CARBURETTOR AND THE PROCESS OF CARBURETION

  Edunes Online Education

B.Tech Mechanical Engineering

Automobile Enginnering

How does a carburettor Works?

Learn About Carburettor and Its Uses

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CARBURETOR – HOW TO THINK ABOUT IT

Definition: A carburetor is a device that mixes air and fuel in the correct proportion for combustion in an internal combustion engine. This mixing process is called carburetion.

🧠 BRAIN IMAGE:
Think of a carburetor as a chef in a kitchen.
Air = Oxygen
Fuel = Petrol
Engine = Stomach

If the mixture is wrong → digestion fails.
If mixture is correct → energy is produced smoothly.

WHY DOES AN ENGINE NEED A CARBURETOR?

An engine cannot burn liquid fuel directly.
Fuel must be:

1. Mixed with air
2. In correct ratio
3. Properly atomized (fine droplets)

Correct Air–Fuel Ratio (for petrol engine):
≈ 14.7 : 1 (14.7 parts air to 1 part fuel)

🧠 Remember:
Too much air → Engine STARVES
Too much fuel → Engine CHOKES

MAIN PARTS OF A CARBURETOR

Part	Function
Throttle Valve	Controls amount of air entering engine
Fuel Valve / Needle Valve	Controls fuel flow
Venturi	Narrow passage that increases air velocity
Float Chamber	Maintains constant fuel level

🧠 Visual Trick:
Venturi = “Wind tunnel”
Throttle = “Gate”
Float chamber = “Fuel tank manager”

WORKING PRINCIPLE – HOW TO THINK STEP BY STEP

Step 1: Throttle opens → Air rushes in
Step 2: Air passes through Venturi (narrow region)
Step 3: Air speed increases → Pressure decreases
Step 4: Low pressure sucks fuel from float chamber
Step 5: Air + Fuel mix → Sent to engine
Step 6: Spark plug ignites mixture → Energy produced

This works on Bernoulli’s Principle:
Higher velocity → Lower pressure

🧠 Mental Movie:
Fast air creates vacuum → Fuel gets pulled → Mixture burns → Engine runs.

LEAN vs RICH MIXTURE (CRITICAL THINKING)

Condition	Meaning	Effect
Lean Mixture	More Air, Less Fuel	Overheating, Poor Power
Rich Mixture	More Fuel, Less Air	Black Smoke, High Emissions

Ask yourself:
Is combustion complete?
Is temperature rising?
Is fuel burning efficiently?

🧠 Lean = “Dry Engine” Rich = “Flooded Engine”

WHY CARBURETORS WERE REPLACED?

Modern vehicles use Fuel Injection Systems because:

1. More accurate fuel control
2. Better fuel efficiency
3. Lower emissions
4. Better performance

🧠 Evolution Thought:
Carburetor = Mechanical mixing
Fuel Injection = Electronic precision

EXAM THINKING STRATEGY

When asked about carburetor:

1. Start with definition
2. Explain Venturi principle
3. Describe parts
4. Explain lean & rich mixture
5. Mention replacement by fuel injection

🧠 Final Compression Formula:

CARBURETOR = Air Control + Fuel Control + Pressure Difference + Combustion Support

If you can visualize airflow → You can answer any question.

CARBURETOR IN PETROL ENGINE – HOW TO THINK CLEARLY

Definition: A carburetor is a device that mixes air and petrol (fuel) in the correct ratio before the mixture enters the combustion chamber of a petrol engine.

🧠 Core Mental Image:
Carburetor = Mixing Chamber + Pressure Trick + Flow Control

If mixture is right → Smooth combustion
If mixture is wrong → Engine trouble

WHY PETROL ENGINE NEEDS A CARBURETOR?

Petrol cannot burn efficiently unless:

1. It is mixed with air.
2. It is finely atomized (tiny droplets).
3. It is in proper ratio.

Ideal Air–Fuel Ratio (Petrol Engine):
≈ 14.7 : 1
(14.7 parts air : 1 part petrol)

🧠 Remember:
Too much air → Lean mixture → Engine overheats
Too much fuel → Rich mixture → Black smoke

WORKING PRINCIPLE – THINK LIKE PHYSICS

Carburetor works on Bernoulli’s Principle:
High velocity → Low pressure

Step-by-step Thinking:

1. Air enters carburetor.
2. Air passes through Venturi (narrow section).
3. Velocity increases.
4. Pressure decreases.
5. Low pressure sucks fuel from fuel bowl.
6. Fuel mixes with air.
7. Mixture goes to engine cylinder.
8. Spark plug ignites mixture.

🧠 Visualize this:
Fast air creates vacuum → Fuel gets pulled → Explosion → Power stroke.

