Internal Combustion Engines Quiz
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Questions and Answers

What is one advantage of a two stroke cycle engine compared to a four stroke cycle engine?

  • Lower initial cost (correct)
  • Less pollution produced
  • Lower consumption of lubricating oil
  • Higher thermal efficiency

    • Which of the following is a disadvantage of a two stroke cycle engine?

  • Improved scavenging
  • Reduced initial cost
  • Large consumption of lubricating oil (correct)
  • Higher thermal efficiency

    • What does the air standard cycle assume about the gas in the engine cylinder?

  • It undergoes chemical change during the cycle.
  • It gains heat during the compression process.
  • It is a perfect gas obeying gas laws. (correct)
  • It is not a closed cycle system.

    • What type of cycle is also known as a constant volume cycle?

    <p>Otto Cycle</p> Signup and view all the answers

    What is one of the purposes of using an air standard cycle in the analysis of internal combustion engines?

    <p>To evaluate effects of modifications on maximum efficiency</p> Signup and view all the answers

    Which process is not assumed to occur in an air standard cycle?

    <p>Irreversible reactions of the gas</p> Signup and view all the answers

    Which of the following statements about thermal efficiency in two stroke and four stroke engines is correct?

    <p>Two stroke engines have lower thermal efficiency than four stroke engines.</p> Signup and view all the answers

    Which measurement is NOT typically included when evaluating engine performance?

    <p>Engine weight</p> Signup and view all the answers

    What does indicated power (IP) measure in an engine?

    <p>The net work transferred from the gas to the piston</p> Signup and view all the answers

    Which of the following is NOT one of the five important engine efficiencies?

    <p>Fuel utilization efficiency</p> Signup and view all the answers

    What does brake power (BP) represent in the context of engine performance?

    <p>Rate at which work is done</p> Signup and view all the answers

    How is the implied relationship between the number of revolutions per cycle different for 4-stroke and 2-stroke engines?

    <p>4-stroke engines have two revolutions per power stroke while 2-stroke have one.</p> Signup and view all the answers

    What is the primary output of a p-V indicator diagram related to an engine?

    <p>Indicated power output</p> Signup and view all the answers

    Which measure can be used to analyze the combustion process and engine emissions?

    <p>Exhaust gas analysis</p> Signup and view all the answers

    What does the term 'friction power' (fp) specifically refer to in an engine?

    <p>Power lost due to friction within the engine</p> Signup and view all the answers

    Which efficiency is a ratio comparing the actual performance of an engine to its ideal performance?

    <p>Relative efficiency</p> Signup and view all the answers

    What effect does a shorter delay period have on engine operation?

    <p>Results in a smoother operation</p> Signup and view all the answers

    What is the typical pressure gradient range that indicates smooth engine operation?

    <p>2 to 3 bar/oCA</p> Signup and view all the answers

    During which phase does the combustion process become difficult to control?

    <p>Period of rapid combustion</p> Signup and view all the answers

    What phenomenon is described as a violent pounding noise resulting from high pressure rise?

    <p>Diesel knock</p> Signup and view all the answers

    What continues to burn during the after-burning period in an engine?

    <p>Un-burnt and partially burnt fuel particles</p> Signup and view all the answers

    What does combustion efficiency ( η_comb) measure in an engine?

    <p>The fraction of fuel that burns during combustion</p> Signup and view all the answers

    Which formula represents the relationship between brake power (BP) and fuel parameters?

    <p>BP = m_f × C.V</p> Signup and view all the answers

    How is thermal efficiency ( η_i) defined in engine performance?

    <p>It indicates the percentage of fuel that converts to shaft work</p> Signup and view all the answers

    What factors affect volumetric efficiency ( η_v) in an engine?

    <p>Pressure and temperature at the end of induction</p> Signup and view all the answers

    What does the formula m_f = m_a × F represent in engine operation?

    <p>The relationship between fuel flow and air flow</p> Signup and view all the answers

    In what unit is brake power (BP) usually expressed?

    <p>Kilowatts</p> Signup and view all the answers

    What does volumetric efficiency ( η_v) specifically compare?

    <p>Inducted fuel and air mass to displaced volume mass</p> Signup and view all the answers

    Why is lower heating value (C.V) used in calculating brake power?

    <p>It excludes the energy in water vapor during combustion</p> Signup and view all the answers

    What is one effect of the flow restrictions in the intake system on volumetric efficiency?

    <p>Reduction in mass of inducted gases</p> Signup and view all the answers

    Under ideal conditions, what value range is typical for proper combustion efficiency ( η_comb) in engines?

    <p>0.95 to 0.98</p> Signup and view all the answers

    What is the swept volume (Vst) calculated for the engine?

    <p>0.47 m3/sec</p> Signup and view all the answers

    What is the mass of air moved per second given a density of 1.21 kg/m3 and a swept volume of 0.47 m3/sec?

    <p>0.569 kg/sec</p> Signup and view all the answers

    What is the theoretical air-fuel ratio (A/F)th calculated in the combustion process?

