Reliable fuel management for ECAs

The provisions of Marpol Annex VI, according to which a seagoing vessel reaching a designated emission control area (ECA) may only use fuels with a sulphur content of less than 0.1%, have been in force since 1 January. This means that a seagoing vessel running on heavy fuel oil (HFO) without a scrubber installed must switch to a low sulphur marine diesel oil (MDO) before entering the ECA zone.

The switchover from heavy oil to fuels with low sulphur content makes special demands on the fuel system and fuel preparation according to the different fuel qualities. Diesel engines are basically designed for one type of fuel – for cost reasons usually HFO – and the different physical properties of other fuels make varying demands on fuel processing and engine components.

The challenges in the switchover processes between heavy fuel oil to low-sulphur distillates arise due to the different temperature and viscosity behaviours of both fuels. Tackling this can lead to high thermal component stresses acting on the fuel supply, the fuel circulation and injection system. Rapid changes in fuel temperatures lead to thermal expansions of significant components such as the injection pump, causing faults and failures,

In addition, high temperatures during switchover lead to a reduction in viscosity of the distillate fuel, which can subsequently lead to increased leakage at fittings and seals, leading to a total pressure drop in the injection system. Leakages may also result in increased fire hazard in case of proximity to hot components. Depending on the requirements of engine manufacturers recommend a maximum permissible temperature gradient of 2-3°C a minute in order to mitigate these issues.

With the failure of the fuel system, total failure of the engine system goes hand in hand, which in turn results in the loss of control of the ship itself. ECAs are coastal areas with increased traffic so, particularly in these busy environments, failures of ship propulsion systems lead to danger for the ship and its crew as well as local traffic and the environment. ECAs are thus naturally subjected to increased scrutiny by port and coastal states.

Managing and monitoring fuel

The basis for the production of heavy oils for shipping is in refining oil residue. But the application of catalytic and thermal cracking processes can result in compatibility problems when mixing different fuel qualities. Characteristics may vary depending on the refinery, oil company or crude oil employed. And any incompatibility of bunkered fuel, or even in the mixture of different batches of the same fuel type, can lead to serious system problems including excessive sludge formation in the fuel preparation.

The fuel preparation therefore needs to be tuned according to the fuels used and the engine requirements. To detect possible incompatibilities the crew use fast-track procedure compatibility tests to compare the different fuels or fuel batches available onboard. The use of a fuel homogenizer can also help to avoid sludge or aspalthen clustering, significantly extending intervals between filter cleaning.

Classification societies and engine manufacturers provide guidelines and recommendations for the switching process between two types of fuel. The guidelines have gradually minimised manual intervention of the crew and the resulting operating errors. Safer, more efficient and environmentally friendly operation of engines requires an automated fuel management onboard to monitor the full operational and functional capacity of the fuel system.

Under existing regulatory processes for switching from HFO to MGO, the following measures require some manual intervention:

• The increase in the viscosity of the fuel injected means that the temperature level must be lowered in order to decrease the temperature difference during switching. This reduces potential thermal stress in the fuel system.

• The fuel volume must be reduced, resulting in a loss of engine power. This enables crew to adjust parameters slowly, but causes a delay in the mixing process.

• Turning off trace heating and fuel preheating to reduce the heat input into the fuel system while MDO is in use.

• Connecting a fuel cooler to remove residual amounts of heat generated during the switching process or heat from the circulation and injection pump.

The second and fourth steps above ensure that the minimum permissible injection viscosity of the engine manufacturer can be adhered to. The measures are linked to fixed time regimes created by the ship’s operator together with the classification society, and processed by the crew according to a schedule before reaching the ECA zones. The predetermined steps for switching between HFO and low sulphur distillate are geared to these predetermined load points and timings which – due to a lack of automated control algorithms – are based on timing schedules that ensure timely switching the fuel before reaching the ECA zones. This results in a very long changeover.

The use of a fuel monitoring and management system – such as the Aquametro diesel switch system – offers the possibility of a secure yet fast switching operation. With constant monitoring and adjustment of fuel system parameters, a reduction in engine power is not required.

Such systems can monitor the mixing ratio of the fuel during the changeover and switch fuel coolers and HFO preheater on/off or controlled in time. Even in the event of fuel incompatibilities the system can optionally start or stop the homogenizer for sludge reduction. The operational management of the fuel system through automated monitoring and management thus ensures a safe switching operation in which all specifications from the engine manufacturers are adhered to. Compliance with time schedules, as they are drawn up by the classification society, are not necessary.

With automatic fuel management, manual intervention in existing regulatory processes are not required, which increases the operational reliability considerably. The automated progressive fuel switching by Aquametro’s diesel switch means that there is no need for further temperature control of the mixing fuel. And knowing the fuel composition at any time during the changeover process allows downstream system components in the fuel system – such as heat tracing, fuel coolers or homogenizers – to switch on or off predictively.

Switching time is therefore solely dependent upon the engine load and the fuel volume flow. Automated switching systems also allow other advantages. Automatic alarms allow for other parameters to be monitored, while systems can also be configured to display fuel viscosity, fuel consumption or differential pressures. Optionally, GPS protocol can be integrated, assigning the ship’s exact position to any status message. And all alarms, status signals and system information can be exported.