Modern Automotive Technology PowerPoint for by Russell Krick Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

Chapter 12 Engine Design Classifications

Contents Engine classifications Alternative engines Typical automotive engines

Engine Classifications 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

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

Common Engine Classifications Combustion chamber design Type of fuel burned Type of ignition Number of strokes per cycle Number of valves per cylinder Type of aspiration

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

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

Cylinder Numbering 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

Firing Order 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

Cylinder Numbering and Firing Order

Cooling System Type 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

Cooling System Type A. Air cooling B. Liquid cooling

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

Ignition Type Two basic methods are used to ignite the fuel in an engine combustion chamber: spark ignition (spark plug) compression ignition (compressed air)

Uses an electric arc at the spark plug to ignite the fuel Spark Ignition Engine Uses an electric arc at the spark plug to ignite the fuel

Compression Ignition Engine Squeezes the air in the combustion chamber until it is hot enough to ignite the fuel

Valve Location Engines are classified by the location of the valves: L-head engine also called a flat head engine I-head engine also called an overhead valve (OHV) engine

Both the intake and exhaust valves are in the block L-Head Engine Both the intake and exhaust valves are in the block

Both valves are in the cylinder head I-Head Engine Both valves are in the cylinder head

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

Camshaft is located in the top of the cylinder head Overhead Cam Engine Camshaft is located in the top of the cylinder head

Overhead Cam Engine 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

Combustion Chamber Shape Four basic combustion chamber shapes are used in most automotive engines: pancake wedge hemispherical pent-roof

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

Wedge Combustion Chamber 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

Wedge Combustion Chamber Provides good air-fuel mixing at low engine speeds

Hemispherical Combustion Chamber 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

Hemispherical Combustion Chamber First used in high-horsepower racing engines Excellent design for high-rpm use

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

Pent-Roof Combustion Chamber

Other Combustion Chamber Types In addition to the four shapes just covered, there are several less common combustion chamber classifications Each type is designed to increase combustion efficiency, gas mileage, and power while reducing exhaust emissions

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

Four-Valve Combustion Chamber Uses two exhaust valves and two intake valves to increase flow

Three-Valve Combustion Chamber Uses two intake valves and one exhaust valve Two intake valves allow ample airflow into the combustion chamber on the intake stroke Single exhaust valve provides enough surface area to handle exhaust flow

Stratified Charge Combustion Chamber Uses a small combustion chamber flame to ignite and burn the fuel in the main, large chamber Lean mixture is admitted into the main chamber Richer mixture is admitted into the small chamber by an extra valve

Stratified Charge Combustion Chamber When the mixture in the small chamber is ignited, flames blow into the main chamber and ignite the lean mixture Allows the engine to operate on a lean, high-efficiency air-fuel ratio fuel economy is increased exhaust emissions are reduced

Air Jet Combustion Chamber Has a single combustion chamber fitted with an extra air valve, called a jet valve The jet valve injects a stream of air into the combustion chamber at idle and at low engine speeds to improve fuel mixing and combustion At higher rpm, normal air-fuel mixing is adequate for efficient combustion

Air Jet Combustion Chamber

Precombustion Chamber Commonly used in automotive diesel engines Used to quiet engine operation and to allow the use of a glow plug to aid cold weather starting During combustion, fuel is injected into the prechamber, where ignition begins As the fuel burns, the flame expands and moves into the main chamber

Precombustion Chamber

Alternative Engines Vehicles generally use internal combustion, 4-stroke cycle, reciprocating piston engines Alternative engines include all other engine types that may be used to power a vehicle

Rotary Engine Uses a triangular rotor instead of pistons The rotor orbits a mainshaft while turning inside a specially shaped chamber This eliminates the reciprocating motion found in piston engines

Rotary Engine

Rotary Engine Operation Three complete power-producing cycles take place during every revolution of the rotor: three rotor faces produce three intake, compression, power, and exhaust events per revolution

Rotary Engine Operation Rotor movement produces a low-pressure area, pulling the air-fuel mixture into the engine As the rotor turns, the mixture is compressed and ignited As the fuel burns, it expands and pushes on the rotor The rotor continues to turn, and burned gases are pushed out of the engine

Rotary Engine Operation

Steam Engine Heats water to produce steam Steam pressure operates the engine pistons Known as an external combustion engine since its fuel is burned outside the engine

Used on some of the first automobiles Steam Engine Used on some of the first automobiles

Gas Turbine Uses burning and expanding fuel vapor to spin fan-type blades Blades are connected to a shaft that can be used for power output Expensive to manufacture because of special metals, ceramics, and precision machining required

Gas Turbine

Two-Stroke-Cycle Engine Not used for automotive applications because of high emission levels and poor fuel efficiency Requires only one revolution of the crankshaft for a complete power-producing cycle Two piston strokes complete the intake, compression, power, and exhaust events

Two-Stroke-Cycle Engine Operation As the piston moves upward, the air-fuel mixture is compressed Vacuum is created in the crankcase, which draws fuel and oil into the crankcase A reed valve or rotary valve controls flow into the crankcase

Two-Stroke-Cycle Engine Operation

Two-Stroke-Cycle Engine Operation When the piston reaches the top of the cylinder, ignition occurs Burning gases force the piston downward The reed valve or rotary valve closes, compressing and pressurizing the fuel mixture in the crankcase

Two-Stroke-Cycle Engine Operation As the piston moves down in the cylinder, it uncovers the exhaust port Burned gases leave the cylinder The piston continues downward, uncovering the transfer port Pressure in the crankcase causes a fresh fuel charge to flow through the transfer port and into the cylinder

Two-Stroke-Cycle Engine Operation

Two-Stroke-Cycle Engine Lubrication The crankcase is used as a storage chamber for each successive fuel charge Lubricating oil is introduced into the crankcase along with the air-fuel charge to provide lubrication Inside the crankcase, some of the oil separates from the fuel The oil mist lubricates and protects the moving parts inside the engine

Miller-Cycle Engine Uses a modified four-stroke cycle Designed with a shorter compression stroke and a longer power stroke to increase efficiency The intake valve remains open longer to delay compression

Miller-Cycle Engine

Miller-Cycle Operation The piston slides down the bore with the intake valve open

Miller-Cycle Operation The intake valve remains open as the piston starts up the bore The supercharger pressurizes the intake to prevent backflow

Miller-Cycle Operation The intake valve closes and compression occurs

Miller-Cycle Operation The power stroke occurs

Miller-Cycle Operation The exhaust stroke occurs

Typical Automotive Engines

Provides the lowest center of gravity of any piston engine Horizontally Opposed Provides the lowest center of gravity of any piston engine

Features four chain-driven camshafts and 32 valves Overhead Cam V-8 Features four chain-driven camshafts and 32 valves

Inline SOHC This 16-valve, four-cylinder engine has a belt-driven camshaft and a balance shaft

This engine uses many aluminum parts Fuel-Injected V-8 This engine uses many aluminum parts

Each cylinder head contains two camshafts DOHC V-6 Each cylinder head contains two camshafts

Note the reciprocating assembly and the valve train V-8 Engine Note the reciprocating assembly and the valve train

Six-cylinder engine with a rear drive belt for the injection pump Inline Diesel Six-cylinder engine with a rear drive belt for the injection pump

Two roller chains drive the overhead camshafts V-12 Engine Two roller chains drive the overhead camshafts