Chapter 7 : IC Engines

Example 7.1 Page No : 23

In [1]:
import math 
			
# Variables :
T = 10.;			#N-m
N = 1500.;			#rpm
IP = 1.85;			#KW

#Calculation
BP = T*2*math.pi*N/60/1000;			#KW
FP = IP-BP;			#KW

# Results
print "Friction power(KW) : %.2f"%FP

Friction power(KW) : 0.28

Example 7.2 Page No : 23

In [1]:
import math			
# Variables :
d = 18./100;			#m
L = 26./100;			#m
N = 400.;			#rpm
positive_mep = 6;			#bar
negative_mep = -0.3;			#bar
n = 180.;			#strokes/min
Etta_m = 0.75;

#Calculation
Pm = positive_mep+negative_mep;			#bar
A = math.pi/4*d**2;			#m**2
IP = Pm*10**5*A*L*n/60/1000;			#KW
BP = IP*Etta_m;			#KW

# Results
print "B.P. of engine in KW : %.3f"%BP

B.P. of engine in KW : 8.485

Example 7.3 Page No : 24

In [4]:
import math 
			
# Variables :
r = 6.;			        #cm
d = 10./100;			#m
L = 12.5/100;			#m
Pmi = 2.6;		    	#bar
W = 60.;		    	#N
S = 19.;			    #N
R = 40./100;			#m
mf = 1.;	    		#Kg/hr
mf = mf/60/60;			#Kg/sec
CV = 42000.;			#KJ/Kg
N = 2000.;  			#rpm

#Calculation and Results
A = math.pi/4*d**2;			#m**2
n = N/2;			#no. of strokes/min
IP = Pmi*10**5*A*L*n/60/1000;			#KW
print "Indicated Power in KW : %.3f"%IP

BP = (W-S)*R*2*math.pi*N/60/1000;			#KW
print "Brake Power in KW : %.3f"%BP
Etta_m = BP/IP*100;			#%
print "Mechanical efficiency in %% : %.2f"%Etta_m
Etta_o = BP/mf/CV*100;			#%
print "Overall efficiency in %% : %.2f"%Etta_o
Gamma = 1.4;			#consmath.tant
Etta_a = (1-1/(r**(Gamma-1)))*100 ;			#%
print "Air standard efficiency in %% : %.2f"%Etta_a
Etta_r = Etta_o/Etta_a*100;			#%
print "Relative efficiency in %% : %.2f"%Etta_r

Indicated Power in KW : 4.254
Brake Power in KW : 3.435
Mechanical efficiency in % : 80.74
Overall efficiency in % : 29.44
Air standard efficiency in % : 51.16
Relative efficiency in % : 57.54

Example 7.4 Page No : 24

In [7]:
import math 
			
# Variables :
IP = 50.;			    #KW
Vf = 16.;			    #litre/hr
Sp_gravity_fuel = 0.755;
CV = 44500.;			#KJ/Kg
N = 3000.;	    		#rpm
Pmi = 5.2;		    	#bar

#Calculation and Results
mf = Vf*10**-3*Sp_gravity_fuel*1000;			#Kg/hr
mf = mf/3600;			#Kg/s
Etta_i = IP/mf/CV*100;			#%
print "Indicated thermal efficiency in %% : %.2f"%Etta_i

#IP = Pmi*10**5*math.pi/4*d**2*L*N/2/60/1000;			#KW
d = (IP*60*1000/Pmi/10**5/(math.pi/4)/1.1/(N/2))**(1./3);			#meter(L = 1.1*d)
print "Bore in cm : %.2f"%(d*100)
L = 1.1*d;			#meter
print "Length of stroke in cm : %.3f"%(L*100)

Indicated thermal efficiency in % : 33.48
Bore in cm : 16.45
Length of stroke in cm : 18.096

Example 7.5 Page No : 25

In [5]:
			
# Variables :
Vs = 5.7;			#litre
Vs = Vs/1000;			#m**3
Pm = 600.;			#KN/m**2
N = 800.;			#rpm

#Calculation
n = N/2;			#No. of strokes/min
IP = Pm*Vs*n/60;			#KW

# Results
print "Indicated power of Engine in KW :  ",IP

Indicated power of Engine in KW :   22.8

Example 7.6 Page No : 25

In [6]:
import math 
			
# Variables :
n1 = 6.;			#cylinders
IP = 100.;			#KW
N = 800.;			#rpm
Lbyd = 1.25;			#stroke to bore ratio
Etta_m = 80./100;
bmep = 5.;			#bar

#Calculation
n = N/2;			#No. of strokes/min
#IP = Pm*math.pi/4*d**2*d*Lbyd*n/60000
d = (IP/(bmep*math.pi/4*Lbyd*n/60000))**(1/3);			#m
L = Lbyd*d;			#m

# Results
print "Diameter in meter : ",d
print "Length ofstroke in meter :  ",L

			#Solution is not complete in the book.

