  This work defines density factor as the ratio of before ignition density to
after ignition density of the ignition mixture. This work provides an
estimation method for explosive limits of various fuels under room temperature
and pressure by showing that for a large universe of fuels, constant adiabatic
flame temperature and density factor are appropriate approximations at the
lower explosive limit while only a constant density factor might be an
appropriate approximation at the upper explosive limit.
  Thus the assumption of a constant adiabatic flame temperature can be used in
calculating lower explosive limit while the assumption of a constant density
factor can be used in approximating upper explosive limit.
