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What stage of combustion in a spark-ignition engine involves the downward movement of the piston creating a vacuum to draw in the air-fuel mixture?
What stage of combustion in a spark-ignition engine involves the downward movement of the piston creating a vacuum to draw in the air-fuel mixture?
During which stage of combustion does a spark plug ignite the compressed air-fuel mixture?
During which stage of combustion does a spark plug ignite the compressed air-fuel mixture?
In a four-stroke spark-ignition engine, how many strokes are involved in a complete combustion cycle?
In a four-stroke spark-ignition engine, how many strokes are involved in a complete combustion cycle?
Which factor influences turbulence in a spark-ignition engine during the combustion process?
Which factor influences turbulence in a spark-ignition engine during the combustion process?
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What is the purpose of the exhaust stroke in a spark-ignition engine?
What is the purpose of the exhaust stroke in a spark-ignition engine?
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How does a two-stroke spark-ignition engine differ from a four-stroke engine in terms of stages involved?
How does a two-stroke spark-ignition engine differ from a four-stroke engine in terms of stages involved?
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What effect does increasing turbulence have on the flame speed in an engine?
What effect does increasing turbulence have on the flame speed in an engine?
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How does an increase in engine speed affect the tendency to knock?
How does an increase in engine speed affect the tendency to knock?
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What is the relationship between engine size and knocking tendency?
What is the relationship between engine size and knocking tendency?
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How does combustion chamber shape influence knocking tendency?
How does combustion chamber shape influence knocking tendency?
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What role does the location of the spark plug play in reducing knocking tendency?
What role does the location of the spark plug play in reducing knocking tendency?
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What happens if the temperature of the unburnt mixture exceeds the self-ignition temperature of the fuel?
What happens if the temperature of the unburnt mixture exceeds the self-ignition temperature of the fuel?
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Why are combustion chambers made as compact as possible?
Why are combustion chambers made as compact as possible?
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What is the purpose of centrally locating the spark plug in a combustion chamber?
What is the purpose of centrally locating the spark plug in a combustion chamber?
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How does a larger engine size contribute to a higher tendency for knocking?
How does a larger engine size contribute to a higher tendency for knocking?
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What is the consequence of the charge reaching its autoignition temperature in an SI engine?
What is the consequence of the charge reaching its autoignition temperature in an SI engine?
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What initiates the combustion process in a Spark Ignition (SI) engine?
What initiates the combustion process in a Spark Ignition (SI) engine?
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What can happen if the ignition lag period is longer than the time required for the flame front to burn through the unburned charge?
What can happen if the ignition lag period is longer than the time required for the flame front to burn through the unburned charge?
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How can knocking combustion impact engine components and structure?
How can knocking combustion impact engine components and structure?
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What distinguishes detonation from normal combustion in an SI engine?
What distinguishes detonation from normal combustion in an SI engine?
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What is one consequence of two flame fronts colliding in an SI engine?
What is one consequence of two flame fronts colliding in an SI engine?
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In an SI engine, what leads to vibrations force the walls of the combustion chamber to vibrate at the same frequency as the gas?
In an SI engine, what leads to vibrations force the walls of the combustion chamber to vibrate at the same frequency as the gas?
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What is one desirable quality for SI engine fuels to avoid detonation?
What is one desirable quality for SI engine fuels to avoid detonation?
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What role does a pressure transducer play in detecting knocking phenomenon in engines?
What role does a pressure transducer play in detecting knocking phenomenon in engines?
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What can be a consequence of a large mixture autoigniting in an SI engine?
What can be a consequence of a large mixture autoigniting in an SI engine?
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What is the main disadvantage of the T-head type of combustion chamber?
What is the main disadvantage of the T-head type of combustion chamber?
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Which type of combustion chamber provides the ability to remove the cylinder head without disturbing the valve gear?
Which type of combustion chamber provides the ability to remove the cylinder head without disturbing the valve gear?
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What are some factors responsible for detonation in spark-ignition (SI) engines?
What are some factors responsible for detonation in spark-ignition (SI) engines?
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What design feature of the Ricardo's turbulent head aims to reduce knocking tendency?
What design feature of the Ricardo's turbulent head aims to reduce knocking tendency?
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Which factor can increase the likelihood of detonation in SI engines?
Which factor can increase the likelihood of detonation in SI engines?
