Flame Trap.

Another way of saying:

Contain Fire?

Why would I want to contain a fire in my engine? Is it possible that Volvo engineers saw a situation where a fire from one part of the engine could spread to another part of the engine--like from a back-fire traveling to the crankcase, possibly filled with volatile fumes?

Manufacturers don't design and manufacture extra parts just for the fun of it.

Yes, there are plenty of cars with plenty of extra parts, serving fairly minor functions.

But here's a part that sounds like it's protecting against a fairly catastrophic failure. The only problem is that it's design is such that it causes problems that wouldn't exist, but for its existence.

Bottom line, keep it, but put it on your list of regular maintenance items.