1. Engine Design and Classification
Chapter Lesson 2
Engine Design and Classification

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

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

4. 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

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

6. 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

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

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

9. Pent-Roof Combustion Chamber

10. 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

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

12. 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

13. 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

14. Precombustion Chamber

15. 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

16. 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

17. Rotary Engine

18. 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

19. 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

20. Rotary Engine Operation

21. 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

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

23. 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

24. Gas Turbine