How Does Carburettor works

How Does Carburettor works?

Introduction

The combustion of the fuel with oxygen in the combustion chamber provides the energy necessary to drive the piston. In the S.I engine the liquid are generally mixed prior to their arrival in the combustion chamber. The process of preparing this mixture is called as carburetion.

In the engine, the desired air-fuel ratio means that gives the maximum economy. Actual air-fuel mixture requirements in an operating engine vary under variable load and speed condition. The air-fuel ratio must be changed based on whether the maximum economy or maximum power is required.

A carburettor is a device which is used in the vehicle to prepare a homogeneous mixture of air and fuel for the working of the engine.

The main function of a carburettor are.....

       1. Combine gasoline and air and produce a high combustible mixture.

       2. Regulate the air-fuel ratio

       3. maintain the engine speed.

working

Liquid fuel is supplied to the carburettor from the fuel tank system which consists of the fuel supply tank, fuel pump, lines and filter. Air is drawn into the carburettor from the atmosphere during suction in the engine cylinders. Most of the air engine induct the air directly into the carburettor through an air cleaner. The carburettor supplies air-fuel mixture to the engine cylinders through intake manifold and quantity of mixture entering the cylinder is regulated by the throttle.

Choke
It usually happens, when the vehicle doesn't get started, and word choke is used but what is it actually, 
To start the cold engine, a rich mixture is needed. To provide the rich mixture, choke valve is fitted in the air intake passage of the carburettor. The choke valve is in the form of a circular disc like the throttle valve. This choke is operated to shut off partially the supply of air to the carburettor. During the suction stroke, less amount of air and the more amount of fuel is sucked and a rich mixture is obtained. Immediately after starting the cold engine the choke valve should be open for full air supply.

Venturi

A venturi is a narrow space in the cylindrical air horn, through which the air passes. As the same amount of air must pass through every point in the air horn, its velocity will be greatest at the narrow point. The more the area is reduced, the greater will be the velocity of air.

The spray of gasoline from the nozzle an air entering through the venturi are mixed together in the mixing chamber which is just below the discharge jet. The mixture passes through the intake manifold into the cylinder.

Throttle valve

It is a circular disc located in the mixing chamber of the air horn. It can be tilted to open or close the air horn to allow more or less air to flow through it. When it is tilted to open, more air passes the venturi sucking more fuel, thus more amount of air-fuel mixture goes to the cylinder. The engine develops more power and tends to run faster. When the throttle valve is tilted to close, less air passes the venturi sucking less fuel, thus less amount of air-fuel mixture goes to the cylinders. The engine develops less power and tends to run slowly.

Metering system

As the engine speed increases beyond the certain limit, suction also increases. The flow of the fuel from the jet increases faster than the corresponding flow of air. Thus mixture becomes richer. To maintain the correct air-fuel mixture at high speed.

Advantages

• Improves atomization
• Better fuel distribution
• Smooth idle
• Improves power and reduce emissions
• It allows use of inferior fuels.
• Maintenances cost is less and easy repair.
• Simple and Overall cost is less.

Disadvantages

• More air emissions than the fuel injector
• To start the cold engine is difficult.
• Complete combustion of is a challenge.
• Spark plug fouling issue is very common.

How Turbocharger Works

Introduction

To run an automobile engine, like diesel or petrol, the fuel from the tank must reach the engine cylinder by some means. In the petrol engine, the fuel(petrol) from the fuel tank reaches through the fuel pump, filter and carburettor to the engine.  In the diesel engine, there is no need of carburettor, the diesel is injected into the engine cylinders by an injector.

The power generated by the IC engine is directly related to the compression force exerted on the air-fuel mixture. If the compression is greater, greater the output of the engine. There are two approaches which can be used to increase the engine compression. One is to modify the internal arrangement of the engine to increase the normal compression ratio. The second method is and it is a less expensive way to increase the mixture compression without physically changing the shape of the combustion chamber is to simply increase the quantity of the intake charge.

