Autoignition Threshold Theory

[Turbinator]

For a turbocharged engine:
What is the relationship between the knock threshold and air pressure? My question is related to running the maximum amount of boost on pump gasoline. I know that as air temperature increases, so does the tendency for engine knock. Independent of temperature, does increased pressure lead to engine knock? For example, say you are running a pressure ratio of 3:1, but it is intercooled down to ambient temperature, would the limiting factors for knock (ignition advance,compression ratio,ect) be the same as for a normally-aspirated engine? Is there any data on this subject? Thank you.

 

[j2bprometheus]

Increased pressure, even if the temperature is constant, will make knock more likely. I cannot point you to any specific data. Some data is definitely out there in technical publications by organizations like SAE or the Combustion Institute.

j2bprometheus

 

[NeuronBreeze]

I have been looking for information on this subject too - hard to find good data. I'll dive into SAE and Combustion Institute soon. For now, check out this page, *specifically the Max Reliable Boost Pressure vs Static Compression Ratio with respect to intercooling.

Note that this chart should vary greatly with response to engine specific combustion dynamics.

 

[NeuronBreeze]

My earlier link didn't post, so I'll try again...

http://www.procharger.com/intercooled.shtml

There, read the chart near the bottom.

 

[Turbinator]

Yes, I've seen that chart- One of the reasons I got interested in the subject! I did find research report that has some interesting knock-threshhold tests:

http://naca.larc.nasa.gov/reports/1946/naca-tn-1131/naca-tn-1131.pdf