Air Temperature

[ruim20]

I was driving the other day and playing with the outside temp button and started wondering about something.

- What's the optimal air temperatura for an engine to run?

take for example a 4 cilinder inline 2000cc engine.

- does it very from engine size and configuration?

Thank you.

[jediali]

well the engine will be designed with a range in mind. From a design point of view the colder the better due to higher density and greater oxygen per unit volume(increase in volumetric efficiency). If the intake is too cold the fuel may have mixing issues in the manifold between injection and valves (i am referring to a indirectly fuel injected petrol)
Generally engines heat the air using exhaust heat if its too cold. This ensures at start-up most of all that the mixture is burning correctly. Because many modern cars adapt the fuel injected to the air density and temperature coming in a mismatch from electronic problems may cause issues.

just of the top of my head, i may be wrong.

[drakkie]

Originally Posted by ruim20

I was driving the other day and playing with the outside temp button and started wondering about something.

- What's the optimal air temperatura for an engine to run?

take for example a 4 cilinder inline 2000cc engine.

- does it very from engine size and configuration?

Thank you.

About 7 or 8 months ago I had to calculate it. it depends on the air pressure, altitude, moist level in the air and many more variables including the engine size, air filter and many many more. AFAIK it is almost impossible to calculate, which was also in my report.

Best is offcourse not too hot and not too cold

[baddabang]

Eleventy billion *C

Thats what like 55*F?

[coolieman1220]

well super hot is not good. i kno that.

[The_Canuck]

Originally Posted by baddabang

Eleventy billion *C

Thats what like 55*F?

More like, 1,000,000,000,000*F

[hightower99]

Originally Posted by drakkie

About 7 or 8 months ago I had to calculate it. it depends on the air pressure, altitude, moist level in the air and many more variables including the engine size, air filter and many many more. AFAIK it is almost impossible to calculate, which was also in my report.

Best is offcourse not too hot and not too cold

I would have thought that only the humidity would have much importance...

how does the rest of the variables you mentioned effect the optimal temperature?

AFAIK you want the air as cold as possible without it being so cold that the water freezes out of the air and without causing problems with fuel atomisation (like jediali mentioned). The air basically has to be warm enough to cause the fuel to become gaseous (before ignition so at latest during the compression stroke).

just realised that compression ratio would be an important variable when considering the optimal temperature.

[fpv_gtho]

Any more than 25 degrees Celcius and you'll probably be making less power than the manufacturer claims. Sometimes its 20 degrees if its measured in DIN.

Other than that i'd imagine the colder the better.

[ruim20]

So the colder the better and without freezing water, so 1 degree celcius would be perfect?

By the way, at at temperture do intercoolers cool the air going in to the engine, diesel and petrol?

Thank you guys.

[drakkie]

Originally Posted by ruim20

So the colder the better and without freezing water, so 1 degree celcius would be perfect?

By the way, at at temperture do intercoolers cool the air going in to the engine, diesel and petrol?

Thank you guys.

The intercooler thing completely depends of the gas law, which i'm sure has been thought on high-school.

Basically the intercooler always cools the air to as low as possible. The temperature of the air inside turbochargers can easily reach 1000+ degrees Celsius. Because of this the gas(=air) uses up less space, so that when compressed in the cilindre more air is present. To keep a good combustion of "labda" more fuel can be put in the cildre as well, which in effect then means more power

[ruim20]

Originally Posted by drakkie

The intercooler thing completely depends of the gas law, which i'm sure has been thought on high-school.

Basically the intercooler always cools the air to as low as possible. The temperature of the air inside turbochargers can easily reach 1000+ degrees Celsius. Because of this the gas(=air) uses up less space, so that when compressed in the cilindre more air is present. To keep a good combustion of "labda" more fuel can be put in the cildre as well, which in effect then means more power

So the car's cpu can modify the temperature at wich the air comes out of the intercooler? depending on throtle position or is this a bit of a stretch? or is it done post intercooler with adding of exaust gas heat?

[hightower99]

Originally Posted by ruim20

So the colder the better and without freezing water, so 1 degree celcius would be perfect?

Not unless you have direct injection. At 1 degree C the petrol will stay in liquid form and it's viscosity will be increased. About the lowest you want to go with multi-port injection is about 10 C colder than that and you have problems with the fuel clumping and falling out of the air stream.

Originally Posted by drakkie

The intercooler thing completely depends of the gas law, which i'm sure has been thought on high-school.

Basically the intercooler always cools the air to as low as possible. The temperature of the air inside turbochargers can easily reach 1000+ degrees Celsius. Because of this the gas(=air) uses up less space, so that when compressed in the cilindre more air is present. To keep a good combustion of "labda" more fuel can be put in the cildre as well, which in effect then means more power

ICs don't work like you would think they would they do not act entirely like radiators (where there cooling potential is only porportionate to vehicle speed and or fan speed). ICs tend to function as large heat sinks. Basically when you hit the gas and go for it heat is dumped into the material of the IC making the whole thing warmer, it then radiates that heat away slowly like a radiator, however when you stop the IC is still hot and dumps most of its heat back into the intake air (because it will be cooler when you are idling).

Also the air in the compressor side of a turbo should not get warmer than about 250C (and most don't go above 120C) or you have a real problem (ie a really inefficient compressor). The exhaust going through the turbine side can reach 1000C+ going into the turbine (the exhaust cools as it travels through the turbine).

Also I would like to comment on the fact that if you warm gas (air) up then it will take up more space and the cylinder will not be able to burn as much fuel (as that is dependant on the amount of oxygen in the cylinder).

also typical air temp after the IC is normally around 50-70C. This means that big gains can be had just by cooling the air down to 20C or less (again 10C is the lower limit). If the air was 70C after the IC and you somehow cooled it down to 10C and somehow maintained pressure then there would be 17.5% more oxygen per unit volume of air going into the engine (and therefore into the cylinders).

[ruim20]

50-70c is very worm still, i thought the temperature would drop a lot more after the IC, do water cooled intercoolers have the same performance? or can they "produce" cooler air?

Also, i'm guessing, the bigger the IC the lower the air temperature gets?

TIA

[Quiggs]

An intercooler that was too large would suffer from huge pressure drops.

[hightower99]

Originally Posted by ruim20

50-70c is very worm still, i thought the temperature would drop a lot more after the IC, do water cooled intercoolers have the same performance? or can they "produce" cooler air?

Also, i'm guessing, the bigger the IC the lower the air temperature gets?

TIA

50-70C isn't too hot at all. But there is power to be gained

Air to water ICs do produce lower temperatures if they are made correctly. Several designs on the market have too much material (metal) and they again act as heat sinks. A well designed water IC can drop the temps to 35-45C but if you have a larger water resivior and you pack it with ice then you can have air temps all the way down to 10-20C (for a short while).

Also you are kinda right about ICs but it isn't the physical size or internal volume that really matters. What matters is the mass of metal used to make it and how much surface area there is between that mass and the mass of the air traveling through it.

Originally Posted by Quiggs

An intercooler that was too large would suffer from huge pressure drops.

Yes and No. A larger internal volume may indeed lead to lower pressures if the engine can swallow more air then the charger provides to the IC, however pressure drops are caused by many things. Increased velocity through the system looses apparent pressure but this is gained in the cylinders because of the increased kinetic energy (so nothing to worry about). The larger mass of metal in a larger IC will cool the air down more and this is the main cause of pressure loss. The IC design has to be able to ramp the pressure back up (by slowing the velocity or dumping it into a large volume) in order for the engine to see any benefit from the colder air (namely increased % oxygen per unit volume).