The IMO NOx regulation Tier 1 for marine engines came into effect on May 19, 2005. Further, more stringent regulation IMO Tier 2 and Tier 3 will become effective in 2011 and in 2016 respectively. Tier 2 NOx regulation shall be reduced by about 20% and Tier 3 NOx regulation shall be reduced by 80% in Emission Control Areas. To comply with these regulations, recent 4-stroke engines have been developed mainly with consideration to the environmental, but also taking economy, durability and maintainability, etc. into account. A concept of simultaneous reduction of both of NOx and BSFC was established by simulation analyses and engine tests by the Niigata Comp. back in the 1990s. This concept has been adopted to our engines to comply with present regulation. Furthermore, other advanced technologies have been studied to comply with future legislation, especially for IMO Tier 2 and Tier 3. Strategies for future emission standards, through developments and studies, are described for the medium speed engines.

View full abstract

The outline of Tier 2 and Tier 3 NOx reduction regulations of IMO became clear at the meeting of MEPC57, which was held on this spring. Tier 2 can be achieved using conventional technologies; timing retard, engine tuning, electronically control of fuel injection and water technologies. However, Tier 3 will not allow such technologies, which are not able to achieve the future regulation line. The most closed technology is the after treatment system; SCR (Selective Catalytic NOx Reduction system) . SCR has some problem to install the vessels which are propelled by the 2-stroke cycle low speed diesel engines. The biggest problem is the low temperature of exhaust gas, which is under the 300 °C. In the atmosphere of the exhaust gas with Ammonium under the 300°C, it is generated the acid ammonium sulfate, which coated on the surface of catalyst and decrease the effectiveness of chemical reaction. In conventional trials of SCR on actual vessels, all SCRs were installed before turbochargers in order to avoid the low temperature exhaust gas. However, with SCR installed before turbocharger is not convenient for the partial load operation or coastwise services.

View full abstract

With order-type tramper allocation, an operator receives an order from a cargo owner for cargo to be transported and so must make a shipping schedule to execute all the order, completely. To transport orders efficiently it is critical to group and ship cargoes together efficiently and avoid the occurrence of conflict in the tramper's hold. We try to solve this order-type tramper allocation problem by applying a network model, and a constraint programming (CP) . This paper describes an optimization algorithm based on the CP. This optimizes a tramper's allocation in terms of fuel consumption. The results of the algorithm are demonstrated.

View full abstract

The International Maritime Organization (IMO) is working for the further advancement of regulation in NOx emission reduction for ship's diesel engines. As for Tier III, which is assumed to be entering into force in 2015, two proposals were discussed at the 11th meeting of BLG Subcommittee in February 2008. One was a uniform regulation over the world with 40% to 50% reduction from the Tier I regulations. The other was a geographically controlled regulation with an 80%, or higher, reduction for a designated area. Tier II level for others are applied. In the present study, a simple diffusion model is employed to estimate the NOx concentration over the land area for the case that each regulation is applied. Simulation studies have revealed that an appropriate distance given as the boundary in the geographical regulation could reduce the NOx concentration over a land area, to a comparable level as the uniform regulation can be estimated to achieve.

View full abstract

The IMO is reviewing the MARPOL 73/78 Convention ANNEX VI to reduce SOx emissions from ships, and to lower the sulphur content in marine fuel oils. This paper estimates the proportion of SOx emissions from world shipping in the biogeochemical sulphur cycling. Also it discusses the situation of supply and demand of elemental sulphur and the increase in refinery energy due to desulphurization of marine fuel oils.
SOx emissions from shipping worldwide are estimated at 4.54 Tg per annum as of elemental sulphur. This accounts for 6.1% of anthropogenic emissions and 8.7% of natural emissions over the land to the atmosphere. The average sulphur content in marine fuel oils at the moment is 2.7% according to the IMO, and if it was reduced to 0.9% (as low as that of diesel oil), then SOx emissions from shipping would be reduced to 3.4% of the natural emissions over the land to the atmosphere. The elemental sulphur desulphurized from marine fuel oils would amount to 2.8 Tg per annum. However, this should find ways to be utilized under the present situation of supply and demand of sulphur. Refinery energy would increase - due to desulphurization - by as much as 6% of the heating value of fuel oils. This implies that it is necessary to further improve transportation efficiency and avoid a carbon dioxide emission increase.

