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Politecnico di Torino team develops Common Feeding injection system as next-gen alternative to common rail

Catania
Diagrammatic view of a possible common feeding injection system application, from the patent document. Click to enlarge.

Andrea Catania and Alessandro Ferrari at the Politecnico di Torino have developed a new fuel injection system (FIS) concept that does away with the rail from the high-pressure circuit of standard common rail (CR) injection systems, replacing it with a new hydraulic layout for high-pressure fuel injection. Removing the rail from the high-pressure circuit can reduce production costs, enable easy installation on the engine, and deliver a fast dynamic response during engine transients, the team says.

Core to the Common Feeding (CF) injection system concept is a newly patented high-pressure pump machined with extra delivery ports in order to obtain direct connection with each of the injector feeding pipes. A special pump delivery-chamber provides the minimum hydraulic capacitance required for a proper control of the high-pressure in the system.

The conventional common rail system comprises a high pressure pump (HP), which pulls fuel from a tank by means of a low pressure pump (LP); multiple injectors, which inject the fuel received from the pump into respective combustion chambers; a rail mounted to the engine between the pump and the injectors; a pressure sensor for measuring the pressure in the rail; and a valve for adjusting the pressure in the rail by means of the action of a control unit and of the pressure sensor.

Previous work has focused on improving CR system performance by focusing on the injectors, especially on making small openings and electromagnetically actuated actuators. CR systems can also suffer from the propagation of undesired pressure waves along the feeding ducts between the rail and the injectors caused by the opening and closing cycles of the injectors; these pressure waves propagate in each feeding duct toward the rail. Studies have also tackled optimizing the geometry of the feeding ducts to either avoid or reduce resonance phenomena caused by pressure valve interference.

Catania, Ferrari and colleagues only recently began investigating the role of the rail, as reported in a 2007 SAE paper, Common Rail without accumulator: development, theoretical-experimental analysis and performance enhancement at DI-HCCI level of a new generation FIS.

Experimental measurements proved that a CR system with a smaller volume than the volumes normally used has operating features similar to those of a system made and operating on currently marketed vehicles.

In the SAE paper, they suggested that the performance of the pressure control system in the rail is linked to the synergy between the actions of the pressure adjusting valve and of the storage volume rather than only the action of the latter. In particular, the working cycle of the adjusting valve can be modified by varying the volume of the rail while the required pressure level can still be satisfactorily controlled.

From this, they said, it was possible to take into consideration the possibility of considerably decreasing the volume of the rail without negatively affecting, rather even improving, the dynamic features of the system.

The new system comprises a low-pressure pump for aspirating fuel from a tank; a constant displacement high pressure pump connected to the delivery of the LP pump; a storage volume connected to the delivery of the HP pump and injectors connected to the storage volume and controlled by a control unit. The storage volume is obtained in the pump body.

The pump body has outlet ports connected to the storage volume in parallel to one another; the ducts which connect the pump to the injectors are mounted directly onto the pump body.

The control device comprises a pressure sensor and a throttling valve, preferably a solenoid valve. The pressure sensor and the throttling valve are installed on the pump body and are fluid-dynamically connected to the storage volume.

The control unit controls the throttling valve so that the latter conveys to the tank all the delivery flow in excess from the pump on the basis of the pressure value measured by the pressure sensor.

In a paper in the March 2012 edition of the journal Applied Energy, Catania and Ferrari report on setting up a prototype of the CF injection system and subjected it to testing on an advanced hydraulic rig. They report on the the hydraulic performance of the new apparatus compared with that of standard Common Rail system in terms of injected flow-rate time histories, cycle-to-cycle dispersion and multiple injection dependence on dwell time.

They also installed the new-generation system on a Euro 5 diesel engine and tested it in a dynamometer-cell. Pollutant emissions were measured at some reference working conditions as well as along the NEDC and compared to analogous data obtained for the same engine using the standard Common Rail.

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