Work and heat transfer in internal combustion engine

Click For Summary

Discussion Overview

The discussion revolves around a homework problem related to the work and heat transfer in a two-cylinder internal combustion engine during the compression stroke. Participants analyze the given parameters, including pressure, volume reduction, and the law of compression, while attempting to determine the power absorbed during the compression strokes.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a homework problem involving the compression of air in an internal combustion engine and seeks help in identifying mistakes in their calculations.
  • Another participant questions whether the law of compression should be expressed as PV^1.4 instead of PV^1.2, suggesting a potential error in the original problem statement.
  • Further replies indicate that the use of 1.4 is appropriate for adiabatic processes, referencing the specific heat ratio for air.
  • Some participants report that using 1.4 yields a different result, around 16 kW, leading to speculation that the original question may be flawed.
  • A later reply emphasizes the importance of correctly calculating the volume swept by the piston, indicating where the initial poster may have gone wrong in their approach.

Areas of Agreement / Disagreement

Participants express disagreement regarding the correct exponent in the compression law (1.2 vs. 1.4) and whether the original problem statement contains errors. There is no consensus on the correct approach or solution to the problem.

Contextual Notes

Participants note potential calculation errors and the need for clarity regarding the volume swept by the piston, which may affect the final results. The discussion highlights unresolved assumptions about the problem's parameters and the applicability of the equations used.

Suman_babai
Messages
8
Reaction score
1
★★ members are requested to crop images so that only that content essential to the thread is posted ★★ ❌

Homework Statement

: [/B]At the beginning of the compression stroke of a two-cylinder internal combustion engine the air is at a pressure of 101.325 kPa. Compression redeuces the volume to 1/5 of its original volume, and the law of compression is given by PV^1.2 = const. If the bore and stroke of each cylinder is 0.15 m and 0.25 m , respectively, determine the power absorbed in kW by compression strokes when the engine speed is such that each cylinder undergoes 500 compression strokes per minute.

The answer is given as : 17.95 kW

2. Homework Equations : I hv written all formulas in the solution (attachment).

The Attempt at a Solution

:[/B] I hv attached the solution I hv done. Please rectify my mistake... where I am doing wrong..my ans is not matching with the given one.
 

Attachments

  • IMG-20161220-WA0010.jpeg
    IMG-20161220-WA0010.jpeg
    26 KB · Views: 1,172
Last edited:
Physics news on Phys.org
Suman_babai said:
given by PV^1.2 = const.
Are yo usure this is not pV^1.4 ?
 
Replusz said:
Are yo usure this is not pV^1.4 ?
that could be a printing mstake... thanks... this book is just full of calculation errors.
 
And if you calculate it with 1.4? do you get the right answer? (it is 1.4 because for adiabatic expressions pV^(1+2/f)=const. and f=5 for air. )
 
Replusz said:
And if you calculate it with 1.4? do you get the right answer? (it is 1.4 because for adiabatic expressions pV^(1+2/f)=const. and f=5 for air. )
no.. it is coming around 16.(something)... may be the question is wrong.. thanks anyway.
 
Suman_babai said:

Homework Statement

: [/B]At the beginning of the compression stroke of a two-cylinder internal combustion engine the air is at a pressure of 101.325 kPa. Compression redeuces the volume to 1/5 of its original volume, and the law of compression is given by PV^1.2 = const. If the bore and stroke of each cylinder is 0.15 m and 0.25 m , respectively, determine the power absorbed in kW by compression strokes when the engine speed is such that each cylinder undergoes 500 compression strokes per minute.

The answer is given as : 17.95 kW

2. Homework Equations : I hv written all formulas in the solution (attachment).

The Attempt at a Solution

:[/B] I hv attached the solution I hv done. Please rectify my mistake... where I am doing wrong..my ans is not matching with the given one.
Here is correct solution bro. V1-V2= Volume swept by piston.
Volume swept by piston not equal to v1, where you went wrong.
 

Attachments

  • IMG_20210328_105808.jpg
    IMG_20210328_105808.jpg
    71.3 KB · Views: 266
Reply
  • Like
Likes   Reactions: Chestermiller

Similar threads

Calculate the torque, total displacement volume, when stroke and bore are equal
  • · Replies 1 ·
Replies
1
Views
3K
Otto Cycle - calculate the net work per cycle in Btu
  • · Replies 7 ·
Replies
7
Views
6K
How does a 4-piston, 4 stroke internal combustion engine work?
  • · Replies 11 ·
Replies
11
Views
4K
Internal combustion engine calculation questions
  • · Replies 9 ·
Replies
9
Views
3K
Solve Otto Cycle Problem: Heat Rejection (300 kW)
  • · Replies 4 ·
Replies
4
Views
7K
Work done by compressed air on the piston
  • · Replies 10 ·
Replies
10
Views
7K
Thank you for your response AM. I appreciate it and will work through the steps.
  • · Replies 1 ·
Replies
1
Views
2K
Steam heating system transfers heat to a room (Thermodynamics)
  • · Replies 1 ·
Replies
1
Views
3K
Mean effective pressure in a diesel engine
  • · Replies 2 ·
Replies
2
Views
3K
Heat transfer and combustion problem
  • · Replies 7 ·
Replies
7
Views
4K