Marine environmental services and fuel testing solutions company CTI-Maritec on Wednesday (8 January) shared on why one of the most important testing parameters or properties of bio-marine fuel is energy content.
Owing to the composition of bio-marine fuels, the accurate measurement of Net Specific Energy (NSE) / Net Heat of Combustion to correctly gauge energy content of bio-marine fuels is key for efficient fuel management onboard ships:
Introduction
Bio-marine fuel is widely adopted as a drop-in fuel to achieve the current emission requirements in the shipping industry. ISO 8217:2024 specification allows bio-marine fuels to contain up to 100% fatty acid methyl ester (FAME). The major production route of FAME is transesterification of vegetable oils, animal fats or used cooking oils with methanol using alkaline catalysts. The ISO 8217:2024 version has included additional test parameters to measure FAME content, energy content and oxidation stability for bio-marine fuels.
Accurate Net Specific Energy (NSE) assists with efficient fuel consumption management
In this newsletter article, we review why one of the most important testing parameter or property of bio-marine fuel is Energy Content. Accurate measurement of NSE for energy content of bio-marine fuels is essential for efficient fuel management onboard ships with respect to:
- Fuel consumption
- Voyage planning
- Operating cost
- Machineries or equipment performance
- Emission & environmental implications
Why accurate testing of Energy Content is an essential test parameter for Bio-marine fuel
Marine fuel containing FAME typically has lower energy content compared to conventional marine fuels.
The heating value of a fuel is the total energy released as heat when a fuel undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat as shown in the equation below:
Hydrocarbon + Oxygen à Carbon Dioxide + Water + Heat Released
Conventionally, NSE of marine fuels (which consist of predominantly hydrocarbons from petroleum sources) is calculated using a formula specified in Annex of ISO 8217 (Annex J of ISO 8217:2024) with acceptable accuracy. For marine fuels containing FAME, the NSE cannot be calculated using the formula specified in Annex J of ISO 8217:2024 and shall be measured using ASTM D240 method. FAME molecules contain the Carbonyl group and Ester bonds as shown in Figure 1 below and do not consist purely of carbon and hydrogen atoms.

Figure 1: An Ester of a Carboxylic Acid
The density of potential energy of a hydrocarbon is determined by the number of carbon to hydrogen bonds that can be replaced by oxygen to carbon (CO2) and oxygen to hydrogen bonds (H2O), in other words, the amount of energy released is dependent on the oxidation state of the carbons in the hydrocarbon. For marine fuel containing FAME, the FAME molecule itself contains oxygen atoms in the Carbonyl group and Ester bond. The Ester group of FAME has a carbon forming 3 bonds with oxygen atoms, this means esters are more oxidised than hydrocarbons and esters release less energy content when compared to hydrocarbon since higher oxidation reactions are needed for hydrocarbons.
The paragraphs above explain the reasons marine fuel containing FAME typically have lower energy content compared to conventional marine fuels, which consist of predominantly hydrocarbons and the calculated formula for NSE is not applicable to marine fuel containing FAME.
According to ASTM D240 test method, heat of combustion is determined by burning a weighed sample in an oxygen bomb calorimeter under controlled conditions. The heat of combustion is computed from temperature observations before, during, and after combustion, with proper allowance for thermochemical and heat transfer corrections. The average of gross specific energy (GSE) or gross heat of combustion, and NSE or net heat of combustion of MGO, VLSFO, HSFO and Bio-marine Fuels are tabulated in Table 1 below:

Note: The average GSE and NSE for each of the fuel types was obtained from at least 50 samples.
Based on Table 1, bio-marine fuel B30 has 8% lower energy content when compared to MGO. The energy content of bio-marine fuel will become lower when the FAME content is higher.
Energy content of marine fuel containing FAME shall be determined by ASTM D240 method and cannot be calculated using the current NSE formula, which is commonly used for the conventional marine fuels.
Note: The full article by CTI-Maritec can be found here.
Photo credit: Louis Reed from Unsplash
Published: 9 January, 2025