What is engine cooling system

In the engine during the process of converting thermal energy into mechanical energy, the high temperatures are produced in the cylinders of the engine as a result of the combustion process. A large portion of the heat from the gases is transferred to the cylinder head and walls, piston and valves. These parts are damaged and the engine will also be damaged unless heat is carried away so the adequate cooling must be required. 

A cooling system must be provided not only to prevent damage to the vital parts of the engine, but the temperature of these components must be maintained within certain limits in order to obtain maximum performance from the engine. Hence, a cooling system is needed to keep the engine from not getting so hot as to cause problems and yet to permit it to run hot enough to ensure maximum efficiency of the engine. 


The function of the cooling system :


The cooling system keeps the engine from getting not too hot but at the same time not to keep it too cool either. 


Characteristics of an efficient cooling system :
  • It should be capable of removing about 30% of the heat generated in the combustion chamber while maintaining the optimum temperature of the engine under all operating conditions of the engine. 
  • It should remove heat at a faster rate when the engine is hot. 
  • During the starting of the engine, the cooling should be minimum so that the working parts of the engine reach their operating temperatures in a short time. 
Types of the cooling system :

For cooling the engine a cooling medium is required. This can be either air or a liquid. 

According to that two types of the cooling system :
  1. Liquid or Indirect cooling system 
  2. Air or Direct cooling system 
In the liquid cooling system, there are five methods to cooled the engine. All five are listed below.
  1. Direct or non-return system 
  2. Thermosyphon system 
  3. Forced circulating cooling system 
  4. Evaporative cooling system 
  5. Pressure cooling system 
In the air cooling system, there are two methods to cooled the engine. These are listed below.
  1. Cooling fins 
  2. Baffles 

Purpose of cooling system in engine

In the engine during the process of converting thermal energy into mechanical energy, the high temperatures are produced in the cylinders of the engine as a result of the combustion process. A large portion of the heat from the gases is transferred to the cylinder head and walls, piston and valves. These parts are damaged and the engine will also be damaged unless heat is carried away so the adequate cooling must be required. 

A cooling system must be provided not only to prevent damage to the vital parts of the engine, but the temperature of these components must be maintained within certain limits in order to obtain maximum performance from the engine. Hence, a cooling system is needed to keep the engine from not getting so hot as to cause problems and yet to permit it to run hot enough to ensure maximum efficiency of the engine. 

The function of the cooling system :

The cooling system keeps the engine from getting not too hot but at the same time not to keep it too cool either. 

What is capacitive discharge ignition system

The capacitor is used to store the ignition energy and the capacitance and the charging voltage of the capacitor determine the amount of stored energy. An induction coil is used to store the ignition energy in the battery ignition system

Construction of the CDI system :

The CDI trigger box includes the capacitor, thyristor power switch, charging device that is used to convert battery voltage to change the voltage of 300 to 500 V by pulse through a voltage transformer and pulse shaping unit and control unit.




Capacitive discharge ignition system


Working of CDI system :

This system works by passing an electrical current over a capacitor. This type of ignition builds up a charge very quickly and starts by generating a charge and storing it up before sending it out to the spark plug in order to ignite the engine. 


The power passes through a capacitor and is transferred to an ignition coil that helps to boost the power by acting as a transformer and allowing the energy to pass through it instead of catching.

This system allows the engine to keep running as long as till charge is available in power source.


Advantages of the CDI system :

  • Insensitive to electrical shunts resulting from spark plug fouling.
  • This system is suited to an application where insufficient dwell time is available because the capacitor can be fully charged in a very short time. 
  • Short transient response.
  • A fast voltage rise and shorter spark duration. 
Disadvantages of the CDI system : 
  • The spark is strong but short in order to 0.1 to 0.3 ms which leads to ignition failure during lean mixture operating conditions because of fast capacitive discharge.
  • This system generates a huge electro-magnetic noise so CDI are rarely used by automobile manufacturers. 

