This presentation overviews the most relevant aspects of Internal Combustion Engines (ICE). It starts by describing the ICE operating principle and classifying ICE types according to the combustion method, cylinder configuration, etc.. Then it explains the phases of the combustion cycle (admission, compression, expansion and exhaust) and in 4-stroke and 2-stroke engines. Both indirect and direct injection systems' technologies and trends are overviewed.
This is a presentation from VIZAG Steel, one of the finalists at the 5th CII-GBC National Award for Excellence in Water Management in 2008
The awards are in 2 categories, Within the Fence for work done on minimizing the organisations water footprint, and Beyond the Fence for work done in the community around the industry.
This presentation was in the "Within the Fence" category.
We thank CII and the respective companies for giving us permission to upload these presentations on the India Water Portal website for dissemination to a wider audience.
Experimental investigation on performance of single cylinder four stroke spar...eSAT Journals
Abstract
A decent swirl advances the quick burning and enhances the efficiency for engine which is preferably running at low speeds in order to have low mechanical losses and empowering good combustion efficiency. Subsequently to create high turbulence preceding burning inside the cylinder, swirl prompted by the bay channel inside the cylinder head will be useful. The automobile vehicles still satisfying demands for high performance, requires immense efforts to create new engine ideas and deliver less emission. Swirl is used in SI engine to speed up the combustion process in four stroke engines It increases turbulence and accelerates chemical action by intimating mixing of fuel and oxygen there by weak mixtures can be burnt effectively. In Petrol engine, swirl can increase the rate of fuel-air mixing, reducing the combustion duration for re-entrant chambers at retarded injection timings. Swirl interaction with compression induced squish flow increases turbulence levels in the combustion bowl, promoting mixing. In order to achieve the swirl the piston crown of the conventional petrol engine was suitably modified by forming different shaped grooves on it. This facilitates increased intensity of the swirl for proper mixing of air fuel and to examine their effects on the performance of this engine fuelled with petrol and its blends with ethanol. In the present work Experiment was carried out with unmodified and modified piston with different shapes without much changing compression ratio comparative results shows that better combustion in gasoline engine was obtained with single groove hemispherical piston. Brake thermal efficiency increased by 1.39% and Brake specific fuel consumption reduced by 3% for E10P90 blend compared to unmodified piston
This is a lecture is a series on combustion chemical kinetics for engineers. The course topics are selections from thermodynamics and kinetics especially geared to the interests of engineers involved in combusition
Literature review on need of composite additives for s.i engineIjrdt Journal
One of the major drawbacks of IC engines is low efficiency and pollution resulting from incomplete combustion. In order to improve the emission properties and performance an additive is blended with gasoline. The main objective of this paper was preparation of premium gasoline. The paper do literature study on effect of different additive on engine performance and emission. Through the study of literature survey, effect of different additives has been studied, it is found that different additive had some negative effect when used individually which conclude that there is need for new composite additives having better performance in respect of engine performance and emission control.
A century and nearly two decades later there has been immense progress in the field of IC engines, though many phenomenon taking place are still to be understood physically. This blog aims at comprehension of some of the astonishing research that has been done in this field restricting our interest to combustion with some amusing facts.
Explain the operation of the various carburetor systems
Compare fuel injection to carburetion
Identify the different types of fuel injection
Describe the design and function of electronic fuel injection components
Understand how a computer feedback system works
Explain the operation of the various carburetor systems
Compare fuel injection to carburetion
Identify the different types of fuel injection
Describe the design and function of electronic fuel injection components
Understand how a computer feedback system works
A COMPREHENSIVE REVIEW ON COMBUSTION OF COMPRESSION IGNITION ENGINES USING BI...IAEME Publication
The world today is confronted with a twin crisis of fossil fuel depletion and environmental degradation. Rapid depletion of petroleum derived fuels has forced the researchers to find out
alternative fuels for IC engines. Biodiesel is an alternative fuel for conventional diesel engines and can be used without major modification of the engines
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
1. 1
Normal combustion
Stages of combustion
Importance of flame speed (petrol engine)
Delay period and its importance (diesel engine)
Effects of engine variables
Abnormal combustion : knock, surface ignition
Diesel knock
Fuel requirements
Fuel rating
Anti-knock additives
Combustion in IC Engines
2. 2
In a conventional SI engine, fuel and air are mixed together in the intake system, inducted through the intake valve into the
cylinder where mixing with residual gas takes place, and then compressed during the compression stroke.
