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 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

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