Basic of Combustion in CI Engines

I.C.ENGINES
ME-501
Unit 3: Combustion in CI Engines
PREPARED BY..
Prof.Sachin Kumar
Nikam
Assistant Professor

1.
• CI Engine introduction
• Combustion in CI Engines
2.
• Various stages of combustion in CI Engines
• Delay period, Diesel knock
3.
• Various types of combustion chambers
4.
• Fuel injection in CI engine(MPFI,
TBI,CRDI
5.
• Types of nozzles
6.
• Theory of carburetion
• Solex Carburetor
CONTENT

CI Engines
A CI engine is an engine in which the fuel charge is ignited by the heat of
compression.
It is also known as Diesel Engine. On September 29, 1913, Rudolf Diesel,
Fuel used :- Diesel

A four-stroke cycle engine is an
internal combustion engine that
utilizes four distinct piston strokes
1.intake,
2.compression,
3.power,
4.Exhaust
to complete one operating cycle.
The piston make two complete
passes in the cylinder to complete
one operating cycle.

Combustion in CI Engines
In CI engine A: F mixture is not homogeneous and fuel remains in liquid particles,
therefore quantity of air supplied is 50% to 70% more than stiochiometric mixture. The
combustion in SI engine starts at one point and generated flame at the point of ignition
propagates through the mixture for burning where as in CI engine, the combustion takes
place at number of points simultaneously and number of flames generated are also many.
To burn the liquid fuel is more difficult as it is to evaporated it is to be elevated to
ignition temperature and then burn.
STAGES OF COMBUSTION IN CI ENGINE
The combustion in CI engine is considered to be taking place in four phases:
• Ignition Delay period/Pre-flame combustion
• Uncontrolled combustion
• Controlled combustion
• After burning After burning

The ignition delay in a diesel engine is defined as the time interval between the start of
injection and the start of combustion.
This delay period consists of
(a) Physical delay, wherein atomization, vaporization and mixing of air fuel occur
Chemical delay attributed to pre-combustion reactions. However, it depends on the
temperature of the surroundings and high temperatures, the chemical reactions are faster
and the physical delay.
Total delay period = Physical delay + Chemical delay
Tt= tp + tc,
In CI engine tp >> tc ,
In SI engine In SI engine tp ≈ 0
Delay period in CI Engine

EFFECT OF VARIOUS FACTORS ON DELAY PERIOD IN CI ENGINE
Many design and operating factors affect the delay period. The important ones are:
1. Compression ratio
2. Engine speed
3. Output
4. Injection timing
5. Quality of the fuel
6. Intake temperature and pressure

Diesel knock
Knocking, in an internal-combustion engine, sharp sounds caused by premature
combustion of part of the compressed air-fuel mixture in the cylinder. In a properly
functioning engine, the charge burns with the flame front progressing smoothly from the
point of ignition across the combustion chamber. However, at high compression ratios,
depending on the composition of the fuel, some of the charge may spontaneously ignite
ahead of the flame front and burn in an uncontrolled manner, producing intense high-
frequency pressure waves. These pressure waves force parts of the engine to vibrate,
which produces an audible knock.
Diesel knock is the clanking, rattling sound emitted from a running Diesel Engine. This
noise is caused by the compression of air in the cylinders and the ignition of the fuel as
it is injected into the cylinder. The detonation and knocking in the engine cylinder can
be detected by the humming or hammer sound from the engine cylinder. The knock can
be heard from the engine cylinder with the continuous metallic sound.

FACTORS AFFECTING DETONATION OR KNOCKING
(i) Compression Ratio:
The compression ratio of the engine is the main factor affecting the detonation or
knocking in the .I.C engine. Since the combustion in the C.I. engine is mainly because
of self-ignition of fuel. The minimum compression ratio is required in the C.I. is 12 for
diesel fuel. The compression ratio is mainly dependent on the clearance volume and
total volume of the engine cylinder. The high compression ratio is desirable in the
engine because the possibility of self-ignition of fuel increases with increase in
compression ratio. But due to mechanical constraint CR is limited to 22.
(ii) Speed of the Engine:
The speed of the engine affects the possibility of detonation or knocking in C.I. engine.
Increase in the speed of the engine reduces the time for transfer heat to cooling system
and gas temperature is higher which reduces the possibility of detonation in C.I. engine.
(iii) Quality of Fuel:
The quality of fuel is a very important factor. If the fuel quality is poor then the
combustion of fuel occurs by delayed self-ignition of fuel which will be responsible for
detonation or knocking in C.I. engine.

