carburetor by nite sh

8/2/2019 Carburetor by Nite Sh

1/15

MALAVIYA NATIONAL INSTITUTE OFTECHNOLOGY JAIPUR

Nitesh Kumar Jatav

2009UME445

M-2

Carburetor

Experiment of Carburetor Design on a HONDAG200 engine


2/15

1

Carburetor|NiteshKumarJatav

Carburetor

Experiment of Carburetor Design on a HONDAG200 engine

ABSTRACT:

Experiment was done on Honda gen -200 at different-2 loads to find out the

design of carburetor. When suction stroke takes place in cylinder of the engine

due to pressure drop at the venturi pressure difference occur b/w main jet and

fuel surface in float chamber so fuel come out of jet and mix with air. Fuel takes

heat from the air and vaporize. This mixture goes into the cylinder and

combustion takes places. In SI engines air-fuel ratio is b/w 8:1 to20:1.Stoichiometric air fuel ratio is about 15.4:1 and best power and best economy

conditions takes place at 12:1 and 16:1 air-fuel ratios respectively. We will

calculate the air fuel ratio and by using that one will find the area of venturi and

main jet. As we know as speed increases suction at venture increases so fuel

consumptions increases. As load increases fuel requirement increases. We

assume that difference b/w the heights of main jet and fuel surface in float

chamber is zero. And we use both actual and approximation formula in which we

assume that air is incompressible.

INTRODUCTION:

A carburetor is a device that blends air and fuel for an internal combustion

engine. It is sometimes shortened to carb in North America and the United

Kingdom [1]. Carburetors commonly used for supplying a combustible mixture of

air and liquid fuel to internal combustion engines, comprise a bowl in which a

supply of the fuel is maintained in the liquid phase and a fuel jet which extends

from the liquid fuel into a passage through which air is drawn by the suction of

the engine cylinders. The pressure difference set up between the carburetor inlet

and the throat of the nozzle is used to meter the appropriate fuel flow for that air

flow. On the suction, or intake stroke of the cylinders, air is drawn over and


3/15

2


around the fuel jet and a charge of liquid fuel is drawn in, broken up and partially

vaporized during its passage to the engine cylinders. Fuel evaporation starts

within the carburetor and continues in the manifold as fuel droplets move with

the air flow and as liquid fuel flows over the throttle and along the manifold walls.

When such a charge is ignited in the engine cylinder, only that portion of the

liquid fuel which has been converted into the vaporous (molecular) state

combines with the air to give an explosive mixture. The remaining portion of the

liquid fuel which is drawn into the engine cylinders and remains in the form of

small droplets does not explode and impart power to the engine, but burns with a

flame and raises the temperature of the engine above that at which the engine

operates most efficiently.

PARTS OF A CARBURETOR:

Fuel strainer- The strainer consists of a fine wire mesh or other type of filtering

device, cone shaped or cylindrical shaped, function of which is to prevent the

possible blockage of the nozzle by dust particles during the fuel flow.

Nozzle-It is a device designed to control the direction or characteristics ofa fluid flow (especially to increase velocity) as it exits (or enters) an enclosed

chamber or pipe via an orifice.

Float chamber- The function of a float chamber in a carburetor is to supply the

fuel to the nozzle at a constant pressure head. This is possible by maintaining a

constant level of the fuel in the float bowl.

Throttle- The speed and the output of an engine are controlled by the use of the

throttle valve. The more the throttle is closed the greater is the obstruction to the

flow of the mixture in the passage and less is the quantity of mixture delivered to

the cylinders.


4/15

3


Choke- It is a device that restricts the flow of air at the entrance to the

carburetor, before the venturi. It is added to enrich the mixture during engine

starting and warm-up to ensure a combustible mixture within each cylinder at the

time of ignition.

A Simple Carburetor [2]

Metering system- It is installed

To proportionate the fuel-air mixtureto decrease the pressure at the discharge nozzle

to limit the air flow at full throttle.

Idle system- It is added to meter the fuel flow at idle and light loads. It goes out

of action when the throttle is opened beyond about 20%.


5/15

4


APPARATUS:

To conduct above experiment following apparatus are required:

a) A stationary petrol engine.b) Manometer (to calculate mass flow rate of air)c) Burette ( to calculate fuel consumption)d) Voltmetere) Ammeterf) Bulbs for applying load.

PROCEDURE:

A.Start the engine and wait for some duration for it to attain steadycondition.

B. Vary the load by lightening bulbs of different wattage as per therequirement.

C. Record water head by manometer to calculate mass flow rate of air andalso record fuel consumption.

D.Note voltage and current by voltmeter and ammeter and record enginespeed by rpm meter.

