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Principles of the Compression Engine

Principles of the Compression Engine. What is a compression engine?. Needs no spark to ignite fuel/air mixture as in a gasoline spark ignition (SI) engine Combustion occurs spontaneously due to compression All diesel engines are compression ignition (CI) engines. Typical diesel engine.

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Principles of the Compression Engine

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  1. Principles of the Compression Engine

  2. What is a compression engine? • Needs no spark to ignite fuel/air mixture as in a gasoline spark ignition (SI) engine • Combustion occurs spontaneously due to compression • All diesel engines are compression ignition (CI) engines

  3. Typical diesel engine

  4. Air cleaner Carburetor Camshaft Rocker arm Intake valve Cam sprocket Exhaust valve Piston Connecting rod Timing belt Timing belt tensor Crankshaft Oil pump Crank sprocket Oil pickup SI Engine with OHC

  5. Definitions • Temperature /oC, F, K • Volume /cm3 or cc • Pressure / atm, psi, Pa • See also glossary of terms

  6. What is diesel? • Crude oil fraction after gasoline (petrol) • C9H20 – C12H26 nonane – dodecane • Exact composition governed by various standards

  7. The Chemistry • Diesel is burnt: CnH2n+2 + O2 H2O + CO2 +HEAT • Inefficient combustion • CO, carbon monoxide • C, soot, diesel particulates • PCAs, benzene etc.

  8. Spark plug for SI engine Fuel injector for CI engine Valves Clearance volume Top Center (TC) Cylinder wall Stroke Bottom Center (BC) Piston TC 0o Crank shaft q 270o 90o 180o BC 4-stroke operating cycle • http://static.howstuffworks.com/flash/diesel.swf

  9. Induction Stroke • Engine pulls piston out of cylinder • Low pressure inside cylinder (< 1 atm.) • Atmospheric pressure pushes air into cylinder • Engine does work on the gases during this stroke

  10. 2. Compression stroke • Engine pushes piston into cylinder • Air is compressed to high pressure and temperature (700psi, 540oC) • Fuel injected as piston reaches top of stroke • Engine does work on the gases during this stroke

  11. 3. Power Stroke • Fuel/air mixture burns to form hot gases (2000oC, 1000psi) • Gases push piston out of cylinder • Gases expand to lower pressure and temperature • Gases do work on engine during this stroke

  12. 4. Exhaust stroke • Engine pushes piston into cylinder • High pressure inside cylinder • Pressure pushes burned gases out of cylinder • Engine does work on the gases during this stroke

  13. 4-stroke cycle • http://static.howstuffworks.com/flash/diesel.swf

  14. Let’s take a closer look

  15. The crankshaft and piston

  16. Number of cylinders Single-cylinder …engine gives one power stroke per crank revolution (2 stroke) or two revolutions (4 stroke). The torque pulses are widely spaced, and engine vibration and smoothness are significant problems. Used in small engine applications where engine size is more important Multi-cylinder …engines spread out the displacement volume amongst multiple smaller cylinders. Increased frequency of power strokes produces smoother torque characteristics. Engine balance (inertia forces associated with accelerating and decelerating piston) better than single cylinder.

  17. Types of injection Glow plug Orifice -plate Direct injection: quiescent chamber Direct injection: swirl in chamber Indirect injection: turbulent and swirl pre-chamber

  18. Critical factors • Compression must be high enough • Batteries • Worn piston/barrel • Valve seating • Fuel and air must mix thoroughly • Injectors working correctly • Glow plugs must work properly where fitted

  19. Any questions?

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