Well you can use the following:
1) Use air pressure hose to blow off dust throughly over and around the engine. (Get it done throughly giving enough time).
2) Spray engine and bay cleaning FOAM all over the engine and let it soak all the dirt and drip out.
3) Repeat step 2 once again (depending on how dirty the engine is).
4) Spray water jet at the periphery of the engine bay (car body only).
5) Use clean dry cloth to wipe off the entire engine, related auxiliaries and engine bay.
Note: No water is sprayed on the engine and related auxiliaries.