There are plenty of different schools of thought on the matter, but the truth depends on what type of car you have.
Researchers from Skoltech have published a paper in the journal Physica D: Nonlinear Phenomena presenting an analysis of steady propagating combustion waves—from slow flames to supersonic detonation ...
Initial stages of explosions (auto-ignition) as a thermal phenomenon -- Spark ignition I: thermal theory of spark ignition -- Propagation of explosions -- Explosions in closed chambers -- Detonation - ...