Ignition Systems MCQ Quiz - Objective Question with Answer for Ignition Systems - Download Free PDF

Explanation:

Role of the Ignition Coil in a Battery or Coil Ignition System

Definition: The ignition coil is a crucial component in a battery or coil ignition system. Its primary role is to transform the low battery voltage into a high voltage required for spark generation in the internal combustion engine. This high voltage is necessary to ignite the air-fuel mixture within the engine's combustion chamber, ensuring the engine runs smoothly and efficiently.

Working Principle: The ignition coil operates on the principle of electromagnetic induction. It consists of two windings: the primary winding and the secondary winding. The primary winding is connected to the battery and the ignition switch, while the secondary winding is connected to the spark plug.

When the ignition switch is turned on, current flows through the primary winding, creating a magnetic field around it. The ignition system then interrupts the current flow in the primary winding, causing the magnetic field to collapse rapidly. This rapid collapse induces a high voltage in the secondary winding, which can be several thousand volts. This high voltage is then directed to the spark plug, where it creates a spark to ignite the air-fuel mixture in the combustion chamber.

Components Involved:

• Primary Winding: Made of thick wire, it has fewer turns and is connected to the battery.
• Secondary Winding: Made of thin wire, it has many more turns than the primary winding and is responsible for generating the high voltage.
• Ignition Switch: Controls the current flow to the primary winding.
• Spark Plug: The component where the high voltage is discharged to create a spark.

Advantages:

• Efficiently converts low battery voltage to high voltage necessary for spark generation.
• Ensures reliable ignition of the air-fuel mixture, leading to better engine performance.
• Relatively simple design with few moving parts, leading to durability and low maintenance.

Disadvantages:

• Failure of the ignition coil can lead to engine misfires and poor performance.
• High voltages can lead to insulation breakdown over time.

Applications: Ignition coils are used in various types of internal combustion engines, including those in cars, motorcycles, and small engines for lawn equipment. They are essential for the proper functioning of both gasoline and diesel engines with spark-ignition systems.

Analysis of Incorrect Options:

It is important to understand why the other options listed in the question are incorrect in the context of the role of the ignition coil:

• Option 1: To compress the air entering the combustion chamber: This is not the role of the ignition coil. The compression of air in the combustion chamber is typically achieved by the pistons during the engine's compression stroke. The ignition coil has no function related to the compression of air.
• Option 2: To regulate the fuel injection timing: The fuel injection timing is controlled by the engine's fuel injection system, which includes components such as the fuel injectors and the engine control unit (ECU). The ignition coil is not involved in regulating fuel injection timing.
• Option 3: To control the engine’s exhaust temperature: The exhaust temperature is influenced by factors such as the air-fuel mixture, combustion efficiency, and exhaust system design. The ignition coil's function is to generate the high voltage for spark ignition, and it does not directly control the exhaust temperature.

In summary, the primary role of the ignition coil in a battery or coil ignition system is to transform the low battery voltage into the high voltage required for spark generation, making option 4 the correct answer. Understanding the specific functions of each component in an engine system is crucial for diagnosing and maintaining engine performance.

Explanation:

Spark Plug:

• A spark plug is a critical component in an internal combustion engine. It provides the necessary spark to ignite the air-fuel mixture in the engine's combustion chamber. The temperature of the spark plug plays a crucial role in engine performance, efficiency, and safety. A "hot" spark plug is one that retains more heat, which can lead to various effects on engine operation. However, not all phenomena can be attributed to a hot spark plug.

Post-Ignition:

• Post-ignition refers to the continuation of combustion after the spark has been extinguished and the power stroke is completed. This phenomenon is not directly caused by a hot spark plug. Instead, post-ignition is typically associated with other factors such as incomplete combustion, fuel characteristics, or residual combustion gases in the chamber. A hot spark plug can initiate pre-ignition or contribute to detonation, but it does not cause combustion to continue after the intended ignition phase is complete.

Detonation

• Detonation, or knocking, happens when the air-fuel mixture explodes violently instead of burning smoothly. A hot spark plug can contribute to detonation by creating hot spots in the combustion chamber, which can cause the mixture to auto-ignite in an uncontrolled manner. Detonation is harmful to the engine as it can cause increased stress on components and lead to overheating.