Advantages and disadvantages of capacitive discharge ignition

Capacitor discharge ignition system is an electronic device that stores an electrical charge over a capacitor charge. The capacitor simply charges and discharges within a fraction of time making it possible to create sparks are commonly found on motorbikes and scooters. Let we check some pros and cons of the CDI system in this article. 

Advantages of the CDI system :

  • Insensitive to electrical shunts resulting from spark plug fouling.
  • It is suited to an application where insufficient dwell time is available because the capacitor can be fully charged in a very short time. 
  • Short transient response.
  • A fast voltage rise and shorter spark duration. 

Disadvantages of the CDI system : 

  • The spark is strong but short in order to 0.1 to 0.3 ms which leads to ignition failure during lean mixture operating conditions because of fast capacitive discharge.
  • This system generates a huge electro-magnetic noise so CDI are rarely used by automobile manufacturers. 

Limitation of battery ignition system

In the battery ignition system, the battery is necessary for the ignition so when the battery is discharged it becomes difficult to start the engine. So now let us check it out the information on limitations of battery ignition system to know more about it. 

Limitations of battery ignition system : 

  • The current switching capability of the breaker system: As the engine speed increases the primary voltage decreases.
  • Dwell period becoming shorter: Time available for a build-up of the current in the primary coil and the stored energy decreases as the engine speed increases. 
  • High source impedance: The system is sensitive to side-tracking across the spark plug insulator. 
  • Wear: The breaker points are continuously subjected to electrical as well as mechanical wear so frequent maintenance required. 
  • As a current increases a rapid reduction in breaker point life and system reliability. 
  • Acceptable life for these systems is obtained with a primary current limited to about 4 amperes. 

Battery ignition system | Components | Working | Limitations

Nowadays most of the spark-ignition engines use a battery ignition system. In this system, the energy required for producing a spark is obtained from a 6 or 12 Volt battery. Construction of a battery ignition system depends on the type of ignition energy storage as well as on the ignition performance. 

Components of battery ignition system :


The essential components of a battery ignition system are :
  1. Battery 
  2. Ignition switch 
  3. Ballast resistor 
  4. Ignition coil 
  5. Contact breaker 
  6. Capacitor 
  7. Distributor 
  8. Spark plug 
Now we can check the details of the various components used in battery ignition system :
  • Battery :
The battery provides electrical energy for ignition. It is charged by a dynamo driven by the engine. A battery converts the chemical energy into electrical energy because of electrochemical reactions. The battery must be mechanically strong to withstand the strains. For doing reasonable care and attention two years or more free life to be obtained from the battery. 

There are two types of batteries are used for spark-ignition engines :
  1. The lead-acid battery 
  2. The alkaline battery  
Mainly lead-acid battery are used in light-duty commercial vehicles and alkaline battery are used for heavy-duty commercial vehicles.

  • Ignition switch :
By the use of the ignition switch and ballast, resistor battery is connected to the primary winding of the ignition coil. By using this ignition switch the ignition system can be turned ON or OFF.

  • Ballast resistor :
A ballast resistor is provided in series with the primary winding to regulate the primary current. The function of this is to provide injury to the spark coil by overheating if the engine should be operated for a long time at low speed.

This coil is made of iron wire, and iron has the property that its electrical resistance increases very rapidly if a certain temperature is exceeded. 

  • Ignition coil :
The ignition coil is the source of ignition energy. The coil stores the energy in its magnetic field and delivers it at the appropriate time in the form of an ignition pulse through the high-tension ignition cables to the respective spark plug. 

The ignition coil consists of a magnetic core of soft iron wire or sheet and two insulated conducting coils, called primary and the secondary winding.

  • Contact breaker :
Contact breaker is a mechanical device for making and breaking the primary circuit of the ignition coil. 

  • Capacitor :
The capacitor is two metal plates separated by an insulating material are placed face to face. The insulation is often only air but in most cases, it consists of some high-quality insulating material suitable for the particular technical requirements, material which because of space limitation must be as thin as possible but nevertheless capable of withstanding electrostatic stresses without suffering damage.

