Engine air temp

[magifesq]

I can't get a straight answer from google, so knowing there's plenty of engineers here I'll post it - I'm looking to find how much ambient air temperature increases in the combustion chamber of a simple 10:1 CR engine. Does the air temp double, triple, go up 10x?

Thanks in advance,

Mike

[ReconRat]

http://papers.sae.org/930217/

Translation: 130 C to 248 C (266 F to 478 F), typically the high range of the value at WOT. Piston head can be as much as 25 C (77 f) higher. Temperatures vary in different areas of the combustion chamber, depending on flow of gases and typically cooler near metal surfaces which act as heat sinks. At no time would temperatures go over 275 C (495 F), at which point gasoline auto-detonates by itself. Carbon or other deposits can raise the temperatures.

Cylinder head combustion chamber and piston temperatures and heat fluxes were measured in a 2.2 L 4 cylinder spark ignition engine. Measurements for the combustion chamber were made at wide open throttle conditions, 1400 rpm to 5000 rpm at 600 rpm increments, additional measurements were made on the combustion chamber at part throttle conditions at 3200 RPM. Piston temperature and heat flux measurements were made at WOT conditions from 1400 to 3200 RPM in 600 RPM increments. Average combustion chamber surface temperatures ranged from 130 deg. C to 248 deg. C, while peak combustion chamber surface temperatures ranged from 142 deg. C to 258 deg. C for WOT conditions. Peak heat flus at the surface for WOT conditions in the combustion chamber ranged from 1.2 MW/m 2 to 5.0 MW/m 2 . Central region heat fluxes were 2.3 to 2.8 times greater than those in the end gas regions of the combustion chamber. Piston temperatures were 10 to 25 degrees centigrade hotter than corresponding combustion chamber surfaces at WOT conditions. Peak heat flux values in the end gas region of the piston were 2 to 4 times greater than corresponding locations on the combustion chamber at WOT conditions. The Woschni heat transfer model correlated well with the experimental instantaneous local heat flus data. Long term heat flus data indicates that deposit formation greatly modifies surface heat transfer.

[ReconRat]

So, your answer: Ambient temperature generally refers to indoor temperatures, not outdoor. But is maybe accepted to be an average 73 F. Obviously outdoor air temperatures will throw the ratio off.

495F/73F = 6.78 max temp ratio

266F/73F = 3.64 min temp ratio

for fun @ 32 F outside, 495F/32F = 15.4 temp ratio

@ 100 F outside, 266F/100F = 2.66 temp ratio

I'd say for the most part, it's about 3.5 ratio at idle, climbing to 6.5 at WOT. But a lot of extra fuel is dumped in at WOT to keep the combustion chamber cooler, so it's hard to say.

Edited June 17, 2012 by ReconRat

[magifesq]

thanks for the info bro

[ReconRat]

Note that compression ratio mostly doesn't effect what happens with heat. It creates more heat, but if the engine is designed right, it gets rid of it, and it's all held to about the same conditions inside the engine. The obvious conditions where it doesn't, like an air cooled engine sitting still without a wind, will elevate the internal temperatures.

Or putting high compression pistons in an air cooled bike that isn't designed for it. Yeah, that doesn't always work out too well.

[TSB67]

What you're looking for is adiabatic compression. There is an engine example on this page.

http://en.wikipedia.org/wiki/Adiabatic_process

Adiabatic means there is no heat transfer into or out of the system, so your calculated result is going to be higher than reality.

[vf1000ride]

Ok, so the simple real world answer is. Hold your hand or throw a digital thermometer on the output line or the head/cylinder of a larger air compressor, something you could run an impact wrench or air nailer off of. The metal line between the head and the tank is usually the hottest. You are compressing air from ambient to 110psi and that is roughly in the same range as the cylinder compression on a motorcycle engine. There is no fuel involved so you are only dealing with the heat caused by friction and the compression of air.

BTW, they get friggin hot so be careful.