METHODS OF CONTROLING DIESEL KNOCK
1. Using a better fuel.
2. Controlling the Rate of Fuel Supply
3. Knock reducing fuel injector
4. By using Ignition accelerators
5. Increasing Swirl
COMPARISON OF KNOCK IN SI AND CI ENGINES

Various types of combustion chambers
COMBUSTION CHAMBER -An enclosed space in which combustion takes place,
especially in an engine or furnace.
CI engine combustion chambers are classified into two categories
Combustion chamber
•Direct-Injection (DI)
•Indirect-Injection (IDI)
Direct-Injection (DI)
This type of combustion chamber is also called an open combustion chamber.
In this type the entire volume of the combustion chamber is located in the main
cylinder and the fuel is injected into this volume.
 Its use is increasing due to their more economical fuel consumption (up to 20%
savings)

FEATURES OF DIRECT INJECTION COMBUSTION CHAMBERS-
For DI engine, ω piston crown recess is most widely used. In this design, the fuel is
injected directly into the cylinder chamber.
Lower combustion surface wall area compared to combustion volume in comparison
with IDI.
More combustion taking place in and on the piston and less contact with coolant.
DI chamber has highest fuel efficiency rating compared to other chamber design.
Smaller engines tend to be of the high-swirl type, while bigger engines tend to be of the
quiescent type.
Classification of direct injection combustion chamber DI combustion chambers can be
classified as
(a) Shallow depth chamber,
(b) Hemispherical chamber,
(c) Cylindrical chamber,
(d) Toroidal chamber

SHALLOW DEPTH CHAMBER :-The
shallow depth combustion chamber has large
diameter cavity in the piston. The depth of the
cavity is moderately small. This chamber is
normally used for large engines running at low
speeds, since the squish is negligible.
HEMISPHERICAL CHAMBER The
hemispherical combustion chamber provides
small squish and swirl. However, in this chamber,
the depth to diameter ratio can be varied to give
any desired squish for engine better performance

CYLINDRICAL CHAMBER :-
Cylindrical combustion chamber is a modified
version of the hemispherical chamber. It has cavity
in the form of a truncated cone with a base angle of
30 degree. The swirl was produced by masking the
valve for nearly 180 degree to the circumference.
Squish can also be varied by varying the depth.
TOROIDAL CHAMBER:-
The toroidal combustion chamber provides a
powerful squish along with the swirl in form of
smoke ring within the chamber. Due to powerful
squish the mask needed on inlet valve is small and
there is better utilization of oxygen. The cone angle
of spray for this type of chamber is 150 to 160
degree.

INDIRECT-INJECTION (IDI) TYPE :-
In this type of combustion chambers, the combustion space is divided into two parts,
one part in the main cylinder and the other part in the cylinder head.
The fuel-injection is effected usually into that part of the chamber located in the
cylinder head.
These chambers are classified further into:-
Pre combustion chamber -in which combustion swirl is induced.
Swirl chamber -in which compression swirl is generated.
Air cell chamber -in which both compression and combustion swirl are induced
THE MAIN ADVANTAGES OF THE INDIRECT-INJECTION COMBUSTION
CHAMBERS ARE:
injection pressure required is low .
direction of spraying is not very important.
These chambers have the following serious drawbacks which have -
Poor cold starting performance requiring heater plugs.
Specific fuel consumption is high because there is a loss of pressure due to air motion
through the duct and heat loss due to large heat transfer area.

PRE-COMBUSTION CHAMBER :-
The combustion space is divided into pre-chamber and a
spherical combustion space. The pre-combustion
chamber is mounted in a heat resisting alloy in the
cylinder head slightly to one side of the single inlet and
exhaust valve seats. During the compression stroke, as
piston approaches TDC, 40% to 50% of compressed air is
forced through the nozzle holes and parallel throat
passage where it is exited into a vigorous and highly
turbulent mass. The fuel is injected through a pintle
nozzle. It has a specially shaped baffle in the centre of the
chamber diffuses the jet of fuel that strikes it and mixes it
thoroughly with the air. The resulting pressure from
burning charge forces burnt and unburnt charge through
the throat into the piston crown. The thrust of combustion
a gases project the directional jet of flame-fronts towards
the cylinder walls and, in doing so, sweeps the burnt
gases and soot to one side while exposing the remaining
fuel vapor to fresh oxygen.

