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?