The document discusses combustion in spark-ignition (SI) engines. It defines combustion as a chemical reaction in which fuel combines with oxygen, liberating heat energy. In an SI engine, fuel and air are mixed and inducted into the cylinder where combustion is initiated by a spark at the spark plug near the end of the compression stroke. The combustion process occurs in three stages: ignition lag, flame propagation, and after burning. Abnormal combustion phenomena like pre-ignition and knocking can occur if conditions are not suitable. Factors like turbulence, fuel-air ratio, temperature and pressure, compression ratio, and engine speed and size can affect the flame speed and combustion characteristics in the engine.
Combustion in a SI engine involves three stages:
1. Flame development stage where the spark ignites the fuel-air mixture and a flame nucleus forms.
2. Flame propagation stage where the flame spreads through the combustion chamber. The flame propagation speed affects combustion efficiency.
3. Flame termination stage where combustion continues after peak pressure is reached if a rich fuel mixture is supplied.
This document discusses combustion in internal combustion engines. It begins by defining combustion as the rapid chemical combination of fuel and oxygen that releases energy in the form of heat. It then describes the different types of combustion that can occur, including complete and incomplete combustion. The document focuses on the combustion processes in spark-ignition (SI) engines and compression-ignition (CI) engines. For SI engines, it describes the typical three stages of combustion: ignition lag, flame propagation, and afterburning. For CI engines, it outlines the four phases of combustion: ignition delay period, uncontrolled combustion, controlled combustion, and afterburning. Key factors that influence combustion in each engine type are also summarized.
This document discusses knocking combustion in internal combustion engines. It defines knocking combustion as abnormal combustion in the combustion chamber that leads to a sudden pressure rise and hammering sound, resulting in reduced performance and potential engine damage. It then discusses the causes and effects of knocking in spark ignition (SI) engines and compression ignition (diesel) engines. Some of the key factors that influence knocking include fuel type, compression ratio, ignition timing, and air-fuel ratio. The document also covers related topics like octane rating, cetane rating, and strategies to prevent knocking.
This presentation discusses a multi-mode engine that can switch between 2-stroke and 4-stroke operations. By doubling the combustion frequency during 2-stroke operation, the engine is able to double its power output while maintaining work output per cycle. This allows the engine to achieve full load range and high efficiency while minimizing NOx emissions. The presentation provides background on increasing fuel scarcity and vehicle pollution, and explains how a multi-mode engine addresses power demands while improving efficiency and reducing emissions over traditional gasoline and diesel engines.
The document discusses the Wankel rotary engine, describing its construction with a triangular rotor inside a stationary housing. It explains the four-stroke combustion cycle is accomplished differently than in a piston engine, with the rotor undergoing continuous unidirectional motion rather than stopping between strokes. Key advantages and challenges of the Wankel engine are outlined, including its higher power-to-weight ratio but also issues with sealing and emissions compared to piston engines.
The document discusses combustion in spark-ignition (SI) engines. It defines combustion as a chemical reaction in which fuel combines with oxygen, liberating heat energy. In an SI engine, fuel and air are mixed and inducted into the cylinder where combustion is initiated by a spark at the spark plug near the end of the compression stroke. There are three stages of combustion: ignition lag, flame propagation, and after burning. Abnormal combustion phenomena like pre-ignition and knocking can occur if conditions are not suitable. Factors like turbulence, fuel-air ratio, temperature and pressure, compression ratio, and engine variables affect the flame speed and combustion process.
This document provides an overview of engine emissions and emission standards. It discusses the types of emissions from internal combustion engines, including hydrocarbons, carbon monoxide, and oxides of nitrogen. It also compares Indian Bharat emission standards to European Euro norms, noting differences in testing temperatures and maximum tested speeds. The document outlines the causes of different emissions and how emission standards aim to regulate the amounts of pollutants released.
A stratified charge engine provides a rich air-fuel mixture close to the spark plug to promote ignition, while using a lean mixture for the remainder of the cylinder. This allows for higher compression ratios and leaner mixtures than conventional engines, improving fuel efficiency. The overall air-fuel ratio can reach 40:1 to 50:1. While injectors increase costs, fuel efficiency gains are offsetting this. At high loads efficiency matches conventional engines due to a stoichiometric mixture. High variability can disrupt stratified mixture formation and reduce combustion if the rich area is not near the spark.
Combustion in a SI engine involves three stages:
1. Flame development stage where the spark ignites the fuel-air mixture and a flame nucleus forms.
2. Flame propagation stage where the flame spreads through the combustion chamber. The flame propagation speed affects combustion efficiency.
3. Flame termination stage where combustion continues after peak pressure is reached if a rich fuel mixture is supplied.
This document discusses combustion in internal combustion engines. It begins by defining combustion as the rapid chemical combination of fuel and oxygen that releases energy in the form of heat. It then describes the different types of combustion that can occur, including complete and incomplete combustion. The document focuses on the combustion processes in spark-ignition (SI) engines and compression-ignition (CI) engines. For SI engines, it describes the typical three stages of combustion: ignition lag, flame propagation, and afterburning. For CI engines, it outlines the four phases of combustion: ignition delay period, uncontrolled combustion, controlled combustion, and afterburning. Key factors that influence combustion in each engine type are also summarized.
This document discusses knocking combustion in internal combustion engines. It defines knocking combustion as abnormal combustion in the combustion chamber that leads to a sudden pressure rise and hammering sound, resulting in reduced performance and potential engine damage. It then discusses the causes and effects of knocking in spark ignition (SI) engines and compression ignition (diesel) engines. Some of the key factors that influence knocking include fuel type, compression ratio, ignition timing, and air-fuel ratio. The document also covers related topics like octane rating, cetane rating, and strategies to prevent knocking.
This presentation discusses a multi-mode engine that can switch between 2-stroke and 4-stroke operations. By doubling the combustion frequency during 2-stroke operation, the engine is able to double its power output while maintaining work output per cycle. This allows the engine to achieve full load range and high efficiency while minimizing NOx emissions. The presentation provides background on increasing fuel scarcity and vehicle pollution, and explains how a multi-mode engine addresses power demands while improving efficiency and reducing emissions over traditional gasoline and diesel engines.
The document discusses the Wankel rotary engine, describing its construction with a triangular rotor inside a stationary housing. It explains the four-stroke combustion cycle is accomplished differently than in a piston engine, with the rotor undergoing continuous unidirectional motion rather than stopping between strokes. Key advantages and challenges of the Wankel engine are outlined, including its higher power-to-weight ratio but also issues with sealing and emissions compared to piston engines.
The document discusses combustion in spark-ignition (SI) engines. It defines combustion as a chemical reaction in which fuel combines with oxygen, liberating heat energy. In an SI engine, fuel and air are mixed and inducted into the cylinder where combustion is initiated by a spark at the spark plug near the end of the compression stroke. There are three stages of combustion: ignition lag, flame propagation, and after burning. Abnormal combustion phenomena like pre-ignition and knocking can occur if conditions are not suitable. Factors like turbulence, fuel-air ratio, temperature and pressure, compression ratio, and engine variables affect the flame speed and combustion process.
