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Chapter: Mechanical and Electrical - Thermal Engineering - Internal Combustion Engines

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Solved Problems: Internal Combustion Engines

Mechanical and Electrical - Thermal Engineering - Internal Combustion Engines


Solved Problems:

 

1. A trial carried out in a four stroke single cylinder gas engine gave the following results. Cylinder dia=300 mm, Engine stroke=500mm, Clearance volume=6750cc, Explosions per minute=100  Pmax KN/m2    = 765 Net work load on the brake=190kg Brake dia=1.5m Rope dia=2 5mm, Speed of the engine=240rpm, Gas used=30 m3/kghr   , Calorific value of gas=2 0515 KJ/ m3 . Determine compression rat io, mechanical efficiency, indicated thermal efficiency, air standard efficiency, relative efficiency, assume r=1.4

GIVEN DATA:-

 

Dia of cylind er (d)=300mm=0.3m

 

Engine stroke(l)=500mm=0.5m

 

Clearance volume(vc)=6750/1003=6.75 m3

 

Explosions pe r minute(n)=100/minute=i.67/sec

 

Pmin=765 KN /m2

 

Brake drum dia(D1)=1.5m

 

Rope dia(d1)= 0.025m

 

Work load on the brake(w)=190kg=1.86KN

 

TO FIND:-

 

Compression rati o (r)

 

Mechanical efficiency mech)

 

Indicated thermal efficiency it)

 

Air standard efficiency (ηair)

 

Relative efficiency (ηrel)

 





 

 

2. The following observat ions are recorded during a test on a four-stroke petrol engine, F.C = 3000 of fuel in 12sec, speed of the engine is 2500rpm, B.P = 20KW, Air intake orifice diameter = 35 mm,Pressure across the orifice = 140mm of water coefficient of discharge of orifice = 0.6 , piston diameter = 150mm, stroke length = 100 mm, Density of the fuel = 0.85gm/cc , r=6 .5, Cv of fuel = 42000KJ/Kg, Barometric pressure = 760mm of Hg , Room temperature = 24oc

 

Determine:

 

(i) Volumetric ef ficiency on the air basis alone

 

(ii)             Air-fuel ratio

 

(iii)           The brake mean effective pressure

 

(iv)           The relative efficiency on the brake thermal efficiency

 


 

Given data:

 

Fuel c onsumption = 30cc in 12sec

Speed (N) = 2500/60 rps

 

Brake power = 20KW

 

Orifice diameter (do) = 0.035 m

 

Pressure across the orifice (Po) = 140mm of water

 

Coefficient of discharge (Cd) = 0.6

 

 

Piston diameter (d) = 150mm = 0.15m Stroke length (l) = 0.1m

Density of fuel (ρ) = 0.85gm/ cc Compression ratio (r) = 6.5 Room temperature (Ta) = 297 K

 

Barometric pressure = 760mm of Hg = 101.325KK/m2= 10.34m of water To Find:

(i)               Volumet ric efficiency on the air basis alone

 

(ii)             Air-fuel ratio

 

(iii)          The brake mean effective pressure

 

(iv)          The relative efficiency on the brake thermal efficiency

 

 

Solution:






 

Relative efficiency on brake thermal efficiency basis (ηrel) = ηBT/ ηair

= 0.22409/0.52703

 

ηrel = 42.52%

 


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