EFFECT OF SWIRL ON COMBUSTION IN A SHORT CYLINDRICAL CHAMBER

Combustion of a swirling, stoichiometric, and homogeneous mixture of n atural gas and air in a short cylindrical chamber has been studied exp erimentally and simulated numerically. Each mixture was given a steady -state swirling motion by a relating roughened disc before being ignit ed at the center of the chamber. By using discs of differing roughness and by varying the disc speed, the Intensities of swirl and turbulenc e could be varied independently so that the effects on combustion of m ixture turbulence and swirl-induced buoyancy could be separately exami ned. Combustion rate and overall chamber heat transfer were inferred f rom chamber pressure-time records. High-speed schlieren photography sh owed the effect of swirl on the early flame kernel. With given swirlin g angular momentum, increased turbulence level always reduced burning duration and increased total heat transfer rate. With given turbulence level, increasing the swirl intensity From zero first decreased, then strongly increased, the burning duration. The swirling Reynolds numbe r (based on chamber radius and peak tangential velocity) at which comb ustion duration was minimized was in the range 30,000-40,000. At high Reynolds number buoyancy forces appear to have a strongly inhibiting e ffect. on flame propagation.