Question

Tractor engine is designed to produce maximum torque at a speed

• A. at which maximum power is developed
• B. lower than the speed at which maximum power is developed
• C. higher than the speed at which maximum power is developed
• D. at which minimum power is developed

Hint:

Torque peaks early (low rpm), Power peaks later (rated rpm). The gap between them provides the engine's 'lugging power'.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Engine characteristic performance curves plot brake torque, brake power, and specific fuel consumption against rotational engine speed (rpm).
Key Formula or Approach:
\[ P_{\text{brake}} = \frac{2\pi N T}{60,000} \text{ (kW)} \]
\[ \text{Torque Backup (\%)} = \frac{T_{\text{max}} - T_{\text{rated}}}{T_{\text{rated}}} \times 100 \]

Step 2: Detailed Explanation:
In tractor diesel engines, maximum torque is deliberately engineered to peak at an engine speed significantly lower than the rated speed for maximum power (typically around 60% to 75% of rated rpm).
When a tractor encounters a sudden heavy draft load (such as a hard soil patch while ploughing), the engine speed naturally drops.
Because maximum torque occurs at a lower speed, dropping rpm causes the engine torque to automatically increase.
This phenomenon, known as torque reserve or torque backup (lugability), prevents the engine from stalling under sudden field overloads.

Step 3: Final Answer:
Therefore, maximum torque is produced at a speed lower than the speed at which maximum power is developed, matching option (B).