#40-60# #""^@C# petroleum ether is the saturated hydrocarbon that boil (that come off the fractionating column) between #40-60# #""^@C#. Refineries sell distillate, whatever comes off the column at a given temperature. #40-60# #""^@C# petroleum ether would include isomeric butanes, pentanes, and hexanes; a mixture of several isomers for the internal combustion engine has been especially tuned for combustion. Gasolines would typically be a specific range of boiling temperatures, probably with special additives to improve (?) performance.
Diesel fuels (which of course are NOT used in the internal combustion engines) are the fractions of higher boiling point: #C_8# to #C_20#, whose boiling points would #>=##100# #""^@C#.
In terms of economy, at an oil refinery it is probably easier to collect a mixture of hydrocarbons that boil over a #20-30# #""^@# range than try to collect specific compounds.
