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2-Stroke & Diesel Theory

2-Stroke & Diesel Theory. Two-Stroke Cycle Engines • Diesel Engines • Valving Systems. Competencies. Explain important features of diesel engines. Explain the function of a 2-stroke engine Explain Torque & Horsepower. 2-Stroke Engines.

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2-Stroke & Diesel Theory

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  1. 2-Stroke & Diesel Theory Two-Stroke Cycle Engines • Diesel Engines • Valving Systems

  2. Competencies • Explain important features of diesel engines. • Explain the function of a 2-stroke engine • Explain Torque & Horsepower

  3. 2-Stroke Engines • Utilize two distinct piston strokes to complete one operating cycle of engine • Crankshaft turns only one revolution for each complete cycle • Provides twice as many power strokes in same number of rotations as a 4-stroke

  4. 2-Stroke Engines • Valving system requires fewer parts • Lighter in weight • Applications: • Chainsaws • Leaf bowers • Trimmers

  5. 2-Stroke Engines • Completes all five events in one operating cycle • Some occur together • Ignition/Power • Exhaust/Intake

  6. Ignition/Power • Piston moves toward TDC & compressed charge in cylinder is ignited • Crankcase already filled with charge • When ignited, piston moves toward BDC • Exhaust port is uncovered & exhaust gases are discharged through side of cylinder

  7. Exhaust/Intake • Occurs as piston moves toward BDC • Intake port opens & air-fuel mixture is routed into cylinder • Compression occurs when piston is at BDC, exhaust gases have been discharged, and cylinder is filled with a new charge

  8. Advantages • Fewer moving parts • No valves required • Less wear & breakage • Less weight for comparable output • Smaller size for comparable output • Can be operated in any position • Power to weight ration greater than a 4-stroke • Lubrication is continuously provided by oil mixed into gasoline

  9. Disadvantages • Higher fuel consumption • Higher operating speed & temperature • Service life not as long as a result • Greater exhaust emissions • Creates smoker exhaust • In older engines becomes more noticeable • Oil & fuel must be mixed properly • No matter how tight, a portion of new charge will leak into exhaust port • Unburned fuel is considered a pollutant

  10. Diesel Engines • Injector is hydraulically activated by pressurized fuel delivered by the injection pump • Heat in glow plug is created by resistance to current in a heating coil • Reciprocating internal combustion engine

  11. Diesel Engines • Five events in operation • intake • compression • ignition • power • exhaust • Turbocharging uses a compressor

  12. Diesel Engines • Ignites fuel by high compression • Does not use spark plugs for ignition • Increases fuel vaporization • Requires higher compression ratios • Have a longer stroke • Produce more torque with same displacement • Can be either 2, or 4-stroke

  13. Diesel Components • Injection pump • Injector • Functions as an ON/OFF valve • Introduces fuel into cylinder • Glow plug • Preheats air inside combustion chamber

  14. Valving Systems • seal the combustion chamber to control flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinder • commonly two valves per system, intake and exhaust • location of valve determines type of head design

  15. Engine Output • Measured by torque & horsepower • Torque measured in pound-feet (lb-ft) or Newton-meters (Nm) • The ability of an engine to do work • Power is the measure of the rate at which work is done • Horsepower (HP) is the most common measurement of power

  16. Types of Horsepower • Brake Horsepower (BP) or shaft power • Amount of usable power taken from an engine • Friction Horsepower (FHP) • Amount of power required to overcome the internal friction of engine moving parts

  17. Types of Horsepower • Indicated Horsepower (IHP) • Power produced inside the engine cylinder • Sum of the usable power (BHP) plus power used to drive engine (FHP) • Accounts for heat energy converted into mechanical energy • Does not account for any energy (power) required to move the engine parts • Indicated horsepower is always greater than BHP

  18. Measuring Horsepower • 1 HP is equal to 746 Watts (W) • When watts produced are known HP is found by: HP/746 • HP = Horsepower • W = Watts • 746 = Constant

  19. Example • What is the horsepower of an engine producing 8952 W at WOT (wide open throttle) and the rate rpm? • HP = 8952/746 • HP = 12 HP

  20. Valving Systems • Features: • Valve Head • Margin • Valve Face • Valve Seat • Valve Stem • Valve Neck • Valve Guide

  21. Valving Systems • Contact between valve face & valve seat provide a seal & cools the valve by transferring heat from valve to cylinder block or head

  22. 2-Stroke Valving Systems • If used at all; • Require fewer parts • Camshaft & tappets are not required • Commonly use a reed valve system, a three-port system, or a rotary valve system

  23. Valving Systems • Small engines typically have two valves • Intake • Exhaust • Both valves must withstand peak temperatures • 3000° F during combustion • 1200° F sustained during operation

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