petrol engine Carburation

8/12/2019 petrol engine Carburation

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CARBURATION

PROF. JIGNESH SOHALIYA

JMS


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PURPOSE OF CARBURATION

S.I engine uses volatile fuels

Formation of a homogenous mixture is normally not completed in inlet

Purpose of carburation is to provide a combustible mixture of fuel & air in required quantity &operation of the engine under all condition.

WHAT IS CARBURATION?

The process of formulation of fuel & air mixture by mixing the proper amount of fuel with air

engine cylinder.

FACTOR AFFECTING CARBURATION

1. Engine speed

2. Vaporization characteristics of the fuel

3. Temp. Of incoming air

4. Design of carburetor

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HIGHER SPEED ENGINE

At 3000rpmonly 10 milliseconds for mixture induction during intake

For 6000rpm- 5 milliseconds

Therefore velocity of the air stream at the point where fuel is injected has to be increase.

This is achieved by venture section in the air.

VAPORIZATION OF FUEL

Presence of high volatile hydrocarbons in fuel.

Distillation curve are necessary for efficient carburation especially at high speed.

TEMP. OF INCOMING AIR

High atmospheric air high temp. Of fuel

Produces more homogenous mixture & reduction in its volumetric efficiency.JMS


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PROPER DESIGN OF CARBURETOR ELEMENTS ALONE ENSURE THE SUPPLY OF DESIRE COM

MIXTURE UNDER DIFFERENT CONDITIONS.

COMPLETE COMBUSTION MEANS ALL CARBONE IN FUEL CONVERTED IN TO CO2 & ALL HY

AIR FUEL MIXTURES

1. Chemically correct mixture or stoichiometric (15:1)

2. Rich mixture (less air 12:1 , 10:1)

3. Lean mixture (more air 17:1, 20:1)

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MIXTURE REQUIREMENT AT DIFFERENT LOADS AND SPEED

Air fuel ratio at which engine operates has a considerable

influence on its performance

For high speed & low speed engine a/f ration is varying.

A/F ratio will affect both the POWER OUTPUT & BRAKE

SPECIFIC FUEL CONSUPTION. Best power mixture (12:1) is much richer than chemically

corrected mixture.

Best economy(16:1) is slightly leaner than chemically correct.

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As indicated in fig. there are three general

ranges of throttle operation. In each of this engine requirements different.

Ranges are.

1. Idling (mixture must be enriched)

2. Cruising (mixture must be leaned)3. High power (mixture must be enriched)

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SIMPLE CARBURETOR

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LIMITATION OF SIMPLE CARBURETOR

IT DO NOT PROVIDE RICH MIXTURE DURING STARTING & IDLING. THROTTLE IS NEARLY CLO

PRODUCE SUFFICIENT PRESSURE DIFFERENCE FOR FUEL.

DURING SUDDEN ACCELERATION RICH MIXTURE IS REQUIRED WHICH CAN NOT PROVIDE B

AT HIGHER SPEED MIXTURE RICHNESS IS AUTOMATICALLY INCREASE.

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MODIFICATIONS OF SIMPLE CARBURETOR

1. STARTING DEVICE(CHOCK)

2. IDLING DEVICE

3. MAIN METERING SYSTEM4. POWER ENRICHMENT

5. ACCELERATION PUMP

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MAIN METERING SYSTEM


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MAIN METERING SYSTEM FOR WIDE RANG OF SPEED & LOAD OF THE ENGINE ----- A/F

RATIO IS VARIES

1. COMPENSATING JET

IT PROVIDES EXTRA AIR FLOW WHEN MAIN JET PROVIDES

MORE FUEL DURING HIGH SPEED.

AREA OF MAIN JET AND COMPENSATING JET IS EQUAL TO

SINGLE JET.

INCREASING SPEEDMAIN JET & C.J DELIVER MORE

FUEL(RICH).

THE FLOW OF FUEL THROUGH COMPENSATING JETINCREASES WITH INCREASING SPEED BUT THE FLOW OF FUEL

FROM THE FLOAT CHAMBER TO COMPENSATING WELL IS

RESTRICTED BY ORIFICE.

