RE: [hreg] What is holding back American car companies?
Depends on the temperature, of course. At atmospheric pressure, the autoignition temperature (AIT) defines the point at which spontaneous ignition occurs. http://en.wikipedia.org/wiki/Autoignition_temperature reports 275°C for gasoline (in air). Normally, AIT is measured at atmospheric pressure.
There is a brief discussion of an apparatus to measure the effect of pressure on the AIT found at http://www.ptb.de/de/org/3/34/341/goedde.htm. Basically, as pressure increases, the AIT decreases, but there is a limit to this effect due since increased pressure also shifts the liquid-vapor equilibrium towards the liquid phase.
The Semenov Equation giving the effect of pressure on AIT is shown on p. 4 of this article, with a graph: http://www.me.berkeley.edu/ME140/Handout-1.pdf
There is a lot more in the literature on this, of course, but those are a few free references that showed up on Google. As the article points out, diesel engines are designed to run in that fashion (no spark); that’s why they are so much fun to start in an Alaskan winter!