The Rotary (Wankel) Engine
Ben Larson
Peter Shreffler
Scott Steinmetz
History
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Ideas have existed since the 16th century
German scientist Felix Wankel was the first to put
the idea into a working design
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Funded by the German Aviation Ministry during WWII
Germany believed that the rotary engine would propel their
industry into eventual greatness
Wankel perfected his design and sold the rights for
the design to several car companies
Mazda produced its first rotary power car in 1961
and created their Rotary Engine Division in 1963
History
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Popularity for the rotary powered vehicles
increased rapidly until the gas crisis in the mid 70’s
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Rotary engines were not very fuel efficient compared to
piston engines
Strict emissions standards could not be met with current
rotary technology
These two factors severely hurt the sale and
development of rotary engines
Mazda was the only car company that continued to
produce cars with rotary engines through the 90’s
History
This graph demonstrates the rise and decline of the rotary engine’s
popularity through the mid to late 90’s
Automotive Success with Rotaries
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In 1991, the Mazda
787B won the 24-hour
Le Mans endurance
race
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Rotary engines were
then banned from the C2
circuit
The RX-8 is able to
produce 238 hp from its
1.3L engine and with
good gas mileage and
favorable emissions
Intake
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Begins when apex
passes intake port
Increase in chamber
volume
Creates low pressure
zone
Pulls in Fuel/Air
mixture
Completes when next
apex passes intake
port
Compression
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Begins after intake
Volume of chamber
decreases
Fuel/Air mixture
compressed
Chamber compresses
to its minimum size
Combustion
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Spark plugs ignite mixture
Two spark plugs to
maximize amount of fuel
ignited
Causes rapid chamber
expansion
Turns rotor which
produces work output on
shaft
Power stroke continues
until apex passes exhaust
port.
Exhaust
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Chamber decreases in
size
Forces combustion biproducts out the
exhaust port
Continues until next
apex passes exhaust
port.
Entire cycle repeats
The Cycle
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Rotor mounted
eccentrically on shaft
One rotation of rotor
provides three rotations
of shaft
Spark plugs fire 3 times
per rotor revolution
One rotation of shaft for
each firing of spark plugs
Port Timing
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Intake ports shape and size can be altered to
change engine timing
Limited by oil and coolant track
Overlap is when intake port opens before exhaust
port closes
Support at least 50% of apex seal
Street ports
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Moved up to delay intake closing
Moved out to open intake earlier
Limited overlap and with reasonable limits of oil tracks
Racing ports
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Very close to oil tracks
Reduced engine life
Sometimes large overlap
Increased power at high RPM
Decreased power at low RPM
Advantages
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Vibration
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Power/Weight
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No unbalanced reciprocating masses
For similar displacements, rotaries are generally 30%
lighter and produce twice as much power
Simplicity
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Contain half as many moving parts
Have no connecting rods, crankshaft, or valve trains
Disadvantages
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Fuel Efficiency and Emission
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The shape of the combustion chamber, which is long
instead of small and concentrated, makes the combustion
travel longer than a piston engine
Due to the longer combustion chamber, the amount of
unburned fuel is higher which is released into the
environment
Cost
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The lack of infrastructure and development for the rotary
engine has caused their production and maintenance
costs generally to be more
Future Trends: Hydrogen
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Highly Flammable
Production Energy from
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Crude Oil, Coal, Natural Gas, and Nuclear
Combustion Results in Water and NOx
Energy Density
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High Per Unit Mass
Low Per Unit Volume
Challenges of Hydrogen
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Storage
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Requires Large Tank
Combustion
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High Temperatures
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Pre-ignition causes backfiring, excessive wear
NOx formation
Injection Components
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Low temp rubber seals
Rotary Hydrogen Solutions
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Low Operating Temperature
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No Backfiring
Very Low Levels of NOx
Separate Intake & Combustion Chambers
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Rubber Injector Seals Exposed Only to Intake
Hydrogen Rotary Timeline
1991
1993
1997
HR-X
HR-X2
Demio FC-EV
2001
2004
2006
Premacy FC-EV
RX-8 RE
Mazda5 RE
RENESIS Hydrogen Rotary
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Dual Fuel
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Direct Injection
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Switches from Hydrogen to Gasoline
Electronically Controlled
Extended Seal Life
Twin Injectors
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Increased Injection Volume
Control Valve
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Adjusts pressure of injected hydrogen
Hydrogen Conclusion
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Cleaner Burning
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Rotary Engine Solves Combustion Issues
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Water, Minimum NOx
Low Temperature
Separate Induction and Combustion Chambers
Dual Fuel Mazda5 RE
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Practical For Gas-Hydrogen Transition