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Which type of engine is superior at high compression ratios according to the text?
Which type of engine is superior at high compression ratios according to the text?
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How can high engine temperature affect detonation in spark-ignition (SI) engines?
How can high engine temperature affect detonation in spark-ignition (SI) engines?
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What characteristic of the I-Head Type combustion chamber contributes to greater freedom from knock?
What characteristic of the I-Head Type combustion chamber contributes to greater freedom from knock?
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What is the effect of using lower octane fuels in a spark-ignition (SI) engine?
What is the effect of using lower octane fuels in a spark-ignition (SI) engine?
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What distinguishes the F-Head Type combustion chamber from other types mentioned?
What distinguishes the F-Head Type combustion chamber from other types mentioned?
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Which component can act as a hot spot, contributing to premature ignition and detonation?
Which component can act as a hot spot, contributing to premature ignition and detonation?
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Which type of engine configuration requires two right angle turns for air flow to enter the cylinder?
Which type of engine configuration requires two right angle turns for air flow to enter the cylinder?
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How does using a fuel with insufficient octane rating affect the likelihood of detonation in a spark-ignition (SI) engine?
How does using a fuel with insufficient octane rating affect the likelihood of detonation in a spark-ignition (SI) engine?
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What can contribute to detonation due to the accumulation of carbon deposits in the combustion chamber?
What can contribute to detonation due to the accumulation of carbon deposits in the combustion chamber?
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What effect does overheating of engine components have on the likelihood of detonation in spark-ignition (SI) engines?
What effect does overheating of engine components have on the likelihood of detonation in spark-ignition (SI) engines?
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How does an incorrectly selected spark plug heat range affect the occurrence of detonation in spark-ignition (SI) engines?
How does an incorrectly selected spark plug heat range affect the occurrence of detonation in spark-ignition (SI) engines?
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What is a potential consequence of having a poorly designed combustion chamber in a spark-ignition (SI) engine?
What is a potential consequence of having a poorly designed combustion chamber in a spark-ignition (SI) engine?
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What is the octane rating of regular unleaded gasoline in the United States?
What is the octane rating of regular unleaded gasoline in the United States?
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Which component in a Spark Ignition engine is crucial for the combustion process?
Which component in a Spark Ignition engine is crucial for the combustion process?
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What is the primary purpose of the detonation control in the combustion chamber design?
What is the primary purpose of the detonation control in the combustion chamber design?
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Why is the compression ratio important in the design of a combustion chamber?
Why is the compression ratio important in the design of a combustion chamber?
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How does the shape and size of the combustion chamber impact combustion?
How does the shape and size of the combustion chamber impact combustion?
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What environmental consequences can detonations lead to?
What environmental consequences can detonations lead to?
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What is the primary purpose of detonations in military or terrorist contexts?
What is the primary purpose of detonations in military or terrorist contexts?
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What is knocking, or detonation, in relation to internal combustion engines?
What is knocking, or detonation, in relation to internal combustion engines?
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What role does the octane rating play in preventing knocking in engines?
What role does the octane rating play in preventing knocking in engines?
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What is the main function of the combustion chamber design?
What is the main function of the combustion chamber design?
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Study Notes
Stages of Combustion in SI Engines
- Intake Stroke: The piston moves downward, creating a vacuum that draws in a mixture of air and fuel into the combustion chamber.
- Compression Stroke: The piston moves back up, compressing the air-fuel mixture, increasing the temperature and pressure within the combustion chamber.
- Ignition: A spark plug generates an electric spark, igniting the compressed air-fuel mixture, marking the beginning of the combustion process.
- Combustion (Power) Stroke: The ignited mixture rapidly burns, producing a high-pressure and high-temperature gas, forcing the piston down, converting the thermal energy into mechanical work.
- Exhaust Stroke: The piston moves back up, pushing the exhaust gases out of the combustion chamber and into the exhaust system.
Factors Influencing Combustion Stages
- Turbulence: Depends on the design of the combustion chamber and engine speed; increases flame speed and reduces the time available for the end charge to attain autoignition conditions.
- Engine Speed: Increases turbulence, flame speed, and reduces the time available for preflame reactions, resulting in reduced knocking tendency.
- Flame Travel Distance: Influences knocking tendency, affected by engine size, combustion chamber size, and spark plug position.
