Biodiesel challenges

What are some operational challenges related to the consumption of biodiesel in two stroke Main Engines?


Biodiesel and biodiesel blends are considered as potential candidates for the reduction of greenhouse gasses (GHGs) and of sulphuric emissions (SOx).

The guidelines published by ISO 8217:2017, CIMAC and engine makers, cover biodiesel with up to 7% FAME (fatty acid methyl ester). The use of biodiesel or blends with FAME higher than 7% is not yet well understood or documented by ISO, engine makers, and regulatory bodies.

Challenges that require investigation by ship operators could be the following:

  • Long term storage instability and biodegradation
  • Lacquer formation leading to sticky fuel pumps, scuffing etc.
  • Wax precipitation at low temperatures
  • Microbial growth
  • Increase of NOx emissions. An exemption from flag is necessary
  • Unknown compatibility with lubricants available in the market
  • Prone to oxidation when in contact with several materials (bronze, brass, copper)
  • Potential violation of ISO 8217:2017 in case biodiesel blends with FAME above 7% are consumed

It is highly recommended to seek guidance from engine makers and analyse carefully all the risks involved before starting to the consumption of biofuel in the main engine and diesel generators.

Helpful Reading: CIMAC WG7 Guidelines for FAME B7, CIMAC WG7 Guidelines for ISO 8217 FAQ, ISO 827:2017 , MAN ES “0.5% S Fuel Operation 2020”


After MEPC78 the Unified interpretation for the application of MARPOL Annex VI Reg. 18.3 for biofuels clarify the following

  • a fuel oil which is a blend of not more than 30% by volume of biofuel should meet the requirements of Reg. 18.3.1 (i.e., such fuel is regarded as oil derived from petroleum refining)
  • a marine diesel engine, which can operate on a biofuel or a biofuel blend, without changes to its NOX critical components or to its settings/operating values outside those given in the engine approved Technical File, should be permitted to use such a fuel oil without any further verification.
  • a marine diesel engine, which made changes to its NOX critical components or to its settings/operating values outside those given in the engine approved Technical File, should be permitted to use fuel oil which is a blend of more than 30% by volume of biofuel, provided that the overall NOX emissions performance has been verified using the onboard simplified measurement method (para. 6.3 of the NOX Technical Code 2008), or the direct measurement and monitoring method (para. 6.4 of the NOX Technical Code 2008), or by reference to relevant test-bed testing.

Thank you for the insight @George.Liadis

@Stela.Spiraj interesting update on the recent MEPC78

Additional comments as follows:

  1. The stem to be consumed as soon as practically possible (within 4-6 months) in order to avoid moisture in the tank. Should the stem is to be stored more than six months onboard, additional fuel samples to be drawn and dispatched to laboratory for analysis (at an interval of 3 months), in order to verify the acid number and oxidation stability. Degraded fuel, may cause excessive filter clogging and/or wear down of fuel system components (fuel pumps/injectors etc. etc.).
  2. There is possibility of frequent clogging of the filters (transfer pump/auto back wash filters).
  3. As soon as the stem is consumed, the storage/settling/service tanks would need to be manually cleaned and the pipelines to be flushed, in order to bunker the next stem (in order to avoid mixing with other fuel).
  4. Sealing gaskets and o-rings (Teflon/Viton type and sealing material), on the high pressure fuel system and fuel oil auxiliary system might not be compatible with the fuel and hence said materials might fail prematurely, causing fuel oil leaks.

Last but not least, approval should be obtained from Flag State prior bunkering/consuming Biodiesel.


@AndreasTravlos thanks a lot!

Hi @AndreasTravlos
The Administration could waive the NOx measurement in accordance with regulation MARPOL Annex VI Regulation when using fuel oil blend up to B30, referring either to Regulation 3.2, or Regulation 4.1 of MARPOL Annex VI. Upon receipt of the letter from the Flag, the Supplement to the IAPP Certificate shall be filled with the description of the “Equivalents” in para 2.6.


Thank you @Stela.Spiraj

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With regards to EUMRV and operational data reporting, the fuel consumption of the custom fuel for each machinery should be reported as “other fuel type” and specify the “other fuel emission factor”. Before the use of the biofuel blend, the RO should be also contacted to provide specific guidelines on the reporting.