This document provides an overview of engine emissions and emission standards. It discusses the types of emissions from internal combustion engines, including hydrocarbons, carbon monoxide, and oxides of nitrogen. It also compares Indian Bharat emission standards to European Euro norms, noting differences in testing temperatures and maximum tested speeds. The document outlines the causes of different emissions and how emission standards aim to regulate the amounts of pollutants released.
A stratified charge engine provides a rich air-fuel mixture close to the spark plug to promote ignition, while using a lean mixture for the remainder of the cylinder. This allows for higher compression ratios and leaner mixtures than conventional engines, improving fuel efficiency. The overall air-fuel ratio can reach 40:1 to 50:1. While injectors increase costs, fuel efficiency gains are offsetting this. At high loads efficiency matches conventional engines due to a stoichiometric mixture. High variability can disrupt stratified mixture formation and reduce combustion if the rich area is not near the spark.
The document discusses different types of scavenging processes used to remove burnt gases from an engine cylinder. It describes three main types: cross flow scavenging, back flow or loop scavenging, and uniflow scavenging. It also discusses detonation in IC engines, ignition and fuel injection systems, cooling systems, lubrication systems, and the effects of engine overheating.
The stratified charge engine provides a rich air-fuel mixture near the spark plug for easy ignition using a separate inlet valve. The remainder of the cylinder contains a lean mixture that is ignited by the burning of the rich mixture. This allows the engine to operate with higher compression ratios and leaner mixtures than conventional engines, improving fuel efficiency. Honda introduced the first production stratified charge engine, the CVCC, in 1976, and it used 15-20% less fuel than non-stratified engines of the time.
The document discusses various alternative fuels that can be used for automobiles instead of fossil fuels. It describes fuels such as methanol, ethanol, natural gas, hydrogen, biodiesel, and electricity. For each fuel, it provides details on their production, use in vehicles, and environmental and performance advantages over gasoline and diesel. The conclusion emphasizes that alternative fuels generally have lower emissions and reduce dependence on petroleum. Comparing the different options economically and environmentally is important for determining the best short and long-term alternatives. Overall alternative fuels can help address issues like air, soil, and water pollution as well as global warming.
The document discusses the key stages of combustion in a compression ignition (CI) engine:
1. Ignition delay period where fuel does not ignite immediately upon injection.
2. Uncontrolled combustion period of rapid, steep pressure rise as accumulated fuel burns.
3. Controlled combustion period where further pressure rise is controlled by injection rate.
4. Afterburning period where unburnt fuel particles continue burning with oxygen.
It also examines factors affecting the ignition delay period like compression ratio, injection timing, and fuel quality. Knocking in a CI engine can occur if the ignition delay is too long, causing excess fuel accumulation and an abrupt pressure spike.
The Wankel engine is a type of internal combustion engine that uses a rotary design instead of pistons. It was developed in 1951 by Felix Wankel and uses a four-stroke combustion cycle. The key components are a triangular rotor that rotates inside an oval-shaped housing, with the rotor acting like a piston in a traditional engine. The rotor spins on an eccentric output shaft, turning three times for every one revolution to power the vehicle. Benefits include simplicity, high power-to-weight ratio, and smooth operation, though fuel efficiency is reduced compared to piston engines. It has seen limited automotive use primarily in Mazda vehicles.
Actual cycles for internal combustion engines differ from air-standard cycles in many respects.
Time loss factor.
Heat loss factor.
Exhaust blow down factor.
The combustion process in a compression ignition (CI) engine occurs differently than in a spark ignition engine. In a CI engine, the air-fuel mixture is not homogeneous since the liquid fuel remains in particle form. Combustion takes place simultaneously at many points as the liquid fuel is evaporated, mixed with air, and raised to its ignition temperature. There are four stages of combustion in a CI engine: 1) an ignition delay period as the fuel is injected and begins to chemically react, 2) a premixed burning phase of maximum heat release, 3) a mixing-controlled combustion phase where fuel burns as it is injected, and 4) a tail/afterburning region where remaining unburned fuel continues burning into the
A coal burner is composed of a pulverized coal machine, combustion machines like a combustion chamber and air supply system, and a control system. The coal is pulverized and mixed with air before being ignited. Coal burners are used to provide heat for boilers, furnaces, and kilns in industrial production and daily life. Pulverized coal burners may be located on furnace walls or corners. Coal used in burners should be bituminous with at least 25% volatile matter, 10% or less ash content, and total sulphur of 1% or less.
The document discusses Homogeneous Charge Compression Ignition (HCCI) engines. HCCI engines compress the fuel-air mixture to the point of auto-ignition, requiring no spark plug. This allows for lower emissions and improved fuel efficiency compared to traditional engines. However, auto-ignition is difficult to control precisely. Various methods are used to control the combustion timing, such as variable compression ratios or induction temperatures. HCCI engines also have a smaller adjustable power range than traditional engines. Major automakers are researching HCCI as a promising future technology.
The document discusses abnormal combustion in spark ignition engines. Under normal combustion, the flame travels uniformly across the combustion chamber. Abnormal combustion occurs when combustion deviates from this normal behavior. Two types of abnormal combustion are pre-ignition and knocking. Pre-ignition occurs when the fuel-air mixture ignites before the spark, while knocking is the auto-ignition of unburned fuel late in the combustion cycle. Both pre-ignition and knocking can damage engine components and reduce performance. The causes of abnormal combustion include issues with fuel quality, engine parts, air quality, cooling, vibration, and operating environment.
The document provides an overview of internal combustion engines. It discusses the basic classifications and cycles of internal combustion engines including two-stroke and four-stroke engines. It also covers the workings of spark ignition and compression ignition engines, as well as common engine components and systems such as carburetors and fuel injection systems. Key topics include the Otto, Diesel, and Carnot power cycles; combustion stages; valve timing diagrams; and scavenging, pre-ignition, detonation, lubrication, and emissions control.
The document discusses various sensors used in modern vehicle ignition systems. It describes common sensors like oxygen sensors, coolant temperature sensors, crankshaft position sensors, throttle position sensors, manifold absolute pressure sensors, and knock sensors. It explains how each sensor works and the important role it plays in engine management and emissions control. Modern ignition systems rely on input from multiple sensors to precisely control ignition timing, fuel delivery, and emissions equipment.
An introductory presentation about the concept of HCCI engines and some basic ways to control it.
At last some of commercial cars that would operate with HCCI in the near future.
This presentation was prepared by Mechanical Engineering professor Dr. Shahid Imran during their lecture with final year in their Internal Combustion Engine program offered at University of Engineering and Technology Lahore.
This lecture provided an overview of combustion in boilers including general boiler designs, applications of different boiler configurations, types of fuels used and related combustion systems, burner designs, and emission control methods. Key topics covered included heat balances and transfers, excess air calculations, sizing of combustion chambers, gas, liquid, and solid fuel burning systems, and techniques for reducing emissions like NOx, CO2, and particulate matter.
This document discusses lubricants used in thermal power plants. It begins by introducing the importance of selecting the proper lubricant and understanding lubrication theory. It then discusses the fundamentals of lubrication in reducing friction and wear. Different types of lubricating oils and their characteristics like viscosity and additives are explained. Common additives are outlined that improve performance by interacting with machine metals. Grease composition and characteristics are also covered. The document concludes by examining lubricant specifications for steam turbines and other thermal power plant equipment.
