What is the chemical composition of gasoline

Passenger car: diesel or petrol?

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This short article deals with the question of the advantages and disadvantages of diesel fuel compared to premium gasoline in cars with internal combustion engines.

Compared to gasoline engines, diesel engines generally have the advantage of being higher Efficiency, i.e. with the same engine output (measured in kW = kilowatts or PS), fuel consumption (measured in liters per 100 km) is around 20 to 30% lower. Diesel fuel is also somewhat cheaper in Germany than premium gasoline (in euros per liter), especially because of the lower taxation. On the other hand, diesel engines are being purchased expensive than gasoline engines.

The figures given below are essentially based on information in the Wikipedia articles "Diesel fuel" and "Motor gasoline" (accessed 2018-03-09).

Important physical and chemical data

Relevant data are in particular the boiling range, the density and the chemical composition (especially the ratio of carbon to hydrogen). Diesel fuel boils significantly higher (range approx. 170 ... 390 ° C, 50% value approx. 270 ° C) than premium gasoline (range approx. 30 ... 215 ° C, 50% value approx. 100 ° C) . Diesel fuel has a higher density (approx. 0.820 ... 0.845 kg / L) than premium gasoline (approx. 0.720 ... 0.775 kg / L, all data for 15 ° C). A typical component of diesel fuel is hexadecane (cetane), empirical formula C.16H34, an unbranched, saturated hydrocarbon. A typical component of premium gasoline (95 RON) is isooctane (100 RON), empirical formula C.8H18, a branched, saturated hydrocarbon (2,2,4-trimethylpentane). In general, the relative carbon content in diesel fuel is a little higher than in premium gasoline.

calorific value

A distinction is made between fuels calorific value other Calorific value. It is about the thermal energy released during complete combustion. The oxidation products of hydrocarbons are carbon dioxide (CO2) and water (H.2O), assuming complete combustion. (If the combustion is incomplete, the highly toxic carbon monoxide, CO.) Is also produced. The carbon dioxide is always produced gaseous. Depending on the "furnace" used, water can be released as water vapor (gaseous) or condensed into liquid water, in which case additional heat of condensation is released. In the former case one speaks of calorific value, in the latter case of calorific value. The calorific value is therefore around the heat of condensation of the water greater than the calorific value, which is used, for example, in modern condensing boilers for heating living spaces. In the case of motor vehicle engines, however, the water escapes as steam, so that only the calorific value can be used.

Calorific value of Diesel fuel (Source: Wikipedia): 43.0 MJ / kg (11.9 kWh / kg, 34.7 MJ / L), 9.7 kWh / L. Carbon dioxide emissions during combustion: 2.65 kg / L.

Calorific value of Premium gasoline (Source: Wikipedia): 40.1 ... 41.8 MJ / kg (11.1 ... 11.6 kWh / kg, approx. 30.5 MJ / L), 8.5 kWh / L. Carbon dioxide emissions during combustion: 2.32 kg / L.


Carbon dioxide: Because of the higher efficiency of the diesel engine and the resulting lower fuel consumption, the carbon dioxide emissions of diesel engines are around 20% less than those of gasoline engines, based on the same distance (e.g. 100 km) with the same engine power.

Nitrogen oxides, NOx, are only a problem with diesel engines. It is a mixture of nitrogen monoxide (NO) and nitrogen dioxide (NO2).

In the SCR process, nitrogen oxides react with aqueous urea solution (AdBlue®; urea: (NH2)2CO) or the ammonia formed from it (NH3) with formation of nitrogen (N2) and water.

BKi, 2018-03-10