MAN B&W common rail fuel system description needed.
13 Jan '17, 14:18
A common rail servo oil system applies the cool, clean and pressurized lube oil to power the fuel injection pump of each cylinder. Each cylinder unit is provided with a servo oil accumulator to ensure sufficiently swift delivery of oil in accordance with the requirements of the injection system, and to avoid heavy pressure oscillations in the associated servo oil pipe system. The movement of the pump plunger is controlled by a fast-acting proportional control valve (a socalled NC valve), which, in turn, is controlled by an electric linear motor thatreceives its control input from a cylinder control unit. The fuel injection pump features well proven technology, and the fuel valves are of a standard design. Second- and third-generation fuel injection pumps are much simpler than the first-generation design, and their components are smaller and easier to manufacture (Figure 10.38). A major feature of the third-generation pump is its ability to operate on heavy fuel oil; the pump plunger is equipped with a modified umbrella design to prevent heavy fuel from entering the lube oil system. The driving piston and injection plunger are simple and kept in contact by the fuel pressure acting on the plunger and the hydraulic oil pressure acting on the driving piston. Both the beginning and the end of the plunger stroke are controlled solely by the fast-acting NC valve, which is computer controlled. Optimum combustion (and thus optimum thermal efficiency) calls for an optimized fuel injection pattern, which in a conventional engine is generated by the fuel injection cam shape. Large two-stroke engines are designed for a specified maximum firing pressure and the fuel injection timing is controlled so as to reach that pressure with the given fuel injection system (cams, pumps, injection nozzles). For modern engines, the optimum injection duration is around 18–20° crank angle at full load, and the maximum firing pressure is reached in the second half of that period. To secure the best thermal efficiency, fuel injected after the maximum firing pressure is reached must be injected (and burned) as quickly as possible in order to obtain the highest expansion ratio for that part of the heat released. From this, it can be deduced that the optimum ‘rate shaping’ of the fuel injection is one showing an increasing injection rate towards the end of injection, thus supplying the remaining fuel as quickly as possible. The camshaft of the conventional engine is designed accordingly, as is the fuel injection system of the ME engine. In contrast to the camshaft-based injection system, however, the ME system can be optimized at a large number of load conditions.MAN Diesel claims that the fuel injection system for the ME engines can execute any sensible injection pattern needed to operate the engine. It can perform as a single-injection system as well as a pre-injection system with a high degree of freedom to modulate the injection in terms of injection rate, timing, duration, pressure or single/double injection. In practice, a number of injection patterns are stored in the computer and selected by the control system for operating the engine with optimum injection characteristics from dead slow to overload, as well as during astern running and crash stop. Changeover from one to another of the stored injection characteristics may be executed from one injection cycle to the next. (Woodyard D. - POUNDER Marine Diesel Engines and Gas Turbines - 9 Edition
13 Jan '17, 14:21