  • Distributor :
The function of a distributor is to distribute the ignition pulses to the individual spark plug in the correct sequence and at the correct instants in time. Depending on whether a particular engine has 4, 6 or 8 cylinders, there are 4, 6 or 8 ignition pulses generated for every rotation of the distributor shaft. The use of distributor represents a considerable simplification in a battery ignition system because in most cases we want to use only a single ignition circuit.

There are two types of distributor :
  1. The brush type 
  2. The gap type 
  • Spark plug :
The spark plug provides the two electrodes with a proper gap across which the high potential discharges to generate a spark and ignite the combustible mixture within the combustion chamber. 

The spark plug consists of a steel shell, an insulator and two electrodes. The central electrode to which the high tension supply from the ignition coil is connected is well insulated with porcelain or other ceramic materials. The electrodes are usually made of high nickel alloy to withstand the severe erosion and corrosion to which they are subjected in use. 

There are two types of spark plug used :
  1. Hot spark plug
  2. Cold spark plug 
Working of a battery ignition system :

In the ignition system, the source of the ignition energy is the ignition coil. This coil stores the energy in its magnetic field and delivers it at the instant of ignition in the form of a pulse of high voltage current through the high tension ignition cables to the correct spark plug. 

Working of a battery ignition system

As we explained above in the ignition coil it is consist of two coils of wire. One wire wound around the other and another is insulated from each other. The primary wining with few turns of heavy copper wire and secondary winding with many turns of fine copper wire. 

One end of the primary winding is connected through the ignition switch to the positive terminal post of the storage battery, and another end is grounded through the contact breaker. The capacitor is connected in parallel with the contact breaker. One end of secondary wining is also grounded through the contact breaker and another end is connected through the distributor and the high tension ignition cables to the centre electrode of the spark plug. 

The primary winding of the coil is connected to the positive terminal post of the stored energy when the ignition switch is closed. If the primary circuit is closed through the breaker contacts, a current flows and its called as primary current. It is flowing through the primary coil, which is wound on a soft iron core produces a magnetic field in the core. A cam driven by the engine shaft is arranged to open the breaker points whenever an ignition discharge is required. When the breaker points open, the current flowing through the points now flows into the condenser. As the condenser becomes charged, the primary current falls and the magnetic field collapses. The condenser then discharges into the battery, reversing the direction of both the primary current and the magnetic field. The secondary winding consists of a large number of turns of very fine wire wound with the primary winding. The high secondary voltage is led to the proper spark plug by means of a rotating switch called the distributor, which is located in the secondary or high tension circuit of the ignition system.  

If a condenser were not used in the primary circuit, the high primary voltage caused by the collapse of the magnetic field around the primary winding would cause an arc across the breaker points. Spark timing is controlled by the crank angle at which the breaker points open, while the distributor merely determines the firing sequence of the spark plug. 

Limitations :
  • The current switching capability of the breaker system: As the engine speed increases the primary voltage decreases.
  • Dwell period becoming shorter: Time available for the build-up of the current in the primary coil and the stored energy decreases as the engine speed increases. 
  • High source impedance: The system is sensitive to side-tracking across the spark plug insulator. 
  • The breaker points are continuously subjected to electrical as well as mechanical wear which results in short maintenance intervals. 
  • As a current increases a rapid reduction in breaker point life and system reliability. 
  • Acceptable life for these systems is obtained with a primary current limited to about 4 amperes. 

Working of battery ignition system


In this battery ignition system, the source of the ignition energy is the ignition coil. This coil stores the energy in its magnetic field and delivers it at the instant of ignition in the form of a pulse of high voltage current through the high tension ignition cables to the correct spark plug. 

Working of battery ignition system

As we explained above in the ignition coil it is consist of two coils of wire. One wire wound around the other and another is insulated from each other. The primary wining with few turns of heavy copper wire and secondary winding with many turns of fine copper wire. 

