wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

A four-stroke, four cylinder SI engine has a brake thermal efficiency of 30% and indicated power is 40kW at full load. At half load it has a mechanical efficiency of 65%. What is the indicated thermal efficiency at full load?

A
64.1%
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
46.1%
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
38.1%
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
D
19.5%
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is C 38.1%
At full load:

bp+fp=40kW

At half loadbp=0.5×bp at full load

ηm=0.65=0.5×bp0.5bp×fp

0.5bp=0.65(0.5,bp+fp)

0.5bp=0.325bp+0.65×fp

fp=0.1750.65×bp=0.27bp

Put in equation (1)

bp+0.27 bp=40

bp=31.5kW

fp=8.5kW

Mechanical efficiency at full laod,ηm=bpbp+fp=31.540

ηm=78.8%

Indicated thermal efficiency at full load

ηm=ηntnm=0.30.788=0.381=38.1%

flag
Suggest Corrections
thumbs-up
5
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
PHYSICS
Watch in App
Join BYJU'S Learning Program
CrossIcon