Explanation:

Capacitor in the Ignition System of an Internal Combustion Engine

• A capacitor, also known as a condenser, is a key component in the ignition system of an internal combustion engine. It temporarily stores electrical energy and releases it when needed to ensure efficient ignition of the air-fuel mixture in the engine's combustion chamber.

Working Principle:

• In an ignition system, the capacitor is connected across the contact breaker points. When the contact points open, the capacitor absorbs the surge of voltage that would otherwise cause arcing across the points.
• This absorption helps in the rapid collapse of the magnetic field in the ignition coil, which is essential for generating a high voltage in the secondary winding of the coil. This high voltage is then used to create a spark at the spark plug, igniting the air-fuel mixture.

Advantages:

• Prevents arcing at the contact breaker points, thereby reducing wear and prolonging the lifespan of the points.
• Ensures a rapid collapse of the magnetic field in the ignition coil, leading to a strong and timely spark at the spark plug.
• Improves the overall efficiency and reliability of the ignition system.

Disadvantages:

• A faulty capacitor can lead to weak or no spark, causing engine misfires or failure to start.
• Capacitors have a finite lifespan and may need periodic replacement.

Applications: Capacitors are used in various types of ignition systems in internal combustion engines, including those in automobiles, motorcycles, and small engines used in lawnmowers and generators.

Explanation:

Polar Inductor Type Magneto Ignition System

• A polar inductor type magneto ignition system is a type of ignition system where both the magnet and the windings remain stationary.
• The system generates a high voltage necessary for spark plug ignition in internal combustion engines without requiring any external battery or power source.
• The polar inductor type magneto ignition system operates based on the principle of electromagnetic induction.
• Here, the stationary magnet and windings create a magnetic field.
• As an inductor or rotor moves within this magnetic field, it causes a change in the magnetic flux.
• This change induces an electromotive force (EMF) in the windings, which is then transformed into the high voltage required for the spark plug to ignite the air-fuel mixture in the engine's cylinder.

Components:

• Stationary Magnet: Creates a stable magnetic field.
• Stationary Windings: Wound around a core and remain fixed in position to induce voltage when there is a change in the magnetic field.
• Rotor or Inductor: A rotating component that alters the magnetic flux through the windings, inducing a voltage.
• Distributor: Directs the high voltage to the appropriate spark plug in a multi-cylinder engine.
• Ignition Coil: Steps up the induced voltage to a level sufficient to create a spark.
• Spark Plug: Converts the high voltage into a spark to ignite the air-fuel mixture.

Advantages:

• Independent operation without the need for an external power source.
• Reliable and consistent spark generation.
• Simple design with fewer moving parts compared to other ignition systems.

Disadvantages:

• Complexity in manufacturing and precise alignment of components.
• Limited to applications where stationary magnet and windings are feasible.

Applications:

• The polar inductor type magneto ignition system is commonly used in small engines, motorcycles, and some aircraft engines where reliability and independence from external power sources are crucial.

Explanation:

Understanding the Correct Option:

To solve the given problem, we need to analyze the two statements about SI (Spark Ignition) and CI (Compression Ignition) engines. Let's start by understanding the definitions and working principles of these engines:

SI Engine: The SI engine, or Spark Ignition engine, is a type of internal combustion engine where the combustion process is initiated by an electric spark from a spark plug. The spark plug ignites the air-fuel mixture, leading to combustion.

CI Engine: The CI engine, or Compression Ignition engine, is another type of internal combustion engine where combustion occurs due to the high temperature achieved by compressing the air inside the cylinder. Unlike SI engines, CI engines do not have spark plugs; instead, they rely on the heat generated by compression to ignite the fuel.

Now, let's analyze the statements:

Statement A: SI engine does not consist of a spark plug.
Statement B: CI engine does not consist of a spark plug.

From the definitions, it is clear that Statement A is false because SI engines do require a spark plug to initiate combustion. On the other hand, Statement B is true because CI engines do not use spark plugs for ignition.

Therefore, the correct answer is:

Option 2: Statement B is true but Statement A is false.

Additional Information

To further understand the analysis, let's evaluate the other options:

Option 1: Both statements are true.

This option is incorrect because, as explained, Statement A is false. SI engines do consist of a spark plug, making the statement "SI engine does not consist of a spark plug" incorrect.

Option 3: Both statements are false.

This option is also incorrect. While Statement A is false, Statement B is true, as CI engines do not consist of a spark plug. Thus, both statements cannot be false.

