7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke and compression stroke. How do the compression stroke and power stroke affect the pressure? 7.3 FIGURE 7.3 below shows a cylinder with the piston at TDC and the same cylinder with the piston at BDC. The following information is applicable: Volume (V1) of the space when the piston is at TDC = 39 cm³ Space between TDC and BDC (V2) = 330 ml Distance between TDC and BDC is 65 mm Answer the questions that follow. 7.3.1 Which term is used to describe the volume V1? 7.3.2 Which term is used to describe the volume V2? 7.3.3 Calculate the total cylinder volume in cm³. 7.3.4 Calculate the bore diameter in mm. 7.3.5 Calculate the compression ratio of this cylinder. 7.4 State TWO methods to lower the compression ratio in an internal combustion engine. 7.5 The following data refers to a two-cylinder two-stroke petrol engine: Engine speed during test: 6 500 r/min Cylinder displacement (volume): 580.7 cm³ Mean effective pressure: 450 kPa Brake power: 48 kW @ 6 500 r/min Determine the following by means of calculations: 7.5.1 Torque 7.5.2 Indicated power in kW 7.5.3 Mechanical efficiency

NSC Mechanical Technology Automotive Basic calculations: 7.1 Define the following terms r

7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke and compression stroke - NSC Mechanical Technology Automotive - Question 7 - 2021 - Paper 1

Question 7

7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke ... show full transcript

Worked Solution & Example Answer:7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke and compression stroke - NSC Mechanical Technology Automotive - Question 7 - 2021 - Paper 1

Step 1

Define Brake Power

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Answer

Brake power is the usable power or actual power developed at the flywheel or at the drive wheels, calculated by the output power divided by the input power.

Step 2

Define Torque

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Answer

Torque is the twisting effort or force applied on a shaft or wheel, measured over the applied radius.

Step 3

How do the compression stroke and power stroke affect the pressure?

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Answer

The compression stroke leads to an increase in pressure as the volume decreases. In contrast, the power stroke results in a decrease in pressure as the combustion process occurs and the volume increases.

Step 4

Which term is used to describe the volume V1?

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Answer

V1 is referred to as the clearance volume.

Step 5

Which term is used to describe the volume V2?

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Answer

V2 is referred to as the swept volume.

Step 6

Calculate the total cylinder volume in cm³.

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Answer

The total cylinder volume is calculated by adding the clearance volume and the swept volume:

Total ext{ }cylinder ext{ }volume = V_1 + V_2 = 39 ext{ cm}^3 + 330 ext{ cm}^3 = 369 ext{ cm}^3.

Step 7

Calculate the bore diameter in mm.

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Answer

Using the formula for the swept volume:

Swept ext{ }Volume = \frac{\pi D^2}{4} \times L

We already know the swept volume as 330 cm³ and the length (L) is 65 mm:

D^2 = \frac{(330 \times 4)}{\pi \times 65} ightarrow D \approx 80.4 ext{ mm}.

Step 8

Calculate the compression ratio of this cylinder.

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The compression ratio (CR) is calculated as follows:

CR = \frac{Total ext{ }cylinder ext{ }volume}{Clearance ext{ }volume} = \frac{369}{39} \approx 9.46.

Step 9

State TWO methods to lower the compression ratio in an internal combustion engine.

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Answer

Fit a thicker gasket between the cylinder block and cylinder head.
Use pistons with suitable lower crowns.

Step 10

Calculate Torque.

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Using the formula:

T = \frac{BP}{2\pi N} = \frac{48 \times 1000}{2\pi \times 6500} \approx 70.52 ext{ Nm}.

Step 11

Calculate Indicated Power in kW.

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Answer

Using the formula:

IP = PLAN = 450 \times 10^3 \times 580.7 \times 10^{-6} \times 108.33\times 2 \approx 56.6125 ext{ kW}.

Step 12

Calculate Mechanical Efficiency.

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Answer

The mechanical efficiency is calculated as:

\eta = \frac{BP}{IP} \times 100 \approx \frac{48}{56.6125} \times 100 \approx 84.78\%.

7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke and compression stroke - NSC Mechanical Technology Automotive - Question 7 - 2021 - Paper 1

Worked Solution & Example Answer:7.1 Define the following terms regarding an internal combustion engine: 7.1.1 Brake power 7.1.2 Torque 7.2 The indicated power diagram represents the power stroke and compression stroke - NSC Mechanical Technology Automotive - Question 7 - 2021 - Paper 1

Define Brake Power

Define Torque

How do the compression stroke and power stroke affect the pressure?

Which term is used to describe the volume V1?

Which term is used to describe the volume V2?

Calculate the total cylinder volume in cm³.

Calculate the bore diameter in mm.

Calculate the compression ratio of this cylinder.

State TWO methods to lower the compression ratio in an internal combustion engine.

Calculate Torque.

Calculate Indicated Power in kW.

Calculate Mechanical Efficiency.

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