β_CM : Correction coefficient of combustion with fuel properties (HFO/MDO)

β_FL : Correction coefficient of load fluctuation

β_OP : Correction coefficient of engine operating point

　

In comparison between load index power and shaft horse power, the relation is shown in equation (5) and (6).

　

P_TM = P₁₃ × C　　(5)

　

C = η / η_o　　(6)

　

where

C : Constant

　

In general, the constant C is within the range of shown in equation (7).

　

　

5. ANALYSIS FOR CAUSES DIFFERENCE BETWEEN LOAD INDEX POWER AND SHAFT HORSE POWER

　

Regarding the engine load fluctuation which are described in equation (4) as cause of worse efficiency, actual results of measurement at sea trial are shown in Figure 4. Load fluctuation were given by steering with predetermined frequency which was longer than rough sea condition. It can be observed to change for the worse of specific fuel consumption on the lower load range especially.

　

Figure 4 Changing of specific fuel consumption by load fluctuation

　

Figure 5 shows the worse of specific fuel consumption with ratio of engine load fluctuation on the horizontal scale. It is confirmed that the engine efficiency becomes worse engine load fluctuation on rough sea.

　

Figure 5 Worse of specific fuel consumption with ratio of engine load fluctuation

　

6.CONCLUSIONS

　

Load index power is calculated with engine load index (pump mark) and engine speed. In other words, this is a method which calculates the engine output power with heat input for the engine and engine efficiency at the shop trial. However, on the sea going, it is considered that the engine efficiency is not same value as the engine shop trial actually, because some deviation of such condition as kind of fuel, load fluctuation and atmospheric. Accordingly, it is required to correct the calculated load index power to shaft horse power by the equation (5).

Load index power gives an indicator of engine heat load, however it is not suitable to measure the shaft horse power indirectly. Therefore, for measurement of shaft horse power during sea trial, we consider it is necessary to use such shaft power meter as torsion meter.

For the subject of future study, it is required to clarify quantitatively the lowering of efficiency caused by kind of fuel and engine load fluctuation.

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