Calculating Power and Efficiency of a Heat Engine with 6 kg/h Gasoline Input

  • Thread starter Thread starter mado134
  • Start date Start date
  • Tags Tags
    Thermodynamic
AI Thread Summary
The discussion focuses on calculating the power output and efficiency of a heat engine using a gasoline input of 6 kg/h with a calorific value of 42000 kJ/kg. The initial calculations incorrectly assumed that multiplying the fuel rate by the calorific value directly yields the power output, neglecting the need to account for heat rejected (Ql). The correct approach involves determining the net power output by subtracting the heat rejected from the total heat input. Additionally, the efficiency formula was misquoted; the correct efficiency equation is 1 - (Ql/Qh), not the version provided. Accurate calculations are essential for determining the engine's performance metrics.
mado134
Messages
2
Reaction score
0
A heat Engine receives 6 kg/h gasoline which has a calorific value of 42000 kj/kg. If heat rejected from the engine is 40 kw, calculate
a- the power done by the engine
b- the engine effiecincy

-this wt i got today in my exam and unfortuntely i didnt study it well but i did the following :
1- 6 kg/h -----> 1/600 kg/s
then i multiplied it by the 42000 kj/kg
so i can get kj/s ( which is the power )
so is that correct ??

2- i said effieciency = w/Qh = 1 - Qh/Ql

and Qh = W - Ql = 42000 - 40

so is that too correct ?

* i knw i didnt study well :cry: and sorry if i posted it in a wrong section
 
Last edited:
Physics news on Phys.org
Efficiency is 1 - Ql/Qh
 
LawrenceC said:
Efficiency is 1 - Ql/Qh

thanks for quick reply
sure i knw that
but my question is : wt i wrote is right or wrong ?? bcse i got diff units and no more details
 
The output of the engine is Qh-Ql. Multiplying fuel rate of use by caloric content only provides Qh. You must subtract Ql from it to arrive at power output. Ql is heat rejected and it is lost.

You have the equation for efficiency wrong. You wrote
"2- i said effieciency = w/Qh = 1 - Qh/Ql "
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

Thermodynamics problem involving engine efficiency
Replies
20
Views
3K
Change in temperature of air in a closed system
Replies
16
Views
2K
Work done by a Carnot Engine. Melting ice
Replies
2
Views
3K
How to Calculate Steam Engine Efficiency and Water Usage in a Power Plant
Replies
18
Views
8K
Temperature in a Carnot heat engine
Replies
2
Views
3K
What are the thermodynamic properties and efficiency of a steam plant?
Replies
9
Views
2K
Thermodynamics - Calculating Work/Heat, Piston/Cylinder
Replies
3
Views
3K
How Does a Heat Engine's Efficiency Impact Its Exhaust Heat Rate?
Replies
1
Views
5K
Heat pump efficiency calculations - Compressor power issue
Replies
23
Views
3K
Calculating Gasoline Needed for 50.0hp Heat Engine Output
Replies
9
Views
2K

Hot Threads

Recent Insights

Back
Top