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Solve the following numerical on four cylinder four stroke engine and calculate diameter of venture and nozzle.

A four cylinder four stroke engine has a cubic capacity of 1490 cc. it develops maximum power at 4200 rpm and air fuel ratio is 13:1. The air speed at venture is limited to 90 m/s. the volumetric efficiency of engine is 70%. Nozzle lip is 6 mm and atmospheric pressure and temperature are 1.013 bar and 293 K. An allowance is to be made for emulsion tube whose diameter should be taken as 1 /2.5 of venture diameter. Taking following data, calculate the diameter of venture and nozzle. Cda-0.85,Cdf=0.66 and density of fuel=740Kg/m3

Mumbai University > Mechanical Engineering > Sem 5 > IC Engines

Marks: 10M

Year: Dec 2015

1 Answer
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A single carburetor supplies air-fuel mixture to the engine. The area through which air is flowing is

Aa=π4(D2d2)

=π4(D2(0.4D)2) as d=0.4D

=π4(D20.16D)

=π4×0.84D2=0.66D2

The volume of air supplied to the engine at atmospheric conditions per second

 = swept volume×RPM2×60ηv=1490×4200×0.72×60

=0.036505m3/sec

The mass of air is given by

ma=ρVRT=1.013×105×0.0360505287×293=0.0434 kg/sec

the air velocity through venturi is given by

Va=2Cv×T1[1(P2P1γ1γ)]

where Cv (coefficient ofvelocity)

Where, the compression of air through venture is considered isentropic.

90=2×1000×293[1(P2P10.286)]

=1(P2P10.286)

=90×902000×293

=0.1382(P2P1)

=(10.01382)3.5

p2=0.9524bar

Considering the compression of air passing through venture is isentropic

p1vγ1=p2vγ2

v2=v1(p1p2)1γ

=1450×106(10.9524)1γ

=0.00150 m3/sec

The volume of air passing through the carburetor is given by

v2=AaVaCda

0.00150=0.66D2×90×0.85×102

D=0.0545 m

The fuel mass flow is given by

mf=ma13=0.0015013=0.0001153

mf=ma13=0.0015013=0.0001153 Kg/sec

The fuel mass flow through the carburetor is given by

mf=AfCdf2ρf(ΔpZgρf)

where Δp=p1p2=1.0130.9524=0.0606 bar

Substituting the values in the above equation

0.0001153=π4d2f×0.662×740(0.0606×1056×103×9.81×740)

df=0.000273 m

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