Under normal operating conditions, combustion is initiated towards the end of compression stroke at the spark plug by an
electric discharge.
Following inflammation, a turbulent flame develops, propagates through the premixed air-fuel mixture (and burned gas
mixture from the previous cycle) until it reaches combustion chamber walls, then it extinguishes.
Normal combustion in SI engines
IGNITION LIMITS
Ignition of charge is only possible within certain limits of fuel-air ratio. Ignition limits correspond approximately to those mixture ratios, at lean
and rich ends of scale, where heat released by spark is no longer sufficient to initiate combustion in neighbouring unburnt mixture. For
hydrocarbons fuel the stoichiometric fuel air ratio is 1:15 and hence the fuel air ratio must be about 1:30 and 1:7
3. 3
Normal combustion in SI engines
Auto-ignition temperature - Diesel -210°C; petrol or gasoline- 246°C
4. 4
There are three stages of combustion in SI Engine
1. Ignition lag stage
2. Flame propagation stage
3. After burning stage
Ignition lag stage:
There is a certain time interval between instant of spark and instant where there is a noticeable rise in pressure due to combustion. This
time lag is called IGNITION LAG.
Ignition lag is the time interval in the process of chemical reaction during which molecules get heated up to self ignition temperature ,
get ignited and produce a self propagating nucleus of flame.
The ignition lag is generally expressed in terms of crank angle (θ1). The period of ignition lag is shown by path ab.
Stages of combustion in SI engines
Flame propagation stage:
Once the flame is formed at “b”, it should be self sustained and must be able to propagate through the mixture. This is possible
when the rate of heat generation by burning is greater than heat lost by flame to surrounding. After the point “b”, the flame
propagation is abnormally low at the beginning as heat lost is more than heat generated. Therefore pressure rise is also slow as
mass of mixture burned is small. Therefore it is necessary to provide angle of advance 30 to 35 deg, if the peak pressure to be
attained 5-10 deg after TDC. The time required for crank to rotate through an angle θ2 is known as combustion period during
which propagation of flame takes place.
After burning:
Combustion will not stop at point “c” but continue after attaining peak pressure and this combustion is known as after burning.
This generally happens when the rich mixture is supplied to engine.
5. 5
Factors effecting flame speed in SI engines
The factors which affect the flame propagations are
1. Air fuel ratio
2. Compression ratio
3. Load on engine
4. Turbulence and engine speed
5. Other factors
Rate of flame propagation affects the combustion process in SI engines. Higher combustion efficiency and fuel
economy can be achieved by higher flame propagation velocities. Unfortunately flame velocities for most of fuel
range between 10 to 30 m/second.
A : F ratio.
The mixture strength influences the rate of combustion and amount of heat
generated. The maximum flame speed for all hydrocarbon fuels occurs at nearly
10% rich mixture. Flame speed is reduced both for lean and as well as for very
rich mixture. Lean mixture releases less heat resulting lower flame temperature
and lower flame speed. Very rich mixture results incomplete combustion (C CO
instead of C0) and also results in production of less heat and flame speed
remains low. The effects of A: F ratio on p-v diagram and p-θ diagram are shown
below
6. 6
The higher compression ratio increases the pressure and temperature of the mixture and
also decreases the concentration of residual gases. All these factors reduce the ignition lag
and help to speed up the second phase of combustion. Figure above shows the effect of
compression ratio on pressure (indirectly on the speed of combustion) with respect to crank
angle for same A: F ratio and same angle of advance. Higher compression ratio increases the
surface to volume ratio and thereby increases the part of the mixture which after-burns in
the third phase. Engine with high C R have higher flame speeds
2. Compression ratio:
3. Load on Engine.
With increase in load, the cycle pressures increase and the flame speed also increases. In S.I. engine, the power developed by
an engine is controlled by throttling. At lower load and higher throttle, the initial and final pressure of the mixture after
compression decrease and mixture is also diluted by the more residual gases. This reduces the flame propagation and
prolongs the ignition lag. This is the reason, the advance mechanism is also provided with change in load on the engine. This
difficulty can be partly overcome by providing rich mixture at part loads but this definitely increases the chances of
afterburning. The after burning is prolonged with richer mixture. In fact, poor combustion at part loads and necessity of
providing richer mixture are the main disadvantages of S,I. engines which causes wastage of fuel and discharge of large
amount of CO with exhaust gases.
