The sequences of operation of a Packard diesel engine compared with
those of a 4-stroke cycle gasoline engine are illustrated in figure 21.
[Illustration: =Brief Analysis of Action in a Four-Cycle Gasoline Engine=
_Mixture of air and gasoline enters cylinder from carburetor._
_Mixture is compressed into smaller volume by piston moving upward._
_An electric spark ignites the compressed mixture causing it to
explode._
_Combustion heat increases the cylinder pressure forcing piston
downward._
_Momentum carries piston upward which pushes burnt gases out through the
exhaust valve._
=Similar Action in the Packard-Diesel Aircraft Engine=
_Atmospheric air only, enters cylinder through single valve._
_Air is so greatly compressed by upward moving piston that it reaches
temperature of 1000 deg. F._
_Just before piston is at dead center fuel oil is sprayed into cylinder
and spontaneously ignited._
_Power of this explosion is passed to crankshaft in conventional
manner._
_Piston forces out burnt gases through same single valve which is cooled
by inrush of new air as cycle repeats._