Spark ignition and the early stages of turbulent flame propagation

Abstract A hydrodynamic mathematical model is presented, without chemical kinetics, for the ignition of gaseous mixtures. Solution schemes are discussed and computed results presented for the initial shock wave propagation and the slower spreading of the thermal wave from the narrow spark discharge channel. Different spark power-time profiles are analyzed and it is clear that a central problem is the slow spread of energy from the discharge channel to ignite a critical volume. An initial high energy input aids this process. Ignition delay times are presented, based upon thermal ignition criteria. Minimum ignition energy is increased for turbulent mixtures because of the effects of flame straining. Ignition experiments are reported for a fan-stirred bomb. Spark power profiles and turbulent velocities were controlled and CH emission intensities measured. Ignition and flame development were traced from high speed schieren photographs. Three regimes are delineated: localized ignition, spark assisted flame propagation, and normal propagation.

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