Basic Mechanical Engineering (3110006)

BE | Semester-1   Summer-2020 | 11-06-2020

Q3) (c)

A petrol engine with a stroke length of 200 mm and diameter of 150 mm has a clearance volume of 7 × 105  mm3. If the indicted thermal efficiency is 0.30, find the relation efficiency. If the effective pressure is 5 bar and engine runs at 1000 rpm. Find the IP of the engine. Take γ = 1.4.

Given data:
L = 0.2  m
d = 0.15 m
VC = 7 × 105  mm3 = 7 × 10-4  m3
ηith = 0.30 bar
pm = 5 bar = 500 kPa
N = 100  rpm
γ = 1.4
Find:
ηrel = ?
I.P. = ?
 
Solution:
 
The relative efficiency is givne by ηrel =  ηith ηair × 100 %
 
But, the air standard efficiency is given by, ηair = 1 - 1 rγ-1
 
Where, r = compression ratio = Vs + Vc Vc =   π 4 × 0.152 × 0.2 + 7 × 10-4 7 × 10-4 = 6.046
 
Now, ηair = 1 - 1 6.0461.4-1 = 0.5131
 
Thus, ηrel =  0.30 0.51 × 100 % = 58.82 %
 
Indicated power is given by,
 
I.P. =  pm LAN60 × 2 × no. of cylinder, kW
 
I.P. =  500 × 0.2 × π4 × 0.152 × 100060 × 2 × 1
 
I.P. = 14.718 kW