2&4 stroke engine cycles

Dr. Walid Abdelghaffar

Intake Stroke

Intake valve opens,

admitting fuel and air.

Exhaust valve closed

for most of stroke

Compression Stroke

Both valves closed,

Fuel/air mixture is

compressed by rising

piston. Spark ignites

mixture near end of

stroke.

Intake

Manifold

Spark

Plug Cylinder

Piston

Connecting

Rod Crank

Power Stroke

Fuel-air mixture burns,

increasing temperature

and pressure, expansion

of combustion gases

drives piston down. Both

valves closed - exhaust

valve opens near end

of stroke

1 2 3 4

Exhaust Stroke

Exhaust valve open,

exhaust products are

displaced from cylinder.

Intake valve opens

near end of stroke.

Crankcase

Exhaust

Manifold

Exhaust Valve Intake Valve

Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar

Power Stroke

Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar

Compression

(ports closed)

Air Taken Into

Crankcase

Combustion

(ports closed) Exhaust

(intake port closed)

Air compressed in crankcase

Scavenging

and Intake

(ports open)

Dr. Walid Abdelghaffar

Mechanical Cycle

v

p

1

2

3

4

TDC BDC

v

p End of combustion

TDC BDC

Ignition

Exhaust

valve

opens

Intake

Inlet

valve

opens

Thermodynamic Cycle The Otto Cycle

pat

m

Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar

Dr. Walid Abdelghaffar

4stroke air standard OTTO cycle, 6-6a-1-2-3-4-5-6, for SI

engine operating at part load

• W6-1 = Pi(V1-V6) = PiVd

• W5-6 = Pext(V6-V5) = PexVd

• (Wpum)net = (Pi- Pext) Vd

• Pmep= (Wpump)net/Vd

• = (Pi - Pext)

Dr. Walid Abdelghaffar

Ref. Internal combustion engines and air pollution, E. F. Obert