Royal Belgian Institute of Marine Engineers Common Rail Injectors With Poppet Valve Switzerland-based Ganser Common Rail Systems (Ganser CRS) tested common rail injectors with its proprietary poppet valve for multiple injection in locomotive engines and micro pilot injection in dual- fuel marine engines. The design of the Ganser CRS injectors includes the proprietary poppet valve, a hydraulic switching device which has proven to be a very stable and reliable solution. In detail investigations of this poppet valve have been evaluated using the dedicated 1-D simulation software LMS Imagine. Lab Amesim, which enables simulations of complex systems with interaction of mechanics, hydraulics and electro mechanics, and have also been confirmed with measurements on several engine applications. Thanks to its unique design, the poppet valve can be applied for the very small injection quantities used in micro pilot applications as well as for large main diesel injections in locomotive engines retrofits. Results of the simulation have shown that the poppet valve movement is governed by three surfaces with the corresponding pressure levels: the high pressure feed, the valve volume and the control volume. Therefore the poppet valve position results from the pressures on its three surfaces. During the non-energized time of the solenoid, the three forces are equalized, resulting in an arbitrary position of the The inside of a Ganser CRS injector used for diesel engines. poppet valve. For the small injection quantities required for micro tate-of-the-art common rail injection is required pilot applications, e.g. 50 mm3/stroke with a common for diesel engines to meet the stringent rail pressure of 1000 bar, the nozzle needle remains Semission requirements and to reduce the fuel in the ballistic domain and does not reach its limit consumption. Besides the increasing demand for stop. As the nozzle needle hits the nozzle seat at the higher injection pressures, a variety of performance end of injection, pressure fluctuations are generated parameters are required. For multiple injections, the and travel through the injector. However, thanks to opening and closing response time of injectors should the design of the poppet valve, these pressure be as fast as possible and the injector should be able fluctuations do not influence the opening to reopen shortly after it was closed. At the same characteristics for multiple injections. These pressure time, the dynamic leakage for actuation of the fluctuations are additionally dampened with Ganser injection valve should be kept low in order to save CRS’s proprietary Wave Dynamics and Dampening pumping energy. device (WDD), which minimizes the influence on A linear relationship between the injection quantity other injectors in the system. and the control signal duration is also desirable for a It has been observed that the injection rate raises good controllability. Last but not least, the injection with a defined slope during the opening of the performance should be guaranteed over a long injector. This is favourable in order to reduce period of time without changes in injection combustion noise and emissions. characteristics. The simulated forces acting on the nozzle needle shaft (closing the needle) and nozzle needle rod (opening the needle) as well as the lifts of the poppet valve and the nozzle needle for a MP type injector. By contrast, the injection rate decreases rapidly when The simulation was extended to the poppet valve the injector closes, leading to favourable end-of- design in applications with multiple injections, and a combustion conditions. locomotive injector with a common rail pressure of For reproducible pre- or post-injections, the 1600 bar and an injection quantity of 1500 hydraulic environment in the injector and the mm3/stroke was modelled. The simulation covered a hydraulic switching elements need to reset to their main injection duration of 4 ms with pre- and post- initial state quickly after any injection. Furthermore, a injections of 0.6 ms each. fast hydraulic switching and nozzle needle movement The simulation has shown that, thanks to the is necessary to allow further injections shortly after poppet valve, very short injection delays can be the previous injection. These requirements are achieved. The injection rates show a characteristic fulfilled with the poppet valve and the corresponding “kink” shortly after start of injection. control hydraulics. Simulated multiple injection rates and injector’s accumulator pressure for a locomotive type injector at 1600 bar and 1500mm3/stroke (cumulated). This is due to the lifting of the nozzle from its seat types: the first one an injector for micro pilot and thus rapidly changing the hydraulic forces acting injection in a six-cylinder dual fuel marine engine, on the nozzle needle. used for gas ignition; in this case the injection The performance of common rail injectors equipped quantity is low, typically about 50-100 mm3/stroke in with the poppet valve has been actually normal operation mode. This was possible thanks to demonstrated on engines with two different injector the accurate switching characteristics of the poppet valve at such small injection quantities. With the The second type was a common rail injector for an application of the Ganser proprietary Wave Dynamics ALCO 16-cylinder vee diesel locomotive engine with and Dampening System and injector-integrated 3-MW output power (a brand of Fairbanks Morse accumulators, the rail could be replaced completely Engine). This specifically designed and built common by so-called jumper lines. rail ALCO injector (CR-ALCO) is replacing the Tests demonstrated that the engine runs stable in gas mechanical ALCO injector without any modifications mode, with gas ignited by the diesel marine oil required to the engine’s cylinder head. The required injected by the MP system, and IMO Tier 3 emission injection quantity at full load is about 1000 level was achieved. mm3/stroke. Performance map of the common rail ALCO injector for different pulse durations and rail pressures. In this retrofit project, the existing mechanical fuel consumption on a typical driving cycle was recorded injection system was replaced by a tailor-made in parallel to substantial emissions reductions. common rail system; the injector included an Multiple injections for noise reduction were also integrated accumulator for maximized and constant successfully implemented, whereas the fuel return injection pressures during the whole injection was found to be only 4% of the injected quantity. process. Each cylinder bank was equipped with a It was thus demonstrated that the poppet valve separate slim rail and a dedicated high pressure design is essential to reach key performance criteria pump, allowing for a freely configurable injection up in both injectors: good controllability, fast end of to 1600 bar. injection, zero static leakage, stroke-to-stroke, and The ALCO engine runs smoothly, efficiently and with excellent long-term stability. a clean exhaust. The start of injection and injection Ganser CRS said the poppet valve design is applicable pressures were optimized at each operating point in in numerous fields, locomotive and marine engines terms of fuel consumption. About 6-10% reduced fuel being only two of them. BY Kilian Zimmermann, Richard Haefeli and Marco Ganser, at Ganser CRS AG, Winterthur, Switzerland Editor’s Note: The detailed paper has been presented and published at the 28th CIMAC World Congress 2016 in Helsinki, Finland. Copyright of this paper is with CIMAC, the International Council on Combustion Engines. Common rail system for one cylinder bank of a 16-cylinder ALCO engine. Source: http://dieselgasturbine.com .