Do you know how a diesel works? Do you know what a BOV does?

When you suddenly close the throttle, the compressor dead-heads against the (closed) throttle. So the BOV releases that sudden surge of pressure. You may have noticed that a diesel engine doesn't have a throttle...

hmmm... guess I haven't played with too many diesels. The one's I've messed with didn't have throttle plates. Full air pressure (no throttling) is required in order to have sufficient temperature for ignition.