Is doing research alone and publishing solo frowned upon by colleagues and superiors in engineering sciences?
I think there is no universal answer. There are fields of pure mathematics where single author papers are quite frequent (the majority?) while there are other areas of the sciences (e.g., the biomedical field) that are so broad that nobody has the requisite knowledge and time to do everything themselves.

So it depends on the field you're in. But beyond that, every field has single-author papers, and a single paper isn't going to make others put you in a box: it is, after all, just a single paper. People will turn out to be surprised if you have been in a field (any field!) for ten years, written 30 papers, and 25 of those are single-authored. For a single paper, there really is no rule to go by: If you have a good idea that you've entirely developed yourself, go write it up and get it published!