INTERNAL COMBUSTION ENGINES

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• Q1: Define I.C Engine.
  Ans: An I.C Engine (Internal Combustion Engine) is an engine in which the fuel burns inside the engine cylinder. The heat energy produced by combustion is directly converted into mechanical energy.
• Q2: Define E.C Engine.
  Ans: An E.C Engine (External Combustion Engine) is an engine in which fuel burns outside the engine cylinder. The heat produced is used to generate steam or another working fluid, which then runs the engine.
• Q3: Name the fuels used in I.C Engine.
  Ans: The fuels used in I.C Engine are:

  • ➔ Petrol
  • ➔ Diesel
  • ➔ Kerosene
  • ➔ CNG (Compressed Natural Gas)
  • ➔ LPG (Liquefied Petroleum Gas)
• Q4: Name the fuels used in E.C Engine.
  Ans: The fuels used in E.C Engine are:

  • ➔ Coal
  • ➔ Wood
  • ➔ Furnace Oil
  • ➔ Nuclear Fuel
• Q5: State the classification of I.C Engine.
  Ans: The classification of I.C Engine is as follows:

  • ➔ According to fuel used
    • ➔ Petrol
    • ➔ Diesel
    • ➔ Gas
  • ➔ According to ignition
    • ➔ Spark Ignition
    • ➔ Compression Ignition
  • ➔ According to number of strokes
    • ➔ Two stroke
    • ➔ Four stroke
  • ➔ According to cooling system
    • ➔ Air cooled
    • ➔ Water cooled
• Q6: Define Petrol Engine.
  Ans: A petrol engine is an I.C engine that uses petrol as fuel. It works on spark ignition system where the air-fuel mixture is ignited by a spark plug.
• Q7: Define Gas Engine.
  Ans: A gas engine is an internal combustion engine that uses gaseous fuel such as CNG or LPG. The fuel mixes with air and burns inside the cylinder to produce power.
• Q8: Define Diesel Engine.
  Ans: A diesel engine is an internal combustion engine that uses diesel as fuel. In this engine, fuel burns due to high compression of air without using a spark plug.
• Q9: Define Spark Ignition Engine.
  Ans: A spark ignition engine is an engine in which the air-fuel mixture is ignited by a spark plug. Petrol engines are examples of spark ignition engines.
• Q10: Define Compression Ignition Engine.
  Ans: A compression ignition engine is an engine in which fuel burns due to high temperature produced by compressing air. Diesel engines are examples of compression ignition engines.
• Q11: Define Hot Spot Ignition Engine.
  Ans: A hot spot ignition engine is an engine in which fuel is ignited by a heated surface inside the combustion chamber. It does not use a spark plug for ignition.
• Q12: Define Two Stroke Cycle Engine.
  Ans: A two stroke cycle engine completes one power cycle in two strokes of the piston (one crankshaft revolution). Suction, compression, expansion, and exhaust processes are completed in two strokes.
• Q13: Define Four Stroke Cycle Engine.
  Ans: A four stroke cycle engine completes one power cycle in four strokes of the piston (two crankshaft revolutions). The four strokes are suction, compression, power, and exhaust.
• Q14: Define OTTO Cycle Engine.
  Ans: An OTTO cycle engine works on the Otto cycle. In this cycle, heat is added at constant volume. Petrol engines generally operate on this cycle.
• Q15: Define Diesel Cycle Engine.
  Ans: A diesel cycle engine works on the diesel cycle. In this cycle, heat is added at constant pressure. Diesel engines operate on this principle.
• Q16: Define Dual Combustion Cycle Engine.
  Ans: A dual combustion cycle engine works on a cycle in which heat is added partly at constant volume and partly at constant pressure.
• Q17: Define Slow Speed Engine.
  Ans: A slow speed engine is an engine that operates at low rotational speed. It is generally used in heavy machinery and marine applications.
• Q18: Define High Speed Engine.
  Ans: A high speed engine is an engine that runs at high rotational speed. It is commonly used in automobiles and motorcycles.
• Q19: Define Medium Speed Engine.
  Ans: A medium speed engine operates at moderate speed between slow and high speed engines.
• Q20: Define Air Cooled Engine.
  Ans: An air cooled engine is an engine in which heat is removed by air flowing over the engine surface.
• Q21: Define Water Cooled Engine.
  Ans: A water cooled engine is an engine in which water is used to remove heat from the engine cylinder.
• Q22: Define Evaporative Cooling Engine.
  Ans: An evaporative cooling engine is an engine in which cooling takes place by evaporation of water. The heat of the engine causes water to evaporate and remove heat.
• Q23: Define Carburettor Engine.
  Ans: A carburettor engine is an engine in which air and fuel are mixed in a carburettor before entering the cylinder.
• Q24: Define Air Injection Engine.
  Ans: An air injection engine is an engine in which fuel is injected into the cylinder using compressed air.
• Q25: Define Solid Injection Engine.
  Ans: A solid injection engine is an engine in which fuel is directly injected into the combustion chamber without using compressed air.
• Q26: Define Radial Engine.
  Ans: A radial engine is a multi-cylinder engine in which cylinders are arranged in a circular pattern around the crankshaft.
• Q27: Define In-line multicylinder Engine.
  Ans: An in-line multicylinder engine is an engine in which multiple cylinders are arranged in a straight line.
• Q28: Define Side Valve Engine.
  Ans: A side valve engine is an engine in which the valves are located beside the cylinder.
• Q29: Define Overhead Valve Engine.
  Ans: An overhead valve engine is an engine in which the valves are placed above the cylinder head.
• Q30: Define Hit and Miss Governed Engine.
  Ans: A hit and miss governed engine controls speed by skipping fuel supply during some cycles when speed increases.
• Q31: Define Quantitatively Governed Engine.
  Ans: A quantitatively governed engine controls speed by varying the quantity of fuel supplied to the engine.
• Q32: Define Qualitatively Governed Engine.
  Ans: A qualitatively governed engine controls speed by varying the quality or strength of the fuel-air mixture.
• Q33: State the processes of the Engine's cycle.
  Ans: The cycle of the Engines consists of following processes:

