In doing research for a class on purging air from hydrocarbon gas lines, I've come across many references that said that as pressure increases Autoignition Temperature goes down, Lower Explosive Limit (LEL) goes down, and Upper Explosive Limit (UEL) goes up. I have been unable (after several hundred hours of searching) to find any trail towards a way to quantify these changes. I've occasionally found someone who claimed that at x pressure, the UEL went up to y%, or Autoignition temp went down to z, but never any references to actual arithmetic.
Does anyone have a feel for the magnitude of these changes or a place to look for the references? I've been doing this class for 10 years, and usually get by with an (unsatisfactory) "the values change with pressure" and rarely get the question "how much?". When I do get the question I shrug and try to change the subject.