SWIRL CHAMBER SYSTEM :-
The swirl indirect injection combustion chamber
is divided in two chambers. The upper half is a
sphere swirl chamber, cast directly in the
cylinder head, and the lower half is a separate a
twin disc shaped recesses in the piston crown as
shown in Fig.4. The combustion is initiated in
the swirl chamber that has approximately 60% of
the compression volume. As soon as combustion
starts in swirl chamber, the air-fuel mixture is
forced under pressure through the throat into the
cylinder chamber, where it is turbulently mixed
with the remaining compressed air as shown in
Fig:-

AIR-CELL CHAMBER :-
This chamber is divided into the main combustion chamber and energy cell.
The energy cell is divided into two parts, major and minor, which are separated from
each other and from the main chamber by narrow orifices.
The high degree turbulence is created by an energy cell. During the compression stroke,
the piston forces a small amount of compressed air into the energy cell. Near the end of
compression stroke, a pintle nozzle injects the fuel, a small quantity of fuel is directed
into the cell and remaining amount is injected into main combustion chamber. While the
fuel charge is travelling across the centre of the main chamber, the fuel mixes with hot air
and instantaneously burns. The remainder of the fuel enters the energy cell and start to
burn. At this moment cell pressure rises sharply, causing the products of combustion to
flow at high velocity back into main combustion chamber as shown in Fig. This setup a
rapid swirling movement of burning charge in each lobe of main chamber promoting fuel
air mixing within remaining charge to ensure complete combustion as shown in Fig.

Fuel injection in CI engine(MPFI, TBI,CRDI
The fuel injection system lies at the very heart of the diesel engine. By pressurizing
and injecting the fuel, the system forces it into air that has been compressed to high
pressure in the combustion chamber. The diesel fuel injection system consists of:
injection nozzle - injects the fuel into the cylinder

THE GOALS OF FUEL INJECTION :-
Get the correct amount of fuel to the combustion chamber at the right time and to the
right place.
Evaporate the liquid fuel.
Mix the fuel vapor with oxygen to obtain good ignitable mixture .
In case the fuel injection is well achieved by the above criteria, the combustion
process typically yields low fuel consumption, emissions and noice (à no pressure
peaks).
Fuel Injection
System
Solid or Air
less injection
Mechanical
Injection
Electronics
Injection
Air injection
Common Rail
Injection
Individual
Pump
Distributor
System
Fuel Injection System for Diesel Engine

The fuel injection systems are of 2 types:
1. Air Injection System:
In this case fuel is injected under the pressure of air. For supplying high pressure air
multistage air compressors are required, which are very much costly and hence this
system is not in use.
2. Solid Injection System:
In this case diesel fuel is directly injected by fuel pump (Bosch Pump).
Further these are of 3 types of solid injection systems:
A. Individual Pump System :
As shown fuel will flow from the storage tank to filters to low pressure pumps. This
low pressure pump pumps the fuel to 4 separate metering and pressure pumps.
These separate metering and pressure pumps will pump the fuel to individual
injectors which are provided in the cylinder heads. These are used in large slow speed
engines.
B. Distributor System :
Fuel will flow from storage tank to low pressure pump through filters, then to
metering and pressure pumps. This metering and pressure pump pumps the fuels to
distributor unit which distributes and sends required quantity of fuel to each
injectors/each cylinders. Used in small and medium size engines.

C. Common Rail System :
In this case fuel flows from storage tank to low pressure pump through filters. Low
pressure pump, pumps the fuel to high pressure pump, which pumps the fuel to high
pressure pump, which pumps the fuel to common rail. Thus high pressure fuel is
collected in common rail and from here through the metering devices required quantity
of fuel goes to injectors/cylinders. Generally Cummins and multi-cylinder engines use
this system.
Electronic Fuel Injection (EFI) System:
Electronics is introduced in automobiles in 1965. About 30—40% of cost of vehicles
is for electronic items. Max power and best economy are attained by using
electronics and computers in automobiles.
EFI systems was various sensors to sense various parameters like temperature,
pressure of gases, position of throttle valve, air flow rate etc.
Sensors feed this data to Electronic Control Unit (ECU)—which is basically a
computer. This ECU—processes the data and operates injectors and other devices to
have maximum power, with best economy, and low emissions.

