Transmission of a detonation wave across a sudden expansion with varying mixture composition

Abstract

Detonation waves were examined in axisymmetric and two-dimensional test configurations to determine the limits at which a detonation will successfully initiate and diffract from a small initiator tube into a larger main combustor. Tests were conducted for various initiator-to-main combustor area ratios. Additionally, for each area ratio, the fuel-oxygen initiator mixture was diluted with various nitrogen concentrations attempting to approach the mass fraction of nitrogen in air (79%). Results of the axisymmetric testing showed that with an expansion area ratio of 2.0, detonations began to fail to initiate in the initiator section with nitrogen dilution as low as 45%. Although, through constructive interference such as wall reflections and shock-shock interactions, a detonation wave initiated in the main combustor for up to 60% nitrogen dilution. Results of the two-dimensional testing showed that for area ratios of 1.33 to 2.67, detonation waves successfully transmitted for all nitrogen dilution cases, including 79%. For an area ratio of 4.0, detonation waves successfully transmitted with 65% nitrogen dilution but failed with 70% nitrogen dilution.