  • ➔ Suction
  • ➔ Compression
  • ➔ Expansion
  • ➔ Exhaust
• Q34: Define Suction Stroke.
  Ans: Suction stroke is the first stroke of an engine cycle. During this stroke, the piston moves downward and the inlet valve opens. The air or air-fuel mixture enters the cylinder.
• Q35: Define Compression Stroke.
  Ans: Compression stroke is the second stroke of an engine cycle. During this stroke, the piston moves upward and compresses the air or air-fuel mixture inside the cylinder. The pressure and temperature of the mixture increase.
• Q36: Define Expansion Stroke.
  Ans: Expansion stroke is the power producing stroke of the engine. During this stroke, the fuel burns and high-pressure gases push the piston downward. This produces useful mechanical work.
• Q37: Define Two Stroke Cycle Engine.
  Ans: A two stroke cycle engine completes one power cycle in two strokes of the piston (one revolution of crankshaft). All four processes — suction, compression, expansion, and exhaust — are completed in two strokes.
• Q38: Define Four Stroke Cycle Engine.
  Ans: A four stroke cycle engine completes one power cycle in four strokes of the piston (two revolutions of crankshaft). The four strokes are suction, compression, power, and exhaust.
• Q39: Define Cylinder Bore.
  Ans: Cylinder bore is the inner diameter of the engine cylinder. It determines the size of the piston and affects the engine capacity.
• Q40: Define Stroke Length.
  Ans: Stroke length is the distance traveled by the piston from top dead center (TDC) to bottom dead center (BDC).
• Q41: Define Clearance Volume.
  Ans: Clearance volume is the small volume of space left in the cylinder when the piston is at top dead center (TDC).
• Q42: Define Total Cylinder Volume.
  Ans: Total cylinder volume is the sum of swept volume and clearance volume.
  Total Volume = Swept Volume + Clearance Volume
• Q43: Define Compression Ratio.
  Ans: Compression ratio is the ratio of total cylinder volume to clearance volume.
  Compression Ratio = Total Cylinder Volume / Clearance Volume
• Q44: Define Mean Effective Pressure.
  Ans: Mean effective pressure is the average pressure acting on the piston during one complete engine cycle. It is used to compare the performance of engines.
• Q45: Briefly explain the working of a Petrol Engine.
  Ans: In a petrol engine, air and petrol are mixed in a carburettor and drawn into the cylinder. The mixture is compressed by the piston. A spark plug ignites the mixture and produces high-pressure gases. These gases push the piston downward to produce power.
• Q46: Briefly explain the working of Two Stroke Petrol Engine.
  Ans: In a two stroke petrol engine, the suction and compression take place in the first stroke. The spark plug ignites the mixture and power is produced in the second stroke. Exhaust gases leave the cylinder and fresh mixture enters during the same stroke.
• Q47: Briefly explain the working of Four Stroke Petrol Engine.
  Ans: In a four stroke petrol engine, the working is completed in four strokes:

  • ➔ Suction Stroke — Air-fuel mixture enters the cylinder.
  • ➔ Compression Stroke — Mixture is compressed.
  • ➔ Power Stroke — Spark plug ignites mixture and piston moves down.
  • ➔ Exhaust Stroke — Burnt gases are expelled out.
• Q48: Briefly explain the working of Diesel Engine.
  Ans: In a diesel engine, only air enters the cylinder during suction stroke. The air is highly compressed, increasing its temperature. Diesel fuel is then injected into the hot air, and it burns automatically. The expanding gases push the piston downward to produce power.
• Q49: Briefly explain the working of Two Stroke Diesel Engine.
  Ans: In a two stroke diesel engine, air enters and gets compressed in the first stroke. Fuel is injected into the hot compressed air and combustion takes place. In the next stroke, power is produced and exhaust gases leave the cylinder.
• Q50: Briefly explain the working of Four Stroke Petrol Engine.
  Ans: In a four stroke petrol engine, suction, compression, power, and exhaust strokes occur separately. The spark plug ignites the compressed air-fuel mixture and produces power.
• Q51: What is Indicated Power?
  Ans: Indicated power is the total power developed inside the engine cylinder due to combustion of fuel.
• Q52: What is Brake Power?
  Ans: Brake power is the useful power available at the crankshaft of the engine.
• Q53: What is Friction Power?
  Ans: Friction power is the power lost due to friction between moving parts of the engine.
  Friction Power = Indicated Power — Brake Power
• Q54: What is Mechanical Efficiency?
  Ans: Mechanical efficiency is the ratio of brake power to indicated power.
  Mechanical Efficiency = Brake Power / Indicated Power
• Q55: What is Overall Efficiency?
  Ans: Overall efficiency is the ratio of brake power to the fuel energy supplied to the engine.
• Q56: What is Relative Efficiency?
  Ans: Relative efficiency is the ratio of actual efficiency to air standard efficiency.
• Q57: What is Volummetric Efficiency?
  Ans: Volumetric efficiency is the ratio of actual volume of air drawn into the cylinder to the swept volume of the cylinder.
• Q58: What is Air Standard Efficiency?
  Ans: Air standard efficiency is the efficiency of an ideal engine cycle working with air as the working fluid.
• Q59: What is Indicated Thermal Efficiency?
  Ans: Indicated thermal efficiency is the ratio of indicated power to the heat energy supplied by fuel.
• Q60: What is Brake Thermal Efficiency?
  Ans: Brake thermal efficiency is the ratio of brake power to the heat energy supplied by fuel.
• Q61: What is Mean Effective Pressure?
  Ans: Mean effective pressure is the average pressure acting on the piston during one cycle that produces the same work as actual varying pressure.
• Q62: What is Swept Volume?
  Ans: Swept volume is the volume displaced by the piston when it moves from top dead center (TDC) to bottom dead center (BDC).
• Q63: What is the Clearance Volume?
  Ans: Clearance volume is the volume remaining in the cylinder when the piston is at top dead center.
• Q64: What is Stroke Length in I.C Engine?
  Ans: Stroke length in an I.C engine is the distance traveled by the piston between top dead center (TDC) and bottom dead center (BDC).
• Q65: How does ignition take place in a Petrol Engine?
  Ans: In a petrol engine, ignition takes place with the help of a spark plug. The spark plug produces an electric spark at the end of compression stroke, which ignites the compressed air-fuel mixture.
• Q66: Write the formula of Indicated Power in an I.C Engine.
  Ans: The formula of Indicated Power (I.P) is:
  I.P = (P_m × L × A × N) / 60
  Where,

  • ➔ P_m = Mean effective pressure
  • ➔ L = Stroke length
  • ➔ A = Area of piston
  • ➔ N = Number of power strokes per minute