MANUFACTURER SPECIFIC NAMES FOR FUEL INJECTORS :
Many manufacturers use different names for their implementation of fuel injection,
below is a quick list of the most common ones.
Mazda Direct Injection Spark Ignition (DISI) :-Which is a direct injection system
as its name implies.
Toyota D4 and D4-S:-The D4 uses the intake port central injection with two
separate fuel injectors and the D4-S is the direct fuel injection implementation of
Toyota.
Mercedes-Benz Charged Gasoline Injection (CGI):-This implementation focuses
mainly on fuel economy using direct fuel injection.
Renault Injection Direct Essence (IDE):-This is also direct fuel injection but
Renault’s design focuses on fuel economy instead of performance.
General Motors Throttle Body injection (TBI):-This is a single-point electronic
fuel injection system.
Mitsubishi Gasoline Direct Injection (GDI):-From its name is fairly obvious,
direct fuel injection.
Ford Smart Charge Injection (SCi):-Which is also direct fuel injection system.
Volkswagen Group Turbocharged Direct Injection (TDI):-Which is the
equivalent implementation for engines equipped with turbochargers

The term MPFI is generally used to specify an engine variant used in the petrol
vehicles. A small computerized system is used to control the engine of the car. A petrol
car will have more than three fuel burning chambers or simply cylinders. The MPFI
engine is abbreviated as the Multi point fuel injection engine. The MPFI engine got this
name because of the reason that each cylinder is having a fuel injector installed near
them. That is why they are called as the Multi point fuel injection engine.
PRINCIPLE BEHIND MPFI:-
At first, the petrol is allowed to mix with air. It is then ignited in a cylinder called as
the combustion chamber. This combustion of the petrol produces a sufficient energy
to run the engine. The Carburetor is being used in the earlier days before the
invention of MPFI engine. It is the duty of the carburetor to mix the fuel and air in a
fixed air-fuel ratio. The fuel thus mixed in the carburetor is then given to the
combustion chamber where this mixture gets ignited. The power thus obtained from the
ignition of gas is used to drive the engine. The main disadvantage of the Carburetor is
that the mixing of fuel and air is not in the proper ratio which leads to the wastage of
fuel and the pollution is high. Since the emission rate is high in carburetor engine, the
MPFI engine is being introduced.
MPFI(Multi- Point Fuel Injection)

Multi Point Fuel Injection (MPFI)

HOW FUEL INJECTION SYSTEM WORKS?
MPFI includes a fuel pressure regulator, fuel injectors, cylinders, pressure spring
and a control diaphragm. It uses multiple individual injectors to insert fuel in each
cylinder through intake port situated upstream of cylinder’s intake value. The fuel
pressure regulator, connected to the fuel rail by means of an inlet and outlet, directs the
flow of the fuel. While the control diaphragm and pressure spring controls the outlet
valve opening and the amount of fuel that can return. The pressure in the intake
manifold significantly changes with the engine speed and load.
fuel injectors

ADVANTAGES OF MULTI POINT FUEL INJECTION SYSTEM?
a) The multi-point fuel injection technology improves fuel efficiency of the vehicles.
MPFI uses individual fuel injector for each cylinder, thus there is no gas wastage
over time. It reduces the fuel consumption and makes the vehicle more efficient
and economical.
b) The vehicles with MPFI automobile technology have lower carbon emissions than
a few decades old vehicles. It reduces the emission of the hazardous chemicals or
smoke, released when fuel is burned. The more precise fuel delivery cleans the
exhaust and produces less toxic byproducts. Therefore, the engine and the air
remain cleaner.
c) MPFI system improves the engine performance. It atomizes the air in small tube
instead additional air intake, and enhances the cylinder-to-cylinder fuel distribution
that aid to the engine performance.
d) It encourages distribution of more uniform air-fuel mixture to each cylinder that
reduces the power difference developed in individual cylinder.
e) The MPFI automobile technology improves the engine response during sudden
acceleration and deceleration.
f) The MPFI engines vibrate less and don’t require to be cranked twice or thrice in
cold weather.
g) It improves functionality and durability of the engine components.
h) The MPFI system encourages effective fuel utilization and distribution. .

