Development and experimental assessment of a Low Speed Sliding Rotary Vane Pump for heavy duty engine cooling systems

Abstract

Sliding Rotary Vane Pumps (SVRPs) are real candidates to replace the conventional centrifugal machines for engine cooling systems. Differently from the centrifugal pumps, SVRP performances are theoretically independent from the operating conditions, preventing in this way a lower efficiency when the machines work far from the design point. To achieve these benefits, however, the SVRP should be properly designed especially in those applications characterized by high flow rate of coolant delivered as in the case of heavy-duty engine cooling systems. A common design approach is the increase of flow rates pushing SVRPs to operate with high speeds of revolution, aiming to minimize the pump dimensions for space and weight constraints on board. Nevertheless, friction power lost is recognized as the main limit of this positive displacement technology and grows with revolution speed. Hence, SVRPs employed in cooling systems of heavy-duty internal combustion engines (ICEs) are particularly critical from this point of view.Considering this aspect, a novel design method is developed based on the reduction of operating revolution speed, increasing the chambers volume, but through a refined optimization of the volumetric, indicated and mechanical efficiencies reached by a model-based approach.Chamber volume enhancement has been performed thanks to a slight increase of the pump radial dimension (+3%) which produces a significant growth (+27 %) of the chamber volume without a significant effect on the overall pump size. This ensures the reduction of revolution speed satisfying the space and weight requirements.Volumetric and indicated efficiencies have been improved adopting a dual intake and exhaust port solution. Mechanical efficiency was investigated and improved via the use of lighter blades (graphite). Attention has been paid to the negative feedback on volumetric efficiency produced by the leakage increase among adjacent chambers.Therefore, a Low-Speed LS SVRP was designed for a Natural Gas 13L engine (IVECO CURSOR 13). A prototype was built and tested for a revolution speed ranging between 250 RPM and 2000 RPM and a pressure rise and flow rate interval equal respectively to 0.05–2 bar and 50–500 L/min. A novel aspect of the experimental campaign is the assessment of pressure variation inside the chambers which provides fundamental information about the fluid-dynamic behavior of the machine. Measurements allowed to characterize volumetric, indicated and mechanical performances. Moreover, data were used to validate a comprehensive model-based platform which was the tool for further design refinement and processes understanding.The experimental analysis shows efficiency values around 60%, well beyond what was achievable with centrifugal pump with an efficiency which keeps significantly higher at off design conditions with respect to a centrifugal pump. Moreover, the LS SVRP was experimentally compared with a SVRP designed with a conventional method observing an efficiency improvement up to 25 %.