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The following computational study examines the structure of sonic hydrogen jets using inlet conditions similar to those encountered in direct-injection hydrogen engines. Cases utilizing the same mass and momentum flux while varying exit-to-chamber pressure ratios have been investigated in a constant-volume computational domain. Furthermore, subsonic versus sonic structures have been compared using both hydrogen and ethylene fuel jets. Finally, the accuracy of scaling arguments to characterize an underexpanded jet by a subsonic “equivalent jet” has been assessed. It is shown that far downstream of the expansion region, the overall jet structure conforms to expectations for self-similarity in the far-field of subsonic jets. In the near-field, variations in fuel inlet-to-chamber pressure ratios are shown to influence the mixing properties of sonic hydrogen jets. In general, higher pressure ratios result in longer shock barrel length, though numerical resolution requirements increase.

This paper provides a comparison of wall heat fluxes and quenching distances as one-dimensional hydrogen and heptane flames impinge head-on onto a wall. It is shown that the quenching distances for stoichiometric H2/air and C7H16/air flames under the specified conditions of this study are about the same, but the wall heat flux for the H2/air flames is approximately a factor of two greater. For lean H2/air mixtures, the quenching distance increases substantially and the wall heat flux decreases. To understand more clearly the interplay of flame speed, temperature, thermal diffusivity, and surface kinetics on the results, studies of H2/O2 flames are also carried out.