Diameter in meter :  1.0
Length ofstroke in meter :   1.25

Example 7.7 Page No : 26

In [8]:
import math 
			
# Variables :
d = 110./1000;			#m
L = 140./1000;			#m
Pmi = 600.;			#KN/m**2
N = 1000.;			#rpm
n = N;			#strokes/min(for 2 stroke)

# Calculations
A = math.pi/4*d**2;			#m**2
IP = Pmi*A*L*n/60;			#KW

# Results
print "Indicated power of the engine in KW : %.3f"%IP

Indicated power of the engine in KW : 13.305

Example 7.8 Page No : 26

In [9]:
import math			
# Variables :
n1 = 6.;			#cylinders
IP = 150.;			#KW
N = 800.;			#rpm
TwoLN = 320.;			#m/s
Lbyd = 1.2;			#stroke to bore ratio
Pmi = 650.;			#Kn/m**2

#Calculation
#IP = n1*Pmi*(math.pi/4*d**2)*L*n/60;			#KW
d = math.sqrt(IP/n1/Pmi/(math.pi/4)*2/TwoLN*2*60);			#meter(L*N replaced by TwoLN/2)
L = Lbyd*d;			#in meter
N = TwoLN/2/L;			#rpm

# Results
print "Engine crank shaft speed in rpm : %.2f"%N

Engine crank shaft speed in rpm : 695.73

Example 7.9 Page No : 26

In [10]:
import math 
			
# Variables :
d = 250./1000;			#meter
L = 400./1000;			#meter
Pmi = 6.50;			    #bar
N = 250.;			    #rpm
NetBrakeLoad = 1080.;		#N
Db = 1.5;	    		#meter
mf = 10.;		    	#Kg/hr
mf = mf/60./60;			#Kg/sec
CV = 44300.;			#KJ/Kg

#Calculation and Results
n = N/2;			#stroke/min
IP = Pmi*10**5*(math.pi/4*d**2)*L*n/60/1000;			#KW
print "Indicated Power in KW : %.2f"%IP

Rb = Db/2;			#meter
BP = NetBrakeLoad*Rb*2*math.pi*N/60/1000;			#KW
print "Brake Power in KW : %.3f"%BP
Etta_m = BP/IP*100;			#%
print "Mechanical Efficiency in %% : %.2f"%Etta_m
Etta_i = IP/mf/CV*100;			#%
print "Indicated Thermal Efficiency in %% : %.2f"%Etta_i

Indicated Power in KW : 26.59
Brake Power in KW : 21.206
Mechanical Efficiency in % : 79.75
Indicated Thermal Efficiency in % : 21.61

Example 7.10 Page No : 27

In [10]:
			
# Variables :
mf = 20.;			#Kg/hr
BP = 80.;			#KW
Etta_m = 80./100;
CV = 45000.;			#KJ/Kg

# Calculations and Results
bsfc = mf/BP;			#break specified fuel consumption in Kg/KWh
print "Break specified fuel consumption in Kg/KWh : ",bsfc

IP = BP/Etta_m;			#KW
mf = mf/60/60;			#Kg/s
n = mf/100;			#Kg/KWh
Etta_b = BP/mf/CV*100;			#%
print "Break Efficiency in % : ",Etta_b
Etta_I = Etta_b/Etta_m;			#
print "Indicated thermal Efficiency in % : ",Etta_I

Break specified fuel consumption in Kg/KWh :  0.25
Break Efficiency in % :  32.0
Indicated thermal Efficiency in % :  40.0

Example 7.11 Page No : 28

In [11]:
import math 
			
# Variables :
d = 270./1000;			#meter
L = 380./1000;			#meter
Pmi = 6.;			#bar
N = 350.;			#rpm
WsubS = 1000.;			#N
Db = 1.5;			#meter
mf = 10.;			#Kg/hr
CV = 44400.;			#KJ/Kg

# Calculations and Results
IP = Pmi*10**5*(math.pi/4*d**2)*L*N/2/60/1000;			#KW
print "Indicated Power in KW : %.3f"%IP

BP = (WsubS)*math.pi*Db*N/60/1000;			#KW
print "Brake Power in KW : %.2f"%BP

Etta_m = BP/IP*100;			#%
print "Mechanical Efficiency in %% : %.1f"%Etta_m

mf = mf/60/60;			#Kg/s
Etta_b = BP/mf/CV*100;			#
print "Indicated thermal Efficiency in %% : %.2f"%Etta_b

Indicated Power in KW : 38.075
Brake Power in KW : 27.49
Mechanical Efficiency in % : 72.2
Indicated thermal Efficiency in % : 22.29