Option 4: Statement A is true but Statement B is false.

This option is incorrect for the same reason mentioned earlier. Statement A is false because SI engines do have a spark plug, and Statement B is true because CI engines do not have a spark plug.

Conclusion:

In conclusion, the correct answer to the question is Option 2. The analysis of the statements shows that Statement A is false because SI engines do have a spark plug, and Statement B is true because CI engines do not have a spark plug. This understanding is crucial in differentiating the components and working principles of SI and CI engines, which are fundamental concepts in the study of internal combustion engines.

Concept:

Lean mixture:

• Mixture which contains more air than the stoichiometric requirement. There is more oxygen than required to burn completely the amount of fuel; after combustion, there is excess oxygen in the exhaust gases.

Rich Mixture:

• Mixture which contains less air than the stoichiometric requirement. There is not enough air to burn completely the amount of fuel; after combustion, there is unburnt fuel in the exhaust gases.

Spark advance/Ignition Advance:

• The purpose of the spark advance mechanism is to assure that under every condition of engine operation, ignition takes place at the most favorable instant in time i.e. most favorable from a standpoint of engine power, fuel economy, and minimum exhaust dilution.
• By means of these mechanisms, the advance angle is accurately set so that ignition occurs before the TDC point of the piston.

Ignition timing:

• Ignition timing is the correct instant for the introduction of a spark near the end of the compression stroke in the cycle.
• There are several factors that affect the ignition timing of an engine like compression ratio, engine speed, engine load, quality of fuel, mixture strength, etc.
• In the case of a rich mixture, the combustion rate is faster and less ignition advance is required. And in the case of a lean mixture, the combustion rate will be slower thus requiring more ignition advance.
• When ignition occurs early in the compression stroke, the engine is said to be advanced. A retardation ignition takes place when the piston is just near the compression stroke.
• If the ignition is advanced too much, it will be completed before the end of the compression stroke. Under these conditions, the crankshaft and connecting rod will have to push the piston upward, compressing the gases. In such a case the force might not be sufficient to overcome the pressure and the engine would stop or stall.
• If the ignition is retarded too much, the combustion of fuel will continue during the power stroke of the piston (Expansion stroke) and the maximum pressure will not be developed, and less work will be obtained from heat energy. Under these conditions, comparatively more exhaust gases will be going out of the engine cylinder overheating the exhaust valve.

Conclusion:

• Rich Mixture with ignition advance: It can complete before the compression stroke.
• Weak Mixture without ignition advance: Combustion can be found to proceed during the expansion stroke.
• The rich mixture should have retarded ignition advance and the lean mixture should have more ignition advance.

Explanation:

The combustion in a CI engine is considered to be taking place in four stages. It is divided into

1. Ignition delay period
2. Period of rapid combustion or uncontrolled combustion
3. Period of controlled combustion
4. Period of after burning

Ignition delay period:

The ignition delay period is also called the preparatory phase during which some fuel has already been admitted but has not yet ignited. This period is counted from the start of injection to the point where the pressure-time curve separates from the monitoring curve indicated as start of combustion.

The fuel does not ignite immediately upon injection into the combustion chamber. There is a definite period of inactivity between the time when the first droplet of fuel hits the hot air in the combustion chamber and the time it starts through the actual burning phase. This period is known as the ignition delay period.

The delay period can be subdivided into physical delay and chemical delay.

Period of rapid or uncontrolled combustion

This period is counted from the end of the delay period to the point of maximum pressure on the indicator diagram.

In this second stage of combustion, the rise of pressure is rapid because during the delay period, the droplets of fuel have had time to spread themselves out over a wide area and they have fresh air all around them.

About one-third of heat is evolved during this process.

Period of controlled combustion :

At the end of second stage of combustion, the temperature and pressure are so high that the fuel droplets injected in the third stage burn almost as they enter.

Period of after burning :

Combustion does not cease with the completion of the injection process. The unburnt and partially burn fuel particles left in the combustion chamber start burning as soon as they come into contact with the oxygen. This period continues for a certain duration called the after-burning period.

Preignition is generally caused by an overheated spot which may occur at the spark plug, combustion chamber deposits or exhaust valves. Consequences of pre-ignition are:

1. Increases the time loss and hence reduces network done.

2. Vicious cycle of pre-ignition and detonation is formed leading to power loss.

Explanation:

• The exact moment at which the inlet and outlet valve opens and closes with reference to the position of the piston and crank shown diagrammatically is known as valve timing diagram. It is expressed in terms of degree crank angle.

