A potential lies within ensuring accurate insight to the engines’ condition and performance, enabling both optimizing the engine’s fuel efficiency and verification of the effect of the measure. With the latest technology and machinery this potential can be realised more or less automatically.
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 on-board 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 change 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
Automatic engine performance optimization (auto-tuning) is applicable for all vessels with 2-stroke (main propulsion) engines that is electronically controlled. The level of parameters possible to tune depends on the engine model. It is assumed that all short-sea vessels, ferry-pax, ferry-Ropax and cruise ships have 4-stroke engines while the others have 2-stroke engines.
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 maximising 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.
Today the task of performance- and condition testing the engine, correcting the results and comparing them to sea-trial, and tuning the engines to optimized Pmax/Pcomp (efficiency) is done manually. However, electronic auto-tuning are beginning to become standard and only option for newbuilds. Most large two stroke engines being delivered from 2016 and forward have one form of such a system. For four strokes this measure is still awaiting to become as mature and available as the two strokes. The auto-tuning systems typically measure the cylinder pressures, and adjust the fuel injection timing, balancing and optimizing parameters like Pmax and Pcomp.
Retrofit of auto-tuning on existing vessels has also recently started to mature and is available for two stroke engines with both mechanically and electronically controlled fuel injection pumps and exhaust valves.
Auto-tuning systems also have the added benefit of being an important safety function controlling and avoiding too high cylinder pressure, -ignition rise, or -Pmax/Pcomp ratio.
Cost of implementation
The cost of implementation is estimated to $3,500 – $6,500 (USD) per cylinder, depending on newbuild/retrofit and engine type. Typical to have 8-16 cylinders.
Reduction potential
The reduction potential is estimated to 1 – 3% of total ship fuel consumption.
References
- MTZ industrial (2024) ‘Diesel Engine Optimisation for Fuel and Wear savings’. Available at: Diesel Engine Optimisation for Fuel and Wear Savings | MTZ industrial (springer.com)
- Sherbaz, S., et al. (2015) ‘Machinery Options for Green Ship’. Available at: Diesel Engine Optimisation for Fuel and Wear Savings | MTZ industrial (springer.com)
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