A PhD is an excellent grounding for someone intent on a career as an academic researcher based in a university. An EngD helps those with ambitions in business, industry and other non-academic organisations.
PhD research is often university-based. Research engineers (REs) studying for an EngD work closely with an industrial sponsor.
PhD research can be quite abstract or theoretical. EngD research usually concerns a topic related to the business activities of the industrial sponsor.
PhD projects are primarily focused on research activities. EngD programmes typically combine research and taught courses.
In one key respect, however, the PhD and EngD share a common objective. The test of intellectual contribution for the award of an EngD is at least equivalent of that for a PhD (ie: a distinct 'contribution to knowledge').