TBI FUEL INJECTION is a type of fuel injection system where the fuel
is injected into the throttle body. The throttle body fuel injection system, or TBI as
referred to by GM or CFI by Ford, works using a single or pair of injectors.
TBI (Throttle body fuel injection system)
INJECTTOR

Throttle Body Injection (TBI), one or two injectors mounted in the throttle body
spray fuel into the intake manifold. Fuel pressure is created by an electric fuel pump
(usually mounted in or near the fuel tank), and the pressure is controlled by a
regulator mounted on the throttle body. Fuel is sprayed into the engine when the
engine computer energizes the injector(s), which occurs in a rapid series of short
bursts rather than a continuous stream. This produces a buzzing noise from the
injectors when the engine is running.
TBI Fuel Injection Advantages
It is less expensive than using other types of fuel injection systems.
It is easier to clean, maintain and service because there are fewer parts.
It is cheaper to manufacture than a port injection system and simpler to diagnose. It
also does not have the same level of injector balance problems that a port injection
system might have when the injectors are clogged.
It greatly improves the fuel metering compared to a carburetor.
You do not have to make any changes to the TBI intake manifold. You also do not
have to change the throttle linkage. Instead, use the existing linkage, air cleaners and
carbs to install the system.
It is also capable of logging data and can be programmed for ignition and fuel. The
TBI system is that it learns and understands your habits when driving so it can easily
map out your actions and the performance of the engine.

TBI Fuel Injection Disadvantages:-
It is almost the same as a TBI carburetor wherein the fuel is not equally distributed to
all the cylinders. This means that the air/fuel mixture injected differs for each cylinder.
It can cool the manifold much faster causing the fuel to puddle and condense in the
manifold. The possibility of condensation is much higher since the fuel travels longer
from the throttle body to the combustion chamber.
Since the system needs to be mounted on top of the combustion chamber, you're
prevented from modifying the manifold design to improve your car's performance.
It is a wet system and the mixture of fuel is still based per cylinder.

Common Rail Direct Injection (CRDi)
CRDi stands for Common Rail Direct Injection meaning, direct injection of the fuel
into the cylinders of a diesel engine via a single, common line, called the common rail
which is connected to all the fuel injectors.

Components of Common
Rail Direct Injection System
1. High Pressure Fuel Pump
2. Common Fuel Rail
3. Injectors
4. Engine Control Unit

WORKING PRINCIPLE:
A high-pressure pump supplies pressurized fuel. The pump compresses the fuel at the
pressures of about 1,000 bar or 15,000 psi. It, then, supplies the pressurized fuel via a
high-pressure pipe to the inlet of the fuel rail. From there, the fuel-rail distributes the
fuel to individual injectors which then inject it into the combustion chamber.
The CRDi technology works with the engine ECU which gets inputs from various
sensors install in the engine. Then it calculates the precise quantity of fuel and timing
of injection. The CRDi fuel system have components which are more intelligent in
nature and controls them electrically. In addition to that, the previous generation
injectors are replaced with more advanced injector which are electrically operated,
solenoid injectors. They are opened by ECU signal, depending upon the variables such
as engine acceleration, load, engine temperature etc. A Common Rail direct injection
system uses ‘common for all cylinders’ fuel-rail or in simple words a 'fuel distribution
pipe'. It maintains optimum fuel pressure and also acts as a fuel reservoir for all the
injectors. In CRDi engine, the fuel-rail constantly stores and supplies the fuel to the
solenoid valve injectors at the required pressure. This is quite opposite to the fuel
injection pump supplying diesel thru’ independent fuel lines to injectors in case of
earlier generation design.

ADVANTAGE AND DISADVANTAGE OF CRDi ENGINE :-
ADVANTAGES :-
CRDi engine produced more power and torque.
This engine has ability to increase engine power and torque by 35%.
This technology increase the increase the efficiency of engine.
this technology decrease tail pipe emissions.
It also decrease noise and vibration on engine.
DISADVANTAGES :-
The cost of technology is high.
This technology is not applicable on all type of engine.
the cost of maintenance of CRDi engine is high.
The cost of spare parts is also high.

