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Engine Fundamentals. Engine Classification. Lesson 9. March 2008. 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. Internal Combustion Engines.

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engine fundamentals

Engine Fundamentals

Engine Classification

Lesson 9

March 2008

engine classification
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
internal combustion engines
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
external combustion engines
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
engine classification6
Engine Classification
  • Cylinder arrangement
  • Number of cylinders
  • Cooling system type
  • Valve location
  • Camshaft location
engine classification cont
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
1 cylinder arrangement
# 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
cylinder arrangement
Cylinder Arrangement

YouTube - engine configurations


Horizontally Opposed

  • Pancake
  • Boxer
2 number of cylinders
# 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
numbering of cylinders
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
3 firing orders
# 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
4 method of cooling
# 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
5 fuel type
# 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
aspiration how does air arrive
Aspiration (how does air arrive)
  • Normal aspiration – atmospheric pressure
  • Forced induction (Turbo or Supercharger)
6 method of ignition
# 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)
7 valve location
# 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
i and l head
‘I’ and ‘L’ Head

Both the intake and exhaust valves are in the block

Flathead-Model T

Both valves are in the cylinder head

8 camshaft location
# 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
cam in block ohv
Cam in Block (OHV)
  • Uses push rods to transfer motion to the rocker arms and valves
  • Also called an overhead valve (OHV) engine
diagram of ohv
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.

cam in head
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
diagram of ohc
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)

9 combustion chamber design
# 9 Combustion Chamber Design
  • Four basic combustion chamber shapes are used in most automotive engines:
    • pancake
    • wedge
    • Hemispherical (hemi)
    • pent-roof
  • Chamber forms a flat pocket over the piston head
  • Valve heads are almost parallel to the top of the piston
  • 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
hemispherical hemi
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
pent roof
Pent Roof
  • Similar to a hemispherical chamber
  • Has flat, angled surfaces rather than a domed surface
  • Improves volumetric efficiency and reduces emissions
pent roof combustion chamber
Pent Roof Combustion Chamber

Uses two exhaust valves and two intake valves to increase flow

additional combustion chamber designs
Additional Combustion Chamber Designs


Causes the air-fuel mixture to swirl as it enters the chamber, improving combustion