Well, let's see. On gassers they sell these special units to induce the incoming air to swirl, and then claim tremendous fuel economy gains.
Then, for diesels with a built in air swirler, they sell something to stop the air from swirling, and claim tremendous fuel economy gains.
What do you think the resulte will be?
Clue: If ANY wonder gadget ever does work, every news channel on the planet will carry the earthshaking news around the clock. A 10% to 25 & fuel economy improvement would truly be earthshattering news. It would mean billions of gallons of oil saved each year.