Jignesh Shah

  four-stroke  (also  four-cycle )  engine  is an  internal combustion  (IC) engine in which the  piston  completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed: Intake : Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion. The piston is moving down as air is being sucked in by the downward motion against the piston. Compression : This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (bel...

Knocking  (also  knock ,  detonation ,  spark knock ,  pinging  or  pinking ) in spark ignition  internal combustion engines  occurs when combustion of some of the  air/fuel mixture  in the cylinder does not result from propagation of the flame front ignited by the  spark plug , but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the  four-stroke cycle . The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive. Knocking should not be confused with  pre-ignition —they are two separate events. However, pre-ignition can be foll...