# Chapter 14 : Engine Friction and Lubrication¶

## Example 14.1 Page No : 313¶

In [1]:
#Given:
bp  =  80.      #Brake power in kW
eta_m  =  80.      #Mechanical efficiency in percent
bsfc  =  258.      #Brake specific fuel consumption in gm/kWh
Reduction  =  3.7      #Reduction in friction power in kW

#Solution:
ip1  =  bp*100/eta_m      #Initial indicated power in kW
fp1  =  ip1-bp      #Initial friction power in kW
fp2  =  fp1-Reduction      #Final friction power in kW
ip2  =  bp+fp2      #Final indicated power in kW
eta_m2  =  bp/ip2      #Final mechanical efficiency
bsfc2  =  bsfc*(eta_m/(100*eta_m2))      #Final brake specific fuel consumption in gm/kWh
Saving  =  bp*(bsfc-bsfc2)/1000      #Saving in fuel in kg/hr

#Results:
print " a)The new mechanical efficiency, eta_m   =   %.3f"%(eta_m2)
print " b)The new bsfc   =   %.1f gm/kWh"%(bsfc2)
print " c)The saving in fuel per hour   =   %.2f kg/hr"%(Saving)
#Answers in the book are wrong

 a)The new mechanical efficiency, eta_m   =   0.831
b)The new bsfc   =   248.5 gm/kWh
c)The saving in fuel per hour   =   0.76 kg/hr


## Example 14.2 Page No : 318¶

In [2]:
#Given:
eta_it  =  30.      #Indicated thermal efficiency in percent
fp_1500  =  18.      #Friction power at 1500 rpm in kW
fp_2500  =  45.      #Friction power at 2500 rpm in kW
bp  =  75.      #Brake power in kW
CV  =  44000.      #Calorific value of fuel in kJ/kg

#Solution:
isfc  =  3600/(CV*eta_it/100)      #Indicated specific fuel consumption in kg/kWh
eta_m_1500  =  bp/(bp+fp_1500)      #Mechanical efficiency at 1500 rpm
bsfc_1500  =  isfc/eta_m_1500      #Brake specific fuel consumption at 1500 rpm in kg/kWh
eta_m_2500  =  bp/(bp+fp_2500)      #Mechanical efficiency at 2500 rpm
bsfc_2500  =  isfc/eta_m_2500      #Brake specific fuel consumption at 2500 rpm in kg/kWh

#Results:
print " The brake specific fuel consumption\tat 1500 rpm, bsfc_1500   =   %.3f kg/kWh\tat 2500 rpm, bsfc_2500   =   %.3f kg/kWh"%(bsfc_1500,bsfc_2500)

 The brake specific fuel consumption	at 1500 rpm, bsfc_1500   =   0.338 kg/kWh	at 2500 rpm, bsfc_2500   =   0.436 kg/kWh