Guidelines for next generation biofuels for use in shipping engines

By Hochschule Bremerhaven

In order to achieve the climate policy goals (reducing GHG emissions in shipping), large quantities of CO₂ -neutral fuels will be needed in the future. In April 2018, the IMO (International Maritime Organization) set out its strategy for reducing ship-based greenhouse gas emissions in its resolution MEPC.304(72). According to this, CO₂ emissions are to be reduced by 40% by 2030 and by 70% by 2050 (compared to 2008). Due to the comparatively long life cycles of ships – Ships built in 2025 will still be in service well after 2040- and their propulsion systems, the key to achieving these ambitious targets appears to lie in the decarbonisation/defossilation of fuels. The IMO distinguishes between short-, medium- and long-term measures that must be taken to achieve these goals [1–4]

The short- and medium-term measures are to be achieved by increasing the production of synthetic fuels. E-fuels are produced, for example, using the CWtL (Carbon Dioxide and Water to Liquid) process using renewable energy from water and CO₂. With respect to marine shipping, both liquid e-fuels such as methanol, Fischer-Tropsch diesel, and oxymethylene ether (OME) and gaseous synthetic fuels such as hydrogen, methane, and ammonia have been discussed [2]. One advantage of E-fuels is that these “designer fuels” can be optimally tailored to the specific application. However, for the synthesis liquid fuels more process steps are required than for gaseous e-fuels, which means that production costs are correspondingly higher [5]. The advantages of liquid fuels lie in the simpler and more cost-effective fuel infrastructure as well as their higher energy density. The large-scale production of many synthetic fuels is usually very cost-intensive or not yet cost-efficient and therefore not yet mature for a current application. The volume structure in marine shipping and competing sectors such as aviation, stand in the way of a timely and widespread use of such fuels in this sector. An alternative solution may be biogenic fuels such as pure vegetable oils, biodiesel (FAME), hydrogenated vegetable oils (HVO), and biomethane (LNG) [6, 7]. Biofuels are already available in substantial quantities and can be blended with conventional fossil fuels in larger quantities as “drop in-fuels”. Biofuel blends thus represent a bridging technology to sustainably reduce greenhouse gas emissions in the short and medium term [8]. If biofuels or E-fuels are introduced into the marine sector, then compatibility with existing fuels, infrastructure, ships and engines plays an important role [3, 4]. The following figure shows an overview of the biogenic and synthetic fuel options discussed for marine shipping. Hereby the biogenic fuels keep the main hydrocarbon backbone from biomass while synthetic fuels originate from C-C coupling.

The requirements for Bio- and E-fuels for application in shipping can be summarised as follows:

Fuels should be based on renewable materials (Re-fuels) or renewable electricity (E-fuels) (Reduction of CO₂-emissions)
Fossil fuels with an advantageous H/C (Hydrogen/Carbon) ratio can act as bridge to Re- and E-fuels
The fuels should be available for research and development activities within short-term (immediate start of technology introduction and short -term CO₂ reduction effects)
Compatibility with existing fuel supply infrastructures and current engine technology (access the marine market and to generate real world CO₂ reductions in short- and medium-term)
To fulfil the previous requirement, the fuels need to be highly compatible with the existing marine fuels
A long-term production perspective for sufficient amounts of Re- and E-fuels for the marine sector is required (complete chain from fuel production over distribution and application has to show sufficient overall efficiency)
As these future fuels will be most certainly more expensive and valuable as current fossil marine fuels, they should offer additional advantages in engine operation, i.e. improved efficiency and decreased level of harmful emissions, simplified design and operation of exhaust gas treatment systems
Besides CO₂-neutrality, the fuels should give the perspective to reduce harmful emissions down to „zero impact“ levels with tenable exhaust gas treatment efforts [3, 4]

The blending of Bio and E-Fuels must be carried out under the condition that application-safe, homogeneous, stable and non-corrosive fuels must be produced in accordance with DIN ISO 8217. Special attention is therefore paid to critical variables such as acid number, flash point, density, viscosity, sediment content, storage and blend stability. Some target parameters, their significance for fuel applications and needed amount for analysis are summarized in the table below.

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[2] R. Backhaus, „Alternative Kraftstoffe CO2-neutral in die Zukunft“, ATZ Automobiltech Z, Jg. 119, Nr. 6, S. 8–13, 2017, doi: 10.1007/s35148-017-0069-x.
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[4] B. Buchholz, K. Schleef und B. Stengel, „Potential of Paraffinic Fuels for the Maritime Energy Transition“ in CIMAC Congress 2019, 10.-13. Juni 2019, Vancouver, Kanada.
[5] W. Maus, Hg., Zukünftige Kraftstoffe: Energiewende des Transports als ein weltweites Klimaziel, 1. Aufl. Berlin: Springer Berlin, 2019. [Online]. Verfügbar unter: http://www.springer.com/
[6] G. Kalghatgi, H. Levinsky und M. Colket, „Future transportation fuels“, Prog. Energy Combust. Sci, Jg. 69, S. 103–105, 2018.
[7] M. Wojcieszyk, Y. Kroyan, M. Larmi, O. Kaario und K. Zenger, „Effect of alternative fuels on marine engine performance“, SAE Technical Paper, 2019.
[8] T. Paulaiskiene, O. Anne, R. Viederyte und L. Abele, „Alternative solutions for marine fuel’s composition towards Marine Strategy Directive performance“ in IOP Conference Series: Earth and Environmental Science.