Internal Combustion Engine Theory Quiz
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Questions and Answers

What is the indicated horsepower (I.P) calculated in kilowatts?

  • 10.78 kw
  • 17.07 kw (correct)
  • 52.06 kw
  • 14.22 kw

What is the formula used to calculate brake power (B.P)?

  • B.P = T × ω (correct)
  • B.P = Q.f / Q.w
  • B.P = m.f × C.V
  • B.P = I.P - Q.st

How much heat is lost to the cooling water (Q.w) in kilowatts?

  • 853.4 kj/min
  • 14.22 kw (correct)
  • 52.06 kw
  • 10.78 kw

What is the total mass of dry exhaust gases (in kg/sec)?

<p>0.03678 kg/sec (A)</p> Signup and view all the answers

What is the heat lost to radiation in kilowatts?

<p>9.31 kw (A)</p> Signup and view all the answers

What is the purpose of the intake stroke in a four-stroke Otto cycle engine?

<p>To draw the fuel-air mixture into the cylinder (D)</p> Signup and view all the answers

Who is considered the inventor of the modern internal combustion engine?

<p>Nikolaus Otto (C)</p> Signup and view all the answers

In the Otto cycle, what initiates combustion in the cylinder?

<p>A spark from the spark plug (C)</p> Signup and view all the answers

During which stroke of the Diesel cycle is the fuel injected into the cylinder?

<p>Compression stroke (A)</p> Signup and view all the answers

What is a potential problem that can occur if the initial pressure in an Otto cycle engine is too high?

<p>Auto-ignition causing knock (A)</p> Signup and view all the answers

How does the Diesel engine differ from the Otto engine in terms of ignition?

<p>Diesel engines use compression to auto-ignite the fuel. (B)</p> Signup and view all the answers

What does the term 'four-stroke engine' refer to?

<p>The complete cycle of an engine involving four different strokes (C)</p> Signup and view all the answers

What key role does the intake manifold play in the functioning of an engine?

<p>To distribute the air mixture to individual cylinders (B)</p> Signup and view all the answers

What occurs during the delay period in a compression ignition engine?

<p>Fuel is injected but does not ignite immediately. (A)</p> Signup and view all the answers

What are the two parts into which the ignition delay period can be divided?

<p>Chemical delay and physical delay. (B)</p> Signup and view all the answers

Which of the following factors affects the rate of vaporization of fuel droplets in a compression ignition engine?

<p>Droplet diameter, velocity, pressure, and temperature of air. (B)</p> Signup and view all the answers

Which stage follows the ignition delay in the combustion process of a C.I. engine?

<p>Rapid combustion. (D)</p> Signup and view all the answers

What is the range of ignition delay for low-compression ratio direct injection (DI) diesel engines?

<p>0.6 to 3 ms. (D)</p> Signup and view all the answers

Which of these is NOT a requirement for good atomization during fuel injection?

<p>Increased fuel viscosity. (C)</p> Signup and view all the answers

During which phase does the fuel continue to burn even after injection ceases?

<p>After burning. (D)</p> Signup and view all the answers

Which process occurs first during the ignition delay period after fuel injection?

<p>Fuel spray atomization and mixing with air. (A)</p> Signup and view all the answers

What does the relative efficiency or efficiency ratio (ηr) represent?

<p>The ratio of actual thermal efficiency to the ideal cycle's thermal efficiency (C)</p> Signup and view all the answers

Which of the following factors influences volumetric efficiency?

<p>Engine speed (A)</p> Signup and view all the answers

What is the ideal air to fuel ratio (A/F ratio) in spark-ignition engines for optimal performance?

<p>14.7:1 (A)</p> Signup and view all the answers

How does a lean air/fuel mixture affect engine performance?

<p>It reduces the tendency for knock to occur (A)</p> Signup and view all the answers

What happens when the air/fuel mixture becomes too weak?

<p>The combustion becomes incomplete (B)</p> Signup and view all the answers

Which component is NOT typically included in a heat balance sheet for engine performance analysis?

<p>Heat loss due to oil consumption (D)</p> Signup and view all the answers

What does a compression ratio indicate in an engine?

<p>The ratio of the cylinder's volume at bottom dead center to its volume at top dead center (A)</p> Signup and view all the answers

Which of the following describes the effect of a rich air/fuel mixture on engine performance?