4. Turbulence :
Turbulence plays very important role in combustion of fuel as the flame speed is directly proportional to the turbulence of the
mixture. This is because, the turbulence increases the mixing and heat transfer coefficient or heat transfer rate between the
burned and unburned mixture. The turbulence of the mixture can be increased at the end of compression by suitable design
of the combustion chamber (geometry of cylinder head and piston crown). Insufficient turbulence provides low flame velocity
and incomplete combustion and reduces the power output. But excessive turbulence is also not desirable as it increases the
combustion rapidly and leads to detonation. Excessive turbulence causes to cool the flame generated and flame propagation
is reduced. Moderate turbulence is always desirable as it accelerates the chemical reaction, reduces ignition lag, increases
flame propagation and even allows weak mixture to burn efficiently.
Factors effecting flame speed in SI engines
7. 7
5. Engine Speed
The turbulence of the mixture increases with an increase in engine speed. For this reason the flame speed almost
increases linearly with engine speed. If the engine speed is doubled, flame to traverse the combustion chamber is
halved. Double the original speed and half the original time give the same number of crank degrees for flame
propagation. The crank angle required for the flame propagation , which is main phase of combustion will remain
almost constant at all speeds. This is an important characteristics of all petrol engines.
6 Engine Size
Engines of similar design generally run at the same piston speed. This is achieved by using small engines having
larger RPM and larger engines having smaller RPM. Due to same piston speed, the inlet velocity, degree of
turbulence and flame speed are nearly same in similar engines regardless of the size. However, in small engines the
flame travel is small and in large engines large. Therefore, if the engine size is doubled the time required for
propagation of flame through combustion space is also doubled. But with lower RPM of large engines the time for
flame propagation in terms of crank would be nearly same as in small engines. In other words, the number of crank
degrees required for flame travel will be about the same irrespective of engine size provided the engines are similar.
7. Other Factors.
Among the other factors, the factors which increase the flame speed are supercharging of the engine, spark timing
and residual gases left in the engine at the end of exhaust stroke. The air humidity also affects the flame velocity but
its exact effect is not known. Anyhow, its effect is not large compared with A :F ratio and turbulence.
Factors effecting flame speed in SI engines
8. Start of
injection
End of
injecction
-10 TC-20 10 20 30 8
Combustion in CI Engine
The combustion process proceeds by the following stages:
Ignition delay (ab) - fuel is injected directly into the cylinder towards the end of the compression stroke. The liquid
fuel atomizes into small drops and penetrates into the combustion chamber. The fuel vaporizes and mixes with the
high-temperature high-pressure air.
Premixed combustion phase (bc) – combustion of the fuel which has mixed with the air to within the flammability
limits (air at high-temperature and high pressure) during the ignition delay period occurs rapidly in a few crank
angles.
Mixing controlled combustion phase (cd) – after premixed gas consumed, the burning rate is controlled by the rate at
which mixture becomes available for burning. The rate of burning is controlled in this phase primarily by the fuel-air
mixing process.
Late combustion phase (de) – heat release may proceed at a lower rate well into the expansion stroke (no additional
fuel injected during this phase). Combustion of any unburned liquid fuel and soot is responsible for this.
Four Stages of Combustion in CI Engines
9. 9
Types of CI Engines
Direct injection:
quiescent chamber
Direct injection:
swirl in chamber Indirect injection: turbulent
and swirl pre-chamber
Orifice
-plate
Glow plug
10. 10
compression ratio
engine speed
output
injection timing
quality of the fuel
intake temperature
intake pressure
Factors effecting delay period in CI engines
1.Compression Ratio.
The increase in the compression temperature of the air with increase in compression ratio evaluated at the end of the compression
stroke is shown in Fig. It is also seen from the same figure that the minimum auto ignition temperature of a fuel decreases due to
increased density of the compressed air. This results in a closer contact between the molecules of fuel and oxygen reducing the time
of reaction. The increase in the compression temperature as well as the decrease in the minimum auto ignition temperature
decrease the delay period. The maximum peak pressure during the combustion process is only marginally affected by the
compression ratio (because delay period is shorter with higher compression ratio and hence the pressure rise is lower).
