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6.1 With reference to the crankshaft, give THREE reasons for using the correct firing order on an internal combustion engine - NSC Mechanical Technology Automotive - Question 6 - 2021 - Paper 1
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6.1 With reference to the crankshaft, give THREE reasons for using the correct firing order on an internal combustion engine. 6.2 State TWO ways in which dynamic im... show full transcript
Worked Solution & Example Answer:6.1 With reference to the crankshaft, give THREE reasons for using the correct firing order on an internal combustion engine - NSC Mechanical Technology Automotive - Question 6 - 2021 - Paper 1
Step 1
With reference to the crankshaft, give THREE reasons for using the correct firing order on an internal combustion engine.
Answer
The correct firing order is crucial for several reasons:
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Twisting Effect Reduction: Correct firing order helps to overcome the twisting effect of power strokes on the crankshaft, which can lead to mechanical failures if not managed properly.
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Vibration Minimization: Using the correct order reduces vibrations within the engine, contributing to smoother operation and reducing wear on components.
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Engine Lifespan Improvement: An appropriate firing order increases the lifespan of the crankshaft and other engine parts by ensuring balanced operation.
Step 2
State TWO ways in which dynamic imbalance of the crankshaft can be corrected.
Answer
Dynamic imbalance can be addressed through:
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Balance Mass Addition: Fitting balance mass pieces to the crank webs to counteract imbalances.
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Material Adjustment: Removing metal from the crank webs to achieve a more balanced configuration.
Step 3
State FOUR causes of engine vibration.
Answer
Common causes of engine vibration include:
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Torque Variability: The varying quantity of torque produced on power strokes can lead to vibrations.
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Crankshaft Imbalance: If the crankshaft is not balanced, it can result in oscillations.
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Faulty Components: Worn or loose engine components may contribute to excessive vibrations.
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Incorrect Air/Fuel Ratio: An incorrect air/fuel ratio can cause engine misfires and vibrations.
Step 4
Give the degrees of crankshaft rotation between power impulses for each of the following four-stroke engines:
Answer
The degrees of crankshaft rotation between power impulses are as follows:
6.4.1 4-cylinder engine: 180°
6.4.2 5-cylinder engine: 144°
6.4.3 6-cylinder engine: 120°
6.4.4 8-cylinder engine: 90°
Step 5
Step 6
Describe the operation of the Roots supercharger.
Answer
The Roots supercharger operates as follows:
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Power Source: The engine drives the rotors using means like belts or gears.
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Rotor Mechanism: It consists of two symmetrical rotors that rotate in opposite directions.
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Air Compression: Air trapped between the rotors and the casing is pushed from the inlet side to the discharge side, increasing pressure.
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Pressure Increase: This design effectively increases the air pressure in the intake manifold, enhancing engine performance.
Step 7
What is the function of the following components on an internal combustion engine equipped with a variable geometry turbocharger:
Answer
The functions are:
6.6.1 Intercooler: It cools the air compressed by the turbocharger, reduces its volume, and increases density, improving volumetric efficiency.
6.6.2 Vanes: The vanes adjust the flow of exhaust gases, optimizing the turbine speed for improved performance.
Step 8
State THREE advantages of a supercharger when compared to a turbocharger.
Answer
Advantages of a supercharger include:
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Instant Response: Superchargers deliver power instantly, as they are mechanically driven by the engine, providing immediate boost.
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Simpler Installation: They are generally easier to install than turbochargers, requiring fewer modifications to the engine setup.
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Cooling System Independence: Superchargers typically do not require an intercooler for operation, simplifying the overall cooling system.