125.0   Fuels for gasoline engines

Select Sheet 
Overview  

Liquid fluids for gasoline engines are mixtures consisting of chain-like and ring-shaped hydrocarbons as well as oxygenated compounds (ether, alcohols). In each country they are offered for sale in either one or several grades.

Requirements, properties, parameters

Fuel is subject to particular requirements aimed at enabling a gasoline engine to be operated reliably under all manner of climatic and driving conditions.

In order to comply with such requirements a variety of specifications must be adhered to which reveal information on the quality of the gasoline.

The minimum requirements and limits of the major specifications are documented in standards. These standards are from time to time adapted to the changing general conditions. Standard EN 228 is valid for gasoline engines in the EU

In our opinion the addition of additives to gasoline to improve quality is absolutely essential from the point of view of the Daimler AG. This has to take place through the fuel manufacturer as he has overall responsibility for his product (refer to the Section "Additives" on this).

Knock resistance

One of the most essential quality characteristic of gasoline fuels is the knock resistance. It is decisive in ensuring a normal combustion process in the engine and thus crucial in terms of efficiency and specific power output.

The knock resistance is measured by the octane rating which in turn is determined through comparison with isooctane/n-heptane mixtures in a C.F.R. engine. There are two measurement methods:

a) research octane number (RON) ISO 5164

b) motor octane number (MON) ISO 5163

The differences lie in the various testing conditions.

A vehicle's octane number requirement can be taken from the owner's manual

Boiling-point curve and vapor pressure (volatility)

The boiling-point curve of typical gasoline fuels starts at approx. 25 °C and ends at approx. 220 °C. The boiling-point curve progression affects
  • Vapor lock formation in fuel lines
  • Engine starting characteristics
  • Evaporation losses from fuel tank
  • Drivability
  • Fuel entry into engine oil
To enable a reliable cold start even at low temperatures in the winter, a vapor pressure DVPE of > 60 kPa is required. To prevent vapor lock formation at hot ambient temperatures in the summer, a vapor pressure of < 60 kPa is required. The seasonal adaptation of the vapor pressure is carried out by the fuel manufacturers; it is stipulated in the fuel standards

The vapor pressure DVPE is measured in accordance with EN 13016-1, for example

Density

The permissible range of fuel density in Europe is stipulated by EN 228 and lies between 720 and 775 kg/m3. The density is measured in accordance with EN ISO 12185 and EN ISO 3675.

Calorific value

The calorific value determines the energy content of the fuel. There are two parameters to be distinguished, the specific calorific value Hu (lower calorific value) and the specific calorific value Ho (higher calorific value). For combustion engines the specific calorific value Hu is relevant; the measuring unit is Mj/kg. The calorific value of fuel is not standardized.

The calorific value of gasoline fuels depends on their composition. In many cases gasoline fuels contain oxygenated components, so-called oxygenates such as, e.g. ethanol, butanol or ether (ETBE, MTBE). These components have a lower calorific value compared to pure hydrocarbons. As a function of their portion, this results in a higher volumetric fuel consumption. With the introduction of Premium 95 E10 with up to 10 % of ethanol, an increased consumption between 1 and 2 % is to be expected in comparison with Premium 95, that generally contains 5 % ethanol

Purity

Solid foreign matter and water may lead to problems arising with the fuel supply. Beyond this water can also cause corrosion; in turn corrosion products can also impair the fuel supply.

Sulfur content

The sulfur content in the gasoline should be as low as possible, we recommend the use of sulfur-free gasoline with < 10 ppm of sulfur

Stability

The quality of the fuels should not deteriorate on the more or less long journey from the manufacturer to the consumer, i.e. the hydrocarbons in the fuel should not react with the oxygen in the air or with each other. This chemical instability results from the presence of unsaturated hydrocarbons in the fuel (e.g. diolefines) and is responsible for the so-called "gum" formation. This becomes noticeable in the form of deposits on the intake valves and in the combustion chamber.

Criteria such as the oxidation stability as under ISO 7536 and the solid residue from evaporation are called on for assessment purposes.

However, a real quality assessment can only be made by means of an engine test.

Corrosion

Fuels are naturally practically anhydric, but they are known to dissolve small quantities of water when being transported. The dilution is dependent on the structure of the hydrocarbons, the alcohol contents as well as the temperature. When cooling down a portion of the diluted water is lost. Water and fuel are separated. As long as the water is dissolved, it does not have a corrosive effect. The presence of free water can lead to corrosion.

Fuel agents, additives

In order to fulfill the specified requirements, additives are added to the fuel. Mercedes-Benz recommends to use brand fuels treated with additives by the fuel manufacturers.

In some countries the fuels may be inadequately treated with additives.

This may result in deposits in the injection system and the combustion chamber of the engines. In this case, the cleaning additive recommended by Mercedes-Benz should be added to the fuel in consultation with a Mercedes-Benz service outlet. Please ensure that you observe the instructions and mixing ratios specified on the container

Oxygenic components

Oxygenic components are added to gasoline fuels for different reasons. Generally, alcohols and ether are concerned here. As oxygenic components alter the properties of a fuel, their portions are regulated in the fuel standards of the individual countries

Applicability of E10 fuel for Mercedes-Benz, Maybach, AMG and smart cars:

The vast majority of all Mercedes-Benz passenger cars as well as all Maybach, AMG and smart vehicles with gasoline engines can be operated with E10 fuel.

Exceptions are Mercedes-Benz models from the first generation of direct injection (C 200 CGI/model 203 and CLK 200 CGI/model 209) from the years 2001 - 2005. Exceptions are as well models which were equipped ex factory without a controlled three-way catalytic converter or with a carburetor. These are generally older than 25 years old. In case of doubt, information on E10 compatibility is also available through the Service Hotline 00800 17777777 or on the Mercedes-Benz homepage

http://www.mercedes‑benz.de

(Option: Mercedes world/Innovation/Biogenic fuels). The homepage also has an interactive tool for an immediate E10 compatibility check for a vehicle when the vehicle identification number is entered.