There are plenty engineering consulting firms. In fact, I'd go so far as to say all engineering firms are consulting firms except the ones that are a department within a larger construction or manufacturing company.
Consulting is when you're hired to advise someone else on a task, right? I'm not sure what service an outside engineer offers except consulting services.
Yes, I know engineering consultancies exist, and I've previously engaged with them.
My point is that engineering consultants, at least in the industries I've worked at, are not paid for the duration of the project, but for specific deliverables. Software is the exception in engineering, not the norm.
Consulting is when you're hired to advise someone else on a task, right? I'm not sure what service an outside engineer offers except consulting services.