Combustion in an SI engine occurs in three stages:
1. The ignition lag stage is the delay between the spark and noticeable pressure rise from combustion. This allows the fuel-air mixture to heat up to its self-ignition temperature.
2. In the flame propagation stage, the flame front travels across the combustion chamber, releasing energy and increasing pressure.
3. The afterburning stage finishes combusting any remaining unburnt fuel-air mixture after the flame front passes.
This document provides a summary of a presentation on ball and tube mills. It discusses the types of coal and reasons for pulverizing coal. It then describes the construction and operating principles of ball and tube mills, including their slow speed of rotation, steel ball grinding mechanism, and use of impact and attrition to pulverize coal. Maintenance practices for the mills are also summarized such as ball charging schedules and preventative maintenance procedures.
1. Combustion involves the rapid chemical combination of fuel and oxygen, resulting in heat release. It requires a combustible mixture, an ignition source, and flame propagation.
2. In spark ignition (SI) engines, a carburetor supplies an air-fuel mixture and a spark plug ignites it. Combustion in SI engines occurs in three stages: ignition lag, flame propagation, and afterburning.
3. Factors like air-fuel ratio, compression ratio, load, turbulence, and engine speed affect the flame propagation rate in SI engines. Higher propagation speeds improve efficiency and fuel economy.
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.
The document discusses different types of scavenging processes used to remove burnt gases from an engine cylinder. It describes three main types: cross flow scavenging, back flow or loop scavenging, and uniflow scavenging. It also discusses detonation in IC engines, ignition and fuel injection systems, cooling systems, lubrication systems, and the effects of engine overheating.
The stratified charge engine provides a rich air-fuel mixture near the spark plug for easy ignition using a separate inlet valve. The remainder of the cylinder contains a lean mixture that is ignited by the burning of the rich mixture. This allows the engine to operate with higher compression ratios and leaner mixtures than conventional engines, improving fuel efficiency. Honda introduced the first production stratified charge engine, the CVCC, in 1976, and it used 15-20% less fuel than non-stratified engines of the time.
The document discusses various alternative fuels that can be used for automobiles instead of fossil fuels. It describes fuels such as methanol, ethanol, natural gas, hydrogen, biodiesel, and electricity. For each fuel, it provides details on their production, use in vehicles, and environmental and performance advantages over gasoline and diesel. The conclusion emphasizes that alternative fuels generally have lower emissions and reduce dependence on petroleum. Comparing the different options economically and environmentally is important for determining the best short and long-term alternatives. Overall alternative fuels can help address issues like air, soil, and water pollution as well as global warming.
The document discusses the key stages of combustion in a compression ignition (CI) engine:
1. Ignition delay period where fuel does not ignite immediately upon injection.
2. Uncontrolled combustion period of rapid, steep pressure rise as accumulated fuel burns.
3. Controlled combustion period where further pressure rise is controlled by injection rate.
4. Afterburning period where unburnt fuel particles continue burning with oxygen.
It also examines factors affecting the ignition delay period like compression ratio, injection timing, and fuel quality. Knocking in a CI engine can occur if the ignition delay is too long, causing excess fuel accumulation and an abrupt pressure spike.
The Wankel engine is a type of internal combustion engine that uses a rotary design instead of pistons. It was developed in 1951 by Felix Wankel and uses a four-stroke combustion cycle. The key components are a triangular rotor that rotates inside an oval-shaped housing, with the rotor acting like a piston in a traditional engine. The rotor spins on an eccentric output shaft, turning three times for every one revolution to power the vehicle. Benefits include simplicity, high power-to-weight ratio, and smooth operation, though fuel efficiency is reduced compared to piston engines. It has seen limited automotive use primarily in Mazda vehicles.
Actual cycles for internal combustion engines differ from air-standard cycles in many respects.
Time loss factor.
Heat loss factor.
Exhaust blow down factor.
The combustion process in a compression ignition (CI) engine occurs differently than in a spark ignition engine. In a CI engine, the air-fuel mixture is not homogeneous since the liquid fuel remains in particle form. Combustion takes place simultaneously at many points as the liquid fuel is evaporated, mixed with air, and raised to its ignition temperature. There are four stages of combustion in a CI engine: 1) an ignition delay period as the fuel is injected and begins to chemically react, 2) a premixed burning phase of maximum heat release, 3) a mixing-controlled combustion phase where fuel burns as it is injected, and 4) a tail/afterburning region where remaining unburned fuel continues burning into the
A coal burner is composed of a pulverized coal machine, combustion machines like a combustion chamber and air supply system, and a control system. The coal is pulverized and mixed with air before being ignited. Coal burners are used to provide heat for boilers, furnaces, and kilns in industrial production and daily life. Pulverized coal burners may be located on furnace walls or corners. Coal used in burners should be bituminous with at least 25% volatile matter, 10% or less ash content, and total sulphur of 1% or less.
The document discusses Homogeneous Charge Compression Ignition (HCCI) engines. HCCI engines compress the fuel-air mixture to the point of auto-ignition, requiring no spark plug. This allows for lower emissions and improved fuel efficiency compared to traditional engines. However, auto-ignition is difficult to control precisely. Various methods are used to control the combustion timing, such as variable compression ratios or induction temperatures. HCCI engines also have a smaller adjustable power range than traditional engines. Major automakers are researching HCCI as a promising future technology.
The document discusses abnormal combustion in spark ignition engines. Under normal combustion, the flame travels uniformly across the combustion chamber. Abnormal combustion occurs when combustion deviates from this normal behavior. Two types of abnormal combustion are pre-ignition and knocking. Pre-ignition occurs when the fuel-air mixture ignites before the spark, while knocking is the auto-ignition of unburned fuel late in the combustion cycle. Both pre-ignition and knocking can damage engine components and reduce performance. The causes of abnormal combustion include issues with fuel quality, engine parts, air quality, cooling, vibration, and operating environment.
The document provides an overview of internal combustion engines. It discusses the basic classifications and cycles of internal combustion engines including two-stroke and four-stroke engines. It also covers the workings of spark ignition and compression ignition engines, as well as common engine components and systems such as carburetors and fuel injection systems. Key topics include the Otto, Diesel, and Carnot power cycles; combustion stages; valve timing diagrams; and scavenging, pre-ignition, detonation, lubrication, and emissions control.
The document discusses various sensors used in modern vehicle ignition systems. It describes common sensors like oxygen sensors, coolant temperature sensors, crankshaft position sensors, throttle position sensors, manifold absolute pressure sensors, and knock sensors. It explains how each sensor works and the important role it plays in engine management and emissions control. Modern ignition systems rely on input from multiple sensors to precisely control ignition timing, fuel delivery, and emissions equipment.
An introductory presentation about the concept of HCCI engines and some basic ways to control it.
At last some of commercial cars that would operate with HCCI in the near future.
This presentation was prepared by Mechanical Engineering professor Dr. Shahid Imran during their lecture with final year in their Internal Combustion Engine program offered at University of Engineering and Technology Lahore.
This lecture provided an overview of combustion in boilers including general boiler designs, applications of different boiler configurations, types of fuels used and related combustion systems, burner designs, and emission control methods. Key topics covered included heat balances and transfers, excess air calculations, sizing of combustion chambers, gas, liquid, and solid fuel burning systems, and techniques for reducing emissions like NOx, CO2, and particulate matter.
