1. Engine Classification
Engine Fundamentals
Engine Classification
Lesson 9
March 2008

2. Engine Classification
Even though basic parts are the same, design differences can change the way engines operate and how they are repaired
For this reason, you must be able to classify engines

3. Internal Combustion Engines
An engine, such as a gasoline or diesel engine, in which fuel is burned inside the engine
Designed to be run on any fuel that vaporizes easily or on any flammable gas

4. External Combustion Engines
An engine, such as a steam engine, in which fuel is burned outside the engine
Fuel is burned to produce heat to make steam
Fuel burning can take place within a few feet of the engine to several miles away

5. Diagram External Combustion

6. Engine Classification
Cylinder arrangement
Number of cylinders
Cooling system type
Valve location
Camshaft location

7. Engine Classification cont.
Combustion chamber design
Type of fuel burned
Type of ignition
Number of strokes per cycle
Number of valves per cylinder
Type of aspiration

8. # 1 Cylinder Arrangement
Refers to the position of the cylinders in relation to the crankshaft
There are five basic cylinder arrangements:
inline
V-type
slant
W-type
opposed

9. Cylinder Arrangement
YouTube - engine configurations

10. Horizontally Opposed
Pancake
Boxer

11. In - Line

12. V configuration

13. # 2 Number of Cylinders
Most car and truck engines have either 4, 6, or 8 cylinders
Some may have 3, 5, 10, 12, or 16 cylinders
Engine power and smoothness are enhanced by using more cylinders

14. Numbering of Cylinders
Engine manufacturers number each engine cylinder to help technicians make repairs
Service manual illustrations are usually provided to show the number of each cylinder
Cylinder numbers may be cast into the intake manifold

15. # 3 Firing Orders Refers to the sequence in which the cylinders fire
Determined by the position of the crankshaft rod journals in relation to each other
May be cast into the intake manifold
Service manual illustrations are usually provided to show the firing order

16. Numbering and Firing Order

17. # 4 Method of Cooling There are two types of cooling systems:
Liquid cooling system
surrounds the cylinder with coolant
coolant carries combustion heat out of the cylinder head and engine block
Air cooling system
circulates air over cooling fins on the cylinders
air removes heat from the cylinders

18. # 5 Fuel Type Engines are classified by the type of fuel used
Gasoline engines burn gasoline
Diesel engines burn diesel fuel
Liquefied petroleum gas (LPG), gasohol (10% alcohol, 90% gasoline), and pure alcohol can also be used to power an engine

19. Aspiration (how does air arrive)
Normal aspiration – atmospheric pressure
Forced induction (Turbo or Supercharger)

23. # 6 Method of Ignition
Two basic methods are used to ignite the fuel in an engine combustion chamber:
spark ignition (spark plug)
compression ignition (compressed air)

24. Spark Ignition

25. Compression Ignition

26. # 7 Valve Location
Engines are classified by the location of the valves:
L-head engine
also called a flat head engine
F-head engine
Compromise between I & L head engines
I-head engine
Both overhead valve (OHV) engines and overhead com (OHC) are I-head

27. ‘I’ and ‘L’ Head Both the intake and exhaust valves are in the block
Flathead-Model T
Both valves are in the cylinder head

28. F Head (1971 Jeep)

29. # 8 Camshaft Location
There are two basic locations for the engine camshaft:
Camshaft located in the block
cam-in-block engine
Camshaft located in the cylinder head
overhead cam (OHC) engine

30. Cam in Block (OHV)
Uses push rods to transfer motion to the rocker arms and valves
Also called an overhead valve (OHV) engine

33. Diagram of OHV
Note the adjustment screw on the end of the rocker arm. Not all rocker arms have this adjustment. Check the shop manual for adjustment procedures.

34. Cam in Head OHC engines may use one or two camshafts per cylinder head
Single overhead cam (SOHC) engine
uses only one camshaft per cylinder head
Dual overhead cam (DOHC) engine
uses two camshafts per cylinder head
one cam operates the intake valves, while the other cam operates the exhaust valves

35. Diagram of OHC Notice that the pushrod and rocker arm have
been eliminated in this OHC engine. Less moving parts in the transmission of camshaft motion to open the valve.
This not only reduces friction points and weight but also less points for wear and component breakage.
NOTE-not all OHC have eliminated the rocker arms.
(See next slide)

36. Diagram of OHC with Rockers

37. Diagram of DOHC

38. # 9 Combustion Chamber Design
Four basic combustion chamber shapes are used in most automotive engines:
pancake
wedge
Hemispherical (hemi)
pent-roof

39. Pancake Chamber forms a flat pocket over the piston head
Valve heads are almost parallel to the top of the piston

40. Wedge The valves are placed side-by-side
The spark plug is located next to the valves
When the piston reaches TDC, the squish area formed on the thin side of the chamber squirts the air-fuel mixture out into the main part of the chamber
this improves air-fuel mixing at low engine speeds

41. Hemispherical (Hemi) Shaped like a dome
The valves are canted on each side of the combustion chamber
The spark plug is located near the center of the chamber, producing a very short flame path for combustion
The surface area is very small, reducing heat loss

42. Pent Roof Similar to a hemispherical chamber
Has flat, angled surfaces rather than a domed surface
Improves volumetric efficiency and reduces emissions

43. Pent Roof Combustion Chamber
Uses two exhaust valves and two intake valves to increase flow

44. Additional Combustion Chamber Designs
Swirl
Causes the air-fuel mixture to swirl as it enters the chamber, improving combustion