<p>It leads to higher unburnt fuel levels and reduced efficiency (D)</p> Signup and view all the answers

What does the brake specific fuel consumption (bsfc) measure?

<p>The efficiency of fuel conversion into brake power (D)</p> Signup and view all the answers

How is the indicated specific fuel consumption (isfc) defined?

<p>The ratio of fuel mass injected to indicated work done (C)</p> Signup and view all the answers

What does a lower specific fuel consumption indicate about engine efficiency?

<p>It suggests higher engine efficiency (A)</p> Signup and view all the answers

What is the mechanical efficiency of an engine calculated from?

<p>The ratio of brake power to indicated power (C)</p> Signup and view all the answers

What is a common range for mechanical efficiency in engines?

<p>0.7 to 0.9 (D)</p> Signup and view all the answers

What are typical values of bsfc for naturally aspirated automobile engines?

<p>200 to 400 g/kWh (A)</p> Signup and view all the answers

What constrains the combustion efficiency in an engine during a cycle?

<p>The brief time available for fuel and oxygen interaction (A)</p> Signup and view all the answers

In SI units, how is brake specific fuel consumption (bsfc) expressed?

<p>kg/kWh (B)</p> Signup and view all the answers

What causes knock in compression ignition (CI) engines?

<p>A long delay period (D)</p> Signup and view all the answers

How does Homogeneous Charge Compression Ignition (HCCI) differ from traditional spark ignition engines?

<p>Utilizes compression to ignite the fuel-air mixture (D)</p> Signup and view all the answers

What is a characteristic feature of the combustion process in HCCI engines?

<p>Simultaneous ignition at multiple sites (A)</p> Signup and view all the answers

Which of the following is an advantage of HCCI combustion?

<p>Ability to operate at very high compression ratios (D)</p> Signup and view all the answers

What is the primary method of combustion initiation in HCCI engines?

<p>Temperature increase during compression (D)</p> Signup and view all the answers

What is one of the disadvantages of HCCI combustion?

<p>Difficulty in controlling auto-ignition (A)</p> Signup and view all the answers

What effect does using very lean mixtures in HCCI engines have on emissions?

<p>Minimizes particulate emissions (B)</p> Signup and view all the answers

Which fuel types can HCCI engines operate on?

<p>Gasoline, diesel fuel, and alternative fuels (D)</p> Signup and view all the answers

Flashcards

Otto Cycle

A four-stroke spark-ignition engine cycle using a spark to ignite the fuel-air mixture.

Four-stroke Otto Cycle

The engine cycle with four steps: intake, compression, power, and exhaust.

Intake Stroke

Drawing fuel-air mixture into the engine cylinder.

Compression Stroke

Raising the temperature of the fuel-air mixture by squeezing it.

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Power Stroke

Combustion makes the engine do work.

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Exhaust Stroke

Expelling the burned gases from the engine.

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Diesel Cycle

A four-stroke compression-ignition engine cycle using high compression to ignite the fuel.

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Compression Ignition

The process where the fuel automatically ignites due to high compression.

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Brake Power (B.P.)

The power delivered by the engine crankshaft to its load. It is the power available for performing useful work.

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Indicated Power (I.P.)

The power developed inside the engine cylinder during combustion. It is the theoretical power produced before any losses.

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Heat Supplied (Q.f)

The heat energy supplied to the engine by burning the fuel. It is the source of the engine's power.

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Heat Lost to Cooling Water (Q.w)

The heat energy lost from the engine to the cooling water. It is a loss of energy that reduces the engine's efficiency.

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Heat Lost to Dry Exhaust Gases (Q.ex)

The heat energy lost from the engine to the dry exhaust gases. It is a significant loss of energy, especially at high engine speeds.

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Brake Specific Fuel Consumption (BSFC)

The fuel flow rate (mass flow) divided by the brake power of the engine.

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Indicated Specific Fuel Consumption (ISFC)

The ratio of fuel mass used during one engine cycle to the indicated cylinder work.

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Engine Speed (N)

The rotational speed of the crankshaft, measured in revolutions per minute (rpm).

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Mechanical Efficiency (ηm)

The ratio of brake power to indicated power, showing how much of the power produced inside the engine is transferred to the output shaft.

