------------- 10.0
233 ----------------------- 0.09 -------------- 11.1
210 ----------------------- 0.08 -------------- 12.5
190 ----------------------- 0.07 -------------- 14.28
175 (min) ----------------  0.063 ------------- 15.87
180 ----------------------- 0.06 -------------- 16.66
218 ----------------------- 0.05 -------------- 20.0

WI at .5 lb/lb fuel 70% methanol 30% water
408 (rich mixture peak)---- 0.10 --------------- 10.0
408 ----------------------- 0.09 --------------- 11.1
375 ----------------------- 0.08 --------------- 12.5
320 ----------------------- 0.07 --------------- 14.28
285 ----------------------- 0.06 --------------- 16.66
280 (min) ----------------- 0.059 -------------- 16.95
325 ----------------------- 0.05 --------------- 20.0
455 (lean mixture peak)---- 0.04 --------------- 25.0
One obvious lesson from these curves is there may be significant power available if the tuner is willing to explore the limits of the tune into areas that are normally considered unreasonable to even approach. Obviously proper test equipment is needed to prevent destructive knock during testing.

All these power outputs were limited by either presence of knock, they had reached max possible fuel flow, or the had reached max manifold pressure of 150 in/hg ( 75 psi boost) or preignition.

Larry
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  #23  
Old 30-09-2004, 11:28 PM
SaabTuner SaabTuner is offline
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Staight Fuel = RED
Water Only = BLUE
Water/Meth = GREEN

y axis = Maximum Break Mean Effective Pressure (essentially torque)
x axis = Air/Fuel Ratio. (water/fuel ratio was constant at 60%)


Several things to note:

0. To convert Fuel/Air ratio to Air/Fuel ratio invert value.

1. As you can see, water and methanol make the best mixture, but this is partly due to the high blending octane of Methanol.

2. At leaner Air/Fuel ratios water can generate huge amounts more power when compared to just fuel. At leaner A/F ratios alcohol only adds to this a little.

3. Water Only in this case peaks at around 12:1 A/F ratio. Beyond that drowns the engine.

4. Meth/Water 70/30 peaks at around 11:1 A/F ratio. In fact, it produces around 60% more torque (and it's reasonable to assume that it would produce that much more horsepower) than just straight fuel. Indeed around 40% more than just water injection.

5. It's estimated that an engine which normally requires 100 octane at MBT, could be run on 80 octane with water/meth injection. Roughly 10 of those octane points are from the high blending octane of Methanol, but the other ten are from the combination of cooling, and retarded Peak Pressure Position.

6. I would say that very similar curves should appear even on an intercooled engine, as long as the water is completely vaporized before the combustion cycle begins. Even a poor water injection setup should accomplish that.

Adrian~
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  #24  
Old 01-10-2004, 12:18 AM
hotrod hotrod is offline
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Default thanks

Thanks for the graphic, its much easier to see on a plot, but I don't have the means to host an image.

Larry
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  #25  
Old 01-10-2004, 12:31 AM
Gelf Gelf is offline
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Default Re: thanks

Quote:
Originally Posted by hotrod
Thanks for the graphic, its much easier to see on a plot, but I don't have the means to host an image.

Larry
Free Image hosting website :smile:

http://www.imagehdd.com/
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  #26  
Old 01-10-2004, 12:33 AM
SaabTuner SaabTuner is offline
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And in case you need a good photoeditor for free ... do a google search on GIMP Photoeditor.

Adrian~
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  #27  
Old 01-10-2004, 07:17 AM
b_boy b_boy is offline
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Well Adrian, what a great graph. I see you address some of the caveats here. I'm glad you posted it on NASIOC as well. Those guys are harsh on WI.

As I said on NASIOC, I find the difference in AFR optimum with WI and w/out very interesting. With it's 12.5:1 and without 9:1--an amazing difference. It really changes the way you think about tuning with WI--less fuel is the way to go, and 12.5 seems the magic number even with the crappy fuel that they were probably using in 1944.

Do they state the octane of the gas in that experiment?

I wish they had done the same experiment with less water than 60% of fuel, something not many are willing to haul around in our cars.

I also wonder if the experiment was performed at mulitple RPMs or just one?

Also, where was the water injected? Pre-turbo? Pre-throttle body? In cylinder? Me thinks it was pre-turbo.
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  #28  
Old 01-10-2004, 08:46 AM
SaabTuner SaabTuner is offline
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The engine was a 7:1 compression single Cyllinder engine with Sodium filled Exhaust valves. RPM was 2500.

Inlet Air was injected by some mechanism. They had the temperature fixed at 250F degrees for the last graph.

I should have shown THIS graph first, as this graph is the same procedure, but done at 150F degrees, which is more indicative of an intercooled engine.

Same colors as before ...



Enjoy.

Adrian~
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  #29  
Old 01-10-2004, 04:58 PM
b_boy b_boy is offline
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Well Adrian, I'm tripping over myself in appreciation for these data. Such carefully controlled conditions go a long way to understanding the effects of WI. I'm a little ashamed that I too have not dug deeply into the ancient literature. As a biologist, I've read back into the 19th century for thoughts on animal and plant development, why not combustion.

It also makes me appreciate how many of the crucal data points were generated in the early era of the automobile, ones that are being repeated in the other data shown on PPP. It makes me wonder how much of the combustion dogma has been reproduced in modern engines. I suppose if radical changes to the dogma had been discovered they would have been widely distributed. But in an age of intellectual property and strict control of engineering info due to incredible competition in the auto industry I'm not sure how much useful data is published.

Your idolation of Saab and their incredibly sophisticated experiments only re-enforce my esteem for Saab. Saab and Mercedes have always pushed the envelop of auto engineering with other companies following their lead. Not to say that other companies have not made contributions, they have, but Saab and Mercedes seem to implement technology in production cars earlier than the rest.

I posted my thoughts on additional safeguards to running WI, that I wrote on the NASIOC board in response to your graph posts their, in the Avoiding Disaster forum on this WI board for further input.
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  #30  
Old 02-10-2004, 12:22 PM
Forum Admin Forum Admin is offline
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Quote:
Originally Posted by SaabTuner
The engine was a 7:1 compression single Cyllinder engine with Sodium filled Exhaust valves. RPM was 2500.

Inlet Air was injected by some mechanism. They had the temperature fixed at 250F degrees for the last graph.

I should have shown THIS graph first, as this graph is the same procedure, but done at 150F degrees, which is more indicative of an intercooled engine.

Same colors as before ...



Enjoy.

Adrian~

It is interesting looking at this plot. It appeared to me that WI injection can make more power at richer a/f ratio than 12:1- at 9.5a/f ratio?

The alcohol plot is quite mis-leaning if it was described in text only. The engione virtually runs on alcohol rather than gasoline. The experiment is probably done on 2-valve per cylinder, long stroke enigne - octane demand/performace is that much greater is BMEP is "detonation threshold limited". However, it give a good indication of fuel quality against power.

Methanol has less than half the calorific value of gasoline, so in-cylinder cooling is doubled since twice the amount of liquid is being evaporated per unit of BHP generated. Due to the cooling and octane effect - antural way of making good power. Need a bigger tank.

I heard Indy car runs methanol and without interccoler and the turboed engine still have problems igniting the alcohol fuel due to excessive presence of liquid. I have also had the pleasure of meeting the people who run a ethanol fuelled Le Mans - problem was to stop the corrosion effect and the entire fueling system has to be washed out with gasoline after the race.
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