There are two artificially methods to increase the amount of air flow into the engine are

Turbocharger

Supercharger

Turbocharger

Turbochargers are used to increase engine power by compressing the air that goes into the chamber. Increased power comes from the additional fuel that the denser air accommodate. Nowadays turbochargers are the most popular method of increasing engine compression. The turbochargers do not require a mechanical connection between the engine and the pressurized pump to compress the intake gases. Exhaust gas is a waste product, the energy develop by the engine is said to be free since it theoretically does not rob the engine of any of the power it helps to produce.

Working

It consists of the turbine housing, turbine wheel, compressor housing, compressor wheel and bearing housing. When the engine is running the exhaust gases leaving the exhaust valve to enter into the exhaust manifold and redirect into the turbine housing. In turbine housing, hot gases strike the fins or blade on the turbine wheel and make it rotate. A turboshaft connects turbine wheel to compressor wheel.

turbocharger

The turbocharger is located to close to the exhaust manifold.A fumes pipe keeps running between the motor ventilation system and the turbine lodging to convey the fumes stream to the turbine wheel.  One more pipe is connected to the compressors housing intake to an injector throttle body.

The turbocharger is darted to the ventilation system of the motor. The fumes from the chamber turn the turbine, which works like a gas turbine motor. The turbine is associated with a pole to the blower, which is Located between the air channel and the admission complex. The blower pressurized the air going into the cylinder. The fumes from the chamber goes through the turbine sharp edges, making the turbine turn. The blower is a kind of radiating pump. It attracts the air at the focal point of its cutting edges and excursions it outward as it turns. Almost 40% of the warmth vitality provided to the motor goes into the fumes and will be squandered. A piece of this vitality could be used to drive a gas turbine which thus runs a blower and subsequently results in the supply of more air to the motor. This lifts the motor power and builds warm effectiveness.

Advantages

1. Reduces specific fuel oil consumption.
2. Improves mechanical and thermal efficiency.
3. It uses the unused energy contained in the hot exhaust gases.
4. Increase the air percentage in the air-fuel mixture.
5. No drive required for the engine to run.
6. Very less moving parts.
7. Smaller and lighter than mechanical blowers.
8. Increase the horsepower

Disadvantages

1. It takes much time to spool up and provide the useful boost.
2. Turbocharger gets heated up very quickly, so coolant is required.
3. Power surge, cause some instability of the car.

How Hydraulic Brakes work.

Hydraulic Brakes
Hydraulic brake system transmit the force pedal to each wheel brakes through the pressurized fluid.when the force is applied on the brake it converts the fluid pressure into the useful work to stop or reduce the speed of the vehicle.The brake fluid is in compressible and it exert equal pressure in all the direction.
Hydraulic brakes based on the principle that " when the pressure is exerted on a confined liquid , it transmits pressure without loss, equally in all direction". when the driver applied the brake, it exert a force on the the piston of the master cylinder then this force is transmitted to the wheel. Each wheel is having the piston wheel cylinder arrangement, piston in the wheel cylinder transfer the force to the brake shoe. when the brake is not applied ,50 to 55 kpa is maintained in the steel piping to keep the wheel cylinder piston in the expanded position.

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components of hydraulic cylinder are:-

1. brake pipe 
2. brake shoe
3. master cylinder
4. brake drum
5. brake pedal
6. wheel cylinder 

1.Brake pipe

usually the brake pipes are the steel pipe, when the force is applied on the brake pedal, hydraulic pressure is generated in the master cylinder .This pressure is equally transmitted through pipe to wheel cylinder.

2. Brake shoe

It create the friction in the drum which is necessary to stop and reduce the speed of vehicle.Friction between lining and drum provide the braking effort.

3. Master Cylinder

master cylinder is filled with the fluid, when the force is applied on the pedal it converts the non-hydraulic into the hydraulic pressure.

4.Brake drum

It uses the friction produce by the brake shoe and oppose the movement of the rotating cylinder .

5.Brake pedal

It exert the force which applied by the driver against the brake disc which slow the wheel down.

6. wheel cylinder

it exert the force on to the shoe as to bring them into contact with the drum and stop the vehicle.

