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135.0   Fatty acid methyl ester (FAME) as diesel fuel

Select Sheet 

Preliminary remarks

MB diesel engines are basically designed for diesel fuels which meet the respective national or European requirements. Other types of fuel are not generally planned for.

In the interest of using biomaterials and supporting domestic agriculture the past few years have entertained discussions on the possible application of "Bio-diesel fuels". In chemical terms these so-called "bio diesels" are mainly vegetable oils, which can be transformed as the result of a chemical reaction into appropriately mixed fatty acid methyl esters (FAME).

Because the most varied of abbreviations are used to describe bio-diesel fuels we have listed below a brief "glossary":

FAME Fatty acid methyl ester generic term, to be used in future in the EU standardization.

PME vegetable oil fatty acid - previously used methyl ester generic term in German linguistic area.

RME rape seed oil fatty acid - specific "organic methyl ester diesel fuel" made from rape seed oil.

Chemically unchanged vegetable oil (e.g. rape seed oil, soybean oil, sunflower oil, etc.) may not be used in Mercedes-Benz diesel engines . This applies irrespective of the degree of purity of the vegetable oil. Compared to conventional diesel fuel, vegetable oils have extremely large molecular weights, which result in several unfavorable properties:
  • extremely high boiling points (incomplete mixture formation)
  • occasional decomposition under carbonization (when heated)
  • high viscosity, etc.
The use of chemically unmodified vegetable oils can cause extremely serious damage to the engine in a short time. The main reasons for the engine damage are: signs of carbonization of the injection nozzles, the combustion chamber surfaces, the piston ring grooves, in the oil holes, etc.).

For the remainder of the text that deals with the transesterified substance, we will refer to "biodiesel fuel" in keeping with the European standard activities as "FAME" (fatty acid methyl ester), although our experience has shown that we basically tend more towards RME.

FAME may have a future as a niche fuel and be used where ecological advantages are required in particular (e.g. in water protection areas).

A distinction is to be made between operating with 100 % FAME and mixtures of FAME with conventional diesel fuel. Items 1 to 3 listed below relate to 100 % FAME, mixtures are dealt with in item 4.

  1. Approval status

    A general approval for passenger cars is not possible due to material incompatibility. As of 8/99, for individual models, E 200/220 D or CDI, C 200/220 D or CDI - irrespective of the respective engine designation - FAME-compatible vehicle equipment is available as special equipment. The vehicles mentioned mainly contain other, consistent elastomers in the fuel and fuel injection system. However, in connection with emission stage EU 4, this FAME compatible special equipment cannot be used for reasons that have to do with exhaust aftertreatment.

    Further details, in particular on the replacement parts valid for this, can be obtained from Service Information 00.40-P0005A dated 30.3.2000.

    The approval of MB commercial vehicles and MB industrial engines for FAME operation is regulated by service information releases (STIN, e.g. No. 00.00S0028), which are available to the MB field organizations; they describe the approval status with regard to vehicle model, manufacture year, any possible conversion measures required, etc. for SK, MK, LK vehicles, buses, vans and Unimogs.

  2. Further development within the EU

    In accordance with the relevant EU recommendation, attempts are being made to increase the 10 % proportion of regenerative constituents (energy recovery) in fuel within the EU.