The replacement of conventional centrifugal pumps of Internal Combustion Engine (ICE) with volumetric pumps, in particular Sliding Rotary Vane Pump (SVRP), leads to a proven reduction of fuel consumption and CO2 emissions. Nevertheless, due to the complex thermo-fluid-dynamic phenomena tanking place inside these machines, their design is not straightforward. In particular for the case of Heavy Duty ICE where the design is more critical due to the wide operating range of the pump in terms of flow rate delivered. In fact, it varies from 50 L/min up to 600 L/min according to the cooling requests and a pressure increase which strongly depends on the cooling circuit of the order of 1-2.5 bar. The adoption of these pumps for cooling needs is unconventional and the study and the prototype presented represent a first attempt to demonstrate the feasibility and the improvements in terms of efficiency with respect to a centrifugal conventional machine. A volumetric machine has, in fact, an efficiency which is less dependent on flow rate and pressure delivered. The only way to increase the flow rate in a SVRP is to increase the revolution speed for a given volumetric design. For a specific flow rate, a SVRP running faster reduces the machine dimension and, consequently, the weight and the space required on board. However, operating at higher speed could severely penalize the pump performance due to the growth of the friction losses and the need to expensive surface treatments or, more generally, with the adoption of materials which resist to higher mechanical stresses. This would increase cost and decrease reliability, both unsuitable for the component which must insure the cooling of the engine.
The research group of University of L’Aquila (having a decennial expertise on the sliding vane rotary machines and on pumps) defined in this research a novel design approach for a SVRP strictly referred to Heavy Duty (HD) ICEs. The proposed design approach is based on the increase of the volumetric capability of the machine, without producing a dimension increase, i.e. weight and dimension. This was possible optimizing the eccentricity (difference between stator and rotor radii) keeping under control all the main parameters involved (blade motion inside the rotor’s slots, noise appearance, shear stress on the blade and its centrifugal force). A particular care is reversed on the design of the intake and exhaust ports which definitively influences the volumetric efficiency, allowing a complete filling and emptying of the vanes, so reducing flow recirculation inside the machine. So, the pump increases the flow rate delivered, for a specific outer dimension, being possible an operation at lower speed which increases mechanical efficiency, reducing friction losses. In order to experimentally demonstrate the benefits introduced of the Low Speed (LS) SVRP, two prototypes were built in collaboration with O.M.P. Officine Mazzocco Pagnoni Srl, a Company leader in the production of oil SVRP in the transportation sector (passenger, light and heavy duty engines). The Company is also widely known as supplier of high efficiency centrifugal pumps in the HD sector. The two prototypes differ on the blades material, being it bronze and graphite, being the latter less conventional than the former. The choice of these two materials was inspired by the reduction of the blade weight (graphite vs bronze) which implies a lower friction loss but a centrifugal force decrease which, reducing the impact of the blade of the stator, tends to increase the leakages among vanes. A trade-off between these two effects is required in order to find the maximum pump efficiency. Experimental evidences of the two pumps demonstrate that also in the case of blades made with a customized graphite the volumetric efficiency keeps close to 90% with a sensible increase of the mechanical efficiency. The advantage on the whole pump performance introduced by the adoption of graphite is significant reaching the prototype a maximum efficiency close to 60% in a wide range of flow rates, sensibly greater than that when a centrifugal pump is considered. Moreover, the SVRP with blades made with bronze also ensures a quite satisfactory performance, slightly lower than 60 % but with a superior reliability due to the reduced tip blade wear. The experimental characterization also regarded the indicated cycle evaluated thanks to high-speed pressure measurements done using piezo-resistive transducers mounted on the machine cover. Thanks to an accurate procedure which suitably sequenced the raw pressure data, the indicated cycle was accurately measured giving a formidable feedback on the thermo-fluid-dynamic phenomena taking place inside the machine. The wide experimental dataset allowed to validate a comprehensive theoretical model of the two prototypes which can be used as a software platform for a model-based design. A further improvement of the pump performance can be expected. Once validated, the model was used to compare the performances of the LS SVRP and the centrifugal pump of the reference ICE (an IVECO CURSOR 13) over a WHTC homologation cycle. The results show that the graphite-blades prototype requires about 11% less energy over the WHTC compared to a state-of-the-art centrifugal pump.
Two different prototypes of the SVRP (bronze blades and graphite blades) were built and tested by O.M.P. – Officine Mazzocco Pagnoni Srl (https://www.omppumps.com/).
Two publications on the subject of the coolant pump have been realised to-date:
- “On the Optimal Design of Sliding Rotary Vane Pump for Heavy-Duty Engine Cooling Systems Corresponding.”
Authors: Fabio Fatigati, Davide Di Battista, Marco Di Bartolomeo, Luigi Mariani and Roberto Cipollone, University of l’Aquila. - “Feasibility Assessment of a Dual Intake-Port Scroll Expander Operating in an ORC-Based Power Unit.”
Authors: Fabio Fatigati, Giammarco Di Giovine, Roberto Cipollone, University of l’Aquila.
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