2.Engine Speed:
The delay period could be given either in terms of absolute time (in milliseconds) or in terms of crank angle degrees With increase
in engine speed, the loss of heat during compression decreases, resulting in the rise of both the temperature and pressure of the
compressed air thus reducing the delay period in milliseconds. However, in degrees of crank travel the delay period increases as the
engine operates at a higher rpm. The fuel pump is geared to the engine, and hence the amount of fuel injected during the delay
period depends on crank degrees and not on absolute time. Hence, at high speeds, there will be more fuel present in the cylinder
to take part in the second stage of uncontrolled combustion resulting in high rate of pressure rise.
11. 11
3 Output
With an increase in engine output the air-fuel ratio decreases, operating temperatures increase and hence
delay period decreases. The rate of pressure rise is unaffected but the peak pressure reached may be high.
4. Injection timing:
The effect of injection advance on the pressure variation is shown in Fig. for three injection advance timings
of 9°, 18°, and 30° before TDC. The injected quantity of fuel per cycle is constant. As the pressure and
temperature at the beginning of injection are lower for higher ignition advance, the delay period increases
with increase in injection advance. The optimum angle of injection advance depends on many factors but
generally it is about 20°bTDC.
5. Quality of Fuel used:
The physical and chemical properties of fuel play very important role in delay period. The most important property of fuel which is
responsible for chemical delay is its selfignition temperature. Lower the self-ignition temperature, lower the delay period. The cetane
number (CN) of the fuel is another important parameter which is responsible for the delay period. A fuel of higher cetane number
gives lower delay period and provides smoother engine operation. The delay period for a fuel having CN = 50 is lowest and pressure
rise is also smooth and maximum pressure rise is least as most of the fuel burns during controlled combustion. The other properties
of fuel which affects the physical delay period are volatility, latent heat, viscosity and surface tension. The viscosity and surface
tension are responsible for the better atomization whereas latent heat and viscosity are responsible for the rapid evaporation of fuel.
6. Intake Temperature
The delay period is reduced either with increased temperature. However, preheating of charge for this purpose is not desirable
because it reduces the density of charge and volumetric efficiency and power output.
7. Intake pressure
Increase in intake pressure or supercharging reduces the auto ignition temperature and hence reduces the delay period. The peak
pressure will be higher since the compression pressure will increase with intake pressure.
Factors effecting delay period in CI engines
12. If the temperature of an air-fuel mixture is raised high enough, the mixture will self-ignite without the need of a
spark plug or other external igniter. The temperature above which occurs is called the self-ignition
temperature (SIT).
On the other hand, self-ignition is not desirable in an SI engine, where a spark plug is used to ignite the air-fuel at
the proper time in the cycle.
When self-ignition does occur in an SI engine higher than desirable, pressure pulses are generated. These high
pressure pulses can cause damage to the engine and quite often are in the audible frequency range. This
phenomenon is often called knock or ping.
Abnormal Combustion
Pre-ignition is usually followed by knocking
Loss of performance
When unburned fuel/air mixture beyond the boundary of the flame front is subjected to a combination of heat
and pressure for a certain duration (beyond the delay period of the fuel used), detonation may occur.
knocking is observed in diesel engines and detonation is observed in petrol engines.
14. 14
Knocking
Knock is the autoignition of the portion of fuel, air and residual gas mixture ahead of the advancing flame, that produces a noise.
As the flame propagates across combustion chamber, end gas is compressed causing pressure, temperature and density to increase. Some of
the end gas fuel-air mixture may undergo chemical reactions before normal combustion causing autoignition - end gases then burn very
rapidly releasing energy at a rate 5 to 25 times in comparison to normal combustion. This causes high frequency pressure oscillations inside
the cylinder that produce sharp metallic noise called knock.
Knock will not occur when the flame front consumes the end gas before these reactions have time to cause fuel-air mixture to autoignite.
Knock will occur if the precombustion reactions produce autoignition before the flame front arrives.
Knocking and Surface Ignition
Surface Ignition
Surface ignition is ignition of the fuel-air charge by overheated valves or spark plugs, by glowing combustion chamber deposits or by any
other hot spot in the engine combustion chamber - it is ignition by any source other than the spark plug.
