{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4d308d0fec72f75adcccd0e11f0a93ed3233fc92f165e05bde04c5273c8504fc","created":"2026-10-03T07:18:04Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"e039cf870d6dc7b496da1f000927e4cb3722812dcfea5e2167e3a7537deee76d","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"fluid.turbulent-combustion.unconfined-ddt","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"A flame (deflagration, burning that spreads slower than sound) usually needs walls or obstacles to build up into a detonation. Simulations suggest that strong turbulence alone can do it in open space; does this happen in real gas mixtures, and by what route?","posed_since":"","precise":"For a premixed fuel-air flame (for example stoichiometric H2-air or CH4-air) in homogeneous isotropic turbulence with no walls or obstacles, determine whether deflagration-to-detonation transition (DDT) occurs, and the threshold in turbulent intensity $u'/S_L$ and integral scale $L/\\delta_L$ ($S_L$ laminar flame speed, $\\delta_L$ laminar flame thickness). Test the proposed route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed (the fastest steady deflagration allowed by conservation laws), so pressure builds up in the flame brush and forms shocks that trigger detonation. An answer is a verified criterion for unconfined DDT as a function of mixture and turbulence.","problem_ref":null,"references":"","settled_by":"Experiments with turbulent premixed flames free of walls and obstacles that observe or exclude DDT at controlled $u'/S_{L}$ and $L$, matched by fully resolved simulations with detailed chemistry.","status_note":"Simulations published in 2019 support the route in which the turbulent flame speed exceeds the Chapman-Jouguet deflagration speed; channel experiments up to 2025 are consistent with it, but no test free of walls and obstacles exists, and only a few mixtures have been tested.","title":"Can turbulence alone turn an unconfined premixed flame into detonation?","topic_ref":"ff8822779d7d3829d62f794eaee78060074a7c7c5588960c0eae974a587339ac"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"f65ad5573805b868449f3e52ead6a433262d6e32c0e5015c17cc573e196f1f62","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"c2868a7a06513a4f3b1694095ca6c4c9755f1b513c1ec2591fea2ea1c571c02d","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"VTOo--GBXDH8UUALl9S3j0nCT0Ay72QbK-5NFBxvfjghUvGh73i_kRmqFBgxPxP5A9ZpvXeiiK3tV4nJB7OAAw"},"schema":"pubphys.envelope/1"},"record_hash":"f65ad5573805b868449f3e52ead6a433262d6e32c0e5015c17cc573e196f1f62","leaf_index":1450}