• The start of combustion (SOC) or Fuel Valve closes (FVC) occurs 10 - 20° crank angle after the top dead centre (TDC) so the best answer is option 3 is correct.

Explanation:

The combustion in a CI engine is considered to be taking place in four stages. It is divided into

1. Ignition delay period

2. Period of rapid combustion or uncontrolled combustion

3. Period of controlled combustion

4. Period of after burning

Ignition delay is the time lag between the start of injection to the ignition.

The physical properties such as Cetane number, viscosity of fuel, nozzle hole size, injected quantity and injection pressure contribute to the delay phenomenon in diesel engines.

The cetane number is an important property of diesel fuel and is a measure of the tendency of a diesel fuel to knock in a diesel engine. Cetane number is a mean of determining the ignition quality of a fuel.

The shorter the ignition delay period, the higher the cetane number of the fuel and the smaller amount of fuel in the combustion chamber when the fuel ignites.

Effect of engine variables on ignition lag:

Ignition lag (the time lag between first ignition of fuel and the commencement of the main phase of combustion) is not a period of inactivity but is a chemical process. The ignition lag in terms of crank angles is 10° to 20° and in terms of time, 0.0015 seconds.

The duration of ignition lag depends on the following factors:

• Fuel: Ignition lag depends on chemical nature of fuel. The higher the self ignition temperature of fuel, longer the ignition lag. It is less for lower self-ignition temperature of the fuel.
• Initial temperature and pressure: Ignition lag is reduced if the initial temperature and pressure are increased (and these can be increased by increasing the compression ratio).

Explanation:

Ignition system:

• All spark ignition engines require an ignition system to ignite a fuel mixture in the cylinder.
• A very high voltage is required to generate sparks to ignite the cylinder charge at the set time.

Two types of ignition systems are used:

• Battery/coil ignition system
• Magneto ignition system

Ignition coil:

• It is used to step up low voltage to high voltage to generate sparks.
• It consists of two windings, one is wound over a soft iron core.
• The secondary winding is grounded over the core. It consists of about 21,000 turns.
• One end of the windings is connected to the secondary terminal and the other end of the primary winding.
• The primary winding is wound over the secondary winding and consists of about 200 - 300 turns.
• The ends are connected to the external terminal. the bakelite cap insulates the secondary terminal from the container and primary terminals.
• In an internal combustion (I.C.) engine with a coil ignition system, the primary circuit is connected to the battery and is responsible for building up magnetic field energy in the ignition coil.
• When the primary circuit is interrupted, the collapse of the magnetic field induces a high voltage (ranging 8000 V to 12,000 V) across the secondary terminal of the ignition coil.
• This high voltage is necessary to create a spark at the spark plug, which ignites the air-fuel mixture in the engine cylinder.
• The voltage produced across the secondary terminal of the ignition coil can be quite high, typically in the range of several thousand volts.
• The exact voltage depends on various factors, including the design of the ignition coil, the resistance and inductance of the primary and secondary circuits, and the specific conditions at the moment of ignition.

Explanation:

Magneto ignition system:

• Magneto is a special type of electric generator. It is mounted on the engine and replaces all the components of the coil ignition system except the spark plug.
• A magneto when rotated by the engine is capable of producing very high voltage and does not need a battery as a source of external energy.
• The use of magneto is best at high speeds and therefore widely used for sports, racing cars, motorcycles, scooters.

The figure shows the schematic diagram of a high tension magneto ignition system.

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Characteristics of Magneto Ignition System

• Simplicity in Construction:

  • The magneto ignition system is typically more complex in construction compared to the coil ignition system. This is because it incorporates both the energy generation and the high-voltage transformation within the same unit.

• Efficiency Relative to Engine Speed:

  • The efficiency of the magneto ignition system improves as the engine speed increases. This is because the magneto generates a stronger spark at higher speeds, making it suitable for high-speed applications like sports cars and aircraft engines​​.

• Maintenance Requirements:

  • Magneto ignition systems generally require less frequent maintenance compared to coil ignition systems since they do not rely on an external battery and have fewer electrical connections. This makes them advantageous for applications where reliability and low maintenance are critical​​.

