text: The pattern of combustion in the cylinder is 
  best illustrated by the second graph of figure 
  2.16. The normal combustion process begins 
  toward the end of the com- 
  by spark ignition 
  pression stroke. The electric spark provides 
  the beginning of combustion and a flame front 
  is propagated smoothly 
  the com- 
  pressed mixture. Such normal combustion is 
  shown by the plot of cylinder pressure versus 
  piston travel. Spark ignition begins a smooth 
  rise of cylinder pressure to some peak value 
  with subsequent expansion through the power 
  stroke. The variation of pressure with piston 
  travel must be controlled to achieve the great- 
  the cycle of operation. 
  est net work during 
  
  through 