Advantages

1. Equal braking action on the wheel.
2. increase braking force.
3. simple in construction.
4. low wear rate of braking linings
5. Does not generate sparks.
6. high horse power to weight ratio.
7. Multiplication of force

How Electronic Ignition System works.

Electronic Ignition System is a advance ignition system, it produces higher voltage than the conventional ignition system.this system generate much stronger sparks which is needed to spark the lean mixture . conventional ignition system produces 10-15 kv to ignite the mixture. But now a days the scenario has been changed,modern high speed engine needed 15-30 kv to ignite the mixture .

In this system the transistor play very important role. A transistor has ability to switch large amount of current without the use of moving parts.The transistor make use of semi conductor and the most common material used for semi conductor is germanium (antimony material added) because its border line acts as good insulator.

Usually PNP transistor is used in the automotive ignition system.If the transistor is consist of 2 section of "P"and one section"N", then it is called PNP transistor.

AutoExpose

The basic parts of  transistor are , Base,Emitter and Collector,denoted by B,E and C respectively.

The electronic ignition system have two circuit, primary circuit and secondary circuit , secondary circuit is same as that of the conventional ignition system. 

Electric source is supplied to the E-B circuit and E-C circuit. The base current is only a fraction of the collector  current, but the collector current can not exist without the base current.if the current flow in the base circuit is interrupted , causes disturbance of large current flow in the collector circuit.

Chevythunder

The collector is connected to primary winding in the ignition coil and the emitter is grounded. when the cam operates,the primary circuit current is disturbed , thereby induces high voltage in the secondary voltage that is used to ignite the lean mixture at the right time in combustion chamber. 

Advantages 

• System can work with or without condenser.
• smooth engine operation.
• More horse power.
• There is no wear on contact set and no points bounce.
• Reduce power loss and fuel consumption.
• Contact points carry small amount of current compare to conventional ignition system.

Disadvantages

• Require regular adjustment to compensate wear.

Also Read How Magneto Ignition System works

                 Ignition System and Battery Ignition System

How Magneto Ignition System works

Ignition system is a group of components which deliver the spark to the spark plug to ignite the air fuel mixture.

Mainly we have three types of ignition system:-

1. Battery Ignition System
2. Magneto Ignition System
3. Electronic Ignition system

2. Magneto Ignition System

Name of the ignition system itself indicate that in this system magnet is used . when magnet is run by the engine it produces current and supplies to the primary winding .system having set of winding namely primary winding and secondary winding.Battery and ignition coil of the battery have been replaced by the compact magneto. low current voltage is converted into high current voltage by disturbing the path of the current which is enough to spark and fire the air fuel mixture.
Components of Magneto Ignition System are- Magneto,breaker points,condenser ,ignition switch, distributor,spark plug

Magneto Ignition system is classified into two types :-

1. Rotating Armature Types

Rotating armature is consist of two coils, one is primary coil,one secondary coil and condenser. primary coil having few hundred winding of wire where as secondary coil having some few thousand turns winding of wire .Contact breaker and condenser is attached to the armature which  rotates between the pole of permanent magnet .

me-mechanicalengineering.com

• when the armature rotates in between the magneto ,magnetic flux in the core reaches zero to maximum.
• As the magnetic flux alternatively increase and decrease, the voltage is induced in the primary coil and secondary coil.
• As we can see in the fig. when the breaker points are closed ,current flow in the primary circuit. breaker points are actuated by the cam which is attached to the rotor of the follower.
• By means of the breaker points ,an increase in the rate of the magnetic flux break down is produced 
• Rapid discharge of the condenser produce an instantaneous break down of the magnetic flux .
• A rapid break down induces very high voltage 10k to 20k volts in the secondary circuit
• This high voltage is distributed by distributor to spark plug according to the firing order of the engine and hence spark plug ignite the mixture in the combustion chamber.
• Engine can be stopped by closing the ignition switch and grounding the primary circuit.

 2.Rotating Magneto Type

working principle of this system same as that of the rotating armature system.Here the magnet itself rotate to produce the require current to produce the spark.

Aircraft systems - Blogger

Also read Ignition System and Battery Ignition System

Need of Lubrication System in Engine and its Function.

