Early work on fluid mechanics in the IC engine

Early work of Ricardo is described, in which squish is used in flat-head en gines to generate turbulence levels comparable to those in overhead-valve e ngines, leading to rapid flame propagation, and suppressing knock. Work by NACA before World War II is described, in which turbulence levels were meas ured in overhead-valve engines, indicating indirectly that surprisingly hig h levels were achieved just before ignition, possibly due to a tumble insta bility. Finally, work of Obukhov of 30 years ago is described, in which ins tabilities of tumbling flow are investigated in ellipsoids crudely modeling the engine cylinder as the piston rises; this suggests that there is an in stability leading to intense small-scale motion just before ignition. Sugge stions for further work are given.