The shipping industry is looking for strategies to comply with increasingly stringent emission regulations. Fuel has a significant impact on emissions, so a switch to alternative fuels needs to be evaluated. This study investigated the emission performances of liquefied natural gas (LNG) and liquefied biogas (LBG) in shipping and compared them to conventional marine diesel oil (MDO) combined with selective catalytic reduction (SCR). For assessing the complete global warming potential of these fuels, the life-cycle approach was used. In addition, the study evaluated the local environmental impacts of combustion of these fuels, which is of particular importance for short sea shipping operations near coastal marine environment and residential areas. All three options examined are in compliance with the most stringent emission control area (ECA) regulations currently in force or entering into force from 2021. In terms of local environmental impacts, the two gaseous fuels had clear advantages over the MDO + SCR combination. However, the use of LNG as marine fuel achieved no significant CO₂-equivalent reduction, thus making little progress towards the International Maritime Organization’s (IMO’s) visions of decarbonizing shipping. Major life cycle GHG emission benefits were identified by replacing fossil fuels with LBG. The most significant challenge facing LBG today is fuel availability in volumes needed for shipping. Without taxation or subsidies, LBG may also find it difficult to compete with the prices of fossil fuels.

This paper evaluates the effect of a large-capacity electrical energy storage, e.g., Li-ion battery, on optimal sailing routes, speeds, fuel choice, and emission abatement technology selection. Despite rapid cost reduction and performance improvement, current Li-ion chemistries are infeasible for providing the total energy demand for ocean-crossing ships because the energy density is up to two orders of magnitude less than in liquid hydrocarbon fuels. However, limited distance zero-emission port arrival, mooring, and port departure are attainable. In this context, we formulate two groups of numerical problems. First, the well-known Emission Control Area (ECA) routing problem is extended with battery-powered zero-emission legs. ECAs have incentivized ship operators to choose longer distance routes to avoid using expensive low sulfur fuel required for compliance, resulting in increased greenhouse gas (GHG) emissions. The second problem evaluates the trade-off between battery capacity and speed on battery-powered zero-emission port arrival and departure legs. We develop a mixed-integer quadratically constrained program to investigate the least cost system configuration and operation. We find that the optimal speed is up to 50% slower on battery-powered legs compared to the baseline without zero-emission constraint. The slower speed on the zero-emission legs is compensated by higher speed throughout the rest of the voyage, which may increase the total amount of GHG emissions.

Sustainable liquid fuels will be needed for decades to fulfil the world’s growing energy demands. Combustion systems must be able to operate with a variety of renewable and sustainable fuels. This study focused on how the use of various alternative fuels affects combustion, especially in-cylinder combustion. The study investigated light fuel oil (LFO) and six alternative liquid fuels in a high-speed, compression-ignition (CI) engine to understand their combustion properties. The fuels were LFO (baseline), marine gas oil (MGO), kerosene, rapeseed methyl ester (RME), renewable diesel (HVO), renewable wood-based naphtha and its blend with LFO. The heat release rate (HRR), mass fraction burned (MFB) and combustion duration (CD) were determined at an intermediate speed at three loads. The combustion parameters seemed to be very similar with all studied fuels. The HRR curve was slightly delayed with RME at the highest load. The combustion duration of neat naphtha decreased compared to LFO as the engine load was reduced. The MFB values of 50% and 90% occurred earlier with neat renewable naphtha than with other fuels. It was concluded that with the exception of renewable naphtha, all investigated alternative fuels can be used in the non-road engine without modifications.

Cruise ships function as a means of transport while simultaneously accommodating thousands of guests, providing a holiday experience with various entertainment options. This translates to high energy requirements for propulsion and hotel operations, typically covered by the combustion of fossil fuels. The operation of cruise vessels with fossil fuels contributes to carbon dioxide and also local harmful emissions in ports when shore power connections are not available. To enable cleaner and sustainable cruising, alternative technologies and fuels must be adopted. The present study evaluated the applicability of hydrogen fuel in combustion engines in a Meraviglia-class cruise ship. The fuel consumption of the ship was based on a real operation in Europe. This study examined how fuel energy in the form of LH₂ could be stored on the ship for a European cruise route and concludes that 3700 m³ of storage space would be needed to accommodate the liquid hydrogen. The mass of the LH₂ would only be one-third of that of fossil fuels, but the weight of the LH₂ tanks would most likely increase the total weight of the hydrogen storage. Additional new technologies and combined power production could significantly reduce the amount of LH₂ to be stored.

Several sustainable liquid fuel alternatives are needed for different compression ignition (CI) engine applications. In the present study, five different fuel blends were investigated. Rapeseed methyl ester (RME) was used as the basic renewable fuel, and it was blended with low-sulfur light fuel oil (LFO), kerosene, marine gas oil (MGO), and naphtha. Of these fuels, MGO is a circulation economy fuel, manufactured from used lubricants. Naphtha is renewable as it is a by-product of renewable diesel production process using tall oil as feedstock. In addition to RME, naphtha was also blended with LFO. The aim of the current study was to determine the most important properties of the five fuel blends in order to gather fundamental knowledge about their suitability for medium-speed CI engines. The share of renewables within these five blends varied from 20 to 100 vol.%. The properties that were investigated and compared were the cetane number, distillation, density, viscosity, cold properties, and lubricity. According to the results, all the studied blends may be operable in medium-speed engines. Blending of new, renewable fuels with more conventional ones will help ease the technical transitional period as long as the availability of renewable fuels is limited.