Ignition System and Battery Ignition System

When the air fuel mixture introduce to the I.C. engine it expand in the cylinder as the piston move from top dead center(TDC) to bottom dead center(BDC). operation of the I.C engine depend upon the burning and expansion of the air fuel mixture within the cylinder.Ignition system is used to ignite the air fuel mixture for complete combustion of the fuel.Ignition of the must be occur at the right time to produce the maximum energy during the expansion of hot gases in combustion chamber.

Ignition system is a group of  component which delivers the sparks to the sparks plug at the right time to fire the air fuel mixture.

• In 2 stroke engine , spark plug produces spark in cylinder for every revolution of the piston.
• In 4 stroke engine, spark plug produces spark in cylinder for every alternate revolution of the piston.

Ignition system transfer low voltage to high voltage and this voltage is used to proper spark at the right tome.

Now a days Lean mixture are used in the vehicle to reduce the pollution level in the environment.

lean mixture is a mixture of air fuel having the air ratio is more than the fuel.such mixture require higher voltage ignition system to ignite the mixture.

Types of ignition system

1. Point ignition system:- Breaker points are used to interrupt the primary current in circuit.

         E.g- Battery ignition system, magneto ignition system

       2.solid state ignition system: This system is used in any engine which uses electronic device like diode. in this system primary current stopped and restarted.

Battery Ignition System

 Most of the I.C engines uses battery ignition system. in this system a 12 volt battery supplies the electric current to the coil and the ignition coil is an electrical transformer which changes low voltage to high voltage current which produces enough current at the right time to fire the mixture.two coils are used in this system ,primary coil and ignition coil . Ignition coil is consist of two winding , primary winding of  150 to 200 turns and the secondary winding of 10000 to 20,000 turns. This helps to transform the low voltage current to  high voltage current.

Primary circuit completed when the contact points are closed and primary current flow through the primary winding. This current induced the EMF in the secondary coil.when the breaker break yhe path of the current flow and it produces high voltage.Hence the ignition coil store the energy in the form of magnetic field and deliver to spark plug at the right time whenever it is require .

commons.wikimedia.org

Advantages

• There is no moving part.
• Produces better sparks at low speed of the engine.
• Distributor set is simple
• Cost is less

Disadvantage

• If battery exhausted , engine will not start
• when the speed of engine increases , sparking voltages gets decreases.

  

Need of Lubrication System in Engine and its Function.

Lubrication System 

The engine is made of many moving parts and these parts are in continuously moving condition. when the two or more parts meet then there is friction and wearing take place, generation of heat and the loss of power in the engine. Hence the lubrication system is necessary to prevent the engine from these harmful effects.

The system which is used to introduce the lubricant to the engine is called the lubrication system.

lubrication system introduced the oil and other lubricants to give a flow to the clean oil at the desired temperature with an appropriate pressure to the moving parts for the smooth function of the moving parts to avoid the harmful effects.

Mainly these losses take place-

1. Direct frictional losses
2. Pumping losses
3. Losses due to driving components

The function of the Lubrication system

1. Reducing frictional effect 
2. cooling effect 
3. sealing effect
4. cleaning effect

lubrication

1. Reducing frictional effects:

when the two moving parts meet rubbing take place and high amount of heat generated. two rubbing surface always produce friction and this friction leads to wear.friction between two parts directly affect the performance of the engine so it must be reduced as far as possible for the smooth function of the engine. this problem can eliminate the proper distribution of the lubricant on the moving parts.

2.Cooling effect:

When the moving parts move like the piston inside the cylinder, piston comes in touch with the cylinder and rubbing take place, parts get heated up.Hence the lubrication is used to cool the engine parts.

3.Sealing effect

as the term itself define the function, there is some gap is found between the parts then there is the possibility of gas leakage from the engine. The gap between the cylinder, and liner, piston and piston ring etc. Hence the cooling system prevents the leakage.

4. Cleaning effect

when the engine is in moving condition, foreign dust particle gets deposited on the surface of the moving parts which can affect the performance of the engine. proper cooling takes away these unwanted particles from the surface.