This document discusses lubricants used in thermal power plants. It begins by introducing the importance of selecting the proper lubricant and understanding lubrication theory. It then discusses the fundamentals of lubrication in reducing friction and wear. Different types of lubricating oils and their characteristics like viscosity and additives are explained. Common additives are outlined that improve performance by interacting with machine metals. Grease composition and characteristics are also covered. The document concludes by examining lubricant specifications for steam turbines and other thermal power plant equipment.
Combustion in an SI engine occurs in three stages:
1. The ignition lag stage is the delay between the spark and noticeable pressure rise from combustion. This allows the fuel-air mixture to heat up to its self-ignition temperature.
2. In the flame propagation stage, the flame front travels across the combustion chamber, releasing energy and increasing pressure.
3. The afterburning stage finishes combusting any remaining unburnt fuel-air mixture after the flame front passes.
This document provides a summary of a presentation on ball and tube mills. It discusses the types of coal and reasons for pulverizing coal. It then describes the construction and operating principles of ball and tube mills, including their slow speed of rotation, steel ball grinding mechanism, and use of impact and attrition to pulverize coal. Maintenance practices for the mills are also summarized such as ball charging schedules and preventative maintenance procedures.
1. Combustion involves the rapid chemical combination of fuel and oxygen, resulting in heat release. It requires a combustible mixture, an ignition source, and flame propagation.
2. In spark ignition (SI) engines, a carburetor supplies an air-fuel mixture and a spark plug ignites it. Combustion in SI engines occurs in three stages: ignition lag, flame propagation, and afterburning.
3. Factors like air-fuel ratio, compression ratio, load, turbulence, and engine speed affect the flame propagation rate in SI engines. Higher propagation speeds improve efficiency and fuel economy.
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.
5+ combustion and combustion chamber for si enginesFasilMelese
Combustion in spark ignition engines can occur via homogeneous or heterogeneous mixtures. In a homogeneous mixture, combustion occurs in three stages: an initial delay period, a flame propagation period where pressure rises rapidly, and a final quenching period. Factors that influence the flame speed include turbulence, fuel-air ratio, temperature/pressure, compression ratio, engine output, and engine speed. Abnormal combustion in the form of knock or surface ignition can damage the engine and cause noise. Knock occurs when end gases autoignite, while surface ignition initiates at hot spots. Various engine variables like temperature, compression ratio, and spark timing can affect knocking.
5.2 combustion and combustion chamber for si enginesFasilMelese
The document discusses combustion and combustion chambers in spark ignition engines. It describes the conditions needed for combustion, the different types of fuel-air mixtures, and the stages of combustion in a homogeneous mixture. The three stages of actual engine combustion are the delay period, flame propagation, and wall quenching. Factors that influence flame speed like turbulence, fuel-air ratio, temperature and pressure are also summarized. Abnormal combustion phenomena of knock and surface ignition are described along with causes of end gas combustion and the effects of various engine variables on knocking.
This document discusses combustion in spark ignition (SI) engines. It defines combustion as the rapid chemical combination of a substance with oxygen, involving heat and light production. The key stages of combustion in an SI engine are discussed as ignition lag, flame propagation, and after burning. Factors that affect flame speed like turbulence, fuel-air ratio, temperature and pressure are also covered. Abnormal combustion phenomena like pre-ignition and knocking are described along with their effects. Turbulence is explained as important for preparing the air-fuel mixture and distributing the flame front uniformly in the combustion chamber. Questions asked during the presentation related to using different fuels, increasing pressure ratio, the role of flame speed and turbulence, spark plug positioning, and
The document discusses factors that affect flame speed in internal combustion engines, including turbulence, engine speed, compression ratio, inlet temperature and pressure, and fuel-air ratio. It also covers abnormal combustion such as knocking, factors influencing knocking like density, time, and fuel composition, combustion chamber designs and their effects on flame speed and knocking, and definitions of octane number and types of knocking. The optimal combustion chamber design has a central spark plug location, minimum heat transfer, low octane requirement, and high turbulence for fast, consistent combustion.
The document discusses combustion in internal combustion engines. It covers:
1) The normal combustion process in spark ignition engines including the 3 stages of combustion and factors affecting flame speed.
2) The combustion process in compression ignition engines including the 4 stages and factors affecting the ignition delay period.
3) Abnormal combustion phenomena like knock and types of abnormal combustion in diesel engines.
Abnormal combustion in engines can occur through pre-ignition, detonation, or knocking. Pre-ignition occurs when the fuel-air mixture ignites before the spark plug fires, often due to hot surfaces in the combustion chamber. Detonation involves spontaneous ignition of the end-gas mixture after normal ignition. Knocking produces an audible pinging from shockwaves caused by the end-gas autoigniting too rapidly. Factors that influence knocking include compression ratio, engine speed, and spark timing.
The combustion process in internal combustion engines occurs differently than in the Otto and Diesel cycles. Spark ignition engines typically have premixed flames while compression ignition engines have diffusion flames with some premixed combustion. The fuel-air mixture in both must be close to stoichiometric for reliable ignition and combustion. Combustion involves complex chemical reactions between the fuel and oxidant that produce heat and light. Important characteristics of fuels used in each type of engine include energy density, stability, toxicity, and compatibility with engine components. Combustion in both engines occurs in stages defined by physical and chemical processes.
This document outlines the topics covered in 5 units of a course on advanced internal combustion engines. Unit I covers spark ignition engines, including air-fuel ratio requirements, stages of combustion, factors affecting knock, and fuel injection systems. Unit II discusses compression ignition engines and combustion analysis. Unit III addresses emission formation and control. Unit IV covers alternate fuels for engines. Unit V presents recent trends, including new engine types and technologies.
This document provides an overview of combustion and fuel characteristics in internal combustion engines. It defines key terms related to combustion processes, such as normal combustion, abnormal combustion, spark knock, and surface ignition. It also discusses knocking phenomenon, factors that contribute to knocking, and ways to reduce knocking. Additionally, it covers fuel characteristics like octane rating and gasoline distillation. Pressure-crank angle diagrams and the Ricardo diagram are presented to illustrate combustion processes. The effects of engine speed on ignition timing are described.
Valve Timing & Combustion Phases in Internal Combustion EnginesHassan Raza
Two-stroke and four-stroke engines have different valve timing strategies. Combustion in engines occurs in distinct phases - ignition lag, flame propagation, and after burning in SI engines, and ignition delay, premixed combustion, controlled combustion, and after burning in CI engines. Factors like fuel type, engine speed, load, and air-fuel ratio affect the timing and progression of combustion.
Ci engine combustion by Akhileshwar NiralaAkhilesh Roy
In a compression ignition (CI) engine, fuel is directly injected into the cylinder and spontaneously ignites when mixed with hot, compressed air. Combustion occurs in four stages: ignition delay, premixed combustion, mixing-controlled combustion, and late combustion. There are two main types of CI engines - direct injection engines which inject fuel directly into the chamber, and indirect injection engines which inject fuel into a prechamber before entering the main chamber. Factors like injection timing and quantity, intake conditions, and fuel properties can affect the ignition delay period.