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Specific Fuel Consumption (SFC)

A comparative measure of engine efficiency, showing how much fuel is used to produce a certain amount of work.

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Engine Efficiency

The effectiveness of converting fuel energy into mechanical work by a machine.

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Volumetric Efficiency

A measure of how well an engine fills its cylinders with air during the intake stroke. It's a crucial factor in engine performance.

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Factors Affecting Volumetric Efficiency

Things like fuel type, engine design, and operating conditions that influence how effectively air fills the engine cylinders.

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Fuel-Air Ratio

The proportion of fuel to air in the combustion process. It significantly affects engine performance and emissions.

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Stoichiometry

The ideal fuel-air ratio for complete combustion in a spark-ignition engine. For gasoline engines, it's typically 14.7:1.

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Lean Mixture

An air/fuel mixture with more air than fuel, resulting in slower combustion and lower peak temperatures.

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Rich Mixture

An air/fuel mixture with more fuel than air, leading to faster combustion and higher peak temperatures.

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Relative Efficiency

A comparison of an engine's actual thermal efficiency to the ideal theoretical efficiency.

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Heat Balance Sheet

A breakdown of how energy is used and lost in an engine, accounting for work done, heat rejection, and other losses.

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Delay Period

The time between fuel injection and the start of noticeable pressure increase in a C.I. engine. During this period, fuel enters the cylinder but doesn't burn immediately.

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Ignition Lag

Another name for the Delay Period, the time delay before combustion begins in a C.I. engine after fuel injection.

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Factors Affecting Delay Period

The delay period in a C.I. engine is influenced by factors like fuel injection pressure, injector hole size, fuel viscosity, and cylinder pressure.

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Rapid Combustion

The rapid increase in pressure that occurs as fuel ignites and burns rapidly in a C.I. engine.

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Controlled Combustion

The gradual and controlled burning of fuel after the rapid combustion phase in a C.I. engine.

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After Burning

The final stage of combustion in a C.I. engine, where any remaining fuel burns after the main injection and combustion phases.

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Physical Delay

The initial part of the Delay Period in a C.I. engine, where the fuel undergoes physical processes like atomization, evaporation, and mixing with air.

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Chemical Delay

The latter part of the Delay Period in a C.I. engine, where the fuel undergoes chemical reactions before initiating combustion.

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Knock in CI engines

Knock in CI engines is caused by a delay in ignition, leading to a rapid pressure rise due to accumulated fuel droplets in the combustion chamber, resulting in rough engine operation.

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HCCI Engine

A type of engine that combines the best aspects of spark ignition and diesel engines by using compression to ignite a homogenous fuel-air mixture.

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HCCI combustion advantage: Efficiency

HCCI engines can achieve higher efficiencies (around 30% more than gasoline engines) due to their ability to operate at higher compression ratios like diesel engines.

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HCCI combustion advantage: Emissions

HCCI engines produce cleaner combustion and lower emissions because the fuel-air mixture is homogenous and burns more completely.

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HCCI Combustion disadvantage: Control

Auto-ignition in HCCI engines is difficult to control compared to spark plugs and fuel injectors used in traditional engines.

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HCCI Combustion: Lean Mixture

HCCI engines utilize very lean fuel-air mixtures to prevent excessive thermal NOx formation and keep peak flame temperature below 1800 K.

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HCCI Combustion: Particulate Emissions

The lean premixed charge in HCCI engines minimizes particulate emissions, contributing to cleaner combustion.

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HCCI Combustion: Fuel Flexibility

HCCI engines can operate on a variety of fuels, including gasoline, diesel, and alternative fuels.

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Study Notes

Introduction to Heat Engines

  • A heat engine is any type of engine or machine that takes heat energy from the combustion of fuel and converts this energy into mechanical work.
  • Heat engines can be grouped into two main classes: external and internal combustion engines.

External Combustion Engines

  • Combustion of fuel occurs outside the cylinder, such as in steam engines.
  • Heat from combustion generates steam which powers a piston or turbine.
  • Examples include steam turbines and gas turbines.
  • Often used for locomotives, ships, and generating electricity.
  • Advantages over internal combustion engines: cheaper fuels (including solids), high starting torque, self-starting with working fluid, flexible arrangement.

