Air temperature effects on performance?
Discussion
Ive had a couple of conversations recently around this topic (ie filters with cold air ducting and power outputs varying on various cars when cold / hot).
Im curious if anyone knows any "rule of thumb" on the effects ambient temperature (or the temperature of air reaching the filter) has on power?
Any idea how negligable the effect is within a normal ambient temperature range?
Cheers in advance
Im curious if anyone knows any "rule of thumb" on the effects ambient temperature (or the temperature of air reaching the filter) has on power?
Any idea how negligable the effect is within a normal ambient temperature range?
Cheers in advance
Basically, the cooler the air, the denser it is, and therefore contains more oxygen. Oxygen is required for the combustion process. Effects can be seen in extreme by using nitrous oxide, where the oxygen density is higher than atmosphere, and the gas actually cools the engine, allowing even more oxygen in. The engine then works out how much more fuel it can burn because of the increase in oxygen available.
Not sure how much the effect can be noticed at ambient ranges though, as the engine needs to be above a certain temperature to operate efficiently, so one cancels the other out. 'I think?'
www.idavette.net/hib/nitrous.htm
Not sure how much the effect can be noticed at ambient ranges though, as the engine needs to be above a certain temperature to operate efficiently, so one cancels the other out. 'I think?'
www.idavette.net/hib/nitrous.htm
Thanks for that guys, Im aware of the principles involved, but trying to find out what the magnitude of the effect is in "normal" conditions.
Havent had much luck with any other sources, and im guessing that the effect is actually quite slight on normally aspirated engines, however thats based more on intuition than hard figures.
Havent had much luck with any other sources, and im guessing that the effect is actually quite slight on normally aspirated engines, however thats based more on intuition than hard figures.
Roughest of rough estimates ... density of a gas is inversely proportional to absolute temperature, so you'd expect air density to vary by about 15% at constant pressure between a hot and cold day in the UK.
Assuming the air hasn't got heated before it enters the cylinders so that this increased density is maintained, it looks like there could be quite a significant benefit from cold weather.
Also, assuming it doesn't impair combustion, the colder the air/fuel charge in the cylinder the better, in terms of the relative expansion after combustion. I suspect that latter effect is fairly minimal because the compression stroke must heat the air up enormously irrespective of its initial temperature.
Assuming the air hasn't got heated before it enters the cylinders so that this increased density is maintained, it looks like there could be quite a significant benefit from cold weather.
Also, assuming it doesn't impair combustion, the colder the air/fuel charge in the cylinder the better, in terms of the relative expansion after combustion. I suspect that latter effect is fairly minimal because the compression stroke must heat the air up enormously irrespective of its initial temperature.
Well to give an example if I have my car running on low boost at around 0.9 bar say, in normal conditions. In the evening when the air has cooled that can increase to around 1.1 bar. This means that the car gets more, colder, denser air and power is increased quite dramatically. It is at it's most powerful when it is cold and icy 
The effect isn't as great on an N/A car but the colder the air, the more power, to put it simply. Actual gains will depend on the car and the situation. Sure we could all help a bit more if you could furnish us with this information.
The effect isn't as great on an N/A car but the colder the air, the more power, to put it simply. Actual gains will depend on the car and the situation. Sure we could all help a bit more if you could furnish us with this information.
I've put a coolair/Ramduct stylee thingy on my CR-X (1.6i 16, NA) and find that the air temp mostly makes a difference to the response of the engine.
You notice that it feels sharper on a cool crisp mornings than on a muggy hot afternoon. I've had the mod for a couple of years now, so I know its not just the ram effect or the wind direction, because those there all the time the car's moving.
From what I've read the bigger the difference between the temp of the charge air and the running temp of the motor, the greater the volumetric efficecey, and so MORE POWER urgh urgh urgh!(just don't run the thing so hot it pops it's head gasket)
The gains aren't huge, in relms of 3 or 4%, but if your running 150bhp+ its more than enough to be noticable.
Hopefully that was more what you had in mind...
...have fun.
Mouse.
>> Edited by danger mouse on Wednesday 30th October 14:25
You notice that it feels sharper on a cool crisp mornings than on a muggy hot afternoon. I've had the mod for a couple of years now, so I know its not just the ram effect or the wind direction, because those there all the time the car's moving.
From what I've read the bigger the difference between the temp of the charge air and the running temp of the motor, the greater the volumetric efficecey, and so MORE POWER urgh urgh urgh!(just don't run the thing so hot it pops it's head gasket)
The gains aren't huge, in relms of 3 or 4%, but if your running 150bhp+ its more than enough to be noticable.
Hopefully that was more what you had in mind...
...have fun.
Mouse.
>> Edited by danger mouse on Wednesday 30th October 14:25
TheLemming said: Thanks for that guys, Im aware of the principles involved, but trying to find out what the magnitude of the effect is in "normal" conditions.
Can't help with the maths, but for reference, Lotus quoted 240 bhp for the 2.0 litre chargecooled turbo GT3. They also noted that the engine could produce up to 260 bhp under certain atmospheric conditions (i.e. a cold day).
