Uec Design Details

Structural and design details are exemplified by the UEC 75LSII and 85LSII engines (Figure 11.10). The bedplate and column are of simple welded monoblock construction, and the partition for each cylinder consists of a single welded plate. Side forces are supported by horizontal steel ribs arranged behind the guide bar. The pistons are of the well

*CIT: Controllable injection timing

Figure 11.10 Construction of UEC 75LSII engine

*CIT: Controllable injection timing

Figure 11.10 Construction of UEC 75LSII engine proven central support type and are fitted with four rings (Figure 11.11). Hard chromium plating applied to the running surfaces of the rings improves wear resistance under high pressure and corrosion resistance in a low temperature corrosive environment. Chromium plating the ring grooves has the same purpose, as well as improving

Figure 11.11 Improvements in piston design from the original UE engine component (left) to the HA model (centre) and the current L and LS types (right)

the durability of the rings by ensuring normal movement in the grooves.

The lower part of the cylinder liners feature controlled swirl scavenging (CSS) ports which promote improved scavenging efficiency and hence favourably influence fuel consumption and thermal load. The angle of the lower scavenging port is directed towards the centre of the cylinder to discharge combustion gas on the piston top; and the angle of the upper port is directed sideways to discharge gas around the inner surface of the liner. The CSS configuration (Figure 11.12). reportedly raises scavenging efficiency by 5-7 per cent over the conventional port arrangement. Two-row bore liner cooling is incorporated and cylinder lubrication is timed so as to reduce oil consumption. Corrosive liner wear, caused by low temperatures, is inhibited by controlled positioning of the cooling bores.

The single exhaust valve of each cylinder has a hydraulic rotation system which rotates the valve to improve running control conditions. The rotation wings are fitted on the actuator piston on the exhaust valve side, an arrangement which is said to offer less obstruction to exhaust gas passage than with the traditional rotator wing mounted on the valve spindle. A water-cooled valve seat is specified.

The Bosch fuel pumps have control racks to adjust the quantity of fuel supplied. The controllable injection timing (CIT) pumps also ensure that engine performance is improved at the service load (Figure

11.13). Two side-injection non-water-cooled fuel injection valves (Figure

11.14) are arranged on each cylinder cover; a steam passage is provided for warming the valve body when the engine is stopped.

Figure 11.12 Comparison of gas flow in cylinder with original UE engine scavenging and controlled swirl scavenging (CSS)
Figure 11.13 Controllable injection timing (CIT) fuel oil pump
Figure 11.14 Lightweight (20 kg) non-cooled fuel injection valve for UEC-LSII eng

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An optional AFR (automatic flexible rating) control system can be specified to reduce fuel consumption during part-load operation by co-ordinating the engine output with the operational conditions of the ship. The system (Figure 11.15) controls the fuel delivery timing of the injection pump by using the CIT system to produce maximum cylinder pressure, and also controls the turbine nozzle area of the variable geometry (VG) turbocharger to secure an optimum scavenging air pressure. The CIT fuel injection pumps, offered as standard with LSII engines, are operated by a governor when the AFR control system is not installed.

A mean time-between-overhaul of four years was targeted for the LSII engines, Mitsubishi citing contributions from the following key elements:

• Piston rings and cylinder liners, yielding respective wear rates of 0.2 mm/1000 hours and 0.02 mm/1000 hours or less.

• Reliable hydraulically rotated exhaust valves with stellite-coated stems and seats.

• Easily maintained fuel injection valves.

• High performance piston gland packing (stuffing box drainage of less than 10 litres/day/cylinder, and a low wear rate scraper ring).

Mitsubishi's R&D priorities mirror those of its two rivals in the low speed engine arena, with emphases on further upratings of designs, enhancing reliability and durability, and reducing noxious emissions. Its resources include the group's main research centre at Nagasaki. Mitsubishi has investigated all aspects of exhaust gas de-NOxing technology, including the direct injection of water into the combustion chamber. Its stratified injection system-based on a fuel valve designed to inject fuel—water—fuel sequentially—has achieved NOx reductions of around 50 per cent without significantly increasing fuel consumption and is offered as an option for UEC-LSE engines (See Chapter 3).

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    How to calculate Rectified fuel pump rack value and Mitsubishi UEC engine?
    2 years ago

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