Chair 11 publishes technical reports as “Algorithm Engineering Reports” (ISSN 1864-4503). Reports are being archived in the chair's library and are also available online.
Apart from that, the faculty's reports are available as "Graue Reihe": Technical Reports in Computer Science. Chair 11 does not publish in this series. Reports of the former Collaborative Research Centre 531 are available at http://sfbci.uni-dortmund.de/?lang=en .