Engine position in the vehicles.

Engine is the heaviest component of the vehicle, and its position directly affect how the car drives. Engine can be placed on chassis in the three different position.
 1. Front position engine 
 2. Rear position engine
 3. under floor position engine
  1.Front position engine
In the front position engine , engine is placed at the front of the engine and rear wheel drive are used. but in some of the vehicle drive is given to the front wheel only.The engine placement is remains the same in the heavy vehicle, but the cab is brought forward over the the engine to increase the pay load. The engine position at the front with rear wheel drive system require greater length of the shaft.

Autoxpat

This engine position gives the protection to the driver when the head collision happen as the mass of the engine is greater than the any other parts of the vehicle .
In case of rear wheel drive

• The weight distribution is reasonably balanced between the front wheel and rear wheel which gives good handling support.
• Due to engine and radiator are at front the forward facing radiator take full benefits of the natural air flowing produce by the vehicle movement.

2. Rear position engine
In this position, the engine is mounted to close to the back axle. The propeller shaft require is reduced and usually it is used for small car.This position provides more space to the passenger cabin.
The major portion of the vehicle lies on the rear wheel and it help to in traction  
up the hill. luggage is kept at the front near to the driver which some how balance the vehicle. 

mindovermotor.com

3.under floor position engine
This position of the engine is also called as Mid position engine. in this the engine is in the center, under the chassis .basically this system is used in the public service vehicle like bus and the heavy lorry. it reduce the crankshaft length from the engine to axle. special features of this system that it eliminate the heat and noise from from the vehicle, to fix the engine problem and maintenance is easy.

wallpapers

Internal Combustion Engine Parts and its Function.

Internal combustion engine is a very complex , it is consist of huge number of parts. so it would be bit difficult to explain each part .
Important parts of the internal combustion engine.

http://www.machinedesign.com/motorsdrives/difference-between-car-engines

1.Cylinder

•  They cylinder  is the main body of an engine in which piston reciprocates to develop power. 
• It has to with stand high pressure and temperature around 2900 degree Celsius. 
• Cylinder block in which houses the engine cylinders.
•  Engine material should be good conductor of heat and should resist wear and tear due to reciprocating.
• Material:- Generally cast iron is used                                                  - for heavy duty engine alloy steel are used

2.Cylinder liners

• It is used to reduce the wear and increase the cylinder life.
• If the cylinder is made up of aluminium alloy then the wear of the cylinder is more.
• Whenever  cylinder block is inserted beyond the allotted space then the liner bring it to it's original position.
• Types of liner
1. Dry liner
2. Wet liner
• Material:- alloy iron*

3.Piston

•  Piston is a reciprocating part of the engine and convert the combustion pressure to force on the crankshaft.
• It has enough strength to withstand the high pressure.
• It's construction is rigid to withstand thermal and the mechanical distortion.
• Piston diameter is smaller than the cylinder bore.
• It has the shape of an inverted bucket,the top portion is called crown or head.
• Material:- aluminium alloys

4.Piston rings

• Piston rings are located on the top of the piston, and it is used to maintain the seal between the piston and the cylinder bore.
•  It is made up of grey cast iron or  alloy cast iron because of its good wearing properties even at the high temperature.
• It provide passage of heat flow from the piston head to the cylinder wall.
• It maintain the lubricating oil in the cylinder wall throughout the movement of piston that reduces the wear between the ring and cylinder wall.
• Types of piston ring
1. compression ring
2. oil ring
• Material:-fine grained alloy cast iron

5.piston pin

• It is used to connect the piston and the connecting rod, it is also called as the wrist ring.
• It is in tabular shape to provide adequate strength with minimum weight.
• The center of piston pin usually be 0.02D to 0.04D above the center of the skirt.
• The piston pin is fastened to the connecting rod by means of bolt and uses the piston bosses for bearing
• Material:- low carbon case hardened steel.

