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Diesel Engines and Efficiency
Transcript of Diesel Engines and Efficiency
Rudolf Diesel 1893
No Spark - ignition by Compression (IC)
Air Compressed - fuel added near TDC
High Compression = High Efficiency
Cheaper fuel - distillation - no cracking
SI Engine has a Throttle
An SI engine has a butterfly valve which controls air flow.
Press down on accelerator - valve opens.
More air - computer/ carburetor adds more fuel.
Diesel Engines Have no Throttle
Push the accelerator -> adds more fuel.
Real Thermal Efficiency
Integrate P wrt V
Including Pumping Work
Real Engine Efficiency
Subtract off Oil Pump, Water Pump, Alternator
1/3 heats water
1/3 leaves as exhaust
After running pumps - 20% left
Mean Effective Pressure (MEP)
Work Per Cycle = MEP * Engine Displacement
Typical MEP = 1000 kPa
Wrong (No pumping loop)
Increase Power - add more fuel.
Cannot get enough oxygen.
To Improve Breathing
Why not just bigger Valves?
.Gas flow is proprtional to this side area
i.e. to valve perimeter.
Hence the more valves the better.
Compress the Air First - Using a Pump
1. Use Exahust to power pump = Turbocharger
2. Use Pump driven from Engine = Supercharger
Wankel Rotary Engine
NSU Ro 80
Felix Wankel (1902-1988)
NSU Kettenkrad 1939
Steering by wheel and track.
No uni. education.
NSU Wankel-Spider (1964)
"Many engines of this category have been built, tested, and finally abandoned, often after the expenditure of vast sums of money."
Charles F Taylor
High v at large P
Low v at high P
(top of stroke)