E. Now calculate the fuel consumption.

BASIC FORMULAE DERIVATION [3]

Applying the steady flow energy equation to sections A-A and B-B per unit mass

flow of air: (1) 21

2

2122

1CChhwq


6/15

5


Here, q and w are the heat and work transfers from the entrance to the throat

and h and C stand for enthalpy and velocity respectively.

If we assume reversible adiabatic conditions, and there is no work transfer, q=0,

w=0, and if approach velocity C10 we get

(2)

Assuming air to be a perfect gas, we get

Tch p Then

(3)

If we assume that the distance from the inlet to the venture throat is short, we

can consider it to be isentropic in the ideal case,

(4)

(5)

Substituting for T1 T2 from Eq. 5 in Eq. 3, we get

)6(12

1

1

2

12

p

pTcC p

By the continuity equation we can write down the theoretical mass flow rate of

air )7(222111.

CACAm a

Where A1 and A2 are the cross-sectional areas at the air inlet (point 1) and venturithroat (point 2).

To calculate the mass flow rate of air at the throat, we have assumed the flow to

be isentropic till the throat so the equation relating p and v (or ) can be used.

)8(2211

Avpvp

212 2 hhC

212

2 TTcC p

1

1

2

121

1

1

2

1

2

1p

pTTT

p

p

T

Tthen


7/15

6


)8(2

2

1

1 Bpp

)9(12

1

1

2

12

1

1

2

1

.

p

pTcA

p

pm pa

For a perfect gas we have )9(1

1

1A

RT

p

Thus )10(12

1

1

2

12

1

1

1

1

2. Ap

pTcART

p

p

pm pa

And rearranging the above equation we have

)10(2

1

1

2

2

1

2

1

12.

Bp

p

p

pc

TR

pAm pa

Since the fluid flowing in the intake is air, we can put in the approximate values ofR = 287 J/kgK, cp= 1005 J/kgK at 300K, and = 1.4 at 300K.

)11(1562.0

1562.0

1

12

71.1

1

2

43.1

1

2

1

12.

T

pA

p

p

p

p

T

pAma

Where71.1

1

2

43.1

1

2

p

p

p

p

1

1

2

12

p

p


8/15

7


Equation 11 gives the theoretical mass flow rate of air. The actual mass flow rate,

am.

can be obtained by multiplying the equation by the coefficient of discharge

for the venturi, Cd,a. Thus

)13(1562.0

1

12

,

.

T

pACm ada

Where )14(.

.

,

a

a

ad

m

mC

The coefficient of discharge and area are both constant for a given venturi, thus

)15(

1

1.

T

pma

Since we have to determine the air-fuel ratio, we have to now calculate the fuel

flow rate. Since the fuel is a liquid before mixing with the air, it can be taken to be

incompressible. We can apply Bernoullis equation between the atmospheric

conditions prevailing at the top of the fuel surface in the float bowl, which

corresponds to point 1 and the point where the fuel will flow out, at the venturi,

which corresponds to point 2. Fuel flow will take place because of the drop in

pressure at point 1 due to the venturi effect. Thus

)16(2

2

21 gzCpp f

ff

wheref is the density of the fuel in kg/m3, Cf is the velocity of the fuel at the exit

of the fuel nozzle (fuel jet), and z is the depth of the jet exit below the level of fuel

in the float bowl. This quantity must always be above zero otherwise fuel will

flow out of the jet at all times. The value of z is usually of the order of 10 mm.

From Eq. 16 we can obtain an expression for the fuel velocity at the jet exit as

)17(2 21

gz

ppC

f

f


9/15

8


Applying the continuity equation for the fuel, we can obtain the theoretical mass

flow rate,.

fm from

)18(2

21

.

gzppA

CAm

fff

ffff

whereAf is the exit area of the fuel jet in m2.If Cd,fis the coefficient of discharge of

the fuel nozzle (jet)

Then .

21,)20(2 gzppACm ffffdf

Since )21(.

.

f

a

m

m

F

A

Fuel

Air

)22(

21562.0

211

12

,

,

gzppT

p

A

A

C

C

F

A

ffffd

ad

If we put 21 pppa , we get the following equation for the air-fuel ratio

)23(2

,

,

gzp

p

A

A

C

C

F

A

fa

a

f

a

ffd

ad

Where )24(

11

2

1

1

2

1

1

2

2

1

2

p

p

p

p

p

p

Air-fuel ratio neglecting compressibility of air

If we assume air to be incompressible, then we can apply Bernoullis equation to

air flow also. Since initial velocity is assumed zero, we have

)29(2

2

221Cpp

aa


10/15

9


Thus )30(2 212

a

ppC

Applying the continuity equation for the fuel, we can obtain the theoretical

mass flow rate,.

am , from

)31(2212

22

.

ppA

CAm

a

aa

Where A2 is the venturi in m2.If Cd,a is the coefficient of discharge of the venturi

Then .

