7.1 Define the term torque - NSC Mechanical Technology Automotive - Question 7 - 2018 - Paper 1

The clearance volume of an engine is the volume of the space above the crown of the piston at Top Dead Center (TDC).

1. Remove shims between the cylinder block and cylinder head.
2. Machine metal from the cylinder head.

The swept volume (SV) can be calculated using the formula: SV = rac{ ext{Bore}^2}{4} imes ext{Stroke} Substituting the values, we have: SV = rac{(75 ext{ mm})^2}{4} imes 80 ext{ mm} = 353.43 ext{ cm}^3

The clearance volume (CV) can be calculated using the compression ratio (CR): CR = rac{SV + CV}{CV} Given that the compression ratio is 8.5 : 1:

1. Rearranging the formula: CV = rac{SV}{CR - 1}
2. Substituting in the values: CV = rac{353.43 ext{ cm}^3}{8.5 - 1} = 47.12 ext{ cm}^3

1. First, we calculate the new swept volume using the new bore of 78 mm: SV_{new} = rac{(78 ext{ mm})^2}{4} imes 80 ext{ mm} = 382.27 ext{ cm}^3

2. The new compression ratio (CR) is then calculated as:

Indicated power (IP) can be calculated using: $IP = P imes L imes A imes N imes n$ Where:

• Mean effective pressure, P = 1400 kPa = 1400 × 10³ Pa
• Stroke, L = 110 mm = 0.11 m
• Area, A = $\frac{D^2}{4} = \frac{(100 ext{ mm})^2}{4} = 7.85 \times 10^{-3} m²$
• Engine revolutions, N = 3600 / 60 × 2 = 30 s⁻¹
• Number of cylinders, n = 4

Substituting the values, we get: $IP = 1400 × 10^3 imes 0.11 imes 7.85 \times 10^{-3} imes 30 imes 4 = 145.07 ext{ kW}$

Brake power (BP) is calculated using the formula: $T = F imes r$ Where:

• Torque, T = (75 mm × 10⁻³) × 0.45 = 337.5 Nm

Now, plug the torque back into the brake power formula: $BP = 2 imes ext{Engine speed} imes T = 2 imes 60 imes 337.5 = 127.23 ext{ kW}$

Mechanical efficiency (