6.connecting rod 

• The connecting rod are used to connect the piston to the crankshaft.
• It converts reciprocating motion of the piston into rotary motion of the crankshaft.
• The upper end of the rod oscillates while the lower end is rotates.
• The rod has an I - beam cross section to provide maximum rigidity with minimum weight.
• Material:- malleable cast iron

7.Crank shaft

• It is used to covert the reciprocating motion of the piston into the rotary motion.
• Crankshaft receive the power from the connecting rod and at the same time transfer to the wheels.
• The  crankshaft is held in position by a number of main bearing and they form for the rotation of the crankshaft.
• material:-alloy steel or cast iron

8.valves

• Valve is a device that regulates or control the flow of fluid and gases.
• Each engine cylinder has two valve called inlet valve and exhaust valve.
• Air-fuel mixture is introduced through the inlet valve and the burn gases escape out from the exhaust valve .
• The inlet and exhaust valve are made up of different material as they are subjected to different operation condition.
• Types of valves
1. Poppet valve 
2. Sleeve valve
3. Rotary valve
• Material:- silicon-chrome steel

Classification of Internal Combustion Engine

Two Stroke engine and its function.

Four stroke engine, Difference Between Four Stroke and twoStroke Engine.

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Classification of Internal Combustion Engine

Internal combustion engine is a heat engine which convert the energy of air fuel mixture burning within a combustion chamber into mechanical energy.

https://i.ytimg.com/vi/zKA4TYMgiqU/maxresdefault.jpg

Classification of I.C Engine
1.Based on the fuel used

• Diesel Engine
• petrol Engine(Gasoline Engine)

2.Based on the cycle

• Otto cycle
• Diesel cycle
• Dual cycle

3.Based on strokes

• Two stroke Engine
• Four stroke Engine

4.Based on cylinders

• Single Cylinder Engine
• Multi Cylinder Engine*

5.Based on the type of ignition

• Spark ignition Engine (S.I)
• Compression ignition (C.I)

6.Based on the lubrication system used

• Dry sump
• Wet sump

7.Based on the cooling system

• Air-cooled Engine
• Water cooled Engine

8.Based on the arrangement of valves

• L-head
• I-head
• T-head
• F-head

9.Based on the position of cylinders

• Horizontal Engine
• Vertical Engine
• Radial Engine
• Opposed piston Engine
• Opposed cylinder Engine
• V Engine
• W Engine
• Inline Engine

10.Based on the application

• Automobile Engine
• Aircraft Engine
• Locomotive Engine
• Marine Engine
• Stationary Engine

Two Stroke engine and its function.

Four stroke engine, Difference Between Four Stroke and two Stroke Engine.

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Two Stroke engine and its function.

 A British engineer Introduce a cycle which could be completed in two strokes rather than four strokes.two stroke engine has  one power cycle which is completed when the piston moves up (TDC) and down(BDC). In other words , A two stroke engine is an engine which complete the 4 stroke mechanism in the 2 stroke only. two stroke engine fire on every revolution of the crank shaft because of this two stroke engine is more powerful than a four stroke engine for the equivalent size.

In this engine the end of combustion stroke and the beginning of compression stroke take place at the same time . 

when the piston moves from top to bottom, the air- fuel mixture in the crankcase is compressed and some amount of air-fuel mixture is pushed up the tubes to finally exit into the space above the piston via hole which called as transfer port . piston continues to rise it first cover that port, then compress the mixture and spark ignites it.

The expanding gases from the spark-ignited exploding mixture forced the piston back down and as it drop another hole is exposed in the front of the cylinder, now the exhausted gas comes out to the atmosphere.

http://www.mpoweruk.com/images/two_stroke.gif

The two stroke engine operate on the same principles as as four stroke engine, All these four process complete in the two stroke only .

1. Intake
2. Compression
3. Power
4. Exhaust

Advantage of two stroke engine.

• Simple construction
• Light weight
• No valves mechanism
• Fire once in every revolution
• High Power to weight ratio 
• Torque produce on the crankshaft is uniform
• Can work in any position

Four stroke engine, Difference Between Four Stroke and two Stroke Engine.

What is Brake? Difference Between "Disc" and "Drum" Brakes.

Four stroke engine, Difference Between Four Stroke and two Stroke Engine.