One end of the primary winding is connected through the ignition switch to the positive terminal post of the storage battery, and another end is grounded through the contact breaker. The capacitor is connected in parallel with the contact breaker. One end of secondary wining is also grounded through the contact breaker and another end is connected through the distributor and the high tension ignition cables to the centre electrode of the spark plug. 

The primary winding of the coil is connected to the positive terminal post of the stored energy when the ignition switch is closed. If the primary circuit is closed through the breaker contacts, a current flows and its called as primary current. It is flowing through the primary coil, which is wound on a soft iron core produces a magnetic field in the core. A cam driven by the engine shaft is arranged to open the breaker points whenever an ignition discharge is required. When the breaker points open, the current flowing through the points now flows into the condenser. As the condenser becomes charged, the primary current falls and the magnetic field collapses. The condenser then discharges into the battery, reversing the direction of both the primary current and the magnetic field. The secondary winding consists of a large number of turns of very fine wire wound with the primary winding. The high secondary voltage is led to the proper spark plug by means of a rotating switch called the distributor, which is located in the secondary or high tension circuit of the ignition system.  

If a condenser were not used in the primary circuit, the high primary voltage caused by the collapse of the magnetic field around the primary winding would cause an arc across the breaker points. Spark timing is controlled by the crank angle at which the breaker points open, while the distributor merely determines the firing sequence of the spark plug. 

Common rail fuel injection system


Nowadays in automobile industries the use of common rail fuel injection system increasing in diesel engines as it has the potential to drastically cut emissions and fuel consumption. 

In the diesel engine :

This technology generates an ideal swirl in the combustion chamber. The new CRDi engine cuts the fuel consumption by 30% and doubles torque at low engine speeds and increases power by 25%. 

This system also brings a significant reduction in noise and vibrations of conventional diesel engines. In emission, greenhouse gases are reduced by 30%. At a constant level of NOx, CO ( Carbon Monoxide ) emissions are reduced by 40% and unburnt hydrocarbons are by 50% and also particulate emissions by 60%. 

In petrol engine :

Petrol engine using a carburettors for the supply of fuel-air mixture before the introduction of the MPFI system. Full form of MPFI is a multi-point fuel injection system. But nowadays carburettors are used for its simplicity and low cost. CRDI principle can be applied to this engine also. 

Some features of common rail fuel injection system :
  • The very high injection pressure of the order of 1500 bar.
  • Complete control over start, and end of injection. 
  • Injection pressure is independent of engine speed. 
  • Ability to have a pilot, main and post-injection.
  • Variable injection pressure. 

Electronic diesel injection system

In order to meet the requirement of proper emission and other norms put a large stress on a fuel injection system of a diesel engine. All the parameters related to the injection process like injection timing, rate of injection, the quantity of injected fuel and end of injection. So this control is difficult with conventional mechanical systems. Hence, different types of injection systems with electronic controls have been developed that are following below :

Electronic fuel injection control of the following characteristics :
  • Injection timing
  • Fuel injection quantity
  • Injection rate during various stages of injection
  • Injection pressure during injection 
  • Nozzle opening speed
  • Pilot injection timing and its quantity
By the use of these following parameters are easy to obtain :
  • Very high injection pressure 
  • Sharp start and stop of injection 
  • Cylinder cut off 
  • Diagnostic capability
  • Turbocharger control 
  • Two-stage injection 
By using this electronic diesel injection system the amount of fuel taking part in the premixed of the uncontrolled combustion phase is minimized and this leads to a reduction in noise as well as NOx levels. 

What is MPFI system


The MPFI system can be divided into three types :
  1. Electronic control system 
  2. Fuel system 
  3. Air induction system  
Before you discuss the MPFI system, first of all, you should know the MPFI full form.

What is MPFI electronic control system?

In the MPFI electronic control system the sensors that monitor intake air temperature, oxygen, water temperature, the starter signal and the throttle position send signals to the ECU. The airflow sensor sends signals to the ECU related to the intake air volume. The ignition sensor sends information about engine speed. 


