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Principles of the Compression Engine

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Presentation on theme: "Principles of the Compression Engine"— Presentation transcript:

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

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 4-stroke operating cycle
Crank shaft 90o 180o BC TC 0o 270o q Spark plug for SI engine Fuel injector for CI engine Top Center (TC) Bottom Center (BC) Valves Clearance volume Cylinder wall Piston Stroke

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

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 Direct injection: quiescent chamber
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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