• Spark Intensity at Low Speed:

  • The magneto ignition system tends to produce a weaker spark at low engine speeds. This can lead to starting difficulties, and sometimes a separate battery is needed to assist with starting the engine​​.

Concept:

Ignition coil:

• The ignition coil is used to step up low voltage to high voltage from 12 V to 22,000 V and supply it to the spark plug with the help of a distributor to generate sparks.
• It consists of two windings, one wound over the soft iron core.
• The secondary winding is wound over the core and It consists of about 21,000 turns. 

• One end of the winding is connected to the secondary terminal and the other end to the primary winding.
• The primary winding is wound over the secondary winding and consists of about 200-300 turns.
• The ends are connected to the external terminal of the coil.
• The Bakelite cap insulates the secondary terminal from the container and primary terminals.

Distributor:

• A distributor is a component in a spark ignition system that channels high voltage pulses from the ignition coil to the spark plugs.

• Distributors are typically driven by the camshaft, which causes them to rotate at exactly one half the speed of the crankshaft. 
• This precise timing is what allows a distributor to provide voltage to each spark plug at the correct time and in the proper sequence which is nothing but the firing order.

Battery:

• The battery is installed for providing the necessary voltage which can be further step upped to create a spark in the SI engines which is important for combustion.

Classification of Injection System

1.      Air Injection System

2.      Solid Injection System

 1. Air Injection System

• In this Injection system, the fuel will be injected into the cylinder by means of compressed air. So it needs an additional compression system for the Injection System.
• Due to this additional system, the weight of the engine will increase which will result in the reduced brake power output.
• This type of fuel injection system is used very less nowadays because of the bulky design of the engine. Since it needs an additional mechanical compressor system.

The following are the advantages of the Air Injection system

• High viscosity fuel can be used which are comparatively less expensive than the fuel used by the Solid Injection System.
• Can achieve higher Mean Effective Pressures (MEP) due to the good mixing of fuel with the air.

2. Solid Injection System

• In this Injection system, the fuel will be directly injected into the cylinder without the aid of the compressed air as like in the Air Injection System.
• This can be also called as the Airless Mechanical Injection System.
• In this Solid Injection System, There are different types of Injection Systems are there.

1. Individual pump and Nozzle system
2. Unit Injector system
3. Common rail system
4. Distributor system

High pressure pumps are used in all the systems with pressure above 200 bar.

Concept:

\(Volume\;swept\;per\;second = \frac{N}{{60}} \times \frac{\pi }{4}{\left( d \right)^2}L\)

Indicated power = IMEP × Vswept

\(Indicated\;thermal\;efficiency\left( \eta \right) = \frac{{Indicated\;power}}{{Heat\;supplied}}\)

Given:

\(Bore\left( d \right) = 0.2m;Stroke\left( L \right) = 0.3m;N = 350\;r.p.m.;IMEP = 275\frac{{kN}}{{{m^2}}};\)

\(Oil\;Consumption\left( {{{\dot m}_{fuel}}} \right) = 4.25\frac{{kg}}{{hr}};Calorific\;Value\;of\;fuel\;\left( {CV} \right) = 44 \times {10^3}\frac{{kJ}}{{kg}}.\)

Calculation:

\(Volume\;swept\;per\;second = \frac{N}{{60}} \times \frac{\pi }{4}{\left( d \right)^2}L\)

\(Volume\;swept\;per\;second = \frac{{350}}{{60}} \times \frac{\pi }{4} \times {\left( {0.2} \right)^2} \times 0.3\)

∴ Volume swept per second = 0.055 m³/s

Now,

Indicated power = IMEP × V_swept

Where, IMEP = Indicated mean effective pressure, V_swept = swept volume

∴ Indicated power = 275 × 0.055

∴ Indicated power = 15.1189 kW

Now,

Heat supplied(Q) = m ̇_fuel × Calorific Value

\(\therefore {\rm{Heat\;supplied}}\left( {\rm{Q}} \right) = \frac{{4.25}}{{3600}} \times 44 \times {10^3}\)

\(\therefore {\rm{Heat\;supplied}}\left( {\rm{Q}} \right) = 51.944\;kW\)

Now,

\(Indicated\;thermal\;efficiency\left( \eta \right) = \frac{{Indicated\;power}}{{Heat\;supplied}}\)

\(\therefore Indicated\;thermal\;efficiency\left( \eta \right) = \frac{{15.1189}}{{51.944}} \times 100\)