An Air Assist system is really necessary to have on your laser machine if you plan on doing engraving.
A small volume of air blowing down on the point where the laser beam meets the wood, will gently blow away soot and ash and give your engraving a more finished look.
Yes, you can engrave without air assist, but your results won’t look as good.
Below are some pictures of my air assist system. I’m using a 60 Liters/Min unit but it is too powerful and I’ve had to reduce the air flow. I adjust a small valve in the air manifold (see the third picture) to reduce the air flow to just the right amount.
If you blow too much air, it will blow the soot and ash onto the surface of the wood and give your engraving a smeared look. So, you don’t need a lot of air pressure.
I think a 30 Liters/Min air compressor would work just fine.