Chemical tanker operator Stolt Tankers shares its views on how main engines will cope with lower sulphur fuels once IMO 2020 kicks in
In 2014, Stolt Tankers began developing the C38 series of chemical tankers. The vessels were to be, as far as possible, future proof within the parameters of known and expected regulatory developments. One of the parameters was IMO 2020 – the regulation requiring vessels to burn 0.5% sulphur content fuel from 1 January 2020.
The C38 chemical tankers are propelled by WinGD 6RT-flex-50D main engines. On these engines, the fuel injection, exhaust valve timing, fuel injection duration and cylinder oil injection duration are all programable. Stolt Tankers has tuned these engines to maximise their efficiencies.
Data is captured from the engine and monitored both onboard and ashore. The company uses a system that allows C38 engines to be compared across the fleet. These ultra-long-stroke engines incorporate high pressure common-rail electronic fuel injection and valve timings and run at higher temperatures than previous generations, a key feature in reducing emissions.
Internally, the cylinder linings are plateau honed. This cross hatching of the surface of the liner is meant to provide better lubrication. The lubricant is meant to travel along the channels, reducing lubricant evaporation and lowering consumption. In addition, the honing has better load-bearing characteristics.
In a paper titled “Increasing Performance in the Dawn of a Digital Era. A Chemical Tankers’ Shipowner Experience” presented by Stolt Tankers’ Jose Gonzalez at this year’s CIMAC Congress, the company noted that these engines were very sensitive to small changes in parameters.
A result of this was an increase in black lacquer, an extremely hard substance that develops on the cylinder liners, increasing resistance associated with the liners. Low engine loads were found to one cause of this; the nature of their operation meant the C38 chemical tankers were often working within this black-lacquer-producing engine range. As a result, in some cases the plateau honing was covered by lacquer and black lacquer also covered the oil lubrication trenches in the cylinder walls.
Conversely, the plateau honing was expected to provide the C38s with lower oil consumption rates compared to previous generations. The formation of black lacquer had not been an issue with the older-generation engines, which ran at lower temperatures and lower cylinder pressures. Black lacquer at low-load operation had also not been a feature of the previous generation chemical tankers, which ran on heavy fuel oil. The higher sulphur content produced sulphuric acid in low-load operation which dissolved the lacquer.
While the cause of black lacquer is not fully understood, it is believed to stem from a combination of combustion by-products and unburned fuel components. These are believed to condense on the cylinder liners at low-load operations. The new high-efficiency engines run at higher pressures, which reduce the dew point in the exhaust gases, increasing the likelihood of condensation in the cylinder. The cylinder is also cooler from the need to maintain lower temperatures to reduce emissions.
To combat this effect, the mechanical fuel pump actuators on the C38 chemical tankers were converted to electronic control, to optimise low loads and reduce black lacquer.
The careful pairing of a lubrication oil with the correct base number (BN) to a residual fuel also helped neutralise the formation of black lacquer. However, the authors of the paper found that this was very difficult to replicate outside the laboratory.
The practical goal of Stolt Tankers was not to eliminate black lacquer, but to minimise its production through monitoring its accumulation and by increasing cylinder oil feed rates as build-up occurred. The smaller amounts of black lacquer thus generated could be dealt with at the time of the next engine overhaul.
Stolt Tankers has also developed better practices around monitoring the residual BN of under-piston drain measurements; when the residual BN moves outside of an acceptable range, engineers respond quickly and effectively to prevent engine damage. This includes managing cooling water temperatures, better injection control and fuel atomisation at low loads, and limiting time running the engines at low loads.
Another issue Stolt Tankers experienced with higher efficiency engines was an increase in fuel quality sensitivity. Initially, it was thought that there were contaminants in the fuel, such as plastic products, which were causing the electronic injection control units to leak. Electronic injection control units offer substantial benefits over traditional cam-controlled push-rod injection, giving better control of injection timing and duration. This micro-managing of the fuel should produce better fuel consumption and fewer mechanical parts offers greater longevity and less overhauls. However, Stolt Tankers found the leaks were increasing the downtime of the electronic injection control units.
Stolt Tankers did not find a definitive answer to the problem. In the paper the authors noted that new fuel purifiers were installed and procedures updated for the onboard treatment of fuel to attain the highest possible quality.
The paper also noted Stolt Tankers efforts to create a uniform digital environment across its 100-strong fleet. The company operates tankers which fall into different generations and has developed an in-house system to gather data from the engines. On the older engines this was hampered by a lack of modern data systems. On the new engines a different problem presented itself; although modern engines have a wealth of real-time data generated by the associated systems, Stolt Tankers found a reluctance from the suppliers to give up their proprietary systems and integrate with Stolt’s systems.
This is a long-term concern for the company, which is investing in specific cyber-attack-resistant software. In addition, the company is developing systems that give employees better visibility of how the systems within the company interact. It acknowledges that not everyone can have equal knowledge and this can lead to conflicts among stakeholders who might consider their specific area of responsibility as being more important. According to the paper, Stolt Tankers has overcome this by stepping back from optimising specific areas of the business, and regarding the system as a whole.
The company has found that using connected onboard systems and technology to increase communication and streamline administrative processes has helped optimise the profitability of the fleet and reduced the number of instances when stakeholder desires supersede the overall goals of the organisation.