Ambient temp for max power?
11-03-2010, 01:47 PM
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Ambient temp for max power?
I guess I could have just PMd Fabrik8, but is there a lowest ambient temp for max power? I know generally the colder the denser the air, but a lot of air is moisture, and moisture is its most dense at 4C, so, I'm thinking there may be a possibility that 4C is the ambient temp at which an engine makes more power. What is the answer?
11-03-2010, 02:06 PM
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Re: Ambient temp for max power?
I guess I could have just PMd Fabrik8, but is there a lowest ambient temp for max power? I know generally the colder the denser the air, but a lot of air is moisture, and moisture is its most dense at 4C, so, I'm thinking there may be a possibility that 4C is the ambient temp at which an engine makes more power. What is the answer?
11-03-2010, 03:31 PM
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Re: Ambient temp for max power?
Here's what my intuition says...
I would imagine that the colder the air the better, because the moisture isn't really adding any power if it's already in vapor form. The purpose of a water mist system is to absorb heat from the intake air by changing the phase of the water (liquid to vapor) but if you're just sucking in moisture then you aren't really adding power unless the moisture is droplets suspended in the air (like fog). If the moisture is droplets suspended in the air, they will still absorb heat and make the intake air charge colder. So that would be the same as having colder ambient air.
Basically, an engine should continue to make more power as long as the air is still in a usable (gaseous) form, assuming that the air isn't getting heated enough by entering the engine to negate any benefits. The combustion efficiency would not be that great though unless the engine was re-optimized to keep combustion temps in the right range. Getting dense air into the engine and making proper use of that dense air are two different things...
The intake manifold tuning would have to change too if the density was that different from more normal operating temps too, because of the relationship of temperature and the speed of sound. Exhaust tuning wouldn't change as long as the exhaust temp range was in a normal range (if the combustion temp was re-optimized).
The bigger problem here is that fuel atomization becomes an issue, as well as mechanical problems like throttle plate sticking. That's the main reason why OEM throttle bodies have coolant lines obviously. Those things are more related to the engine design than the relationship between air density and power output though. I know natural gas engines have horrible problems with cold gas temps and cold intake air temps because the vapor turns back to liquid at a relatively high temperature. Any change in air velocity can change the effective temp quite a bit (when it comes to throttle bodies, etc.) because of convective cooling, and can also cause moisture to fall out of the air. I've seen some really cool videos of sea caves (with chambers of air completely enclosed by water) that fill with fog every time a wave comes in and the pressure changes, and then the fog dissappears when the wave goes out. It's fog-nofog-fog-nofog at the frequency of the waves coming in. I don't know where I was going with that.
I'm still thinking about this one...
More!
I think this would work really well with direct injection; the fuel temp wouldn't become an issue because of when the fuel is injected. Because the air temp increases during compression, the intake air charge could easily gain enough temp to make good fuel atomization easily achievable.
I would imagine that the colder the air the better, because the moisture isn't really adding any power if it's already in vapor form. The purpose of a water mist system is to absorb heat from the intake air by changing the phase of the water (liquid to vapor) but if you're just sucking in moisture then you aren't really adding power unless the moisture is droplets suspended in the air (like fog). If the moisture is droplets suspended in the air, they will still absorb heat and make the intake air charge colder. So that would be the same as having colder ambient air.
Basically, an engine should continue to make more power as long as the air is still in a usable (gaseous) form, assuming that the air isn't getting heated enough by entering the engine to negate any benefits. The combustion efficiency would not be that great though unless the engine was re-optimized to keep combustion temps in the right range. Getting dense air into the engine and making proper use of that dense air are two different things...
The intake manifold tuning would have to change too if the density was that different from more normal operating temps too, because of the relationship of temperature and the speed of sound. Exhaust tuning wouldn't change as long as the exhaust temp range was in a normal range (if the combustion temp was re-optimized).
The bigger problem here is that fuel atomization becomes an issue, as well as mechanical problems like throttle plate sticking. That's the main reason why OEM throttle bodies have coolant lines obviously. Those things are more related to the engine design than the relationship between air density and power output though. I know natural gas engines have horrible problems with cold gas temps and cold intake air temps because the vapor turns back to liquid at a relatively high temperature. Any change in air velocity can change the effective temp quite a bit (when it comes to throttle bodies, etc.) because of convective cooling, and can also cause moisture to fall out of the air. I've seen some really cool videos of sea caves (with chambers of air completely enclosed by water) that fill with fog every time a wave comes in and the pressure changes, and then the fog dissappears when the wave goes out. It's fog-nofog-fog-nofog at the frequency of the waves coming in. I don't know where I was going with that.
I'm still thinking about this one...
More!
I think this would work really well with direct injection; the fuel temp wouldn't become an issue because of when the fuel is injected. Because the air temp increases during compression, the intake air charge could easily gain enough temp to make good fuel atomization easily achievable.
Last edited by Fabrik8; 11-03-2010 at 03:47 PM.
11-03-2010, 03:40 PM
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Re: Ambient temp for max power?
Throttle bodies have coolant lines going to them??? Mine doesn't. What purpose would they serve? I'm not sure I understand why a throttle plate would stick in cold weather.
11-03-2010, 03:43 PM
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Re: Ambient temp for max power?
11-03-2010, 03:46 PM
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Re: Ambient temp for max power?
there would have to be some type of moisture separator prior to the TB wouldnt there? but even then once the air gets to dence to burn would become iratic and uncontrolable. air is composed of about 1% CO2 witch has a boiling point of -70degrees F so thar may be an issue also
11-03-2010, 03:47 PM
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Re: Ambient temp for max power?
I still don't understand the throttle plate sticking in cold though. There's nothing to stick from what I can see. On mine, it's just a metal plate connected to a mechanical linkage. Is it just because I have the benefit of a linkage rather than a cable?
Also, are large displacement engines impacted more by temp changes?
I would have thought the gas sitting on top of an intake valve would be enough to keep it from condensing down, no? Intake valve has got to be pretty hot on a running engine, though maybe you'd have to give it a while to warm up.
Also, are large displacement engines impacted more by temp changes?
I would have thought the gas sitting on top of an intake valve would be enough to keep it from condensing down, no? Intake valve has got to be pretty hot on a running engine, though maybe you'd have to give it a while to warm up.
Last edited by marlinspike; 11-03-2010 at 03:49 PM.
