HEINZMANN and ABC taking forward marine propulsion with dual-fuel
Press Release (June, 2013)
Reducing operating costs and complying with emissions legislation are of key interest to marine carriers. Cost transparency and reliability are, too. The use of LNG (liquified natural gas) instead of diesel or heavy fuel oil can reduce fuel costs and also decrease emissions in compliance with current environmental requirements.
Sophisticated dual-fuel technologies allow the conversion of diesel engines to gas operation with a high diesel-to-gas conversion ratio and improved efficiency. Complemented by monitoring of fuel consumption and performance, this offers carriers a comprehensive solution for maintaining engine operation at its most efficient, ensuring a high level of availability and detecting damaging faults at an early stage.
There is a general trend towards the use of gas in mobile applications like ships. Using gas as the fuel enables the stipulated emissions limits to be met comfortably. However, installing gas tanks and handling refuelling in ports will be a major problem. It will certainly not be possible to refuel with gas at every port. For this reason, it is highly likely that dual fuel engines rather than pure gas engines will initially be widely used in shipping. Dual fuel essentially involves a diesel engine that can also be operated using gas. Diesel pilot injection is used for ignition. The main argument in favour of this kind of system is that the engine can still be operated with pure diesel if gas is not available.
Dual fuel engine for ships with direct propulsion
As an sophisticated solution for marine applications, engine manufacturer Anglo Belgian Corporation and system supplier HEINZMANN have been developing a special dual fuel engine for ships with direct propulsion. Both companies benefit from many years' experience with diesel engines in shipping. For this project, diesel engines optimised for dual fuel operation were used. These optimisations enable conversion rates of steady state 95 % to be achieved (95 % gas / 5 % diesel).The key challenges for the engine management system are the variable speed/load and the fact that the torque/power output of the engine is not known. Maintaining a high conversion rate in dynamic operation calls for sophisticated control concepts. In addition, rapid switching functions back to 100 % diesel are used, for example to prevent misfires due to insufficient pilot injection.
A gas metering control unit is used to control the gas mass flow rate. The gas flow rate provides a similar linear relationship to the power output as for the diesel level. This enables the diesel and gas power produced to be calculated and the engine to be protected against overload.
A specially optimised engine was used for this dual fuel project in the marine sector. This engine has been successfully used for a long time as a dual fuel engine for stationary generator applications. For use in the marine sector, the concept has been significantly revised and adapted to reflect the ambient conditions. The diesel side is powered by a mechanical injection system which is connected to an electric actuator. Figure 2 provides a schematic view of the system. In dual fuel mode, this diesel controller is still responsible for the actual speed/power control. An additional control loop then controls the optimum gas quantity. This enables the diesel injection system to respond dynamically to rapid fluctuations or step changes. If the load is disconnected, the engine can quickly be switched back to pure diesel operation. This prevents the diesel level from falling below the minimum required for combustion and thus causing misfires.
A key factor for dual fuel use is protecting the engine against overload. In a fully optimised and utilised system, both the diesel injection system and the gas system (with a small diesel proportion as pilot fuel) can handle almost the entire engine load. When combined, the engine can easily be overloaded. In generator applications, the load signal from the generator management system is then used as a limit. However, in directly powered ships, there is no such torque/load signal. Therefore, the dual fuel control unit determines the power generated by the diesel and gas fuels dynamically during operation. To calculate the power generated by the diesel fuel, the power depending on fill level and speed is recorded on the test bench and plotted in a characteristic map.
To record the power generated by the gas, a gas flow metering unit is used, which uses a differential pressure measurement to determine the gas flow and can control it using a throttle valve. The gas data (density and calorific value) can be used to calculate the gas power from the gas flow. The dual fuel controller transmits this data along with a gas power setpoint.
The total power that the engine delivers at the crankshaft is calculated from the actual gas power and the diesel power. As the gas quality will fluctuate according to the gas types in the different ports, a facility has been provided for specifying the gas quality using the visualisation unit. A conceivable scenario would be that an engineer receives a measuring report for the gas when refuelling and has to enter the corresponding quality. Otherwise, a corresponding safety factor would have to be maintained.
Reduction of emissions by dual fuel technology
Emissions of nitrogen oxides (NOx) are reduced. Here, dual fuel operation has a clear advantage over pure diesel operation. One of the other major advantages is the reduction in the greenhouse gas (CO2) caused by the design principle. The diesel process produces soot particles and these are significantly reduced. Additional possibility for optimisation of the emissions is an optimised gas/air mixture. Optimising the ignition point in dual fuel mode would be another option. This would require a common rail system or an electronic pump pipe nozzle (E-PPN) system. The E-PPN system that is currently in development would be an economical alternative, which could also be retrofitted.
Monitoring of consumption and performance with FuelMACS
In July 2011, IMO’s Commitee MEPC decided to change the MARPOL Convention, Appendix VI to include efficiency requirements (EEDI – Energy Efficiency Design Index) on new ships. For existing ships the owners have to develop a plan for improving efficiency: SEEMP (Ship Energy Efficiency Management Plan). To meet these requirements,
Processing, calculation and presentation of data in the FuelMACS system is performed on a computer based operator station. For a stand-alone FuelMACS system, this is done on a dedicated computer located where suitable (i.e. engine control room, bridge). Monitoring of necessary data is performed by distributed I/O modules located as close to the process as possible. The I/O modules are connected to the computer with a data communication bus (i.e. Ethernet). HEINZMANN’s dual fuel applications can easily be integrated with the FuelMACS in order to monitor both gas and diesel consumption.The system can also be extended by separate displays showing selected fuel performance indicators. This can be an option if the computer is located in the engine control room but the operators at the bridge also need instant data presented.
To ensure flexibility, regarding the practical use and implementation of FuelMACS, the software is modularised in such a way that the system is easy to adapt to the various needs of different shipowners, and it can also be extended/modified over the lifetime of the vessel. The modularisation of the functions is built up according to what kind of performance indicators the shipowner wants and what kind of instrumentation is needed.
The 4 main function blocks include:
- Fuel consumption: This option measures the fuel consumption on each consumer (engine), and calculates parameters/indexes as: accumulated fuel consumption, accumulated emissions and costs over time. FuelMACS is designed to monitor different types of fuel, and can easily be integrated with HEINZMANN duel fuel applications.
- Vessel performance: By implementing measurement of the ship speed in addition to the above, performance relative to travelled distance can be calculated, such as: fuel consumption per nautical mile, EEOI, etc.
- Engine performance: If the produced power of the different engines/consumers are measured, fuel performance indicators will be calculated relative to the produced power; such as specific fuel consumption, load utilisation, etc.
- Hull performance: Measurement of propulsion power compared to the vessels speed enables calculation of performance indicators that, if trended over a long time, will indicate if the hull resistance is increasing.
In order to support the shipowners’ SEEMP, the data analysis and longtime trending have to be performed on shore. FuelMACS will export data over the shipowners WAN. The staff on-shore will then be able to perform long-term trending and analysis of each vessel’s behaviour over time, and will also be able to perform comparison between different vessels. The shipowner will then see the effect of the measures he implements in order to reduce fuel consumption.