The ECU processes all these signals and sends appropriate commands to the injectors, to control the volume of the fuel for injection. When the cold start injector timing switch off the ECU operates the cold start injector which is a part of the fuel system.


MPFI system

What is a multi-point fuel injection system?

In the MPFI fuel system, the fuel is supplied by the fuel pump. At the time of starting, the cold start injector is operated by the cold start injector time switch. The cold start injector injects fuel into the air intake chamber so that the enriching the air-fuel mixture. The pressure regulator regulates the pressure of the fuel. The injector receives signals from the ECU and injects the fuel into the intake manifold. 

What is MPFI air induction system?

The MPFI air induction system the air cleaner, the air-flow meter, the throttle body and the air valve supply a proper amount of air to the air intake chamber and intake manifold. The quantity of air supplied is just what is necessary for complete combustion. 

Electronically controlled diesel injection system

There are different versions of electronically controlled diesel injection system :
  1. Electronically controlled injection pumps 
  2. Electronically controlled unit injectors 
  3. Common rail fuel injection system 
These systems use the following parameters as inputs:
  1. Engine speed
  2. Crankshaft position 
  3. Intake air temperature 
  4. Accelerator pedal position 
  5. Lubricating oil temperature 
  6. Ambient air temperature 
  7. Turbocharger boost pressure 
  8. Intake air mass flow rate 
The parameters which can significantly affect the performance of the engine :
  • The frequency of injection depends on the engine speed and number of cylinders.
  • The timing of injection has to be advanced as the speed increases. 
  • The accelerator pedal position indicates the load on the engine. 
  • Intake air temperature and pressure indicates atmospheric conditions based on which the injection quantity and timing may have to be altered.
  • The lubricating oil and coolant temperatures indicate the engine condition. 

What is injection timing | How it works?

What is injection timing?

The fuel is injected into the inlet manifold of each cylinder at different timings. The timing at which the injection of the fuel takes place inside the inlet manifold is called the injection timing. 

How injection timing works?

For any number of cylinder engine, the injection has done one by one cylinder. In one cylinder, the piston moves up from BDC to TDC during the exhaust stroke. Just before the piston reaches TDC during this exhaust stroke, injection of the fuel takes place into the inlet manifold of this cylinder at about 600 crank angle before TDC. This injected fuel mixes with the air in the air intake chamber. Thus the air-fuel mixture is obtained. In a suction stroke, the intake valve opens and the fuel-air mixture is sucked into the cylinder. 

According to the firing order, the injection of the fuel takes place inside the inlet manifolds of the other cylinders at various timings. 

The ECU plays the key role in injection timing it calculates the appropriate injection timing for each cylinder. In order to meet the operating condition, the injection valve is kept open for a longer time by ECU. In the case of accelerating condition, the injection valve will be opened for a longer time to supply additional fuel to the engine. 

What is multi point fuel injection system | Function | Types

The function of the MPFI system :

The main function of this system is to supply a proper ratio of gasoline and air to the cylinders. 

These systems function under two basic arrangements. 
  • Port injection 
  • Throttle body injection
Port injection system :

In this arrangement, the injector is placed on the side of the intake manifold near the intake port. The injector sprays gasoline into the air, inside the intake manifold and mixes with the air in a uniform manner. This mixture of gasoline and air then passes through the intake valve and enters into the cylinder.   



Port injection system
Each cylinder is provided with an injector in its intake manifold. For every cylinder, there is one injector. If there are 5 cylinders then there will be 5 injectors.

Throttle body injection system :



Throttle body injection system

With the use of a throttle valve controlling the amount of air entering the intake manifold similar to the carburettor throttle system. 


The injector is placed slightly above the throttle body. The injector sprays gasoline into the air in the intake manifold where the gasoline mixes with the air. This mixture then passes through the valve and enters into the intake manifold. 

Multi-point fuel injection systems are classified into two types :



  1. D-MPFI 
  2. L-MPFI 
D-MPFI system :

It is the manifold fuel injection system, the vacuum in the intake manifold is first senses the volume of air by its density.  