- Engine Size: Larger engines have a greater tendency for knocking due to longer flame travel time.
- Combustion Chamber Shape: A more compact shape reduces flame travel and combustion time, resulting in better anti-knock characteristics.
- Location of Spark Plug: Centrally located spark plug reduces flame travel, resulting in minimum knocking tendency.
The Phenomenon of Knock in SI Engines
- Knocking occurs when autoignition occurs, causing a rapid increase in pressure and temperature.
- Autoignition is influenced by the properties of the fuel, and occurs when the unburned mixture reaches its self-ignition temperature.
- Ignition lag period and flame travel time affect the onset of knocking.
- High autoignition temperature and long ignition lag are desirable qualities for SI engine fuels to avoid detonation.
- Knocking can cause engine failure, noise, and vibration, and can be detected by a pressure transducer and audible sound.
Detonation
- Detonation refers to the abnormal combustion of the air-fuel mixture in the combustion chamber.
- Characterized by an uncontrolled and rapid increase in pressure and temperature, causing damage to the engine.
- Factors contributing to detonation include high temperature, pressure, or the presence of hot spots in the combustion chamber.
Combustion Chambers
- T-Head Type: Early design, prone to knocking due to long flame travel distance.
- L-Head Type: Modification of T-Head, providing two valves on the same side of the cylinder, reducing knocking tendency.
- I-Head Type or Overhead Valve: Superior to side valve engines, characterized by less surface to volume ratio, less flame travel length, and higher volumetric efficiency.
- F-Head Type: Compromise between L-Head and I-Head types, with one valve in the cylinder head and the other in the cylinder block.
Factors Responsible for Detonation
- High Compression Ratio: Increases temperature and pressure, making spontaneous ignition more likely.
- Advanced Ignition Timing: Igniting the air-fuel mixture too early in the compression stroke can lead to detonation.
- Lean Air-Fuel Mixture: Higher combustion temperatures increase the likelihood of detonation.
- High Engine Temperature: Elevated engine temperatures contribute to detonation.
- Low Octane Fuel: Lower octane fuels have a lower resistance to detonation.
- Carbon Deposits: Hot spots initiate premature ignition.
- Poorly Designed Combustion Chamber: Promotes turbulence and hot spots.
- Excessive Carbon Buildup: Leads to hot spots and contributes to detonation.
- Engine Overheating: Increases the chances of detonation.
- Incorrect Spark Plug Heat Range: Leads to overheating and contributes to detonation.
Effect of Detonation on SI Engine
- Shock Waves: Powerful shock waves cause damage to structures and materials.
- Heat and Fire: Intense heat leads to the ignition of surrounding materials.
- Blast Pressure: High-pressure environment causes structural damage, injury, and fatalities.
- Fragmentation: Dispersal of fragments or shrapnel upon detonation.### Detonation
- Can cause additional injuries and damage over a wider area
- Can lead to crater formation, especially in explosions involving earth or underground structures
- Can have environmental consequences, such as air and water pollution, depending on the materials involved
Octane Rating
- Measures a fuel's resistance to knocking during combustion in internal combustion engines
- Represented by two numbers, e.g., 87 octane or 91 octane
- Determined by comparing a fuel's performance to a mixture of iso-octane and heptane
- A higher octane rating indicates a greater resistance to knocking
- Higher-performance or high-compression engines often require fuels with higher octane ratings to prevent knocking and optimize performance
- Regular unleaded gasoline in the US typically has an octane rating of 87, while premium gasoline can have octane ratings of 91 or higher
Combustion Chambers for SI Engines
- Must facilitate proper air-fuel mixture formation, typically through carburetion or fuel injection systems
- Design should support ignition system, including spark plug location and orientation
- Affects compression ratio, which is crucial for engine performance and efficiency
- Should be designed to dissipate heat efficiently to prevent knocking and reduced efficiency
- Shape and size influence turbulence and swirl of air-fuel mixture, affecting combustion efficiency
- Should minimize likelihood of detonation through design factors, such as chamber shape and spark plug location
- Impacts emissions formation, with modern SI engines striving to minimize pollutants
- Crucial for achieving a balance between power output, fuel efficiency, and emissions
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Description
Learn about the stages of combustion in a spark-ignition (SI) engine, also known as a gasoline engine. Understand the processes involved in the intake stroke, compression stroke, and ignition for efficient engine operation.
