High Altitude FE?

[ConnClark]

Ummmm.... humidity hurts FE and robs power from the engine.

This is the only reference I can find at the moment.

"Fog and humidity affect the performance of aircraft. During takeoff, two things are done to compensate for their effect on takeoff performance. First, since humid air is less dense than dry air, the allowable takeoff gross weight is generally reduced for operations in areas that are consistently humid. Second, because power output is decreased by humidity, pilots must compensate for the power loss."

SPECIFIC HUMIDITY

Not only for that reason but it also decrease the specific heat ratio of the combustion gases.

[dcb]

Originally Posted by ConnClark

Ummmm.... humidity hurts FE and robs power from the engine.

Not sure on the FE part. Humid air is less dense, like hot, or rarefied, air, that is where the power loss comes in (and usually where the FE gains)

Originally Posted by Christ

So what if I just inject steam into the intake? (Steam, scavenging heat from exhaust.)

It is an interesting thought, would like to know myself.

[ConnClark]

"High air humidity decreases the thermal efficiency and, thus, reduces the engine mean effective pressure"

http://www.scielo.br/pdf/jbsms/v25n3/a10v25n3.pdf


Pumping steam into the intake every now and then might be a good way to clean carbon out which might improve FE

[dcb]

I'm sure I don't know enough about it, and the state of the water is likely a factor as well. But there have been reports of improved mpg with (a very well tuned) water injection though.
WATER INJECTION WIZARDRY

Of course it is not at all the same mechanism as HAI or high altitude driving. I think it is more akin to that 6 stroke thing that squirts water in on one of the strokes (it is basically %50 steam engine).

[ConnClark]

People have also claimed FE improvements using acetone and HHO systems despite evidence to the contrary. I will admit that water injection can show FE improvements but it only really comes into play at full load. Also FE gains resulting from water injection are usually less than 5% .

Water injection is different than high humidity. As the mist evaporates it cools the air which results in more mass trapped in the cylinder on the intake stroke. Assuming the use of EGR those two factors mean less heat loss to the engine block during the power stroke. The end result is more power in the output. High humidity alone just thins the air.

[basjoos]

Originally Posted by ConnClark

Ummmm.... humidity hurts FE and robs power from the engine.

This is the only reference I can find at the moment.

"Fog and humidity affect the performance of aircraft. During takeoff, two things are done to compensate for their effect on takeoff performance. First, since humid air is less dense than dry air, the allowable takeoff gross weight is generally reduced for operations in areas that are consistently humid. Second, because power output is decreased by humidity, pilots must compensate for the power loss."

SPECIFIC HUMIDITY

Not only for that reason but it also decrease the specific heat ratio of the combustion gases.

Increased humidity (and air temperature) increases the density altitude seen by aircraft operating under those conditions. An increased density altitude means the aircraft is operating as if it were at a higher altitude than it actually it. In other words, an aircraft taking off from a runway at 1000 ft elevation when the density altitude is 1800 feet will perform as though it were at 1800 ft elevation. Pilots have temperature/humidity tables they can use to calculate density altitude, which they add or subtract from their actual elevation. As altitude increases, the stall speed increases (but not the indicated airspeed), which increases takeoff and landing distances. Also the power output of normally aspirated piston engines is reduced, further, increasing the takeoff distance. This is why they reduce the gross weight as mentioned mentioned above. But, provided their air-fuel mixture is leaned properly, a normally aspirated piston engine will burn less fuel while operating under higher density or actual altitudes

[dcb]

Originally Posted by ConnClark

... comes into play at full load...

...Like your typical P&G hyper-miler would use. So if your average idiot gets %5 improvement...

[tjts1]

The reduced aerodynamic drag at altitude is the only effect on you'll notice on FE. You still require the same amout of fuel and oxygen to generate 100hp at 15,000 feet as you do at sea level. The only difference is at the lower air pressure you'll require less HP to reach and maintain a specific speed.

[dcb]

plus the fact that the throttle might be open wider, so less pumping losses.

[Christ]

Ok, so now I'm confused... using steam to lower effective displacement will work, or no?

I know about water/meth injection, but it doesn't really apply to our situation, I don't think?

What I'm looking for is if I circulate water around the exhuast pipe to heat it up, then inject it into the intake as steam, will it work to reduce effective displacement, and help to cool the engine while one is burning a lean mixture? (I mean REALLY lean, like 17-19:1)?

Could a diesel benefit from steam injection?