It is also proved from the combustion pressure diagram in the cylinder in Fig.3 that the ignition lag is increased by the increase of the water addition ratio under the constant load, and the CO concentration in the exhaust gas is rapidly increased when the load reaches 50% or under as illustrated in Fig.4, and its trend becomes remarkable as the water addition ratio is increased. The increase in the CO concentration is an index to indicate the defective combustion, and in summing up, it is proved that the operation using the emulsified fuel in the low load area is not suitable at any water addition ratio.
The load on the electric generator means the power load to be consumed onboard the ship, which is fluctuated according to the time zone, and is not always constant due to the presence of the equipment in the engine room to repeat the stop/start, and due to the change in the navigational condition and the life pattern of the crew. Taking into consideration these factors, the water addition ratio in the full operation was decided to 30% which is relatively small in influence on the diesel engine against the fluctuating load in an extensive range, and effective in reducing the NOx concentration.
In addition, the additive was poured in the emulsified fuel. This was poured for the purpose of promoting and maintaining the unification of the properties, and keeping the lubrication effect in each parts of the fuel system2), and the pouring ratio was set as the volumetric ratio to the emulsified fuel.
3.1 Full running condition of emulsified fuel
Based on the results of the above-described analyses, the emulsified fuel running conditions in the full running operation to examine the influence on the components of the equipment (hereinafter, referred to as "full running") are as follows.
1] The electric loads are 200kW (50%) to 300kW (75%) in principle, and the loads shall be stable. (For example, the unstable loads in leaving/arriving conditions shall be avoided.)
2] The water addition ratio shall be constant at 30%.
3] The additive pouring ratio shall be constant at 0.5%.
3.2 Precautions in operation
In achieving the full running using the emulsified fuel, the precautions predicted from the results of the measurement operation were determined as follows.
1] When the emulsified fuel running is completed, the operation of the diesel engine is continued for about one hour even after the switching operation in order to sufficiently switch the A-oil in the fuel oil system.
2] In addition to the monitoring of the regular operation of the diesel engine, the drain is removed from the bottom part of the secondary filter of the fuel oil system one a day, the drain is separated to remove water settled therein, and the emulsifying condition of the emulsified fuel.
3] When the power load is out of the emulsified fuel running condition, the fuel is switched to the A-oil if the power reaches 200kW or under, or the other diesel engine is started to achieve the parallel running if the power reaches 300kW or over.
4. Full running operation of emulsified fuel
4.1 Operational schedule and maintenance
Three sets of diesel engines are equipped on board Nippon Maru for electric generators, and the annual operational schedule of each diesel engine is substantially uniformly divided into three parts (about 2,900 hours). The electric generator No.3 served for the test was also operated following the regular schedule. The regular maintenance work was also achieved with the normal maintenance intervals.