MAIN COMPONENTS – THINK FUNCTIONALLY

Component	Purpose
Venturi	Creates pressure drop to suck fuel
Throttle Valve	Controls engine speed (air amount)
Choke	Provides rich mixture during cold start
Idle Speed Screw	Controls idle RPM
Fuel Bowl	Stores fuel at constant level

🧠 Functional Memory Trick:

Venturi → “Suction Creator”
Throttle → “Speed Controller”
Choke → “Cold Start Helper”
Fuel Bowl → “Fuel Reservoir”

CHOKE – SPECIAL THINKING POINT

When engine is cold: Fuel does not vaporize easily. So we need richer mixture.

Choke partially blocks air → Less air enters → Mixture becomes fuel-rich → Engine starts easily.

🧠 Cold Engine = Needs Extra Fuel Choke = Artificially Reduce Air

CARBURETOR vs FUEL INJECTION

Carburetor	Fuel Injection
Mechanical	Electronic Control
Less precise	Highly precise
More emissions	Less emissions
Used in older engines	Used in modern engines

🧠 Evolution Concept: Carburetor = Mechanical mixing Fuel Injection = Computer-controlled spraying

EXAM THINKING STRUCTURE

When writing answer:

1. Start with definition.
2. Mention Venturi principle.
3. Explain components.
4. Explain working step-by-step.
5. Mention lean & rich mixture.
6. Compare with fuel injection.

Final Compression Formula: CARBURETOR = Venturi Effect + Fuel Suction + Air Control + Spark Ignition

🧠 If you can visualize airflow and pressure drop, you can answer any carburetor question confidently.

CARBURETOR IN DIESEL ENGINE – THINK CLEARLY FIRST

Does a diesel engine use a carburetor?

NO. Diesel engines DO NOT use carburetors.

🧠 First Neural Anchor:
Petrol Engine → Spark Plug → Carburetor
Diesel Engine → No Spark Plug → No Carburetor

WHY DIESEL ENGINE DOES NOT NEED A CARBURETOR?

To understand this, think about the combustion difference:

Petrol Engine:

1. Air + Fuel mixed first
2. Then compressed
3. Spark plug ignites mixture

Diesel Engine:

1. Only air is compressed
2. Air becomes extremely hot
3. Fuel injected directly into hot air
4. Fuel ignites automatically

Diesel works on Self-Ignition Principle. No spark plug required.

🧠 Mental Movie:
Diesel engine first squeezes air HARD → Air becomes very hot → Fuel injected → BOOM (self ignition).

WHAT REPLACES THE CARBURETOR IN DIESEL ENGINE?

Diesel engines use a Fuel Injection System.

Carburetor (Petrol)	Fuel Injection (Diesel)
Mixes air & fuel before cylinder	Injects fuel directly into cylinder
Low pressure system	Very high pressure system
Uses spark plug	No spark plug

🧠 Easy Comparison Trick: Carburetor = Premix Diesel Injection = Direct Spray

HOW DIESEL COMBUSTION REALLY WORKS (THINK PHYSICS)

Step 1: Air enters cylinder.
Step 2: Piston compresses air strongly.
Step 3: Compression ratio is very high (≈ 14:1 to 25:1).
Step 4: Air temperature rises sharply.
Step 5: Injector sprays fuel at high pressure.
Step 6: Fuel ignites automatically.

Higher Compression → Higher Temperature → Self Ignition

🧠 Core Formula for Memory:
Diesel = Air Compression + Direct Injection + Self Ignition

WHY FUEL INJECTION IN DIESEL IS COMPLEX?

Diesel injection must control:

1. Exact quantity of fuel
2. Exact injection timing
3. Very high injection pressure
4. Spray pattern (atomization)

Precision control improves:

• Combustion efficiency
• Fuel economy
• Emission control

🧠 Diesel System = High Pressure + High Precision

FINAL THINKING STRUCTURE FOR EXAM

When asked about carburetor in diesel engine:

1. Clearly state diesel engines do NOT use carburetors.
2. Explain reason (self ignition).
3. Describe fuel injection system.
4. Compare with petrol engine.

Final Compression Thought:
Petrol = Mix → Compress → Spark
Diesel = Compress → Inject → Self Ignite

🧠 If you remember the combustion difference, you will never confuse petrol and diesel systems.

COMPONENTS OF A CARBURETOR (PETROL ENGINE)

A Carburetor is the device that prepares the correct air–fuel mixture before it enters the combustion chamber.

🧠 Master Mental Model:
Carburetor = Air Control + Fuel Storage + Suction Effect + Mixture Adjustment If you understand FLOW and PRESSURE, you understand carburetor.

1️⃣ VENTURI – THE HEART OF THE CARBURETOR

Works on Venturi Effect (Bernoulli’s Principle):
Higher velocity → Lower pressure

Think step-by-step:

1. Air enters carburetor.
2. It passes through narrow section (Venturi).
3. Velocity increases.
4. Pressure decreases.
5. Low pressure sucks fuel into air stream.

🧠 Visual Memory: Venturi = “Air Speeds Up → Pressure Drops → Fuel Gets Pulled”

2️⃣ THROTTLE VALVE – THE SPEED CONTROLLER

Also called Butterfly Valve. Controls amount of air entering engine.