View full abstract

The three-dimensional flows in the Weis-Fogh mechanism are studied by flow, and numerical simulation by the vortex method. The vortex method -- especially the vortex stick method, is employed to investigate the vortex structure in the wake of the two wings. The pressure is estimated by the Bemoulli equation, and the lift on the wing is also obtained. It was found that the eddies near the leading edge of each wing, in the fling stage take, take a convex shape. This was because the eddies shed from both tips entrain the flows, and the downwash in the rotating stage is deflected toward the outside. The outside tip vortex is stronger than the inside vortex. The lift coefficient on the wings in this mechanism is almost independent of the Reynolds number.

View full abstract

Most catastrophic mechanical failures in propeller shafts occur by the surface cracks. These, are due to fatigue under cyclic bending combined with steady torsion: Mode I combined with steady Mode III. An analysis of the influence of steady torsion loading on a fatigue crack in shafts is presented for semi-elliptical surface cracks; this by way of the VNA Solution-Finite Element Alternating Method (VNA-FEAM) . Long cracks growth analysis has been done on cylindrical models in steel. Cyclic bending combined with steady torsion in order to simulate real conditions on power rotor shafts. The growth and shape of the evolution of semi-elliptical surface cracks, starting from the surface of a cylindrical model, has been analyzed under several loading conditions. The results show a significant reduction of the crack growth rate when a steady torsion Mode III is superimposed to cyclic Mode I. In this paper, the VNA-FEAM analysis also indicates that Stress Intensity Factor (SIF) values at the corner of the crack's surface, of the shaft model, are closely related with the steady torsion value and depend on the direction of the applied torque.

View full abstract

The authors have studied the torsional vibration characteristics of a crankshaft system consisting of a six-cylinder engine for a large ship which has a five-bladed propeller in the case where one cylinder misfires. In such a case, the amplitude of torsional vibrations due to the sixth torsional harmonic reduces compared with that in case of a normal operation. However, the forth and fifth torsional harmonics increase; therefore, the amplitude of the torsional vibrations corresponding to these components also increases. In particular, the torsional vibration stress due to the forth torsional harmonic component increases; therefore, it is necessary to ensure that the allowable stresses on the shaft are not exceeded.

View full abstract

We present here the numerical simulation on the dynamic characteristics of a waste heat recovery Stirling engine. This Stirling engine employs the high temperature exhaust energy of a marine Diesel engine as a heat source. The engine has an electric generator in the crank space. That is to say of the hermetic type, and the electric output from the generator serves as a continuous battery charger. The charged electricity in the batteries will be used as a power source for working machines in a harbor and thus contribute to a reduction of harmful exhaust gases in the harbor area. During a voyage the engine deals with various changes in running conditions, such as heat input and load conditions. So, it is very important to understand the engine dynamic behavior, even in unexpected conditional changes, such as a sudden loss of load from the engine. In this paper we demonstrate how to build up a simulation, and some dynamic simulation results are presented. Finally, we discuss one of the results when compared with an experimental result.

View full abstract

The purpose of this study is to establish a practical method based on a chemical kinetic model for three-dimensional numerical analysis of the combustion process in direct-injection diesel engines. For saving computational time, a reduced elementary reaction scheme for diesel fuel was constructed. The basis was the Golovitchev detailed elementary reaction scheme. Using an original engine combustion simulation code GTT-CHEM along with the reduced elementary reaction scheme, the combustion process was three-dimensionally analyzed in a direct-injection diesel engine with high-EGR ratios.
As a result, the combustion process and NO emission were quantitatively predicted by estimating the initial gas state and the initial composition appropriately. The emission tendency of soot was reasonably assessed by means of φ-T maps.

View full abstract