Subtopic: Thermodynamic principles of I.C. engines
Question Statement:
Which of the following statements regarding tractive efficiency and traction mechanics of agricultural tractors are CORRECT?
Options:
(A) Tractive efficiency is defined as the ratio of drawbar power to axle power delivered to the drive wheels.
(B) Tractive efficiency reaches zero at both $0\%$ slip (zero net pull) and $100\%$ slip (zero forward velocity).
(C) On firm cohesive soils, optimum tractive efficiency for 2WD tractors typically occurs in the slip range of $8\%$ to $15\%$.
(D) Ballasting drive wheels always increases rolling resistance without any effect on dynamic traction coefficient.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
Statements A, B, and C are correct:
- Tractive efficiency $\eta_t = P_{db} / P_{axle} = (P \cdot v) / (T \cdot \omega)$.
- At zero slip, net pull is zero; at 100% slip, forward speed is zero, so $\eta_t = 0$ at both extremes.
- Optimum tractive efficiency occurs between 8% and 15% slip on firm soil (10-18% on tilled soil).
- Statement D is false: proper ballast increases dynamic weight and available tractive pull, significantly improving traction coefficient on firm soil.