Otto cycle plotter

Objective

Build a Python script that maps the pressure–volume loop of an ideal Otto‑cycle engine.

Problem statement

Write a Python code to plot the process curve of a petrol engine

Solution procedure

Code:

import matplotlib.pyplot as plt

import math

# input values

p1=101325

t1=500

bore=.1

stroke=.1

con_rod=.15

cr=12 #compression ratio

gamma=1.4

t3=2300

t=100

v_s=(math.pi/4)*pow(bore,2)*stroke

v_c=v_s/(cr-1)

#function for plotting the isentropic compression and expansion

def isentropic_plot(stroke,con_rod,v_c,theta_start,theta_end,no_theta):

theta_start=math.radians(theta_start)

theta_end=math.radians(theta_end)

v=[]

d_theta=(theta_end-theta_start)/(no_theta-1)

for i in range(0, no_theta):

theta=theta_start+i*d_theta

a=stroke/2

R=con_rod/a

item1=1/2*(cr-1)

item2=pow(R,2)-pow(math.sin(theta),2)

item3=R+1-math.cos(theta)-pow(item2,.5)

v.append((1+item1*item3)*v_c)

return v

# initial condition

v1=v_s+v_c

ideal_gas_const=p1*v1/t1

# properties at the end of isentropic compression (0 to 180)

v2=v_c

p2=pow(v1/v2,gamma)*p1

t2=p2*v2/ideal_gas_const

#list of v and p

# properties at the end of constant volume heat addition (2-3)

v3=v2

p3=ideal_gas_const*t3/v3

#list of v and p

# isentropic expansion (3-4) (180 to 0)

v4=v1

p4=pow(v3/v4,gamma)*p3

t4=p4*v4/ideal_gas_const

#list of v and p

# isentropic compression path

p_compression=[]

v_compression=isentropic_plot(stroke,con_rod,v_c,180,0,t)

for v in v_compression:

p_compression.append(pow(v3/v,gamma)*p3)

# isentropic expansion path

p_expansion=[]

v_expansion=isentropic_plot(stroke,con_rod,v_c,0,180,t)

for v in v_expansion:

p_expansion.append(pow(v1/v,gamma)*p1)

plt.plot(v_compression,p_compression)

plt.plot(v_expansion,p_expansion)

plt.plot([v1,v4],[p1,p4])

plt.plot([v3,v2],[p3,p2])

plt.show()

1. First, I imported all the necessary modules
2. Then I assign all the constant values
3. Then I defined a function that will help me to plot the isentropic process curve. This function will be used later in the script.
4. Now I have all the state 1 conditions.ns
5. With the help of the ideal gas equation and PV^gamma =constant (isentropic process equation), all other state parameters are calculated.
6. Then, at last, using the isentropic_plot function that I have defined earlier, I found the values of volume for isentropic processes, and with these values, I found the corresponding pressure value.
7. with this isenropic pressure and volume value and state properties and using the plot function I ploted the Pv diagram.

Results

When the code is run, the plot for the Otto cycle is plotted.

(Plot is uploaded as a file)

Discussion

Such a script helps to visualize the processes of Ic engine