Believe me - this was a really noticable difference. If you drove the car on a hot sticky day it felt ok/quick. A dry cold autumn day however and it was blinding!
Rob
(ex-esprit gt3 driver)
Guess the cold up at those altitudes didn't help much as the air would be far less dense negating the advantage. With the air being so thin wouldn't the engine tend to run rich, making it run cooler and retarding ignition anyway? hang on, just answered my own question.... d'aaargh.
Suppose the superchargers on the Merlin would have sorted that problem out. Water injection certainly has its followers, though there is some debate as I understand it, as to how much real effect it has. I know it's commonly used on rally beasts like the Impreza and Lancer, and they wouldn't carry the extra weight around for nothing.
Suppose the superchargers on the Merlin would have sorted that problem out. Water injection certainly has its followers, though there is some debate as I understand it, as to how much real effect it has. I know it's commonly used on rally beasts like the Impreza and Lancer, and they wouldn't carry the extra weight around for nothing.
danger mouse said:Water injection certainly has its followers, though there is some debate as I understand it, as to how much real effect it has. I know it's commonly used on rally beasts like the Impreza and Lancer, and they wouldn't carry the extra weight around for nothing.
I was under the impression that the water spray on these cars was used to douse the intercooler rather than injecting liquid into the engine?
Ive had a couple of conversations recently around this topic (ie filters with cold air ducting and power outputs varying on various cars when cold / hot).
Im curious if anyone knows any "rule of thumb" on the effects ambient temperature (or the temperature of air reaching the filter) has on power?
Any idea how negligable the effect is within a normal ambient temperature range?
Cheers in advance
3 dec C corresponds causes roughly 1% loss of power. So if you've got a TVR putting out (say) in the region of 300 BHP, that's one degree C per BHP. In other words, its a huge effect.
Cheers,
Peter Humphries (and a green V8S)
Some cars have a water spray which cools the outside surface of the intercooler.
More common however is Water Injection, where water, methanol, or a 50/50 mix of the two is injected into the inlet tract post-intercooler. Heat from the charge evaporates the droplets of liquid into a vapour, ie heat energy is transferred to the water, therefore the incoming charge is cooler when it reaches the cylinder.
Used to prevent pre-ignition/detonation.
More common however is Water Injection, where water, methanol, or a 50/50 mix of the two is injected into the inlet tract post-intercooler. Heat from the charge evaporates the droplets of liquid into a vapour, ie heat energy is transferred to the water, therefore the incoming charge is cooler when it reaches the cylinder.
Used to prevent pre-ignition/detonation.
danger mouse said:
With the air being so thin wouldn't the engine tend to run rich, making it run cooler and retarding ignition anyway?
No, because the effect of pressing the accelerator doesn't push more fuel into the engine directly. The accelerator controls the air flow into the engine. The ECU works out how much fuel the engine can handle depending on how much air is available to burn it. If the atmosphere is thinner, the ratio of oxygen, nitrogen etc in the air remains the same, but the air is less compressed.
Therefore the engine will never run rich because of this.
It will not run rich or lean, since the fuel injected is proportional to the air available. The loss of power will be due to the lack of both air and fuel as a result.
www.howstuffworks.com/fuel-injection2.htm
>> Edited by nmlowe on Wednesday 30th October 20:37
nmlowe said:
danger mouse said:
With the air being so thin wouldn't the engine tend to run rich, making it run cooler and retarding ignition anyway?
No, because the effect of pressing the accelerator doesn't push more fuel into the engine directly. The accelerator controls the air flow into the engine. The ECU works out how much fuel the engine can handle depending on how much air is available to burn it. If the atmosphere is thinner, the ratio of oxygen, nitrogen etc in the air remains the same, but the air is less compressed.
Therefore the engine will never run rich because of this.
It will not run rich or lean, since the fuel injected is proportional to the air available. The loss of power will be due to the lack of both air and fuel as a result.
www.howstuffworks.com/fuel-injection2.htm
>> Edited by nmlowe on Wednesday 30th October 20:37
Sooooooooooooooooooooooo the Spitfire(SuperMarine) had an ECU...
nmlowe said:
danger mouse said:
With the air being so thin wouldn't the engine tend to run rich, making it run cooler and retarding ignition anyway?
No, because the effect of pressing the accelerator doesn't push more fuel into the engine directly. The accelerator controls the air flow into the engine. The ECU works out how much fuel the engine can handle depending on how much air is available to burn it. If the atmosphere is thinner, the ratio of oxygen, nitrogen etc in the air remains the same, but the air is less compressed.
Therefore the engine will never run rich because of this.
It will not run rich or lean, since the fuel injected is proportional to the air available. The loss of power will be due to the lack of both air and fuel as a result.
www.howstuffworks.com/fuel-injection2.htm
>> Edited by nmlowe on Wednesday 30th October 20:37
Didn't realise WWII fighters had ECUs
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