It may occur before the spark plug ignites the charge (preignition) or after normal ignition (postignition).
It may produce a single flame or many flames.
Surface ignition may result in knock.
15. 15
Diesel Knock
Knocking is violet gas vibration and audible sound produced by extreme pressure differentials leading to the
very rapid rise during the early part of uncontrolled second phase of combustion.
In C.I. engines the injection process takes place over a definite interval of time. Consequently, as the first few
droplets injected are passing through the ignition lag period, additional droplets are being injected into the
chamber. If the ignition delay is longer, the actual burning of the first few droplets is delayed and a greater
quantity of fuel droplets gets accumulated in the chamber.
When the actual burning commences, the additional fuel can cause too rapid a rate of pressure rise, as
shown on pressure crank angle diagram below, resulting in Jamming of forces against the piston (as if struck
by a hammer) and rough engine operation.
If the ignition delay is quite long, so much fuel can accumulate that the rate of pressure rise is almost
instantaneous. Such, a situation produces extreme pressure differentials and violent gas vibration known as
knocking (diesel knock), and is evidenced by audible knock.
The phenomenon is similar to that in the SI engine. However, in SI Engine knocking occurs near the end of
combustion whereas in CI engine, knocking the occurs near the beginning of combustion.
Delay period is directly related to Knocking in CI engine. An extensive delay period
can be due to following factors:
A low compression ratio permitting only a marginal self ignition temperature to be reached.
A low combustion pressure due to worn out piston, rings and bad valves
Low cetane number of fuel
Poorly atomized fuel spray preventing early combustion
Coarse droplet formation due to malfunctioning of injector parts like spring
Low intake temperature and pressure of air
17. OCTANE NUMBER
The fuel property that describes how well a fuel will or will not self-ignite is called the octane
number or just octane.
The higher the octane number of a fuel, the less likely it will self-ignite.
Engines with low compression ratios can use fuels with lower octane numbers, but high-
compression engines must use high-octane fuel to avoid self-ignition and knock.
The tendency to detonate depends on composition of fuel.
Fuel differ widely in their ability to resist knock.
It is defined as the percentage of Iso-octane by volume in a mixture of Iso-octane and n-heptane
which exactly matches the knocking tendency of a given fuel, in a standard fuel under given
standard operating conditions.
The rating of a particular SI fuel is done by comparing its antiknock performance with that of
standard reference fuel which is usually combination of Iso-octane and nheptane.
Iso-octane (C8H18) which has a very high resistance to knock and therefore it is arbitrarily
assigned a rating of 100 octane number. N-heptane (C7H16) which is very prone to knock and
therefore given a zero value.
For example: Octane number 80 means that the fuel has same knocking tendency as mixture of
80% iso-octane and 20% n-heptane (by volume basis).
A fuel having an octane number of 110 means fuel has the same tendency to resist as a mixture of
10 cc of Tetra ethyl lead (TEL) in one U.S gallon of Iso-octane.
18. 18
CETANE NUMBER
In a CI engine, self-ignition of the air-fuel mixture is a necessitity.
The correct fuel must be chosen which will self-ignite at the precise proper time in the engine cycle.
The property that quantifies this is called the cetane number.
The larger the cetane number, the shorter is the ID and the quicker the fuel will self-ignite in the combustion
chamber.
The cetane number is a numerical measure of the influence the diesel fuel has in determining the ignition delay.
Higher the cetane rating of the fuel lesser is the propensity for diesel knock.
The cetane number of a diesel fuel is a measure of its ignition quality. The cetane number of a fuel is the
percentage by volume of cetane in a mixture of cetane [C16H34] and a -methylnapthalane [C10H7 CH3] that has
same performance in the standard test engine as that of the fuel.
Cetane is arbitrarily assigned a number 100 and originally a -methylnapthalane was given a number 0 but now
reference fuels is heptamethylnonane (HMN) which is given a value of 15. HMN is used because it is more stable
compound and has slightly better ignition quality.
Cetane number 40 means a mixture containing 40 % cetane and 60 % of heptamethylnonane (HMN) by volume
which gives same ignition delay as tested fuel.
For high sped engine, cetane number of 50 is required, for medium speed engine about 30.
