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Diesel Engines and Efficiency

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David Williams

on 3 June 2016

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Transcript of Diesel Engines and Efficiency

Diesel Engines
Rudolf Diesel 1893
Compression Ignition
Fire Piston
Major Difference
No Spark - ignition by Compression (IC)
Air Compressed - fuel added near TDC
Major Advantages
High Compression = High Efficiency
No electrics
Long Life
Cheaper fuel - distillation - no cracking
Efficiency (Thermal)
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
Energy Loss
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)
Engine Breathing
Increase Power - add more fuel.
Cannot get enough oxygen.
To Improve Breathing
More Valves
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
1935 Mercedes
Other Engines
Two Stroke
Wankel Rotary Engine
NSU Ro 80
Mazda Rx8
Felix Wankel (1902-1988)
NSU Kettenkrad 1939
Steering by wheel and track.
No uni. education.
No apprenticeship.
and inventor.
Too poor.
NSU Wankel-Spider (1964)
Slip Angle
(and other)
Rotary Engines
"Many engines of this category have been built, tested, and finally abandoned, often after the expenditure of vast sums of money."
Charles F Taylor
Sealing Problems
Line Contact
Surface contact.
High v at large P
Low v at high P
(top of stroke)
Extreme Supercharging
Full transcript