High Altitude FE?

[ConnClark]

Actually you need more fuel and Oxygen to make 100HP in high humidity.

See Figure 4 in the Technical Note

http://aerade.cranfield.ac.uk/ara/1929/naca-tn-309.pdf

[Christ]

So that means that steaming the engine would mean less power, but it would take more fuel to make the same power... so that's not a good thing then.

I guess I'll save the steam for cleaning, eh?

[ConnClark]

Originally Posted by Christ

So that means that steaming the engine would mean less power, but it would take more fuel to make the same power... so that's not a good thing then.

I guess I'll save the steam for cleaning, eh?

Good plan

[dcb]

Originally Posted by ConnClark

Actually you need more fuel and Oxygen to make 100HP in high humidity.

facinating stuff from 1929. Hard to draw any such conclusions from it though. They were tuning for optimum power, not bsfc for one thing. And as AV is liken to do, they run rich almost constantly, perhaps made more rich by displacing oxygen with water vapor. And of course it is a non-feedback carb.

However, if you look at figure 2, the "presumably" smallest/leanest orafice produces more gain than any of the other orafices lose when humidity approaches %100.

[ConnClark]

Test Series No. 3

" For this series of tests the carburetor was equipped with a needle valve, and test were made over a range corresponding roughly to air-fuel ratios of 9 to 17. Carburetor air temperature was maintained at 41 deg C.

At two humidities, corresponding to 13.4mm Hg and 52.2 mm Hg, fuel consumption, power, and optimum spark advance readings were taken at 12 points over the range of air fuel ratios stated above. "

The range of fuel mixtures is wider than test number 2. Optimal settings were used to determine the BSFC. Also since readings were done at steady state a feed back carburetor is of no use.

Note that no fuel consumption figures were compiled in test 2. Also they attribute the power rise using the smallest orifice to automatic enrichment of the mixture at higher humidities. This would drop FE.

[dcb]

First sentence:
"Tests made by A. W. Gardiner using a one-cylinder engine having indicated that atmospheric humidity has a very appreciable effect on some phases of engine performance"

This paper does not refute that. In fact the proto rocket scientists seem to think the number of cylinders is the variable here.


There are only 2 lines in figure 4, so they are averaging the effects across various mixtures with a large bias towards richness, where we can observe in figure 2 is a "phase" where humidity does not seem to have a positive effect.

Sorry, but I don't think you can connect the dots to your conclusions with this paper alone. You have to understand the paper that preceded it for one thing, which was geared for an automotive audience.

[dcb]

This paper does seem to conclude in fairly certain terms however that efficiency is reduced on a lean burn engine (without taking compensating measures) by increases in ambient humidity. NOx is also reduced by increases in humidity.

http://www.cimac.com/cimac_cms/uploa...l_20090325.pdf

Though I'm at a loss at why the summer months are the least efficient in the graph, that is when I get my best numbers.

[Christ]

I think because hot air tends to contain a higher relative humidity? Once air gets below 30*, the relative humidity drops... the air gets very dry. If they're comparing efficiency to average relative humidity, that would kind of explain summer being worst time of the year, wouldn't it?

*I haven't looked at the papers more than a glance and skim, yet*

DCB: The first diagram in your paper shows that efficiency and NOx emissions are kind of on the level playing field in lean burn engines, and does show that as relative humidity rises, efficiency falls, as do NOx emissions. I don't think they're paying too much attention to actual temperature ranges, just the relative humidity throughout the year.

It does mention that there is no compensation for ambient humidity changes, so they're testing the same engine maps, I presume, all year 'round. (Without trying to "fix" the maps to keep the efficiency in higher humidity.)