Engine performance optimization (manual)

A potential lies within ensuring accurate insight to the engine’s condition and performance, enabling both optimizing the engine’s fuel efficiency and verification of the optimization’s effect. For the majority of existing vessels this potential is only possible to realize manually, unless costly retrofits are made.

Maintenance, periodic testing and tuning of marine internal combustion engines, for either propulsion or power production, is today an inherent part of the daily work and procedures onboard vessels. Testing is usually done on a monthly basis to ensure correct levels and balance of cylinder pressures, including exhaust temperatures and other parameters. However, these tests are often done with simple tools not calibrated, and performed by crew with limited access to advanced interpretations of the results. As such, test reports are often limited to being reviewed for engine condition via e.g. the exhaust temperature balance only. When changes in engine settings are done based on these tests, the tuning might also not yield the condition and performance sought for due to inaccurate tools, benchmarks and measurements, including unfavourable testing conditions. Also, to ensure achievement of the desired effect from any engine tuning a concurrent re-testing is always recommended, but unfortunately often challenging to make time for.

Applicability and assumptions

All cylinders’ pressure development over 360 degree crank rotation from actual cylinder pressure measurement onboard a vessel – DNV GL

Figure 1: All cylinders’ pressure development over 360 degree crank rotation from actual cylinder pressure measurement onboard a vessel, source: DNV GL

It is assumed that most ship and engine types and ages have an improvement potential in optimization of engine efficiency, except for a few “best in class” players including occasional special cases. Also, both 2- and 4-stroke engines, mechanic and electronic, are eligible for optimization, and the principles do not change much with use of different fuels either.

Improved balance of the cylinder pressures, and maximum combustion pressures closer to the rated values, is the detailed aim of this measure. The cylinder pressure balance is one important goal to improve the engine condition, enabling more efficient combustion. Peak engine efficiency is another important goal targeted by maximizing the ratio of maximum combustion pressure (Pmax) over the compression pressure (Pcomp), and subsequently the mean effective pressure (Pmep), within acceptable limits. The level of Pmax itself, and the Pmax/Pcomp and Pmax/Pmep ratio, is strongly correlated to the engine efficiency. Increased engine efficiency leads to reduced fuel consumption and a cleaner engine with less carbon deposits in the cylinders and turbocharger, thereby also reducing the maintenance cost. Optimizing an engine to increase efficiency is however usually the opposite of reducing NOx-emissions, which is important to note as this fact limits any optimization by the applicable NOx-emission tier level requirements.

The potential for reduced fuel consumption in this measure is twofold, where the first part is testing the engine’s condition and

performance with accurate tools and methods, under comparable conditions with sea trial performance data. The second part relates to actually acting on the potential for improvement identified, and verifying the results through re-testing.

Zoom in of the compression pressure (Pcomp) and maximum combustion pressure (Pmax) from actual cylinder pressure measurement onboard a vessel – DNV GL

Figure 2: Zoom in of the compression pressure (Pcomp) and maximum combustion pressure (Pmax) from actual cylinder pressure measurement onboard a vessel, source: DNV GL

 

 

Regarding the tool to be used for measurement of cylinder pressures, the minimum required quality is advised to be an electronic combustion analyser. The analyser should provide the reader with a full overview of the combustion cycle and the pressure development presented in both absolute numbers and graphs, with possibility to zoom in/out and compare multiple cylinders. See Figure 1 and Figure 2 for examples.

Cost of implementation

The cost of implementation is estimated at $5,000 to $10,000 (USD).

Variable cost will come in addition to the cost of the measurement tool relating to education/training, establishing the methodology and needed procedures, carrying out the job itself, establishing software analysis and trending tools.

Reduction potential

The estimated reduction potential is 1% to 4% of total ship fuel consumption.

The changes in engine settings to optimize an engine with regards to efficiency differs from case to case and engine type to engine type, but one of the most typical changes is setting of the fuel injection timing. In terms of absolute fuel consumption reduction it is evident that the larger 2-stroke propulsion engines possess the largest absolute fuel reduction potential.