Abnormal combustion in si engines ppt ic engine

ABNORMAL COMBUSTION IN SI ENGINES
PRESENTED BY
ANURAG RATAN SHAKYA
B.TECH MECHANICAL
ROLL NO- 1700850 FINAL YEAR

What is mean by Combustion?
 As per Oxford Dictionary: The process of burning something
(from Latin: comburere)
 Chemistry : Rapid chemical combination of a substance with
oxygen, involving the production of heat and light.
 Thermo Dynamics: Combustion is a chemical reaction in
which certain elements of the fuel like hydrogen and carbon
combine with oxygen liberating heat energy and causing an
increase in temperature of the gases

Combustion in SI Engines
 In any conventional spark-ignition (SI) engine, the fuel and air are
homogeneously mixed together in the intake system, inducted through
the intake valve into the cylinder where it mixes with residual gases and
is then compressed.
 Under normal operating conditions, combustion is initiated towards the
end of the compression stroke at the spark plug by an electric discharge.
 A turbulent flame develops following the ignition and propagates through
this Combustion in SI Engines

Combustion in SI Engine
Normal Combustion Abnormal Combustion
When the flame
travels evenly or
uniformly across the
combustion chamber.
When the combustion gets
deviated from the normal
behaviour and resulting in
loss of performance or
damaging the engine

Abnormal Combustion in SI Engine
Pre-Ignition Knocking
Pre-ignition (self-
ignition) occurs
when the fuel
mixture in the
cylinder burns
before the spark-
ignition event at
the spark plug.
Knocking is due to
auto-ignition of end
portion of unburned
charge in combustion
chamber.

PRE-IGNITION
 Pre-ignition is the ignition of the homogeneous mixture of charge as it
comes in contact with hot surfaces, in the absence of spark.
 Pre-ignition is initiated by some overheated projecting part such as the
sparking plug electrodes, exhaust valve head, metal corners in the
combustion chamber, carbon deposits or protruding cylinder head
gasket rim etc.
 Auto ignition may overheat the spark plug and exhaust valve and it
remains so hot that Engine efficiency will decrease due to pre- ignition
 Pre-ignition causes holes melted in pistons, spark plugs melted away,
and engine failure happens pretty much immediately.

Knocking or Detonation
 Normal flame front travels at 15 to 30 m/s speed
 Temperature increases due to flame front advance, radiation and reactions of
unburnt mixture
 During abnormal combustion end charge auto-ignites before the flame front
reaches
 Velocities reached during detonation are 300 to 1000 m/s
 Press rise almost 3 to 4 times i.e. 50 bar to 150-200 bar

Knocking or Detonation
 This pressure frequency or vibration frequency in SI engine can
be up to 5000 Cycles per second.
 Denotation is undesirable as it affects the engine performance and
life, as it abruptly increases sudden large amount of heat energy. It
also put a limit on compression ratio at which engine can be
operated which directly affects the engine efficiency and output.

Effect of Knocking
The harmful effects of detonation are as follows:
 Noise and roughness
 Mechanical damage
 Carbon deposits
 Increase in heat transfer
 Decrease in power output and efficiency

Cause of Abnormal combustion
1.Fuel condition including quality , quantity and other attributes.
2.Engine scantling
(Condition of piston, Piston rings, Turbocharger functioning (if fitted),Bearing
condition, nuts and bolts, Valves, Lubrication, Spark plug etc.)
3.Suction air quality and quantity.
4. Engine colling efficiency
5. Vibration.

6. Atmosphere in which engine is operating .
7. Orientation of engine.
8.mechanical efficiency of parts.
9. Mechanical properties of different scantling materials.
10.condition of timing gears and chains operating cams

Abnormal combustion in si engines ppt ic engine

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Abnormal combustion in si engines ppt ic engine