This document discusses hot surface ignition of combustible fuels. It begins with an introduction explaining how fuel leakage onto hot surfaces can cause aviation and industrial fires. It then provides background on key concepts like auto ignition temperature (AIT), thermal ignition, and hot surface ignition temperature (HSIT). The mechanism of ignition involves both boiling modes (nucleate, transition, and film boiling) and ignition modes (hood fires, gutter fires, and airborne fires). Experimental techniques like the ASTM E659 standard and factors affecting HSIT are also reviewed. Overall, the document aims to build understanding of the process and conditions governing hot surface ignition, which occurs at higher temperatures than AIT due to heat and vapor losses.
Combustion and its effects on Engine CyclesHassan Raza
This presentation was prepared by Mechanical Engineers during their final year in their Internal Combustion Engine program offered at University of Engineering and Technology Lahore.
Combustion behaviour in Internal Combustion engines.pptAyisha586983
1. Combustion in a CI engine occurs in four stages: ignition delay, premixed combustion, mixing-controlled combustion, and late combustion.
2. During ignition delay, injected fuel atomizes, vaporizes, and mixes with air. Premixed combustion then occurs rapidly.
3. Mixing-controlled combustion makes up 70-80% of heat release as the burning rate is controlled by fuel-air mixing. Late combustion involves residual fuel burning.
4. Key factors that affect ignition delay include injection timing and pressure, fuel properties like cetane number, and in-cylinder conditions like temperature and pressure. Short ignition delay leads to smoother operation.
The document discusses combustion in compression ignition (CI) engines. It describes the four stages of combustion in CI engines: (1) ignition delay period, (2) uncontrolled combustion, (3) controlled combustion, and (4) after burning. It explains that the ignition delay period allows fuel to accumulate, causing uncontrolled combustion and a steep pressure rise when ignition occurs. Controlled combustion then follows, where combustion is matched to the fuel injection rate.
The document discusses the combustion stages in a compression ignition (CI) engine:
1. Ignition delay stage where fuel does not ignite immediately upon injection.
2. Uncontrolled combustion stage where rapid combustion occurs causing a steep pressure rise.
3. Controlled combustion stage where further pressure rise is controlled by injection rate.
4. Afterburning stage where unburnt fuel particles continue burning in the expansion stroke.
Diesel knock can occur if the ignition delay is long, allowing too much fuel to accumulate and cause an excessively rapid pressure rise when combustion begins. Methods to control knocking include using higher cetane fuel or modifying the combustion chamber design.
This document discusses combustion and fuel characteristics in internal combustion engines. It covers topics such as combustion process terms like normal combustion and abnormal combustion. It also discusses spark knock, surface ignition, ignition delay, combustion requirements, air-fuel ratios, ignition timing, and advance timing. The goal is to understand the combustion process in spark ignition and compression ignition engines as well as the phenomenon of knocking.
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This document provides information about an Environment & Ecology course at the National Institute of Technology Raipur in India. It includes the course objectives, contents, and assessment pattern. The course objectives are to develop awareness of environmental issues, impacts of technology, and environmentally-benign solutions. The course content covers fundamentals of the environment and ecology, natural resources, pollution and control measures, and monitoring techniques. Students are assessed through mid-semester and end-semester exams, as well as a teacher assessment and lab work. The document emphasizes understanding human impacts and developing sustainable solutions to environmental challenges.
The document discusses paint composition and the painting system used for Indian Railways coaches. It notes that paint is composed of pigments, additives, binders, and solvents. The painting system for LHB coaches uses an epoxy-polyester-polyurethane system for its durability and resistance to corrosion. The painting procedure involves surface preparation, primer application, putty application and rub-down on joints, and a final polyurethane primer application.
The document discusses paint composition and the painting system used for Indian Railways coaches. It notes that paint is composed of pigments, additives, binders, and solvents. The painting system for LHB coaches uses an epoxy-polyester-polyurethane system for its durability and resistance to corrosion. The painting procedure involves surface preparation, primer application, putty application and rub-down on joints, and a final polyurethane primer application.
This document discusses air brake systems used on trains. It begins with an introduction and then describes the working principle and components of a single pipe air brake system, including the compressor, main reservoir, brake pipe, angle cocks, brake cylinder, auxiliary reservoir, and brake blocks. It explains the functions of each component and how they work together. The document also briefly describes twin pipe air brake systems and notes some advantages of air brakes like their ability to operate anywhere and effectively stop trains even with leaks. It concludes that air brakes are preferred for heavy vehicles due to their maximum effectiveness.
CNC machines allow for complex geometries to be machined repeatably and accurately through computerized control of cutting tools. They have advantages over manual machining like easier programming, avoiding human errors, and producing complex and simple geometries with equal ease. CNC machines move tools or workpieces along linear axes, with typical machines having X, Y, and Z axes. Programming involves specifying coordinates, cutting parameters, and coded instructions to direct the machine's motions.
CNC machining allows for the economical production of complex geometries with repeatable accuracy. It provides advantages over manual machining like easier programming, storage of programs, avoidance of human errors, and safer operation. A CNC machine typically has three linear axes (X, Y, Z) and can add additional rotary axes. Programming involves using G and M codes to specify functions like tool movements, feed rates, spindle speeds, and coolant control. Proper programming considers factors like interpolation types, tool compensations, and machine features.
The document discusses various aspects of emissions and emission control in internal combustion engines. It covers the formation of CO, hydrocarbons, NOx and particulates in both diesel and gasoline engines. It also discusses various emission control techniques like catalytic converters, exhaust gas recirculation and particulate traps that are used to control engine-out emissions and help meet emission regulations. The highest level of control is achieved through precise fuel injection and ignition timing along with feedback from oxygen sensors in closed-loop three-way catalytic converter systems.
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The document discusses India's present and future power scenario. It provides the following key details:
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3) Future generation is projected to reach 600 GW by 2025 with significant capacity additions planned through both public and private sector investments across various energy sources and regions.
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Reimagining Your Library Space: How to Increase the Vibes in Your Library No ...Diana Rendina
Librarians are leading the way in creating future-ready citizens – now we need to update our spaces to match. In this session, attendees will get inspiration for transforming their library spaces. You’ll learn how to survey students and patrons, create a focus group, and use design thinking to brainstorm ideas for your space. We’ll discuss budget friendly ways to change your space as well as how to find funding. No matter where you’re at, you’ll find ideas for reimagining your space in this session.
This presentation was provided by Steph Pollock of The American Psychological Association’s Journals Program, and Damita Snow, of The American Society of Civil Engineers (ASCE), for the initial session of NISO's 2024 Training Series "DEIA in the Scholarly Landscape." Session One: 'Setting Expectations: a DEIA Primer,' was held June 6, 2024.
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
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Chapter wise All Notes of First year Basic Civil Engineering.pptxDenish Jangid
Chapter wise All Notes of First year Basic Civil Engineering
Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
Linear Measurements: Instruments used. Linear Measurement by Tape, Ranging out Survey Lines and overcoming Obstructions; Measurements on sloping ground; Tape corrections, conventional symbols. Angular Measurements: Instruments used; Introduction to Compass Surveying, Bearings and Longitude & Latitude of a Line, Introduction to total station.
Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
Buildings: Selection of site for Buildings, Layout of Building Plan, Types of buildings, Plinth area, carpet area, floor space index, Introduction to building byelaws, concept of sun light & ventilation. Components of Buildings & their functions, Basic concept of R.C.C., Introduction to types of foundation
Chapter 5
Transportation: Introduction to Transportation Engineering; Traffic and Road Safety: Types and Characteristics of Various Modes of Transportation; Various Road Traffic Signs, Causes of Accidents and Road Safety Measures.
Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
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Main Java[All of the Base Concepts}.docxadhitya5119
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This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
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LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
1. Combustion in SI Engines
Sreenidhi Institute of Science and Technology
Yamnampet, Ghatkesar, Hyderabad, Telangana 501301
UNIT – III
2.
3. 3
As per Oxford Dictionary: The process of
burning something (from Latin: comburere)
Chemistry: Rapid chemical combination of a
substance with oxygen, involving the
production of heat and light.
Thermo Dynamics: Combustion is a chemical
reaction in which certain elements of the fuel
like hydrogen and carbon combine with
oxygen liberating heat energy
and causing an
increase in temperature of the gases.
Meaning of Combustion
4. 4
It is a chemical reaction- Hydrogen and
Carbon in the fuel combine with oxygen,
liberating heat energy and causing an
increase in temperature of the gases.
Combustion Process
Biodiesel releases
higher NOx than
Diesel fuel
7. In any conventional spark-ignition (SI)
engine, the fuel and air are homogeneously
mixed together in the intake system, inducted
through the intake valve into the cylinder
where it mixes with residual gases and is
then compressed.
Under normal operating conditions,
combustion is initiated towards the end of the
compression stroke at the spark plug by an
electric discharge.
A turbulent flame develops following the
Combustion in SI Engines
8. If the spark occurs too early, combustion
takes place before the compression stroke is
completed. So, the pressure developed
opposes the piston movement and the engine
power is reduced.
If the spark occurs too late, the piston would
have already completed a portion of the
expansion stroke before the pressure rise
occurs and a corresponding amount of
engine power is lost.
The correct instant for the introduction of the
spark is decided by the ignition lag.
Combustion in SI Engines
10. Combustion is dependent upon the
rate of propagation of flame front or
flame speed.
Flame Front: Boundary or front
surface of the flame that separates
the burnt charges from the unburnt
one.
Flame Speed: The speed at which
the flame front travels.
10
Boundary
11. Combustion is dependent upon the rate of propagation of flame
front or flame speed.
Flame Front: Boundary or front surface of the flame
that separates the burnt charges from the unburnt
one.
Flame Speed: The speed at which the flame
front travels.
Flame speed affects the combustion
phenomena, pressure developed
and power produced.
Burning rate of mixture
depends on the flame speed
and shape/contour of
combustion chamber.
11
13. 13
FYI: Engine Speed and A/F Ratio - Flame Speed
As engine speed increases, the flame speed also
increases
For lean mixture, the flame speed have slower speeds
while for the rich mixture, the fast flame speed
14. Stages of Combustion in SI engine
(Theoritical p-θ Diagram)
In an ideal engine the entire
pressure rise during
combustion takes place at
constant volume i.e., at TDC.
However, in an actual engine
it does not happen as shown
in Fig.
Compression (a b),
Combustion (b c)
Expansion (c d)
15. Stages of Combustion in SI engine
A is the point of
passage of spark
(say 20° bTDC),
B is the point at
which the beginning
of pressure rise can
be detected (say 8°
bTDC)
C the attainment of
peak pressure.
Thus AB represents
the first stage, BC
the second stage
and CD the third
stage.
PRESSURE VARIATION DUE TO COMBUSTION IN A PRACTICAL ENGINE
16. Stages of Combustion in SI
engine
Sir Ricardo describes the combustion
Process as 3 stages:
1. Ignition lag stage
2. Flame propagation stage
3. After burning stage
17. Ignition Lag
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.
18. Ignition Lag….
The period of ignition lag is
shown by path AB.
Ignition lag is very small and lies between
0.00015 to 0.0002 (2ms) seconds.
This is a chemical process depending upon the
nature/properties of fuel, temperature and
pressure in combustion chamber, proportions
of exhaust gas and rate of oxidation or burning.
19. Flame propagation stage
The second stage (BC) is a physical
one and it is concerned with spread of the flame
(progressive) throughout the combustion chamber.
The starting point of the second stage is where the first
measurable pressure rise is seen on the indicator
diagram i.e., the point where the line of combustion
departs from the compression line (point B).
During the second stage the flame propagates
practically at a constant velocity.
20. Flame propagation stage
Heat transfer to the cylinder wall is low, because only a
small part of the burning mixture comes in contact with
the cylinder wall during this period.
The rate of heat-release depends largely on the
turbulence intensity and also on the reaction rate which
is dependent on the mixture composition.
The rate of pressure rise is proportional to the rate of
heat release because during this stage, the combustion
chamber volume remains practically constant (since
piston is near the top dead center).
Rate of pressure rise α Rate of heat release
21. After burning
The starting point of the third stage
is usually taken as the instant at
which the maximum pressure is reached on the
indicator diagram (point C).
The flame velocity decreases during this stage.
The rate of combustion becomes low due to lower
flame velocity and reduced flame front surface.
Since the expansion stroke starts before this stage of
combustion, with the piston moving away from the top
dead center, there can be no pressure rise during this
stage.
26. Combustion in SI
Engine 26
When the flame travels
evenly or uniformly
across the combustion
chamber.
Normal Combustion Abnormal Combustion
When the combustion gets
deviated from the normal
behaviour and resulting in
loss of performance or
damaging the engine
30. Abnormal Combustion in SI Engine
30
Pre-ignition (self-
ignition) occurs when
the fuel mixture in the
cylinder burns before
the spark-ignition event
at the spark plug.
Pre-Ignition Knocking
Knocking is due to
auto-ignition of end
portion of unburned
charge in
combustion
chamber.
31.
32. PRE-IGNITION
Pre-ignition is the ignition of the
homogeneous mixture of charge as it comes
in contact with hot surfaces, in the absence
of spark.
Pre-ignition is initiated by some overheated
projecting part such as the sparking plug
electrodes, exhaust valve head, metal
corners in the combustion chamber, carbon
deposits or protruding cylinder head gasket
rim etc.
Auto ignition may overheat the spark plug
and exhaust valve and it remains so hot that
33. FYI: PRE-IGNITION
Engine efficiency will decrease due to pre-
ignition
pre-ignition causes holes melted in pistons,
spark plugs melted away, and engine failure
happens pretty much immediately.
34.
35.
36. PHENOMENON OF KNOCK IN SI ENGINES
The Figure shows the cross-section of the combustion
chamber with flame advancing from the spark plug location
In the normal combustion the flame travels across the
combustion chamber from A towards D. The advancing flame
front compresses the end charge BB'D farthest from the
spark plug thus raising its temperature.
The temperature is also increased due to heat transfer
from the hot advancing flame-front.
37. If the temperature of the end charge had not reached
its self-ignition temperature, the charge would not
auto-ignite and the flame will advance further and
consume the charge BB‘D.
PHENOMENON OF KNOCK IN SI ENGINES
38. KNOCKING
38
Now, if the final temperature is greater
than and equal to the auto-ignition
temperature, the charge BB´D auto-
ignites (knocking).
