Engine Classification 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 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 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

Diagram External Combustion

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

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 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 YouTube - engine configurations

Horizontally Opposed Pancake Boxer

In - Line

V configuration

# 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 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 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

Numbering and Firing Order

# 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 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) Normal aspiration – atmospheric pressure Forced induction (Turbo or Supercharger)

# 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)

Spark Ignition

Compression Ignition

# 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 Both the intake and exhaust valves are in the block Flathead-Model T Both valves are in the cylinder head

F Head (1971 Jeep)

# 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) Uses push rods to transfer motion to the rocker arms and valves Also called an overhead valve (OHV) engine

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 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 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)

Diagram of OHC with Rockers

Diagram of DOHC

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

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

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

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

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

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