Engine Cooling Systems Questions and Answers

Answer: B

The pump is a centrifugal pump.

In the forced (pump) circulation cooling system of a tractor engine, a small centrifugal impeller pump, usually driven by the same V-belt as the fan, circulates coolant from the bottom of the radiator through the water jackets of the cylinder block and head and back to the radiator. The job needs a large flow at a low head, and a centrifugal pump does that simply, with no valves and no risk of damage if the flow is throttled by the thermostat.

Piston, gear and vane pumps are positive displacement pumps. They suit high pressure and small flow, such as fuel injection or the lubrication and hydraulic systems, and would be needlessly complex and noisy for coolant circulation.

Answer: C

The fan efficiency is about 63%.

Brake power of the engine:

\[ \begin{aligned} P_{b} &= \frac{2\pi N T}{60} = \frac{2(3.14)(2000)(382)}{60} \\ &\approx 79\,965\ \text{W} \end{aligned} \]

The fan takes 5% of this, about 3998 W. The useful (air) power it delivers is the volume flow times the pressure rise:

\[ \begin{aligned} P_{air} &= Q\,\Delta p = 2.8 \times 900 = 2520\ \text{W} \\ \eta &= \frac{2520}{3998} \approx 0.63 \end{aligned} \]

So the efficiency is nearest to 63%. Rounding the brake power to 80 kW (fan input 4000 W) still gives 63%. The distractors would need different fan inputs: 65% about 3880 W, 60% 4200 W and 58% about 4350 W, none of which is 5% of this engine's brake power.