A second flame front develops and
moves in opposite direction, where the
collision occurs between the flames. This
39. ABNORMAL COMBUSTION
PHENOMENON OF KNOCK IN SI ENGINES
However, if the end charge BB'D reaches its auto-ignition temperature
and remains for some length of time equal to the time of preflame
reactions the charge will auto ignite, leading to knocking combustion.
In Figure, it is assumed that when flame has reached the position BB',
the charge ahead of it has reached critical auto ignition temperature.
During the preflame reaction period if the flame front could move
from BB' to only CC’ then the charge ahead of CC' would auto-ignite.
40. ENGINE DAMAGE FROM SEVERE KNOCK
Damage to the engine is caused by a combination
of high temperature and high pressure.
Piston Piston crown
Cylinder head gasket Aluminum cylinder head
40
43. COMPARISON OF ABNORMAL COMBUSTION
Pre-ignition
Pre-ignition is the ignition of the
homogeneous mixture of charge as it
comes in contact with hot surfaces, in
the absence of spark.
Pre-ignition is initiated by some
overheated projecting part such as the
sparking plug electrodes, exhaust valve
head, metal corners in the combustion
chamber, carbon deposits or protruding
cylinder head gasket rim etc.
Auto ignition may overheat the spark
plug and exhaust valve and it remains
so hot that its temperature is sufficient to
ignite the charge in next cycle during the
compression stroke before spark occurs
and this causes the pre-ignition of the
charge.
Knocking
Knocking is due to auto ignition of end
portion of unburned charge in
combustion chamber.
The pressure and temperature of
unburned charge increase due to
compression by burned portion of
charge. This unburned compressed
charge may auto ignite under certain
temperature condition and release the
energy at a very rapid rate compared
to normal combustion.
This rapid release of energy during
auto ignition causes a vibrations and
pinging noise.
44. IMPORTANCE OF FLAME SPEED AND
EFFECT OF ENGINE VARIABLES
44
Factors affecting/influencing the flame speed:
1. Turbulence
2. Fuel-Air Ratio
3. Temperature and Pressure of Intake
4. Compression Ratio (CR)
5. Engine Output
6. Engine Speed
7. Engine Size
46. Turbulence….
Turbulence is necessary to prepare the
homogeneous air fuel mixture
It breaks 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
47. Turbulence ….
The flame speed is quite low in non-turbulent
mixtures and increases with increasing
turbulence.
This is mainly due to the additional physical
intermingling of the burning and unburned
particles at the flame front which expedites
reaction by increasing the rate of contact.
Turbulence is mainly dependent on
• Design of combustion chamber
(Geometry of cylinder head)
48. Turbulence ….
The turbulence in the incoming mixture is
generated during the admission of fuel air mixture
through comparatively narrow sections of the
intake pipe, valve openings etc., in the suction
stroke.
49. Turbulence ….
Turbulence is created by
• Swirl Motion and
• Tumble Motion
When flame speed increases
due to
turbulence that reduces the
combustion duration and
hence minimizes the
tendency of abnormal
combustion
50. Fuel-Air Ratio
50
The highest flame speeds (minimum time for
complete combustion) are obtained with slightly
rich mixture at Point A as shown in Figure.
When the mixture is linear or richer, the flame
speed decreases, because
• a lean mixture releases less
thermal energy that causes lower
flame temperature
• while a rich mixture leads to
incomplete combustion, and hence
releases less thermal energy.
52. Inlet Temperature and Pressure
52
A higher initial pressure and
temperature may help to form a
better homogeneous air-fuel vapour
mixture which helps in increasing
the flame speed.
This is possible because of an
overall increase in the density of
the charge.
Flame speed increases with an
53. Compression Ratio (CR)
53
CR is the ratio of total cylinder volume to clearance
volume.
CR = Total volume
Clearance volume
Value of “CR” for,
Petrol engine lies between 6 to 10 :1
Diesel engine lies between 12 to 22 : 1
54. Compression Ratio (CR)
54
A higher compression ratio increases
the pressure and temperature of the
working mixture which reduce the initial
preparation phase of combustion and
hence less ignition advance is
needed.
High pressures and temperatures of the
compressed mixture also speed up the
second phase of combustion.
55. Compression Ratio (CR)…
55
Increased compression ratio,
reduces the clearance volume and
therefore increases the density of the
cylinder gases during burning.
This increases the peak pressure and
temperature and the total combustion
duration is reduced.
Thus engines having higher
compression ratios have higher
56. Engine Output
The cycle pressure increases when the engine
output is increased. With the increased throttle
opening the cylinder gets filled to a higher density.
This results in increased flame speed.
When the output is decreased by throttling, the
initial and final compression pressures decrease
and the dilution of the working mixture increases.
The smooth development of self-propagating
nucleus of flame becomes unsteady and difficult .
57. Engine Output
The main disadvantages of SI engines are the poor
combustion at low loads and the necessity of mixture
enrichment (between 1.2 to 1.3) which causes
wastage of fuel and discharge of unburnt
hydrocarbon and the products of incomplete
combustion like carbon monoxide etc. in the
atmosphere.
58. Engine Speed
The flame speed increases almost linearly with engine
speed since the increase in engine speed increases the
turbulence inside the cylinder.
The time required for the flame to traverse the
combustion space would be halved, if the engine speed is
doubled.
Double the engine speed and hence half the original time
would give the same number of crank degrees for flame
propagation.
The crank angle required for the flame propagation
during the entire phase of combustion, will remain
nearly constant at all speeds.
59. Engine Size
The size of the engine does not have much effect on
the rate of flame propagation.
In large engines the time required for complete
combustion is more because the flame has to travel a
longer distance.
This requires increased crank angle duration during
the combustion. This is one of the reasons why large
sized engines are designed to operate at low speeds.
60. 60
1. Compression Ratio
2. Mixture Strength
3. Throttle Opening
4. Engine Temperature
5.Combustion chamber Design and
6. Engine Speed
Factors affecting Ignition Lag
61. 61
Knock in S.I. Engines:
After the combustion is initiated with the help of
the spark plug, the flame spreads across to the
other end of the combustion chamber
• The heat released during the combustion
increases the temperature and consequently
the pressure of the burned part of the mixture
above those of the unburned part.
• This process continues as the flame front
advances through the mixture – the
temperature and pressure of the unburnt
mixture are increased further.
PHENOMENON OF KNOCK IN SI ENGINES
62. 62
If the temperature of the unburnt mixture exceeds
the self-ignition temperature of the fuel above this
temperature during the period of pre-flame
reactions (Ignition Lag)
-Spontaneous ignition – or Auto-ignition
occurs at various pin-point locations.
This Phenomenon is called Knocking.- The process
of Auto-ignition leads to the engine knock.
In normal combustion- the pressure changes are
smooth and there is No Knock.
In Abnormal Combustion- due to auto-ignition, a
second flame will initiate and move in the opposite
direction- resulting in vibration
Knock in SI Engines Contd.
63. 63
Onset of Knocking- the two flame fronts
collide.
A severe pressure pulse is generated.
The gas in the chamber is subjected to compression
and rarefaction along the pressure pulse until
pressure equilibrium is restored.
The order of vibration is ~ 5000 cps.
The onset of knocking is dependent on the
properties of the Fuel.
If the un-burnt fuel does not reach auto-ignition
temperature, there will not be knocking.
