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PhD Thesis - Energy Systems Research Unit - University of Strathclyde

PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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engines running respectively). If the possible percentage load is below 100%<br />

and above minimum load, one engine is used at this percentage. The desired<br />

number <strong>of</strong> engines will always be available, otherwise, the condition that<br />

there was not enough fuel to meet the required consumption would not have<br />

been met. The specific fuel consumption must then be recalculated at this new<br />

percentage loading, and the process repeated until the difference between the<br />

last calculated specific fuel consumption and the current calculated specific fuel<br />

consumption is minimal (e.g. plus or minus 0.0001).<br />

If the efficiency is being used, the above process cannot be followed, as the<br />

calculation <strong>of</strong> the possible engine power, which may be calculated by rearranging<br />

Equations 5.33, 5.35 or 5.36 as appropriate, would result in ever<br />

decreasing operating powers. This is due to the fact that, in the equations, the<br />

efficiency is being multiplied by, rather than divided by, which is the case with<br />

the specific fuel consumption. Another approach has, therefore, been taken<br />

where the actual fuel consumptions at the percentages for which the efficiency<br />

values are quoted, are calculated, and the possible percentage load with the fuel<br />

available is calculated by interpolation between these points. If more than one<br />

engine is available, the fuel available is checked to see if it is above four times<br />

the 100% load fuel consumption. If so, the fuel available is divided by five, all<br />

five engines are used, and the percentage load possible with the available fuel is<br />

calculated. If this results in a loading less than the minimum load, four engines<br />

are run at full load. This is repeated for above three times the 100% load fuel<br />

consumption, above two times, and above the 100% load fuel consumption. If<br />

less than the 100% load fuel consumption is available, one engine is used, and<br />

the fuel consumption is calculated as before. This approach is slightly less<br />

accurate due to its use <strong>of</strong> linear variation between the percentage load points, but<br />

it is adequate for this purpose. The algorithm for determining the fuel<br />

consumption and finding the percentage load that is possible with the available<br />

fuel as necessary, if the efficiency is being used, is shown in Figure 5.14.<br />

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