(a）Evaporation from liner

（b) oil blow through the ring end gap

(c)Throw--off at the top ring

(d)oil scaraping of piston top edge

Figure 7  four modes of oil consumpation in difeerernt cases

Figure 8 average oil consumption at different engine speeds

Figure 9 average oil consumption at different loads

3。2   Effect of piston ring parameters  on oil consumption 

The piston ring plays the role of sealing, scraping oil and conducting  heat。  It  directly  contacts  with  the  oil  and significantly  influences  the  cylinder  oil  consumption。  The effects of factors of the piston ring, such as the ring height, 

the  surface  pressure,  the  radial  thickness,  the  closed  gap, the fracture surface pattern and the compatibility, on the oil consumption  and  lubricating  effect  have  been  studied  by many  researchers。  In  the  following  part,  the  effects  of the  closed  gap  of  the  second  piston  ring  and  the  elastic force  of  each  piston  ring  on  the  oil  consumption  of  the 

cylinder  are  analyzed  under  the  condition  of  a  constant groove size of the piston ring。 

3。2。1   Influence of the closed gap of second piston ring  on oil consumption 

In  the  case  of  large  torque  conditions,  the  effect  of  the closed  gap  of  the  second  ring  on  the  oil  consumption  is analyzed under the four modes。 The original second closed gap  of  the  diesel  engine  is  0。575  mm,  and  it  is  changed  to 0。300  mm,  1。000  mm,  2。000  mm。  The  computation  results are  shown  in  Fig。  10。  The  amount  of  oil  blow  through  the opening  gap  of  the  top  ring  decreases  with  the  increase  of the  gap,  because  the  increased  gap  allows  the  gas  in  the second  ring  side  to  vent  out  quickly。  In  the  suction  stroke, 

the  pressure  difference  between  the  upper  and  under surfaces  of  the  top  ring  decreases  and  the  “upstream”  gas also  decreases,  which  leads  to  the  decrease  of  the  sucked oil。 Meanwhile, with the gap becomes larger, the amount of gas leakage increases。 So a balanced scheme is needed。 The evaporation  oil  on  the  cylinder  liner  wall,  the  dumped  oil by  the  top  ring,  and  the  scraped  oil  by  the  piston  top  land 

are  not  changed  with  the  variation  of  the  gap,  since theirinfluencing factors are not changed。 

(a）Evaporation from liner

(b) oil blow through ring end gap

(c)Throw--off at the top ring

Figure 10 four modes of oil consumption for different second closed gap

3。2。2   Influence of elastic force of each piston ring 

  on oil consumption 

The  effects  of  the  tangential  elastic  force  of  the  piston ring  on  the  oil  consumption  for  the  four  modes  are investigated  under  large  torque  condition。  Elastic  forces  of the  three  rings  of  the  original  diesel  engine  are  changed from 30 N-30 N-75 N to 20 N-20 N-50 N, 40 N-40 N-100 N, 50 N-50 N-125 N。 The results are shown in Fig。 11。 The oil  thrown  off  by  the  top  ring  and  the  oil  scraped  of  the piston  top  land  decrease  with  the  increase  of  the  elastic force,  because  the  increased  elastic  force  leads  to  the increase  of  the  surface  pressure  of  the  cylinder  liner  wall, thus  reducing  the  thickness  of  the  oil  film  and  the  amount of oil scraped by the rings and the piston top land。 The oil