Figure 2-27. The Rotary Engine
b. Operation(Fig. 2-28).
shaft so that it only goes around once for every three
turns of the eccentric shaft. This works out to one power
stroke to every eccentric shaft rotation. This is illustrated
(1) Intake. Looking at the rotor face (1), note
in figure 2-29.
that as it moves by the intake port, the space between it
and the rotor housing increases. This causes a fuel and
c. Advantages. If the eccentric shaft receives one
air mixture to be drawn in through the intake port.
power stroke for each eccentric shaft revolution, then the
rotor is equivalent to a two-piston, four-stroke cycle
As the rotor face (1)
engine. As a result, the engine is a much more compact
continues around the inside of the housing, it moves
unit. The absence of the reciprocating parts and the
away from the intake port. As it moves away, the space
absence of the valve train serve to help the engine attain
between the rotor face and the housing decreases. This
higher speeds safely, giving it more flexibility in usage.
compresses the fuel and air mixture.
The absence of these parts also serves to make this
(3) Power. When the rotor face (1) reaches the
engine smoother than its piston engine counterpart.
point where it is compressing the fuel and air mixture the
d. Disadvantages. A large percentage of the
tightest, the spark plug ignites the mixture and pushes
the rotor around in the housing.
combustion area is exposed to the intake charge
because of the rotary engine design. This large surface
(4) Exhaust. As the rotor face (1) continues
area, when wetted with fuel during intake and ignited at
around, it becomes exposed to the exhaust port. At this
the beginning of the power stroke, produces dirty
point, the space decreases in size again. As the space
combustion. While rubbing against the housing, the
size decreases, it causes the burnt gases to be pushed
seals on each corner of the triangular-shaped rotor are
out through the exhaust port. This is a continuous cycle.
subjected to high rotational speeds. This results in rapid
seal wear and is of a major concern to manufacturers.
(5) Three Rotor Faces. Note the three rotor
The many irregular curves in the design make the
faces (1, 2, and 3) illustrated in figure 2-28. Each one of
machining processes of the rotary engine difficult. The
these faces goes through its own complete operating
rotary engine also is hard to modify for development
cycle every time the rotor goes around In the housing.
purposes. The rotary engine has not had a major impact
The rotor is geared to the eccentric
on automotive engine development. Lack of research
and development have kept it from realizing its full