NOZZLE
A Nozzle is a device designed to control the direction or characteristics of a fluid flow
(especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.
Nozzle is that part of an injector through which the liquid fuel is sprayed into the
combustion chamber. It is used in Diesel engine in which fuel is drawn separately
through injector at end of compression stroke and air is drawn into cylinder in suction
stroke. The nozzle used in IC engine should follow following functions.
It should automizate fuel. This is a very important function since it is the first phase
in obtaining proper mixing of the fuel and air in the combustion chamber.
Distribute the fuel in require area within the combustion chamber.
To prevent fuel from impinging directly on the walls of combustion chamber or
piston. This is necessary because fuel striking the walls decomposes and produces
carbon deposits. This causes smoky exhaust as well as increase in fuel consumption.
To mix the fuel with air in case of non-turbulent type of combustion chamber.

Types of Nozzle in IC Engine:
The design of nozzle must be such that the liquid fuel forced through the nozzle will
broke up into fine droplets, or atomize, as it passes into the combustion chamber.
Various types of nozzles are used in IC engines.
1. The Pintle Nozzle:
2. The Single Hole Nozzle:
3. The Multi Hole Nozzle:
4. Pintaux Nozzle:
Nozzle

The Pintle Nozzle:
In this type of nozzle the stem of nozzle valve is
extended to from a pin or Pintle which protrudes
through the mouth of the nozzle. The size and
shape of the Pintle can be varied according to the
requirement. It provides a spray operating at low
injection pressures of 8-10MPa. The spray cone
angle is generally 60 degree. The main advantage
of this nozzle is that it avoids weak injection and
dribbling. It prevents the carbon deposition on the
nozzle hole.
The Single Hole Nozzle:
In this type of nozzle at the center of the body
there is a single hole which is closed by the
nozzle valve. The size of the hole is usually of the
order of 0.2 mm. Injection pressure is of order of
8-10MPa and spray cone angle is about 15 degree.
One of the major disadvantages of this nozzle is
that they tends to drible. Besides, their spray
angle it too narrow to facilitate good mixing
unless higher velocities are used.

The Multi Hole Nozzle:
This nozzle consists of a number of holes bored in the tip
of the nozzle. The number of holes varies from 4 to 18
and the size from 35 to 200 micro meters. The hole angle
may be from 20 degree upwards. These nozzles operate
at high injection pressure of the order of 18 MPa. Their
advantage lies in the ability to distribute the fuel properly
even with lower air motion available in open combustion
chambers.
Pintaux Nozzle:
This type of nozzle is a type of Pintle nozzle which has
an auxiliary hole drilled in the nozzle body. It injects a
small amount of fuel through this additional hole which is
called pilot injection in upstream direction slightly before
the main injection. The needle valve does not lift fully at
low speeds and most of the fuel is injected through the
auxiliary hole. The main advantage of this nozzle is
better cold starting performance. A major drawback of
this nozzle is that its injection characteristics are poorer
than the multi hole nozzle.

Carburetor
A carburetor is a device that mixes air and fuel for internal combustion engines in the
proper air–fuel ratio for combustion.
The first carburetor was invented by Samuel Moreyin 1826. The first person to patent
a carburetor for use in a petroleum engine was Siegfried Marcus with his 6 July 1872
patent for a device which mixes fuel with air.
A carburetor was among the early patents by Karl Benz (1888) as he developed
internal combustion engines.
The carburetor works on Bernoulli's principle the faster air moves, the lower its static
pressure, and higher the dynamic pressure is.

Types of Carburetor:
There are three types of carburetors according to the direction in which the mixture is
supplied.
Up-draft carburetor:- If the air is supplied from the bottom of the mixing chamber
Horizontal type carburetor:- If the air is supplied from one side of the carburetor
Down-draft type carburetor:- if the air is supplied from the above portion of the
mixing chamber
1. 2.
3.

