Two-Cycle and Four-Cycle Engines

1
Two-Cycle and Four-Cycle Engines

• Chapter 5

2
Objectives

• Describe four-stroke cycle engine operation and
  explain the purpose of each stroke.
• Explain the concept of valve timing.
• Compare the lubrication system in a four-cycle
  engine to the system in a two-stroke engine.
• Describe two-stroke cycle engine operation and
  explain the principles of two-cycle operation.
• List the advantages and disadvantages of
  two-cycle and four-cycle engines.

3
Stroke

• Each time the piston moves from one end of its
  travel to the other (BDC to TDC and vice-versa).
• Strokes are identified by the job they do.
• Four-cycle engines require four strokes to
  complete one operating cycle.
• Two stroke engines require?-

4
Four- Stroke Cycle Engine

• Intake-
• Compression-
• Power-
• Exhaust-

5
Intake

• Intake Valve-
• Key Functions
• 1.
• 2.
• 3.

6
Compression

• Valves-
• Piston Rings-
• Why does compression increase the force of
  combustion?
• 1.
• 2.

7
Power

• Valves-
• What happens?
• Top dead center (TDC)-
• Compression Ratio

8
Exhaust

• Valves-
• Scavenging-
• How does the valve cool?

9
Valve Timing

• Figure 5-5 in book.
• Valve Overlap-
• How are the valves timed?

10
Lubrication of a Four-Stroke

• Provided by placing the correct quantity and
  quality of oil in the crankcase.
• Pressurized System-
• Splash System-
• Can engine operate upside-down?

11
Lubrication of a Two-Stroke

• Can be operated at extreme anglesWhy?
• Fuel Mixture-
• Advantages-
• Disadvantages-

12
Two-Stroke Design

• Two Basic Designs (Fig 5-8)
• Cross-scavenged-(Rotary and Reed Valves)
• Loop-scavenged-(3rd port design)

13
Principles of Operation

• Intake into Crankcase
• Fuel Transfer
• Ignition/Power
• Exhaust

14
Scavenging and Tuning

• How to get the exhaust out and keep the fuel in?

15
Different Valves

• Rotary Disc
• Reed

16
List at least 10 differences in the
characteristics between 4 and 2 stroke engines.
17
Objectives

• Describe four-stroke cycle engine operation and
  explain the purpose of each stroke.
• Explain the concept of valve timing.
• Compare the lubrication system in a four-cycle
  engine to the system in a two-stroke engine.
• Describe two-stroke cycle engine operation and
  explain the principles of two-cycle operation.
• List the advantages and disadvantages of
  two-cycle and four-cycle engines.