ABSTRACT
Premixed fuel:air mixtures are used in residential, commercial, and industrial devices. The flow could be either laminar or turbulent. Further, the mixture could be either partially premixed (residential) or fully premixed (oxyacetylene welding torch). As the fuel is burned in a constant-diameter combustion chamber, the velocity increases owing to decrease in density. In Chapter 14, we formulated governing equations to relate the density and pressure changes due to change in velocity and temperature in an open system. Further, we saw that if a combustible gas:air mixture is ignited, the flame propagates either at deflagration velocity or detonation velocity into the unburned mixture. Limiting conditions for those velocities were obtained under a given heat input but without finite chemistry and detailed flame structure. We also determined that change in pressure is negligible under deflagration conditions but not so under detonation conditions. This chapter deals with combustion wave propagation in premixed fuel:air mixtures under deflagration conditions. We will also obtain relations for the flame speed (v
or S), lean (
f
) and rich (
f
) limits called the flammability limits, quench diameter, and minimum ignition energy. We obtain deflagration velocity or flame propagation velocity under subsonic conditions when kinetics limit the combustion rate. Even though typical combustion occurs under turbulent conditions, laminar theory is still required to model the turbulent flames and interpret the results.
