7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 1/11
Fuel systems(Carburetor)
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 2/11
•To meter the liquid fuel as required by the engine
•Atomize the fuel and mix it with the air stream
•Enable the engine to run smoothly in all engine operating conditions.
Function of the carburetor
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 3/11
Pa = P
!P = P "P# P#
Aair
Afuel
$ %hanging
Aair &Afuel ''
(imple %arburetor
Throttle opening
!P
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 4/11
(imple %arburetor problems
)dling circuitAcceleration *+esponse time,
%hoc- *%old starting,
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 5/11
%arburetor )dle circuit and mix
adustment
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 6/11
/ariable 0et %arburetor
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 7/11
)nta-e (ystem of a 1asoline )nternal
%ombustion Engine with a Two23arrel
%arburetor
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 8/11
# 4
Air
# 4
Fuel
Assumptions5• )ncompressible flow• 6o 7eat transfer • Frictionless flow
• 6o external wor-• 8istance between 9enture inlet and
throat is negligible
%alculation of F&A ratio
A. For air
Apply 3ernoulli equation between and #
2
2
2
2
2
1
2
1
1
1
22 gZ
V P gZ
V P ++=++
ρ ρ
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 9/11
# 4
Air
# 4
Fuel
)1....(..........2
2
2
1
2
2
2
1
2
221
21
V V P V V P P
a
a
a
a
−=→−
=−
∴
==
ρ ρ
ρ ρ ρ
Apply continuity equation
factor approuch A
AWhere
A
A
P
V
A
AV
P
A
AV V
P
in From
A
AV V V AV A
a
a
a
a
a
a
2
1
2
2
1
2
2
2
1
22
2
2
1
22
2
2
2
1
221222111
1
1
2
122
12
)2....(..........
−
−
∆
=∴
−=
∆→
−=
∆→
=→=
ρ
ρ ρ
ρ ρ
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 10/11
# 4
Air
# 4
Fuel
→=
− 11
2
1
2
A
A
)f A::: A#
a
a P
V ρ
∆=
2
2
Actual 9elocity5)f %a = flow coefficient
%a = /a,act & /a,th
%a ; < /#,act ; /#,th
ass flow rate5
aaaa
aaaa
a
a
aaaaa
P C
P C
P C V AC m
ρ ρ
ρ ρ
ρ ρ ρ
2
2
2
22
∆=
∆=
∆==
7/23/2019 Fuel System 10
http://slidepdf.com/reader/full/fuel-system-10 11/11
f
a
f
a
f
a
f
a
f
a
P
P
A
A
C
C
m
m
F
A
∆∆
==∴
ρ
ρ
# 4
Air
# 4
Fuel
3. For Fuel
f f f f f P C m ρ ρ 2∆=
(imilarly as air