Comparison on the energy absorbed of volumetric and centrifugal pumps for automotive engine cooling

Engine thermal management can reduce significantly CO2 emissions in road vehicles without altering sensibly the engine layout. However, more efficient auxiliaries also participate to fuel consumption saving and, therefore, to CO2 emissions reduction. Typically, centrifugal cooling pumps are adopted as circulating devices, but their efficiency varies highly with rotational speed, wasting energy during real operation despite being optimized at the design point. Instead, volumetric pumps keep a high efficiency also far from it, enhancing the overall engine efficiency. In this paper, the performances of a screw-type volumetric pump have been compared with those of a centrifugal pump considering the same cooling circuit of a mid-size engine for passenger vehicles. Both pumps have been designed to satisfy the cooling flow rate required by the engine during a homologation cycle, while verifying their capability to cool the engine operating at maximum power. Once prototyped, the pumps performance maps have been measured, showing a high Best Efficiency Point for both cases. However, the screw pump has better performance in off-design conditions, being the centrifugal pump efficiency strictly dependent on its rotational speed which significantly changes during a real driving. The comparison of the two pumps has been done by reproducing the WLTC on a dynamic test bench. The rotational speed of the volumetric pump has been adjusted to deliver the same flow rate produced by the centrifugal pump as requested by the engine. Results show that the prototyped screw-type volumetric pump absorbs 21% less energy than the prototyped centrifugal pump, reducing CO2 emissions by 0.28 g/km.