Why petrol has low flash point and high auto ignition point than diesel?

the higher self ignition temperature of the petrol is due to the low density than the diesel.

as

density = pressure / (R* temperature)

R= universal gas constant.

ex. hydrogen (gas) has density = .082 at 300 k

while kerosene has =810

(both are in kg/m^3)

and auto ignition temperatures are

hydrogen =500

kreosene=295

similarly , petrol-density=737

diesel has=820 to 950 .