Internal Combustion Engines

  • Combustion of fuel occurs inside the cylinder.
  • Fuel mixes with oxygen in the air inside the engine cylinder.
  • Engines using mixtures of combustible gases and air are called gas engines.
  • Engines using lighter liquid fuels (e.g., petrol) are called petrol engines.
  • Engines using heavier liquid fuels (e.g., oil) are called compression ignition engines or diesel engines.
  • Commonly used in road vehicles, aircraft, locomotives, and industrial applications.

Advantages of Reciprocating Internal Combustion Engines

  • Higher overall efficiency
  • Greater mechanical simplicity
  • Easy starting from cold conditions
  • Lower weight to power ratio
  • Lower initial cost
  • Compact units, requiring less space

Principles of Internal Combustion Engines

  • Conventional internal combustion engines have one or more cylinders in which combustion of the fuel takes place.
  • Main cylinder parts include: cylinder head, valve stem, clearance volume, cylinder, bottom dead center, spark plug, inlet valve, air, fuel injector, exhaust valve, connecting rod, crankshaft, crank case, sump.

Engine Components

  • Cylinder: Cylindrical container for piston movement.
  • Cylinder Head: Top end of the cylinder, houses valves and spark plugs.
  • Inlet and Exhaust Valves: Control air and exhaust flow.
  • Piston: Transmits combustion force to connecting rod.
  • Connecting Rod: Connects piston to crankshaft.
  • Crank Shaft: Rotates to produce rotational energy.
  • Crankcase: Main engine body housing crankshaft, and bearings.
  • Flywheel: A large wheel mounted on the crankshaft to maintain constant speed.

Cylinder Geometry

  • Cylinder Bore (D): Inner diameter of the cylinder.
  • Piston Area (A): Area of a circle with a diameter equal to the bore.
  • Stroke (L): Linear distance of piston travel.
  • Bore Stroke Ratio: Ratio of bore to stroke.
    • Square: Equal bore and stroke.
    • Over-square: Stroke shorter than bore.
    • Under-square: Stroke longer than bore.

Engine Classifications

  • Based on ignition type (spark ignition or compression ignition).
  • Based on number of strokes per cycle (two-stroke or four-stroke).
  • Based on application (automotive, marine, etc.).

Working Cycle

  • Four-stroke: intake, compression, power, exhaust.
  • Two-stroke: much simpler but less efficient than four-stroke.
  • Supercharging/Turbocharging: increase air density for higher power output.
    • Mechanical supercharger: Driven by engine crankshaft.
    • Turbocharger: Turbine driven by exhaust gases.

Valve Location

  • Valve in block, L head: Older applications.
  • Valve in head, I head: Standard for modern automobiles.
  • One valve in head and one in block, F head: Less common.
  • Valves in block on opposite sides of cylinder, T head.

Fuel Used

  • Gasoline (petrol)
  • Fuel oil (diesel fuel)
  • Natural gas
  • Liquid petroleum gas
  • Alcohols (e.g., methanol, ethanol)
  • Hydrogen

Method of Mixture Preparation

  • Carburetor
  • Fuel injection into intake ports/manifold
  • Fuel injection into the engine cylinder

Method of Ignition

  • Spark ignition: Spark plug initiates combustion.
  • Compression ignition: Fuel self-ignites due to high compression temperatures.

Combustion Chamber Design

  • Shape of combustion chamber impacts knock and performance.
  • Used in connection with spark ignition engines.

Method of Load Control

  • Throttling of fuel/air flow.
  • Control of fuel flow alone.

Method of Cooling

  • Water cooled
  • Air cooled

Engine Cycles

  • Otto Cycle: Four-stroke, spark ignition.
  • Diesel Cycle: Four-stroke, compression ignition.
  • Dual Cycle

Engine Performance

  • Evaluating engine performance depends on measures.
  • Specific fuel consumption (brake and indicated)
  • Brake mean effective pressure
  • Specific power output, specific weight, exhaust smoke, other emissions.

Additional Notes

  • Many different types of internal combustion engines exist with various characteristics and applications.

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Description

Test your knowledge on internal combustion engines with this quiz. It covers important concepts such as horsepower, brake power, and the functions of various engine strokes. Perfect for students studying mechanical engineering or automotive technology.

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