4-STROKE ENGINE
A four stroke engine delivers one power stroke for every two cycle of the piston, it utilize four distinct piston stroke to complete one operating cycle .The piston make two complete passes in the cylinder to complete one operating cycle.
STROKE
The movement of the piston from TDC to  BDC is called stroke 
4 cycles of the engine -

1. Intake
2. Compression
3. Power 
4. Exhaust

https://marinesteer.com/index.php/marine-academy/marine-engineering/4-stroke-engines/

1.Intake(Suction)

Air-fuel mixture is introduced to fill the combustion chamber. Intake take place when the piston moves from TDC(top dead center) to BDC(bottom dead center).

•  Intake valve is open
•  Exhaust valve is closed.

 2.Compression

 When the filled air-fuel mixture is compressed inside the cylinder . the compression chamber is sealed from the charge, and its ready for ignition.Piston move from BDC to TDC

• Intake valve is closed
• Exhaust valve is closed

3.Power
This stroke begin with the expansion of air-fuel mixture ignition with the help of spark plug. It is an engine operating stroke in which hot expending gases force the piston head away from the cylinder, this force is transferred to connecting rod to apply torque on the shaft.

• Intake valve is closed
• Exhaust valve is closed

4.Exhaust

In this stroke , the exhaust stroke is the final stroke and take place when the exhaust valve is open and the intake valve is closed. piston movement evacuated gases to the atmosphere .

• Intake valve is closed
• Exhaust valve is open

Difference between 4-Stroke and 2-Stroke Engine

Sl.no.	4-Stroke engine	2-Stroke engine
1.	One power stroke in every two revolution of crank shaft.	One power stroke in each revolution of crank shaft.
2.	Volumetric efficiency is more due to greater time if induction.	Volumetric efficiency less due to lesser time of friction.
3.	Heavier flywheel due to non-uniform turning movement.	Lighter flywheel due to more uniform turning movement.
4.	Thermal efficiency is high.	Thermal efficiency is less.
5.	Complicated valve mechanism, heavy weight	Valve mechanism and light weight.
6.	Used where high efficiency is important. e.g. automobile, power generation, aeroplane etc.	Used for light weight, low cost and efficiency is not big issue. e.g. scooter, bike..etc.
8.	Lesser cooling and lubricating requirement.	Greater cooling and lubricating requirement.
9	High initial cost.	Low initial cost.
10	More moving part.	Less moving part.

    Disc Vs Drum Brake

What is Brake? Difference Between "Disc" and "Drum" Brakes.

 Brake

 Definition

      Brake is a mechanical device which is used to stop or reduce the speed of a vehicle, wheels,axle..etc.

A brake system is one of the most important parts of a vehicle ,no matter what kind of vehicle people use , an efficient braking system will always be of utmost concern to ensure the safety.

• Brakes uses friction of brake shoes and to convert kinetic energy developed by the vehicle into heat energy.
• When we apply brakes , the pads or shoes that press against the brake drums or rotor convert kinetic energy into thermal energy via friction.

Types Of Brakes

Mechanical Brakes

• Drum brake
• Disc Brake

Hydraulic Brakes

• Power brakes
• Air Brake
• Air hydraulic brake
• Vacuum brake 
• Electric Brake

Difference Between Disc and Drum Brakes

https://autoziast.wordpress.com/2017/06/13/brakes-from-drums-to-discs/

Sl. No	DISC BRAKE	DRUM BRAKE
1.	It has better anti-fade characteristics	The brake effect decrease with constant, prolonged application of brake.
2.	The weight is less, resulting in lower inertia.	Comparatively, the weight of the drum brakes is more.
3.	The total frictional area is less.	Total frictional area is more.
4.	Wear on the frictional surfaces is more uniform.	Non uniform wear of friction surfaces.
5.	It is more stable.	Comparatively Less stable.
6.	Maintenance and services of the brakes is easy.	For service, drum is to be removed which takes more time
7.	Better ventilation property.	Lower ventilation property.
8.	Fast braking and better braking force.	Slow braking.
9.	Generally used for modern bikes, car.	Used for trucks, bus.
10.	Cost is more.	Comparatively, cost is Less