Solex Carburetor:
Solex is a French manufacturer of carburettors and the powere bicycle VéloSoleX.
Solex carburettor is used in may European automobile industries. Such big industries
as Rolls-Royce, Volkswagen and Mercedes Benz..
Solex carburettors are invented by Marcel Mennesson and Maurice Goudard founder
of Solex company. Solex carburetors widely used by many European makers also used
in passenger cars and commercial vehicles.
Solex Carburetor is a downdraught Carburetor. This is used mostly in the automobile
engines.
This Carburetor has different fuel discharge circuits so that it can deliver different
mixtures for the different operating conditions such as the
Engine Starting,
Engine Idling,
Low-speed Operation,
Normal Operating,
Acceleration.

CONSTRUCTION AND WORKING OFA SOLEX CARBURETOR:-
Solex Carburetor:
The Main metering Jet will discharge the fuel into the venturi throat tube.
The fuel from the main metering jet will go into the air-bleed emulsion system; this
has the lateral holes as shown in the schematic diagram.
Air correction jet calibrates the air entering through it and ensures the air-fuel
balance.
The metered emulsion of fuel and air is supplied through the spraying orifice or
nozzles. These nozzles are drilled horizontally on the vertical pipe in the choke tube as
shown in the schematic diagram.
There is a throttle valve provided at the end of the tube to control the air-fuel
mixture quantity supply into the engine. This valve also knows as the conventional
butterfly valve.
With this circuit, the engine can run at the normal running with this Solex Carburetor.
But for the other operating conditions of the engine, we will use different fuel circuits
for different operating conditions.
Cold starting and warming
The main advantage with the Solex Carburetor is that it has the Bi-Starter also known
as the progressive starter. Initially, the engine needs a richer mixture and the after
starting of the engine, the mixture supposed to be lean. So this progressive starter will
do the job for the engine.

This starter is in the form of a flat disc with the holes of different sizes.
The starter petrol jet and the starter jet (Air) are connected together by the holes present
in the starter disc and open into the passage arranged to below the throttle valve.
There is a starter lever that used to adjust the hole sizes so that the amount of the fuel
and the air will be passed to the engine cylinder in the suction stroke.
When we starting the engine we will close the throttle and provide the air-fuel mixture
from the starting passage which is having a richer mixture from this Bi-Starter setup.
Once the engine started, we have to warm it up by accelerating a couple of times and
then release the throttle valve and pass the lean/normal mixture thru the venturi throat.
Idling and Slow Running of the Engine(Cruising)
Idling of the engine is at where the engine will not deliver any work it only delivers
enough power for its auxiliaries. During this idling or slow running of the engine needs to
have a rich mixture and because of the cylinder pressure is less and then there is a chance
of re sucking of the exhaust gases and cause the poor combustion to make the engine
stumble. So this rich mixture helps in making it happen smooth.
•During the Idling, the throttle valve is closed completely.
•The suction created by the suction stroke is acted on the pilot jet directly.
•The fuel will be inducted from the pilot jet and mixed with the less amount of air sucked
from the pilot air-bleed orifice from the outside atmosphere.

•This rich mixture will be directly sent to the cylinder by a tube directly opened right
below the throttle valve as shown in the schematic diagram.
•There is an idle speed adjustment screw is arranged so that we can set the idle speed of
the engine by controlling the amount of mixture injected.
•For the smooth running adjustment, we will have an additional by-pass adjustment.
Which will make the less rich mixture and the throttle will also open a little bit. so that
engine can run smoothly with the full movement of the air-fuel mixture.
Acceleration of Engine:
For the Engine acceleration, and additional acceleration pump injector equipment is
arranged right side of the floating chamber as you can see from the schematic diagram.
This acceleration pump will supply the additional fuel for the engine with the help of the
Acceleration pump injector directly on top of the venture. The operating of the Carburetor
is the same as the normal running but with the additional fuel drops the engine get excited
when we press the accelerator pedal. When you release the pedal the accelerator pump
will suck the fuel from the float chamber and stores for the next pedal movement.
Advantages of Solex Carburetor:
1. The main advantage of Solex carburetor is easy starting.
2. It is reliable and gives high performance.
3. All circuits above-mentioned circuits work separately.
4. It reduces waste and carbon formation.
5. Throttle response is very high as compared to other carburetors

Basic of Combustion in CI Engines

Basic of Combustion in CI Engines

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