2.1 Data concerning all engines
2.1.7 Load application
PDS: 230 110
Load application from 0% to 100% rating (ISO 8528-5 requirements)
For applications in the range from 0% to 100%
of the site rating, the requirements according to Section 9 and Figure 6 of ISO 8528-5: 1993 ap-ply. Please also refer the figure below.
Depending on the mean effective pressure of the engines a load application from 0 to 100% re-sults in the number of load steps an their per-centages given in the table below.
Figure 2-13 Load application in steps as per ISO 8528-5
Table 2-1 Mean effective pressures and application loads according to ISO 8528-5 The percentage of the load steps referring to a bmep of 24.8bar in the diagram.
Engine bmep 1st step 2nd step 3rd step 4th step
bar % % % %
32/40 21.9 ... 24.9
33 23 18 26
48/60 22.6 ... 23.2
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Load application from any basic load (ISO 8528-5 requirements)
Based on ISO 8528-5 requirements, the applica-tion rates shown in the following figure are re-quired for load application from any basic load:
Figure 2-14 Load application depending on the current load according to ISO 8528-5 Reference pressure bmep = 24.8bar
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Load application allowed by MAN B&W Die-sel
As a standard MAN B&W Diesel allows higher load application than required by ISO 8528-5, see the figure below.
Figure 2-15 Load application depending on the current load allowed by MAN B&W Diesel AG
Requirements for plant design
• Load application according to Table 2-1, Page 2-18, and Table 2-14, Page 2-19, must be taken into consideration for the plant de-sign.
• Running-up and loading times have to be in accordance with Chapter 2.1.4 "Engine Run-ning-in", Page 2-12.
• For the design of a plant with isolated electri-cal systems take Chapter 2.1.10 "Generator plants in isolated operation", Page 2-30, into consideration.
Jet-Assist
For power plants, jet-assist is necessary if load application >25% of the engine output is re-quired.
Important
It is absolutely necessary that all questions re-garding the dynamical behaviour of the engines are clarified prior to contract conclusion and for all customer requirements and MAN B&W Diesel AG confirmations are fixed in writing in the deliv-ery contract.
Load reduction
Sudden load throw-off
The sudden load throw-off represents a rather exceptional situation and corresponds to open-ing the generator switch of a Diesel-electric plant.
Care is to be taken that, after a sudden load throw-off, the system circuits remain in opera-tion at least 5 min. to 10 min. in order to dissi-pate the residual engine heat.
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Recommended load reduction / stopping the engine
• Unloading the engine
In principle, there are no regulations with re-gard to unloading the engine. However, a minimum of 1 min. is recommended for un-loading the engine from 100% PNominal to ap-prox. 25% PNominal.
• Engine stop
As from 25% PNominal, further engine unload-ing is possible, without interruption, and af-terwards the engine can be stopped.
• Run-down cooling
In order to dissipate the residual engine heat, the system circuits should be kept in opera-tion for a minimum of 5 min.
Part-load operation
Definition
Generally the following load conditions are dif-ferentiated:
• Over-load (for regulation):
>100% of full load output
• Full-load: 100% of full load output
• Part-load: <100% of full load output
• Low-load: <25% of full load output
Correlations
The ideal operating conditions for the engine prevail under even loading at 60% to 90% of the full-load output. Engine control and rating of all systems are based on the full-load output.
In the idling mode or during low-load engine op-eration, combustion in the cylinders is not ideal.
Deposits may form in the combustion chamber, which result in a higher soot emission and an in-crease of cylinder contamination.
Moreover, in low-load operation the cooling wa-ter temperatures cannot be regulated optimally
high for all load conditions which, however is of particular importance during operation on heavy fuel oil.
Better conditions
Engines are genuinely better equipped for low-load operation
• if they have a two-stage charge-air cooler, the second stage of which can be switched off in order to improve the operating data or
• if they have a two-stage charge-air cooler and switch-over from HT to LT has been pro-vided for, permitting the admission of HT wa-ter to the LT stage.
HT: High temperature LT: Low temperature
Operation on heavy fuel oil
Because of the aforementioned reasons, low-load operation <20% of full low-load on heavy fuel oil is subjected to certain limitations. According to Figure 2-16, Page 2-22, the engine must, after a phase of part-load operation, either be switched over to Diesel operation or be operat-ed at high load (>70% of full load output) for a certain period of time in order to reduce the de-posits in the cylinder and exhaust gas turbo-charger again.
In case the engine is to be operated at low-load for a period exceeding that shown in Figure 2-16, Page 2-22, the engine is to be switched over to Diesel oil operation beforehand.
For continuous heavy fuel oil operation at part loads in the range <25% of the full engine out-put, co-ordination with MAN B&W Diesel is ab-solutely necessary.
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Operation on Diesel fuel
For low-load operation on Diesel fuel oil, the fol-lowing rules apply:
• A continuous operation below 15% of full load is to be avoided, if possible.
Should this be absolutely necessary, MAN B&W Diesel has to be consulted for special
arrangements (e.g. the use of part-load injec-tion nozzles).
• A no-load operation, especially at nominal speed (generator operation) is only permitted for a maximum period of 1...2 hours
No limitations are required for loads above 15%
of full load, as long as the specified operating data of the engine will not be exceeded.
Figure 2-16 Time limits for part-load operation on heavy fuel oil (on the left), duration of “relieving operation“(on the right)
P Full load output [%] t Operating period [h]
Explanations
• Figure on the left:
Time limits for part-load operation on heavy fuel oil
• Figure on the right:
Necessary operation time at >70% of full-load output after part-full-load operation on heavy fuel oil. Acceleration time from present output to 70% of full-load output not less than 15 minutes.
Example Line a:
At 10% of full-load output, HFO operation is permissible for maximum 19 hours, then switch over to Diesel fuel oil, or
Line b:
Operate the engine for approx. 1.2 hours at not less than 70% of full-load output to burn away the deposits that have formed. Subsequently, part-load operation on heavy fuel oil can be con-tinued.
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