Module 1: An Overview of Engine Emissions and Air Pollution
  Lecture 1: Introduction to IC Engines and Air Pollution

Main Events in Four-Stroke SI Engine Cycle

Figure 1.1 shows typical pressure –crank angle (P-θ) history for a four-stroke SI engine cycle. The sequence of main events in the cycle are given in Table 1.2

Figure 1.1
 Sequence of Events in 4-Stroke SI Engine Cycles

Table 1.2

Sequence of Events in 4-Stroke SI Engine Cycle


Time of Occurrence, Crank angle

Intake valve opens (IO)

20 - 5º CA  bTDC at the end of exhaust stroke

Exhaust valve closes (EC)

8 to 20º  CA  aTDC in the beginning of intake stroke

Intake valve closes (IC)

60 -40º  CA aBDC in the beginning of compression stroke

Spark ignition

45 -15º  CA  bTDC towards the end of compression stroke

Combustion by turbulent flame propagation

Begins shortly after ignition up to 15 to 30º  CA  aTDC Early in the expansion stroke

Exhaust valve opens (EC)

50 -30º  CA bBDC Shortly before the end of expansion stroke

CA: Crank Angle,    ATDC: After Top Dead Centre; BTDC: Before Top Dead Centre; ABDC: After Bottom Dead Centre;
BBDC:Before Bottom Dead Centre;