ring  and  the  oil  consumption  after  removing  the  cylinder liner wall evaporation is established by using the nonlinear mapping  function  of  neural  networks。  The  parameters  of the  piston  ring  are  optimized  based  on  this  model。  Various 

combinations  of  optimal  parameters  are  obtained,  and  the efficiency  of  the  piston  ring  is  improved,  which  will provide  some  theoretical  guidance  to  the  design  of  piston rings。 

2   Mechanism of Lubricating Oil  Consumption in Cylinder 

2。1   Evaporation from liner wall 

The loss of lubricating oil remaining on the liner wall as a wafer thin film is defined by mass transfer over the phase boundary in the medium of hot combustion gas with certain 

gas turbulence, as shown in Fig。 1。 

Oil  is  either  carried  away  by  the  gas  or  is  burned  at sufficiently  high  temperatures。  The  steady-state  convective mass  transfer  applied  to  simulate  the  evaporation  rate  is shown in Eq。 (1)

where   β —Material transmission coefficient, 

        Tf—Oil film temperature, 

        pf—Oil film pressure, 

        Dd—Diffusion coefficient, 

        em--Mass flow through liner surface。 

                                                                                                                2。2   Throw-off above the top ring 

The  flow  balance  of  lubricating  oil  over  the  first  piston ring and the consideration of the piston acceleration enables the calculation of the throw-off oil quantity。 

The  possible  throw-off  oil  quantity  is  determined  by  the current oil volume above the top ring (between the piston top and and the liner wall) and the acceleration of the piston。 

It  is  assumed  that  any  cumulated  oil  will  adhere  to  the top land of the piston。 The following transport mechanisms lead  to  a  rate  of  change  of  the  oil  mass  above  the  first compression,  where  the  inpidual  oil  flows  are  defined  as 

follows。 Oil  scraping  of  the  top  ring。  The  amount  of  oil 

scraped  is  determined  by  the  difference  of  the  left  oil  film thickness during the upward and downward motions of the top ring (Fig。 2)。 The rate of scraping is given in Eq。 (2)

where  sm —Mass flow of oil scraping of the top ring, 

       hs—Left  oil  film  of  the  top  ring  on  the  cylinder surface, 

       ρ—Density of the oil, 

       D—Cylinder bore diameter, 

       Δs —Stroke increment,