Attention to all marine engineers!
Rules for proper evaluation of the M/E performance (for two stroke MAN ES).
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The maximum pressure (Pmax) of each cylinder should not differ more than ±3 bar from the average Pmax of all cylinders. The Pmax is related to the fuel injection timing and is a result of both injection and ignition timing.If it does, the engine is considered imbalanced.
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If the average Pmax of all cylinders deviates more than –3bar compared to the Test-Bed Average Pmax that indicates a retarded ignition timing. This could be caused by:
- Poor fuel characteristics
- VIT adjustment (in MC engines)
- Malfunction of the Hydraulic Cylinder Unit and/or tacho system (in ME engines)
- Worn fuel equipment (fuel valves, fuel pumps, suction valves etc.)
- Fuel oil pressure
- Low Pcomp
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The maximum pressure at compression (Pcomp) of each cylinder should not deviate more than ±3 bar from the average Pcomp of all cylinders. If it does, the engine is considered imbalanced.
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If the average Pcomp of all cylinders if deviates more than –3bar compared to the Test-Bed Average Pcomp, it indicates possible blow-by, due to:
- Poor scavenge air pressure
- Blow-by due to leaking exhaust valve(s)
- Low exhaust valve opening / or closing stroke
- Malfunction of the Hydraulic Cylinder Unit (in ME engines)
- Blow-by from piston rings
- Blow-by from cylinder liners
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The Pi of each individual cylinder must not deviate more than ±0.5bar compared to all the cylinders average Pi. The Pi corresponds to cylinder’s load. If it does, the engine is considered unbalanced.
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The average Pi of all cylinders if deviates more than ±0.5bar compared to the Test-Bed average Pi indicates possible worn fuel equipment. This is to be examined together with Fuel Index.
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The Pressure Rise (Pmax – Pcomp) must not exceed the specified limit, i.e.:
- MC/MC-C-35 bar
- ME/ME-C-38-40 bar
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The exhaust gas temperature of each cylinder’s outlet should not vary more than ±50°C from the average temperature. If the temperature deviates more than ±60°C, the slowdown function is activated. Check cylinder pressure performance, but never adjust it based on exhaust temperature, as it will disrupt Pi balance.
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The LO pressure at the M/E turbocharger inlet should never go above 1.5 - 2.2 bar. If it does, it is a sign that a pipe is obstructed and/or there is a clogged orifice in the pipe connection, which could result in damage to the T/C bearings.
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If the M/E turbocharger turbine outlet pressure (back pressure) goes above 300mmWC @ MCR (without a funnel, economizer, or scrubber) or exceeds 150% of the pressure stated in the Shop Test Performance, it suggests a blockage in the exhaust pipe after the turbine or a clogged turbocharger nozzle ring. If an economizer is installed, this could also indicate obstructed gas pathways. This parameter should be evaluated along with exhaust temperatures.
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The scavenge temperature should not exceed 45⁰C (normally). The cooler it is, the better. This is considered as a general principle. In central cooling systems, the 3-way valve should be set to 10 ⁰C to guarantee that the water remains as cold as possible.
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The pressure drop across the air cooler air should not go above 240mmWC @ MCR or exceed 150% of the pressure drop specified in the shop test performance. If it does, it’s a clear sign that the air cooler is clogged and needs cleaning.
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The difference between the air cooler’s air outlet temperature and the air cooler’s water inlet temperature should not exceed 12-14⁰C. If it does, the cooler’s water pathways may be clogged and its cooling efficiency could be impacted.
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The scavenge air temperature must not be increased more than 2-4⁰C after the Air Cooler’s Outlet. If this is exceeded, it is an indication of blow-by in one or more cylinders. This must be followed by indications of Pcomp per cylinder and evaluation of the under-piston temperatures.
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The pressure of the scavenge air must always be greater than the pressure of the exhaust gas at the receiver. If this is not the case, it could indicate:
- Incorrect measurement
- Malfunction of U-tube manometers
- Possible fouling of the turbine’s nozzle ring.
16.All U-tube manometers should be clean and operational at all times.
(Any additions would be more than welcome)