    <p>14.8</p> Signup and view all the answers

    What is the indicated brake horsepower (B.H.P.) delivered by the engine during testing?

    <p>89.44 H.P</p> Signup and view all the answers

    How is the brake specific fuel consumption (b.s.f.c.) calculated?

    <p>m.f / B.P</p> Signup and view all the answers

    What is the brake specific air consumption (b.s.a.c.) found during the engine test?

    <p>3.649 kg/kw.hr</p> Signup and view all the answers

    What is the brake thermal efficiency ($, ext{ exteta}_ ext{ith}$) of the engine?

    <p>25%</p> Signup and view all the answers

    What does the b.m.e.p. stand for in engine testing?

    <p>Brake Mean Effective Pressure</p> Signup and view all the answers

    What is the volumetric efficiency of the engine if it is not provided in the content?

    <p>It cannot be calculated without more data</p> Signup and view all the answers

    Study Notes

    Heat Engines

    • Any machine that uses heat energy from fuel combustion to create mechanical work is a heat engine.
    • Heat engines are categorized into two main types: external combustion engines and internal combustion engines.

    External Combustion Engines

    • Combustion occurs outside the cylinder.
    • Examples include steam engines and gas turbines.
    • These engines are used in locomotives, ships, and electric power generation.
    • Advantages over internal combustion engines:
      • Cheaper fuels can be used (even solid fuels).
      • High starting torque.
      • Self-starting with the working fluid.
      • Flexibility in arrangement.

    Internal Combustion Engines

    • Combustion occurs within the cylinder.
    • Examples include gas engines (using lighter liquid fuels) and diesel engines (using heavier liquid fuels).
    • These engines are commonly used in road vehicles, aircraft, locomotives, and industrial applications.
    • Advantages over external 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

    • Internal combustion engines have one or more cylinders where fuel combustion occurs. (See Figure for labeled parts of an engine cylinder).
    • Key components include a cylinder head valve stem, exhaust valve, inlet valve, spark plug, piston rings, piston, connecting rod, crankshaft, crank case, and sump.

    Cylinder

    • A cylindrical container for piston movement.
    • Must withstand high pressure and temperature.
    • Typically made from cast iron for ordinary engines, and steel alloys or aluminum alloys for heavy-duty engines.
    • Cooled using a water jacket (liquid cooling) or fins (air cooling).
    • The cylinder head encloses the top end, typically bolted to the cylinder block with a gasket for an airtight seal.

    Piston

    • A component that moves up and down inside the cylinder.
    • Transmits the force of burning charge to the connecting rod.
    • Usually made from aluminum alloy for its good heat conductivity and strength at high temperatures.

    Ports and Manifolds

    • Passages in the cylinder head leading to valves.
    • Inlet manifold: system of pipes connecting intake ports to a common intake for various cylinders
    • Exhaust manifold: system of pipes connecting exhaust ports to a common exhaust pipe.

    Connecting Rod

    • Component linking the piston to the crankshaft.
    • Transfers piston motion and thrust to the crankshaft.

    Crankshaft

    • The main rotating part of the engine.
    • Converts the reciprocating motion of the piston to rotational motion.
    • Shape and size depend on the number and arrangement of cylinders.

    Crankcase

    • The main engine body that holds cylinders, crankshaft, and crankshaft bearings.

    Flywheel

    • A large wheel on the crankshaft.
    • Maintains constant speed by storing excess energy during the power stroke and returning it during the other strokes.
    • Keeps the engine running smoothly.
    • Protects parts from explosion and inertia forces.

    Engine Cylinders Geometry

    • Cylinder bore (diameter): Inside diameter of a cylinder.
    • Piston area (A): Area of a circle with diameter equal to the cylinder bore.
    • Stroke (L): Distance the piston travels in a complete up and down motion.
    • Bore/stroke ratio: Relationship between bore and stroke that helps determine the best application for a given engine.
    • Square engine: Engine with equal bore and stroke dimensions (i.e. bore-stroke ratio is 1)
    • Under-square engine: An engine with a longer stroke than bore.
    • Over-square engine: An engine with a shorter stroke than bore.

    Engine Classifications

    • Spark ignition engines (SI): Use spark plugs to ignite the air-fuel mixture (e.g. Otto cycle, gasoline).
    • Compression ignition engines: Use high compression to ignite the air-fuel mixture (e.g. Diesel cycle).

    Fuel Used

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

    Ignition

    • Spark ignition: Uses a spark plug to ignite the air-fuel mixture.
    • Compression ignition: The high temperature from compression ignites the fuel-air mixture.

    Combustion Chamber

    • The chamber where the fuel burns.
    • The design affects performance and knock properties.
    • Different designs are used for SI engines (e.g., non-turbulent L, turbulent wedge L, non-turbulent T, hemispherical) and CI engines (e.g., Honda stratified charge, MCA jet valve).

    Method of Load Control

    • Throttling of fuel and air flow: Mixture composition remains unchanged while throttle valve regulates airflow and hence power.
    • Fuel flow control: Inlet air remains unthrottled and engine power is regulated by the amount of fuel injected.