COMPENSATING JET DELIVER LEAN MIXTURE & IT IS MAINTAIN

BY MAIN JET UNDER HIGH SPEED.JMS

Emulsion tube


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Emulsion tube

Main metering jet is kept at level of 25mmbelow

the fuel level in float chamber therefore its called

SUBMERGED JET.

Jet located on the bottom of the well.

The side of the well have holes. Holes are incommunication with atmosphere.

When throttle is open pressure at venturi throat

decreasing & petrol is drawn into the air stream.

This result uncovering the holes in central tube

leading to increasing air fuel ratio or decreasing

richness of mixture when all holes are uncover. Normally flow take place from the main jet.

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BACK SUCTION CONTROL


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BACK SUCTION CONTROL

TOP OF THE FUEL FLOAT CHAMBER IS CONNECTED

TO AIR ENTRY BY MEANS OF CONTROL VALVE.

ANOTHER LINE A SMALL ORIFICE CONNECTS THE

TOP OF THE FUEL FLOAT CHAMBER WITH THE

VENTURI THROAT.

WHEN C.V OPEN LINE IS UNRESTRICTED FLOAT

CHAMBER IS (P1) & THROAT PRESSURE WILL BE P2.

IF THE VALVE IS CLOSED THEN FLOAT CHAMBER

PRESSURE IS EQUAL TO THROAT PRESSURE SO NO

FUEL CAN FLOW.

ALTERING THE QUANTITY OF FUEL DISCHARGED

FROM THE NOZZLE THE REQUIRED AIR FUEL RATIO

MIXTURE CAN BE ACHIEVED.

ONLY FOR LARGE CARBURETORS.JMS

ECONOMIZER OR POWER ENRICHMENT


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ECONOMIZER OR POWER ENRICHMENT

SYSTEM

MAX. POWER RANGE RICH AIR FUEL RATIO

IS REQUIRED.

ECONOMIZER IS DEVICE WHICH REMAINS

CLOSED AT NORMAL CRUISING RANG.

IT REGULATES ADDITIONAL FUEL SUPPLY

DURING THE FULL THROTTLE.

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AUXILIARY VALVE


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AUXILIARY VALVE

PROVIDES EXTRA AIR AT HIGHER

LOAD ON ENGINE

LOAD INCREASING VACUUM IN

VENTURE INCREASING & HENCE

AUXILIARY VALVE IS ALLOW

ADDITIONAL AIR.

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SOLEX CARBURETOR

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STARTING :-


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TO GET THE RICH MIXTURE DURING STARTING BI-STARTER DISK USED WHICH IS OPERATED

STARTER LEVER.

BI- STARTER DISC CONSIST OF DIFFERENT SIZES OF HOLE.

AT THE TIME OF STARTING VALVE IS OPEN.

NORMAL WORKING-

IDLING AND LOW LOAD

RICH MIXTURE WILL PROVIDE BY PILOT JET.

AT THE SPEED INCREASES BY OPENING THE THROTTLE, PRESSURE BELOW THE THROTTLE VA

FLOW

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CARTER CARBURETOR


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CARTER CARBURETOR Carter carburetor is normally used in jeeps.

The gasoline enter the float chamber (1).

Chock valve (2) is always open during normal condition.

Carter carburetor comprises three venture.

Smallest venturis(3) is above the fuel level, two venturis

5,6 are below the fuel level.

LOW SPEED

Suction in the venturi 3, is sufficient to induct the fuel.

Nozzle 4, enters the ventrui 3, & throws the fuel up

against the air stream.

The mixture from venture 3, flows centrally through the

second venture 5, where it is surrounded by air stream& finally goes to the third venture 6,

So well mixed & gives more homogenous & better

mixture at every low speed.

Metering rod 7, which is directly connected to the main

throttle valve.JMS

Idle & low speed circuit


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p

Rich mixture in small quantity required.

Throttle valve 8, practically closed.

The entire suction pressure created by piston in the

engine suction stroke & is exerted at the idle port 9.

