Because of its design and the
180 degree offset between the two rotors, the
engine operates with almost no vibrations.
It is able to reach much higher RPM than piston
engine. It also has wider RPM range, so it can
adjust better to different scenarios.
Much greater power to weight ratio compared to
piston engine
Fewer parts - It is cheaper to produce. This
also makes it lighter.
The front face of the engine is small, therefore
the nose of an aircraft can be more aerodynamic.
Wankel engines are reliable, because the engine
lacks connecting rods, pistons, valves or a
crankshaft, all the parts that are exposed to
high stress and lead to critical failure when
they break and seize the engine.
Wankel engine cannot suffer a critical failure
where the engine gets completely stuck, because
the rotor is made out of iron and the housing
out of aluminum which expands more when heated
up, therefore the engine cannot seize. It may
lose compression and power but it will be still
producing some power allowing for safer landing
when used in aircraft.
Disadvantages
Sealing the combustion
chamber. Due to the different temperatures
across the housing and different thermal
expansion coefficients leads to imperfect
sealing. To spread the heat evenly engineers
experimented with heat pipes that would
transfer heat from the hot the cold side of
the engine. Wankel engine does not use
gasoline premixed with and the apex seals
are not lubricated by the engine oil from
the inside, therefore oil is injected
directly to the chamber to prevent the apex
seals from scratching the housing and
wearing out quickly.
Apex seal lift. During low RPM the apex
seals might not be pushed hard enough
against the housing, which results in lower
pressure in the chamber, because the air
fuel mixture escaped through the gaps.
Slow combustion. Because the combustion
chamber is long, thin, and is spinning, the
flame does not have enough time to burn all
the fuel, which results in high fuel
consumption, poor efficiency and high
emissions. Problem with high emissions was
solved for a few years with direct
injection, but now it does not meet emission
standards, because they got more strict.