    Method of Cooling

    • The system of pipes that connects the inlet ports of the various cylinders to a common air or air-fuel intake for the engine.
    • The system of pipes that connects the exhaust ports of the various cylinders to a common exhaust pipe for the engine is exhaust manifold.
    • Water cooled: Water jacket for cooling.
    • Air cooled: Fins for cooling.

    Engine Cycles

    • Otto cycle (spark ignition)
    • Diesel cycle (compression ignition)
    • Dual cycle: Combined features of Otto and Diesel cycles.

    Valve Location

    • Valve in block, L head: Older cars.
    • Valve in head, I head: Common in modern cars.
    • One valve in head and one valve in block, F head: Less common now.
    • Valves in block on opposite sides of cylinder, T head.

    Method of Mixture Preparation

    • Carburetor: mixes air and fuel.
    • Fuel injection: Fuel injected into intake ports, intake manifold, or directly into the engine cylinder.

    Method of Ignition

    • Spark ignition: Spark plug ignites the fuel-air mixture.
    • Compression ignition: High compression ignites the air-fuel mixture.

    Engine Classification

    • Engine is classified by type of ignition, cycle, and fuel and cooling
    • Classification table is presented

    Basic Engine Design

    • Engine structures (e.g., in-line, V, horizontally opposed, radial).
    • Diagram shows the types of engines

    Working Cycle(s)

    • Four-stroke cycle: Four strokes per crankshaft revolution. Each stroke consists of: intake, compression, power, exhaust
    • Two-stroke cycle: Two strokes per crankshaft revolution. The scavenging stroke is used to push out the burned gases.

    Valve Timing

    • Inlet and exhaust valves have specific timing for different operating conditions and engine speeds. Valves can overlap during certain points of the engine cycle.

    Throttle Valves

    • Used to control air intake and maintain appropriate air-fuel ratios during various loads.

    Operation at Full Load

    • Area A: Represents the indicated net work produced within the cylinder
    • Area B: Represents the indicated pumping losses during the engine cycle

    Engines Performance

    • Engine performance is measured by several metrics, including specific fuel consumption, brake mean effective pressure, specific power output, specific weight, and exhaust smoke/emissions.

    Energy Distribution

    • A diagram displaying the distribution of fuel energy into indicated/effective power, heat loss, etc
    • Explanations for losses involved

    Specific Fuel Consumption

    • A measure of fuel efficiency over given time and power
    • The indicated specific fuel consumption (ISFC) and the brake specific fuel consumption(BSFC) are two methods to assess efficiency

    Engine Efficiencies

    • Indicated thermal efficiency (nth)
    • Brake thermal efficiency (n_bth)
    • Mechanical efficiency (n_m)
    • Volumetric efficiency (n_v)
    • Relative efficiency/ Efficiency ratio(n_rel)

    Effect of Fuel-Air Ratio

    • Fuel-to-air ratio influences emissions (e.g., HC, CO, NOx).
    • Optimal ratio for best performance, efficiency, and low emissions.

    Combustion in Spark Ignition Engines

    • The presence of combustible mix for ignition
    • Conditions needed for combustion to take place
    • Mixture preparation in SI engine
    • Methods for mixing the fuel (e.g., carburetor, fuel injection).
    • Ignition process (e.g., spark plug).

    Abnormal Combustion in SI Engines

    • Surface ignition
    • Knock (self-ignition)

    Ignition Delay Period

    • Explanation of the delay period in the combustion process for SI engines.

    Period of Rapid Combustion

    • Explanation of the rapid combustion period in the combustion process.
    • Conditions that contribute to rapid combustion, etc

    After-Burning

    • Explanation of the controlled phase of combustion after the ignition delay stage.

    Diesel Knock

    • Factors related to knock during combustion in diesel engines

    Photochemical Smog

    • NO2 decomposition into NO and monatomic oxygen
    • Ozone formation from monatomic oxygen.
    • Impact of photochemical smog

    Particulate Matter Emissions

    • Sources, characteristics and impact of particulate matter emissions from combustion, etc

    Sulphur Emissions

    • Sulphur compounds and their contribution toward acid rain

    Engine Emission Control Methods

    • Modification in engine design for pollution reduction
    • Exhaust gas treatment methods (e.g., catalysts, EGR).
    • Fuel modifications (e.g., biodiesel blends).

    Supercharging

    • Three approaches are discussed (raising compression ratio, increasing engine speed, and increasing inlet air pressure).
    • Supercharging and turbocharging for increased power
    • Intercooler to improve efficiency
    • Advantages of supercharging/turbocharging

    Octane rating

    • Explanation of the octane number of a given fuel
    • Fuel comparison.

    Cetane Number

    • Explanation of the Cetane number of a given fuel
    • Fuel comparison.

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    Test your knowledge on the differences between two-stroke and four-stroke engines. This quiz covers concepts like thermal efficiency, air standard cycles, and engine performance measurements. Perfect for students studying automotive engineering or related fields.

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