So gasoline is inducted through the idle feed jet 9 & air

is inducted through first by pass 11, and rich mixture is

provided.

Accelerating pump.

Purpose is to avoid flat spot in acceleration.

Pump comprises plunger13, inside cylinder consisting non

return inlet check valve 14, & outlet check valve 15.

The plunger of the pump is connected to the acceleration

pedal by throttle control rod 16.

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On rapidly opening the throttle by pressing the


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accelerating pedal, the pump is actuated & small

amount of gasoline spurts in to the chock tube by jet 17.

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S.U. CARBURETOR


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S.U carburetor is constant vacuum carburetor.

In this carburetor venture are vary with the speed which maintain constant pressure.

While other carburetor venture area is constant so P is varies with respect to speed.

A tapered pin is connected to variable chock.

Lower partition of the variable chock is maintain at atmospheric pressure. Upper portion is below atmospheric pressure.

Pe will be varies according to suction pressure which change as per the speed of engine.

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OPERATING DIFFICULTY IN CARBURETOR


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OPERATING DIFFICULTY IN CARBURETOR

1. ICE FORMATION :-

FUEL SPRAY BY THE MAIN JET IN VENTURY WHERE FUEL ATOMIZE & VAPORIZE.

FOR VAPORIZATION OF THE FUEL IT REQUIRED LATENT HEAT WHICH IS TAKEN FROM INCO

SURROUNDING.

IF TEMP. BECOME LOWER THAN THE DEW POINT OF WATER, WATER VAPOR IN THE INCOM

FREEZE & FORM ICE.

2. VAPOR LOCK :-

FOR BETTER COMBUSTION HIGHER VOLATILE FUEL IS PREFERRED & TO PREVENT ICE FORMA

VAPORIZATION.

VAPORIZATION OF FUEL BETWEEN FUEL TANK & CARBURETOR CREATES THIS PROBLEM.

MAINLY DUE TO HIGHER SPEED, DURING HOT DAYS, HIGH LOAD.

VAPOR IS COMPRESSIBLE & HENCE, THERE IS DIFFICULTY IN PUMPING OF FUEL FROM FULL

STOPS WHICH IS KNOWN AS VAPOR LOCK.

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3. BACK FIRING :-


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BACK FIRING WILL TAKE PLACE IN INTAKE OR EXHAUST MANIFOLD.

IF THE MIXTURE IS TOO LEAN , THE RATE OF COMBUSTION IS TOO SLOW.

IN THIS CONDITION BACK FIRING IS TAKE PLACE.

4. NON UNIFORM DISTRIBUTION OF A/F MIXTURE IN MULTI CYLINDER ENGINE.

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PETROL INJECTION SYSTEM


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PETROL INJECTION SYSTEM There are number of drawback & limitation of carburetor in petrol engine & it can b

injection system.

In petrol injection system, metered air is supplied to intake manifold or fuel may be dire

manifold or in cylinder like diesel engine. Quantity of air & fuel continuously changing according to reqirement of an engine at var

Various sensor are placed which gives signal to electric control unit (ECU).

Computer simulates all the data & actuates fuel injector & injection system for best perfo

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TYPES OF PETROL INJECTION SYSTEM


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TYPES OF PETROL INJECTION SYSTEM

PetrolInje

ctionsyste

m

Indirect injection

Multi point fuelinjection

Port

Thrott

Single pointinjection

Port

ThrottGasoline directinjection

Indirect Injection


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The Term Indirect Injection, In An Internal Combustion Engine, Refers To Fuel Injection Where

Injected Into The Combustion Chamber.

Gasoline Engines Are Usually Equipped With Indirect Injection Systems,

Wherein A Fuel Injector Delivers The Fuel At Some Point Before The Intake Valve.

An Indirect Injection Diesel Engine Delivers Fuel Into A Chamber Off The Combustion C

Prechamber, Where Combustion Begins And Then Spreads Into The Main Combustion Chambe

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Gasoline Direct Injection


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In Internal Combustion Engines,

Gasoline Direct Injection (GDI), Also Known As Petrol Direct

Injection Or Direct Petrol Injection Or Spark Ignited Direct

Injection (SIDI) Or Fuel Stratified Injection (FSI).

