The Profesional Doctorate in Engineering (PDEng) is equivalent in level to a Ph.D. but more vocationally oriented.  The traditional Ph.D. requires a contribution to scientific knowledge.  In contrast, the Professional Doctorate requires a contribution to professional practice.  rather than one lengthy academically-oriented Ph.D. research project, the Professional Doctorate programme involves solving a significant organisational problem, typically based on the candidate's work environment.

Further details can be found here