the diesels that are in the buses that run around town run on natural gas and or propane. If I remember they use spark plugs they do not auto ignite.

I'm getting old so I could be wrong (bad memory) haven't look at one in twenty years.

 

Here are the auto ignition temps of some gases, oils and alcohols

The Auto-Ignition Temperature - or the minimum temperature required to ignite a gas or vapor in air without a spark or flame being present - are indicated for some common fuels below:
Fuel or Chemical Temperature
(oC) (oF)


Ethylene 490 914
Ehtyl Alcohol 365 689
Fuel Oil No.1 210 410
Fuel Oil No.2 256 494
Fuel Oil No.4 262 505
Hydrogen 500 932
Gas oil 336 637
Gasoline 280 536
Kerosene 295 563
Isopropyl Alcohol 399 750
(Natural Gas) 580 1076
Methyl Alcohol 385 725
Naphtha 550 1022
Propane 480 842
Propylene 458 856