chugging

(aerospace engineering) Also known as bumping; chuffing. A form of combustion instability in a rocket engine, characterized by a pulsing operation at a fairly low frequency, sometimes defined as occurring between particular frequency limits. The noise that is made in this kind of combustion.
(nucleonics) An instability in a water-moderated reactor in which the formation of steam bubbles in the core and their subsequent collapse cause oscillations in the reactivity.