Engine performance optimization (automatic)

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. With the latest technology and machinery this potential can be realized 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 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

Automatic engine performance optimization (auto-tuning) is applicable for all vessels with 2-stroke (main propulsion) engines, irrespective of ages.

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 (P_max) over the compression pressure (P_comp), and subsequently the mean effective pressure (P_mep), within acceptable limits. The level of P_max itself, and the P_max/P_comp and P_max/P_mep 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 NO_x-emissions, which is important to note as this fact limits any optimization by the applicable NO_x-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 P_max/P_comp (efficiency) is done manually. However, electronic auto-tuning is beginning to become standard and the only option for newbuilds. Most large 2-stroke engines being delivered from 2016 onwards have one form of such a system. For 4-stroke this measure is still to become as mature and available. The auto-tuning systems typically measure the cylinder pressures, and adjust the fuel injection timing, balancing and optimizing parameters like P_max and P_comp.

Retrofit of auto-tuning on existing vessels has also recently started to mature and is available for 2-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 P_max/P_comp ratio.

Cost of implementation

The cost of implementation is estimated at $3,000 to $7,000 (USD) per cylinder, depending on newbuild/retrofit and engine type.

Reduction potential

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

Other References

1. Air pollution and energy efficiency / IMO energy efficiency appraisal tool
2. Diesel Engines optimization and Fuel savings / Karlsson, Magnus / How to achieve reduction of fuel oil consumption and maintenance cost through carried out optimization of diesel engines / 2013