Flame propagation: the effect of pressure variation on burning velocities

The burning velocity of mixtures of methane, propane, ethylene and propylene with air are determined under constant-pressure conditions in a tube of rectangular section at pressures from $\frac{1}{2}$ to 9 atm. For methane and also for propane, the effect of mixture strength was also investigated. Schlieren photographs of the passage of the combustion wave were obtained. The conditions leading to vibrations and to turbulence in the flame front, and also to change in the shape of the surface of the advancing flame, were investigated. The burning velocity was obtained from measurements of the speed of uniform movement and the flame area. A special valve maintained communication with an atmosphere of nitrogen during passage of the flame so as to maintain the pressure constant. The results are compared with other measurements. The pressure exponent is about 0$\cdot $5 for methane and for other gases approximately 0$\cdot $3, but there is some variation with change of mixture strength; the richer mixtures are less affected by pressure. The results indicate that both heat and diffusion (particularly of hydrogen atoms) play a part in flame propagation.