212,

.

)33(2 ppACm aada

Since

)34(.

.

f

a

m

m

F

A

Fuel

Air

)35(21

212

,

,

gzpp

pp

A

A

C

C

F

A

ff

a

ffd

ad

If we assume z = 0, then [2]

)36(2

,

,

f

a

ffd

ad

A

A

C

C

F

A


11/15

10


LINE DIAGRAM OF SETUP:

1) Air inlet orifice2) Carburetor3) Water head measurement through orifice meter.4) Fuel consumption measurement.5) Gasoline engine ( G-200, HONDA 5.0 )6) Generator and bulb setup {for brake power (b.p.) measurement}7)

Rotating disc {for rpm measurement}

Calculation:

Area of main jet and venturi

Measured data:-

S. no. Load

(Watt.)

Fuel

flow

rate

(Ml/s)

Water

head

(cm)


12/15

11


1 500 .465 11.5

2 1000 .513 12.5

Air head=water head*(pw/pa)

=99.13m

Velocity of air = (2gh)

=44.10 m/s

Ma= cd*paAV

=3.277*10-3kg/s

Mf= .465*740*10-6

=3.44*10-4

A/F ratio=Ma/Mf

=9.5:1

By using the approximation formula

f

av

fd

ad

Aj

A

C

C

F

A

,

,

Av/Aj =186.30

By using actual formula

211

1

,

,

21562.0

ppT

p

Aj

Av

C

C

F

A

ffd

ad

71.1

1

2

43.1

1

2

p

p

p

p

P2= pressure at venturi

P1= atmospheric pressure=1 bar


13/15

12


From calculation

We get pressure ratio

X=.97

P2=.97 bar

By putting this value in

71.1

1

2

43.1

1

2

1

12.

1562.0

p

p

p

p

T

pAMa

Area of venturi

= 4.03*10-5

m2

Diameter of venturi = 7.163 mm

Area of jet = 2.613*10-7m2

Diameter of jet

= .524mm

DATA USED FOR CALCULATION:

Initial temperature and pressure 300K, 1.013 barP 36.4 mm of HgOrifice diameter 12 mmDensity of fuel 740 kg/m3Density of air 1.12 kg/m3Cd,f 0.66Cd,a 0.63 (orifice) and 0.85 (venturi)


14/15

13


RESULTS AND DISCUSSIONS:

The average diameter of Venture throat -7.163 mm. The average diameter of fuel jet- .524 mm. Untilfgz pa, (z is nozzle tip) no fuel shall come out of the nozzle to mix

with air. As speed increasespa increases therefore fuel flow rate

increases, more fuel is sucked in.

A choke must be added to enrich the mixture during cold starting andwarm up to ensure that a combustible mixture is provided to each cylinder

at the time of ignition.

At low loads, or 25% to 75% throttle opening, the air-fuel mixture is leaneror near stoichiometric (equivalence ratio 0.9). At higher loads, wide open

throttle, the air fuel ratio is rich (equivalence ratio ~1.1 for best power).

Conclusions:At the time of starting of engine we need a rich mixture therefore we

open the chalk to allow air enter in the carburetor.

While accelerating a rich mixture, throttle opening also increases duringacceleration, but a temporary lean mixture forms, to compensate thisacceleration should be installed.

During throttle opening from 25%to 75% (cruising stage) lean mixture issupplied. Max. Efficiency we get.


15/15

14


Chalk is needed for rich mixture in cold.Reducing the A/F ratio to 9 to 11, causes unsteady and non-smooth,

combustion of most of the mixture occurs in the exhaust system.

In order to reduce the compensation of fuel, multiple venturi systemcan also be installed.

Mixture-control systems like back suction type, needle type, air-porttype can also be installed.

REFERENCES:

www.wikipedia.org, Carburetor. Ganesan, V., Text book of I.C ENGINES. Prof. Poonia, M.P, Class notes I.C. Engines, 2011 www.ieee.org
http://www.wikipedia.org/http://www.wikipedia.org/http://www.ieee.org/http://www.ieee.org/http://www.ieee.org/http://www.wikipedia.org/

carburetor by nite sh

Documents