2. DESIGN CONCEPT
The developments of this V20FX high power density diesel engine is based on the three pillars as well as the present high-speed including other FX series engine and medium-speed engine program. The formers are theoretical analysis, experimental analysis s and much service experience as shown in Fig.2. Furthermore, the later is based on the 16Vl6FX (16 cylinders - 165 mm bore × 185 mm stroke, Pme: 1.97 MPa, Cm: 12.0 m/s) which have been widely applied for land and marine uses since 1992.
Through these analyses and experience, the following basic designs were introduced to accomplish the above targets.
2.1. Light Weight and Compactness
(1) 60 degrees vee angle with reducing the total width to a minimum.
(2) The minimum between centers with maintaining the required bearing width.
(3) Adoptions of high efficiency auxiliary equipment and generous use of lightweight alloys.
The target of masses to power ratio was set up about 3 kg/kW.
2.2. Durability and Reliability
(1) Composite piston constituted steel crown with bore cooling used for V20FX by high Pmax and high Pme. Furthermore, thermal load and mechanical load on the components around the combustion chamber, including pistons, cylinder heads and liners, were kept to the present levels.
(2) To ensure low vibrations, a balance rate of 15% was achieved by fitting large balance weight to crank shaft and by reducing the weight of the piston and connecting rod. Furthermore, machined area was significantly increased to reduce the deviation in weight.
(3) Lube oil condition is one of the most important factor of high reliability and durability of bearing and other components. Therefore, inlet temperature of lube oil are kept below 70℃.
2.3. High Performance and Low Emission
(1) Introduction of high efficiency turbocharger
(2) High pressure and short period injection with optimum swirl
(3) Optimum Pmax/Pcomp combustion for reducing NOx
2.4. Simple Structure and Easy Maintenance
(1) By reducing the number of external pipes and installing an intake and exhaust system in V-shaped bank, a significant space around the fuel injection pump could be kept.
(2) The exhaust pipe system was simplified by the compact static pressure charging system.
(3) By installing crank case doors on both sides, maintenance and inspection within the engine room could be facilitated for dismantle of the piston and inspection of the main bearing
3. DESIGN OF PRINCIPAL COMPONENT
3.1 Crankshaft
The ship's classification dictates the dimensions for the crankshaft. However, there are cases where depending on the materials and size of non-metal inclusion, the fatigue strength may drop significantly. Therefore, we used highly pure materials with a maximum non-metal inclusion content (S content) of 0.01%. [l] [2]
Furthermore, the roughness of the machined surfaces of the crankshaft's pin and journal influences on the degree of wear on the shaft and bearing. When the roughness decreases, the wear on the shaft decreases. [2] Fig.4 shows the relationship between shaft roughness and wears on the shaft and bearing.
From this result and the experience of Vl6FX engine, which used the crankshaft manufactured above method, we set the maximum Rmax less than 1S. [1] [3]