D-MPFI system

The functioning of D-MPFI system : 

As shown in the figure above as air enters into the intake manifold, the manifold pressure sensor detects the intake manifold vacuum and sends the information to the ECU. The speed sensor also sends the information about the RPM of the engine to the ECU. ECU sends commands to the injector to regulate the amount of gasoline supply for injection. When the injector sprays fuel in the intake manifold the gasoline mixes with the air and the air-fuel mixture enters the cylinder. 

L-MPFI system :

The L-MPFI system is a port fuel-injection system. In this type, the fuel metering is regulated by the engine speed and the amount of air that actually enters the engine. This is called air-mass metering or air-flow metering. 


L-MPFI system

The function of L-MPFI system :

As shown in the figure above the air enters into the intake manifold, the airflow sensor measures the amount of air and sends information to the ECU. Likewise, the speed sensor sends information about the speed of the engine to the ECU. ECU received the information and sends appropriate commands to the injector, in order to regulate the amount of gasoline supply for injection. When the injection takes place, the gasoline mixes with the air and the air-fuel mixture enters the cylinder. 

SU carburetor | Construction | Working | Types | Application

SU carburettors, in general, a constant torque type carburettor. Zenith, Solex and carter carburettor are an example of this type.

SU carburettor differs completely from them being constant vacuum or constant depression type with automatic variable chock.


Construction and working of SU carburettor:



SU carburetor

SU carburettor consists of a sliding piston. The lower end of the piston is provided with a taper needle which is inserted into the main jet. When the piston is moved up and down the needle also moved up and down with the main jet. The upper end of the piston is given a flat from which is known as a suction disc. The up and down movement of the piston and the suction disc is guided by means of the piston rod and piston rod guide. 


The piston always remains loaded by a helical spring. The movement of the piston controls the air passage. The portion above the disk is called suction chamber which connects the air passage by means of slot provided in the piston. The Main jet of the carburettor can be moved up and down along the tapered needle by operating a lever from the dashboard. This moment is required to adjust the mixture strength throughout the operating range of the carburettor. The carburettor consists of an ordinary butterfly type throttle valve. The lower portion of this is connected to the atmosphere by means of a rectifier hole and the upper portion to the total throttle air passage. The system doesn't have any separate idling show running and accelerating system. 


Types of SU carburettors:

SU carburettor identification is made by letter prefix which indicates the float types :
H, HD, HS, HIF, HV, OM, KIF with different sizes include 1 to 1/8", 1 to 1/4", 1 to 1/2" 1 to 3/4" 1 to 7/8" and 2". 

SU carburettor applications :

  • SU carburettor was used in Rolls-Royce, Bentley, Rover, Riley, Turner and Aston-Martine, Jaguar, Triumph and also in Volvo. 
  • It also used in aircraft engines. 
  • Nowadays Hitachi also built carburettor based on SU carburettor technique that used in Datsun cars.

Solex carburetor | Working condition

The Solex carburettor is famous for its ease of starting, good performance and reliability. It is one type of down draught carburettor. This carburettor is made in various models and is also used n many automobile engines. This carburettor has also various fuel circuits same as in simple carburettor. 

In Solex carburettor the incorporates device called bi-starter which is unique for this carburettor. This device is very useful for cold starting of the engine. 


Solex carburetor

We can check to work of this carburettor in different conditions : 

All description shows from the above figure. 

  • Normal running :
In normal running, afloat with a tapered needle valve at the top face of the float is fixed in the float chamber. This tapered valve takes care of the level of fluid in float-chamber. The main metering jet supplies fuel and the air comes through the venturi. The fuel from the main jet goes into the well of the air-bleed emulsion system. Air correction jet calibrates the air entering through it and ensures automatically the correct-balance of the air and fuel. The metered emulsion of fuel and air is supplied through the spraying orifice or nozzles. These nozzles are drilled horizontally in the vertical standpipe in the middle of the chock tube or the venturi. 

