Solved Problems: 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  P_max 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(v_c)=6750/100³=6.75 m³

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

P_min=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 (η_mech)

Indicated thermal efficiency (η_it)

Air standard efficiency (η_air)

Relative efficiency (η_rel)

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 = 24^oc

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 (d_o) = 0.035 m

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

Coefficient of discharge (C_d) = 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 (η_rel) = η_BT/ η_air

= 0.22409/0.52703

η_rel = 42.52%