I've got very weird smells on engine starts after a compressor wash. I was very concerned about it the very first time that happened to me. But, It's very usual in some hubs where this type of maintenance is performed.
If it's windy, specially when you have a tailwind, we get some burned jet fuel smell. Some of those exhaust particles are pushed to the engine inlet again and therefore to the air conditioning system. Not a big deal.
Cheers.