  • Cold starting and warming : 
In a cold starting condition starter valve is in the form of a flat disc with hoes of different sizes. These holes connect the starter gasoline jet and starter air jet sides to the passage which opens into a hole just below the throttle valve. Smaller or bigger size holes come opposite the passage depending upon the position of the starter lever. The starter level is operated by flexible cable from the dashboard control. After that inducting gasoline from jet and air from jet are shaped that the mixture provided to the carburettor is rich enough for starting. 

  • Idling and slow running :
From the well of the emulsion system, a hole leads to the pilot jet. During idling, the throttle is practically closed and therefore the suction created by the engine on suction stroke gets communicated to the pilot jet. Fuel is inducted from there and mixed with little quantity of air coming from the small pilot air-bleed orifice. This emulsion which is sent down the vertical tube to below the throttle valve, but through the idling volume control screw. The idle running adjustment is done by the idle adjustment screw. The idling speed can be thus varied and set to the desired value. 

  • Acceleration :
Pump supplied extra fuel needed for acceleration through pump injector. Pump lever is connected to the accelerator. When the pedal is pressed by foot the lever moves towards left and presses the pump diaphragm towards left. This force the gasoline through pump jet and injector. On releasing the pressure on the pedal, the lever moves the diaphragm back towards the right so it creates vacuum towards left. The vacuum so created opens the pump inlet valve and gasoline from the float chamber enters the pump. 

Types of carburetor

There are three general types of carburettor depending on the direction of flow of air.
  1. Up draught type 
  2. Down draught type
  3. Cross draught type 
In up draught type, carburettor air enters at the bottom and leaves at the top so that the direction of its flow is upward. 

In down draught type carburettor air and mixture generally, follow a downward course. It is placed at a level higher than the inlet manifold. 

A cross draught type carburettor consists of horizontal mixing tube with a float chamber on one side of it.

Apart from that, some other types of carburettors are :
  1. Constant chock carburettor 
  2. Constant vacuum carburettor
  3. Multiple venturi carburettor
  4. Multijet carburettor 
The air and fuel flow areas are always maintained to be constant in a constant chock carburettor. The pressure difference causes the flow of fuel and air are being varied as per the demand on the engine. 

Example : 
  1. Solex carburettor 
  2. Zenith carburettor 
The air and fuel flow areas are being varied as per the demand on the engine and the vacuum maintained to be always same in a constant vacuum carburettor.

Example :
  1. SU carburettor 
  2. Carter carburettor 
In multiple venturi carburettor used double or triple venturi. These ventures arranged in a series, are used in certain carburettors. There are three venturi namely, the primary venturi, the secondary venturi and the main venturi.  The output of the primary venturi is placed in the throat of the secondary venturi. The outlet of the secondary venturi is situated in the throat of the main venturi. You can check it out the advantages of multiple venturi carburettor. 

In our simple carburettor is called single barrel carburettor. Whereas a dual carburettor has two barrels so-called as a multijet carburettor. Each of these two barrels in a dual carburettor contains a fuel jet, a venturi tube, and idling system and chock and a throttle. 

Example: Passenger cars with six or more cylinders are provided with dual carburettors.

Modern carburetor | Requirement of vehicles

There are some new systems used in the modern carburettor for meeting the requirement of vehicles so now in this article, we will discuss those systems.


  • Anti-dieseling system :
A spark-ignition engine sometimes continues to run for a very small period even after the ignition is switched off. This phenomenon is called dieseling. 

It may take place due to one or more of the following factors below :
  • High engine idling speed
  • Compression ratio increase due to the carbon deposits 
  • Low octane rating
  • Engine overheating
  • Spark plug heat range too high
  • Incorrect adjustment of idle fuel-air mixture
  • Sticking of throttle 
  • Engine tune-up required
  • Oil entry into the cylinder
So as we discuss above modern carburettor use an anti dieseling system to prevent dieseling system. This system has a solenoid valve operated the idling circuit. With ignition key turn on current flow in the solenoid coil of the solenoid while generating force. This force opens the passage for a slow mixture when the ignition key is turn off the magnetic force disappears. The needle valve is brought to original by the action of the spring in the solenoid valve. By this way, the slow mixture passage is cut off and hence the engine stops. This reduces hydrocarbon emissions.

