Rules for the proper evaluation of M/E performance (two stroke MAN ES)

Attention to all marine engineers!
Rules for proper evaluation of the M/E performance (for two stroke MAN ES).

  1. 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.

  2. 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
  1. 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.

  2. 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
  1. 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.

  2. 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.

  3. The Pressure Rise (Pmax – Pcomp) must not exceed the specified limit, i.e.:

  • MC/MC-C-35 bar
  • ME/ME-C-38-40 bar
  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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)

7 Likes

@Oswald.Alving Thank you so much for the comprehensive and useful guidelines!
In addition to point (7), Pmax- Pcomp difference must not be less than ~20bars (at loads > 75%) , as this indicates poor engine performance and usually results in high fuel consumption.

6 Likes

Thank you! I would like to share a diagram that helps me a lot.

3 Likes

Many thanks @Oswald.Alving for your detailed guidance.

I would only like to highlight just one point related with the determination of the actual load of the Engine. When the engine is of the electronically controlled type (ME-B/C) the load can be easily taken from the PMI or MOP. On the other hand in cases of MC & MC-C Engines the pump mark or pump index is mistakenly considered as the engines actual load. This acceptance can lead to wrong results as the fuel index is dependent on the condition of the fuel pumps.
The best way to determine the load is to consider the T/C rpm or Scavenge Air pressure.
In addition to that always compare the received performance to the test bed values and not to the sea trials. During shop testing an adjustable constant water brake is attached to the engine’s shaft.

3 Likes

Thank you @Dim Dim. This is indeed very useful feedback.