In This System Petrol Is Directly Injected Inside The Cylinder

At The End Of Compression Stroke. As in diesel injection

system.

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Multi-point Fuel Injection


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Multi-point Fuel Injection Systems Involve The Use Of Numerous Individual Injectors Fo

Two Basic Arrangements

1. Port Injection

2. Throttle Body Injection

Port Injection

In P.I , The Injector Is Placed On The Side Of The Intake Manifold Near The Intake Por

The Injector Sprays Gasoline Into The Air, Inside The Intake Manifold.

Gasoline Mix With Air Uniform Manner.

Every Cylinder Provided With An Injector In Its Intake Manifold.

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Throttle Body Injection


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This Throttle Body Is Similar To The Carburetor Throttle Body, With The Throttle Valve

Amount Of Air Entering The Intake Manifold.

An Injector Is Placed Slightly Above The Throttle Throat Of The Throttle Body.

The Injector Sprays Gasoline Into The Air In The Intake Manifold Where The Gasoline

This Mixture Then Passes Through The Throttle Valve & Enters Into The Intake Manifold

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M.P.F.I SYSTEM FOR MODERN AUTOMOBILE


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MULTIPOINT FUEL INJECTION SYSTEM (MPFI) :- SEPARATE FUEL INJECTOR TO SUPPLY FUEL

SINGLE POINT FUEL INJECTION (SPFI) :- ONLY ONE CENTRALLY LOCATED FUEL INJECTOR

IN BEGINNING IT IS ONLY USED FOR AERO PLANE ENGINES

THIS SYSTEM IS COMBINE ELECTRICAL+ELECTRONICS+COMPUTER+MECHANICAL

DAEWOO MATIZ IS THE FIRST VEHICLE EQUIPPED WITH MPFI SYSTEM IN INDIAN AUTOMO

COMPONENTS

1. ELECTRONIC CONTROL UNIT (ECU) :- IT CONTROLS THE IGNITION TIMING & QUANTITY2. SENSORS :- TO MONITOR AMBIENT, COOLANT & EXHAUST GAS TEMP, INTAKE PRESSURE

3. SOLENOID INJECTOR

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CLASSIFICATION OF MPFI SYSTEM


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1. D-M.P.F.I

2. L- M.P.F.I

D-M.P.F.I

As the air enters into the intake manifold , the intake

manifold sensor detect the intake manifold vacuum &

send the information to ECU.

The speed sensor also sends information about the RPM

of the engine to ECU.

The ECU in turns sends commands to the injector to

regulate the amount of fuel supply for injection.

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INTAKE MAINFOLDVACCUME SENSOR

ENGINE

INJECTOR

ECU

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L-MPFI SYSTEM


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IN THIS SYSTEM THE FUEL METERING IS REGULATED BY THE ENGINE

SPEED AND THE AMOUNT OF AIR THAT ACTUALLY ENTERS THE

ENGINE.

AIR FLOW SENSOR---ECU

SPEED SENSOR-----ECU

ECU-----SIGNAL TO THE INJECTOR.

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ADVANTAGES & DISADVANTAGES


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ENGINE REQUIRES DEFERENT A/F RATIO AT DIFFTERNT OPERATING CONDITION. THIS SYSTE

CONDITION.

THERE IS NO VENTURY AS IN CARBURETOR SO THERE IS SMOOTH FLOW OF AIR, HENCE VO

INCREASES.

LESS PROBLEM OF ICING & VAPOR LOCK.

EASY STARTING

IN MULTI CYLINDER SAME A/F RATIO WILL PROVIDE.

IMPROVE BSFC RESULTS

DISADVANTAGES

HIGH INITIAL COST

MAJOR PART ARE ELECTRONICS SO CAN NOT BE REPAIR.

SKILLED WORKER & SPECIAL SERVICE EQUIPMENTJMS


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THANK YOU

JMS

petrol engine Carburation

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