  • Richer coasting system :
This system is incorporated in some modern cars. When the car is travelling at high speed and when the accelerator pedal is suddenly released, the wheel will motor the engine at a high speed. Consequently, the vacuum in the inlet manifold and the combustion chamber increased too much and cause incomplete combustion. This system is designed to overcome this problem by supplying a proper mixture to the intake manifold for stable combustion. 

  • Acceleration pump system :
It is a transient phenomenon. To accelerate the vehicle and consequently its engine, the mixture required is very rich and the richness of the mixture has to be obtained quickly and very rapidly. So when the situation arise of the acceleration this requires an increased output from the engine in a very short time. If the throttle is suddenly opened there is a corresponding increase in the airflow. But because of the inertia of the liquid fuel, the fuel flow doesn't increase in proportion to the increase in airflow. This results in a temporary lean mixture causing the engine to misfire and a temporary reduction in power output. To prevent this condition, all modern carburettor is used in this system in carburetion. 

  • Economizer or Power enrichment system :
At the maximum power range of operation from 80% to 100% load, a rich air-fuel ratio is required. It is about 12 to 14. Is a valve which remains closed at normal cruise operation a gets opened to supply rich mixture at full throttle condition. It regulates the additional fuel supply during the full-throttle operation. so economizer is supplied economy mixture. It also called a power enrichment system. 

Parts of carburetor and function

A carburettor consists of the following main parts :
  • Fuel strainer
  • Float chamber
  • Main fuel metering and idling nozzles 
  • Chock and throttle 
Parts that mentioned above are discussed briefly below : 

  • The fuel strainer :
As the petrol has to pass through a narrow nozzle exit there is every possibility that the nozzle may get clogged prolonged operation of the engine. To prevent this possibility of blockage of the nozzle by dust particles, the petrol is filtered by installing a fuel strainer at the inlet of the float chamber. 

The strainer made of a fine wire mesh or another type of filtering device. The fuel strainer is an either cone-shaped or cylindrical shape. 


  • The float chamber :
The float chamber is to supply the fuel to the nozzle at a constant pressure head. This is possible by maintaining a constant level of fuel in the float bowl. The float in a carburettor is provided to control the level of fuel in the float chamber. In order to provide the correct amount of fuel and to prevent the leakage of fuel from the nozzle fuel level must be maintained slightly below the discharge nozzle outlet holes. 

  • The main fuel metering and idling system :
The main fuel metering system of the carburettor controls the fuel feed for cruising and the full-throttle operations. 

It consists of three principles:
  • The fuel metering orifice through which fuel is drawn from the float chamber.
  • The main discharge nozzle.
  • The passage leading to the idling system. 
The main three functions of the main metering system are :
  • To proportion the air-fuel mixture.
  • To decrease the pressure at the discharge nozzle exit.
  • To limit the airflow at full throttle. 

  • Chock and throttle :
When the vehicle is kept stationary for a long period during cold whether it may be overnight too then starting of the vehicle becomes more difficult. 

For low cranking speeds and intake temperatures, a very rich mixture is required to initiate the combustion. The main reason is that a very large fraction of fuel may remain as liquid suspended in the air even in the cylinder. The most popular method of providing such mixture is by the use of chock valve.

Throttle valve controlled the speed and the output of an engine. The more the throttle is closed the greater is the obstruction to the flow of the mixture placed in the passage and the less is the quantity of mixture delivered to the cylinders. 

As the throttle is opened, the output of the engine increases. But this is not always the case as the load on the engine is also a factor.  


As we discuss the throttle is simply a means to regulate the output of the engine by varying the quantity of charge going into the cylinder.