When you press accelerator:

1. Throttle opens wider.
2. More air enters.
3. More fuel is drawn.
4. Engine speed increases.

🧠 Think: Throttle = Engine’s “Breathing Control” More air → More power.

3️⃣ CHOKE – COLD START HELPER

Used during cold starting.

Cold engine problem: Fuel does not vaporize easily. Solution:

1. Choke partially blocks air.
2. Less air enters.
3. Mixture becomes fuel-rich.
4. Engine starts easily.

🧠 Cold Engine = Needs Extra Fuel
Choke = Reduce Air to Increase Fuel Ratio

4️⃣ IDLE SPEED ADJUSTMENT SCREW

Controls engine speed when accelerator is not pressed.

Even when throttle is closed:
A small amount of air must enter. Idle screw:

• Allows controlled air bypass.
• Maintains steady idle RPM.

🧠 Idle = Engine’s “Resting Heartbeat”

5️⃣ FUEL BOWL – THE RESERVOIR

Stores fuel at a constant level.

Why important?
If fuel level changes:

• Mixture becomes inconsistent.
• Engine performance fluctuates.

🧠 Fuel Bowl = “Mini Tank Inside Carburetor”
Stable fuel level = Stable mixture.

COMPONENT SUMMARY TABLE

Component	Main Function	Think It As
Venturi	Creates suction	Pressure magician
Throttle	Controls air flow	Breathing controller
Choke	Enriches mixture	Cold start helper
Idle Screw	Maintains idle speed	Heartbeat adjuster
Fuel Bowl	Stores fuel	Mini reservoir

HOW TO STRUCTURE ANSWER IN EXAM

1. Start with definition.
2. Explain Venturi principle first (core physics).
3. Then describe each component.
4. Connect each part to engine performance.

Final Compression Concept:

CARBURETOR = Venturi Effect + Throttle Control + Fuel Storage + Mixture Adjustment

🧠 If you can visualize air speeding up in a narrow tube and pulling fuel with it, you have mastered the carburetor.

CARBURETOR IN DIESEL ENGINE – THINK BEFORE YOU WRITE

Do diesel engines use carburetors?

No. Diesel engines DO NOT use carburetors.

🧠 First Brain Lock: Petrol = Spark + Premixed Fuel
Diesel = Compression + Direct Injection
If there is no spark plug → There is no carburetor.

WHY DIESEL ENGINE DOES NOT NEED A CARBURETOR

Understand the combustion difference:
Petrol Engine:

1. Air and fuel mixed first.
2. Mixture compressed.
3. Spark plug ignites mixture.

Diesel Engine:

1. Only air is compressed.
2. Compression ratio is very high.
3. Air temperature rises sharply.
4. Fuel injected into hot air.
5. Fuel ignites automatically.

Diesel engines work on Compression Ignition principle.

🧠 Visualize This:

Step 1 → Squeeze air HARD
Step 2 → Air becomes very hot
Step 3 → Spray fuel
Step 4 → Self ignition

No spark needed.

FUEL INJECTION SYSTEM (REPLACES CARBURETOR)

Diesel engines use a High-Pressure Fuel Injection System.

Fuel Injection System includes:

1. High-pressure pump
2. Fuel injectors
3. Control mechanism (mechanical/electronic)

Injector sprays fuel as a fine mist
at precise timing
under very high pressure
directly into combustion chamber.

🧠 Key Concept:

Carburetor = Mix before cylinder
Diesel Injection = Spray inside cylinder

NO SPARK PLUG IN DIESEL ENGINE

Diesel engines do NOT use spark plugs.

Why? Because:

• Compression ratio is high.
• Temperature becomes sufficient for ignition.
• Fuel ignites automatically.

🧠 Diesel Equation: High Compression + High Temperature = Self Ignition

WHY DIESEL FUEL INJECTION IS COMPLEX

Injection system must control:

1. Exact quantity of fuel
2. Exact injection timing
3. High injection pressure
4. Proper spray pattern

This improves:

• Fuel efficiency
• Combustion quality
• Emission control

🧠 Diesel = Precision + Pressure + Timing

PETROL vs DIESEL – QUICK COMPARISON

Petrol Engine	Diesel Engine
Uses Carburetor (older engines)	No Carburetor
Uses Spark Plug	No Spark Plug
Low Compression Ratio	High Compression Ratio
Premixed Air-Fuel	Direct Fuel Injection

HOW TO STRUCTURE ANSWER IN EXAM

1. Clearly state diesel engines do not use carburetors.
2. Explain compression ignition principle.
3. Describe fuel injection system.
4. Mention absence of spark plug.
5. Compare briefly with petrol engine.

Final Memory Compression:

Petrol → Mix → Compress → Spark
Diesel → Compress → Inject → Self Ignite

🧠 If you remember the ignition difference, you will never confuse diesel and petrol systems again.

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