Knocking in SI Engines (contd.)
64. 64
Similarly if the ignition lag period is
longer than the time required for the
flame front to burn through the
unburnt charge- there will be no
Knocking.
If the critical temperature is reached
and maintained, and the ignition lag
is shorter than the time taken for the
flame front to burn through the un-
burnt charge -
The End Charge will Detonate.
Knocking in SI Engines (contd.)
65. Knock-limited Parameters
It should be the aim of the engine designer to reduce
the tendency of knocking in the engine.
1. Knock Limited Compression Ratio
2. Knock Limited Inlet Pressure
3. Knock Limited Indicated Mean Effective
Pressure
66. • 1. Knock Limited Compression Ratio
▫ Compression ratio is gradually increased till incipient
knocking is observed
▫ Any change in operating conditions which improve the
knock limited CR is said to reduce the tendency
towards knocking
• 2. Knock limited Inlet Pressure
▫ The inlet pressure is gradually increased and when the
incipient knock is observed- this is Knock Limited Inlet
Pressure
• 3. Knock Limited Indicated Mean
Effective Pressure
▫ Klimep where the incipient knock is observed
66
67. • Performance Number
▫ Performance number is defined as the ratio of
Klimep with the given fuel to Klimep with Iso-
octane with the inlet pressure kept constant.
▫ This performance number is related to octane
number and can also be applied to fuels whose
knocking characteristics are superior to that of
Iso-octane. Thus it extends the octane scale
beyond 100
• Relative Performance Number
▫ rpn = Actual performance number / Perf. No.
corresponding to imep of 100
67
Knock-limited Parameters
68. Effect of Engine variables on Knock
• A. Density Factors B. Time Factors
• C. Composition Factors
Density Factors
▫ 1.Compression Ratio
▫ An increase in C.R. increases Press and Temp.-
reduces ignition delay and increases tendency for
knocking and vice versa
▫ The increased density of the charge increases pre-
flame reactions in the end charge and increases the
knocking tendency in engine
68
69. Knock in SI Engines (contd.)
▫ ii. Mass of Inducted Charge- A reduction by throttling
etc. reduces the temperature and density of the charge
and reduces tendency of knocking
▫ iii. Inlet Temperature of the Mixture
▫ Increase in inlet temp increases tendency of knocking
▫ iv. Temperature of the combustion chamber walls
▫ The hot spots in the combustion chamber walls
should be avoided.
▫ Since the spark plug and exhaust valves are two
hottest spots in the engine, the end charge should not
be compressed against them.
69
70. Knock in SI Engines (contd.)
▫ v. Retarding the spark timing
▫ By retarding the spark timing from the optimized
timing – that is, by having the spark closer to TDC
▫ The peak pressures are reached farther down on the
power stroke with a relatively lower magnitude- this
might reduce knocking
▫ However, this is different from MBT timing and affects
the Brake torque and engine power output
▫ vi. Power output of the Engine
▫ A decrease in output of the engine decreases the
temperature of the cylinder and the combustion
chamber walls, pressure of the charge and end gas
temperature
▫ This reduces the tendency to Knock
70
71. Knock in SI Engines (contd.)
• B. Time Factors
• to reduce knocking tendency:
▫ i. Increasing Flame speed
▫ ii. Increasing Duration of Ignition Lag
▫ iii. Reducing the time of exposure of un-burnt
mixture to Auto ignition
▫ iv. Turbulence – depends on combustion chamber
design and engine speed.
▫ Increasing turbulence increases the flame speed
and reduces the time available for the end charge
to reach auto-ign. Conditions and decreases the
tendency to knock
71
72. Knock in SI Engines (contd.)
▫ Engine Speed- An increase in speed increases the
turbulence of the mixture – increased flame speed-
reduces time available for pre-flame reactions-
decreases knocking tendency.
▫ Flame Travel Distance- A shorter distance is
beneficial- Engine size and spark plug positioning play
critical role
▫ Combustion chamber shape- A compact combustion
chamber reduces flame travel length – Thus spherical
shape preferred plus measures to improve turbulence
▫ Location of Spark Plug- Centrally located spark plug
reduces the flame travel distance hence better
▫ Use of two or more spark plugs (!) in case of large
engines
72
73. Knock in SI Engines (contd.)
C. Composition Factors
i. Fuel-Air Ratio
▫ Equivalence ratio~1.1-1.2 gives minimum reaction
time for auto ignition – Better
▫ ii. Octane value of the fuel
▫ iii. A higher self-ignition temperature of the fuel and
▫ iv. A low pre-flame reactivity reduce the tendency to
knock.
▫ v. Paraffin series have higher tendency and aromatic
series minimum tendency to knock
▫ vi. Compounds with more compact molecular
structure are less prone to knock
73
74. Knock in SI Engines (contd.)
74
Effect of Equivalence Ratio on
Knock Limited Compression Ratio
75. 75
Summary of Parameters affecting Knock in SI Engines
Sl.
No.
Increase in
variable
Major effect
on unburned
reduced
charge
Action to
be taken
to control
Knocking
Can
Operator
usually
control ?
1 Compression
Ratio
Increases
Temperature
and Pressure
Reduce No
2 Mass of
Charge
Inducted
Increases
Pressure
Reduce Yes
3 Inlet
Temperature
Increases
Temperature
Reduce In some
cases
4 Chamber
Wall
Temperature
Increases
temperature
Reduce Not
ordinarily
76. 76
Summary of Parameters affecting Knock in SI Engines (Contd.)
Sl.
No
.
Increase in
variable
Major effect on
unburned
reduced charge
Action to be
taken to
control
Knocking
Can
Operator
usually
control?
5 Spark
Advance
Increases temp.
and pressure
Retard In some
cases
6 A/F Ratio Increases temp
and Pressure
Make very
rich
In some
cases
7 Turbulence Decreases time
factor
Increase Some what
(through
engine
speed)
77. 77
Summary of Parameters affecting Knock in SI Engines
(Contd.)
Sl.
No.
Increase in
variable
Major effect on
unburned
reduced charge
Action to be
taken to
control
Knocking
Can
Operator
usually
control?
8 Engine
speed
Decreases time
factor
Increase Yes
9. Distance of
Flame
travel
Increases time
factor
Reduce No
78. 78
i. Reduce the Distance of Flame Travel
ii. - Centrally locate the spark plug
iii. - Avoid pockets of Stagnant Charge.
iv. Cooling of the Spark plug and Exhaust valve area
These are sources of hot spots in the majority of the
combustion chambers.
v. Reducing the temperature of the charge
- adopting a high surface –to- volume ratio in the part
where the last portion of the charge burns
- Heat transfer to the combustion chamber walls can be
improved by using high surface-to-volume ratio – there
by reducing the temperature
Reducing the Possibility of Knocking
79. 79
- Use of Measures as below:
i. A High Degree of Turbulence:- This improves the flame velocity
- Introduction of SQUISH (or Rapid radial movement of the gas
trapped in between the piston and the cylinder head)
- with a bowl in the piston
- and dome shaped cylinder head
ii. A High Volumetric Efficiency – (more charge during suction stroke)
– Results in Increased Power output
iii. Design of Combustion Chamber for improved anti-knock
characteristics
Developing Engines for High Power output and Increased
Thermal Efficiency