Yes, a lower-limit (and an upper limit) explosion will produce a pressure-rise less than a stoichiometric mixture, but there are other factors that can reduce the pressure rise when compared to a well-mixed stoichioemtric mixture of air and fuel. In a well mixed situation, the chemical kinetics control the rate of reaction. In the case of a non-well-mixed fuel air mixture where regions of rich mixtures are present, the rate of physical mixing controls the rates of reaction. In addition, the integrity of the structure plays a role in the peak pressure rise. The local loss of structural integrity creates opening or vents that allow the pressure rise to be "vented," thus reducing the peak pressure rise due to conservation of mass.

If physical mixing is the controlling phenomenon (diffusion flame), then the structure, flame radiation, and duration are different than for a premixed flame produced by a well-mixed stoichioemtric mixture.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com