Chapter 12 Lesson 2 Engine Design and Classification

Chapter 12 Lesson 2 Engine Design and Classification

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

Pancake Combustion 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

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

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

�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

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