High octane number implies low cetane number . In other words good SI engine fuel is bad CI engine fuel.
19. 19
Anti Knock Agents
The knock resistance tendency of a fuel can be increased by adding anti-knock agents. The anti knock agents are substances which
decreases the rate of preflame reaction by delaying the auto ignition of the end mixture in engine until flame generated by spark
plug. TEL [P (C2H5)4]is most powerful anti knock agents. TEL increase the efficiency of engine and increase the specific output of SI
engine. Its use will not improve the performance of engine which is not knocking unless the spark advanced. CR is increased or
higher inlet pressure is used to take advantage of an increase in octane number. The use of leaded gasoline. However is not perfect
solution to problem. It leads to emission of lead into atmosphere which is known to be very hazardous.
20. 20
Why Turbulence and swirl is created?
Turbulence is necessary to break the flame front into pieces so that each and every
part of combustion chamber gets flame to ignite the homogeneous air fuel mixture.
If there is uneven flame distribution then there is incomplete combustion which
gives less torque and also causes pollution
In case of CI engines fuel is injected in the highly compressed air. There is always
possibility that the portion of air near the injector will get more fuel and thus again
farthest point from injector will get less fuel supply. This again gives rise to unequal
fuel distribution and incomplete combustion.
But for CI engines arrangement is made such that air inside the cylinder is flown
past the injector at last once for proper mixing.
There is difference between turbulence and swirl. Turbulence is random movement
but swirl is orderly movement which is particularly used for CI engines.
How it is created?
Development of CI engine involves various methods to produce swirl.
Some of the common methods used are induction swirl, divided chamber etc.
SI engines have different shapes of piston head which create turbulence.
F head, I head, Ricardo head are examples for that.
21. 21
Swirl & Squish
The intake valve/port is usually placed to give the mixture a pronounced "swirl" (the term is preferable to
"turbulence", which implies movement without overall pattern) above the rising piston, improving mixing and
combustion. The shape of the piston top also affects the amount of swirl. Another design feature to promote
turbulence for good fuel/air mixing is "squish", where the fuel/air mix is "squished" at high pressure by the
rising piston
A piston ring is a split ring that fits into a groove on the outer diameter of
a piston in an internal combustion engine
The three main functions of piston rings in reciprocating engines are :
Sealing the combustion chamber so that there is no transfer of gases
from the combustion chamber to the crank.
Supporting heat transfer from the piston to the cylinder wall.
Regulating engine oil consumption.
The gap in the piston ring compresses to a few thousandths of an inch when inside
the cylinder bore. Piston rings are a major source of hint to identify if the engine is
two stroke or four stroke. Three piston rings suggest that it is a four stroke engine
while two piston rings suggest that it is a two stroke engine.
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Air–fuel equivalence ratio (λ)
Air–fuel equivalence ratio, λ (lambda), is the ratio of actual AFR to stoichiometry for a
given mixture.
λ= 1.0 is at stoichiometry,
rich mixtures λ < 1.0, and
lean mixtures λ > 1.0.
Effect of variables on Knock – Density factors
Density factors that reduce the density of the charge also reduce the knocking tendency
by providing lower energy release.
1. compression ratio: when CR ratio increases , P & T increases and an overall
increase in density of charge raises the knocking tendency
2. Mass of inducted charge: A reduction in mass reduces T & ρ at the time of
ignition. This decreases knocking tendency
3. Inlet temperature of mixture: Increase in inlet temperature of mixture makes
compression temperature higher. Volumetric efficiency is also lowered.
4. Retarding spark timing: It will effect the power output and torque
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Effect of variables on Knock – time factors
Increasing the flame speed or the ignition lag will tend to reduce the tendency to knock..
1. Turbulence: increase of turbulence increases the flame speed and reduces
time to reach auto-ignition. This reduces the knocking
2. Engine size: Flame requires more time to travel In CC of large engines. Hence
large engines will have more tendency to knock
3.Eninee speed : Knocking tendency reduces at higher speeds
4. spark plug locations : Central location minimizes flame travel distance.
Effect of variables on Knock –composition factors
1. Fuel air ratio : flame speeds are affected by air-fuel ratio.
2. Octane value: Paraffin series have he maximum and aromatic series have minimum
tendency to knock