Make it harder ? Thought it would make it faster as intake of smoke would be secluded
If you were to do such a thing, & i highly suggest you don't please...Being in a car would just complicate things, the only benefit as such would be to render your corpse unrecognisable without proper Dna testing. As its not the smoke that will kill you, its the burns.
People who set themselves on fire are generally aware of everything that is going on, as every single nerve fibre is burnt one by one & can survive for a number of hours/days before dying.
Please, do not do this.