Why does diesel fuel smell so bad

Diesel fuel

Lexicon> Letter D> Diesel fuel

Definition: a liquid fuel for use in diesel engines

Alternative terms: diesel oil, diesel

More general terms: fuel

More specific terms: biodiesel, summer diesel, winter diesel, polar diesel, marine diesel

English: diesel fuel

Categories: Energy carriers, vehicles, engines and power plants

Author: Dr. Rüdiger Paschotta

How to quote; suggest additional literature

Original creation: 03/12/2010; last change: 03.01.2021

URL: https://www.energie-lexikon.info/dieselkraftstoff.html

Diesel fuel (also Diesel oil or simply diesel) is a liquid fuel used in diesel engines, most of which is produced from petroleum in petroleum refineries. It essentially consists of various hydrocarbons. Its composition is similar to that of heating oil and can vary depending on the purpose. Compared to gasoline, diesel fuel is significantly less flammable and volatile (so it also leads to significantly lower evaporative emissions). The combustion of diesel mainly produces carbon dioxide (CO2) and water vapor, but also various toxic air pollutants.

The calorific value of diesel fuel is approx. 42.5 MJ / kg, the calorific value 45.4 MJ / kg. However, these values ​​depend somewhat on the variety (see below). The mass-related values ​​are slightly lower than those of gasoline; because of the significantly higher density (maximum 845 kg / m3) is still the calorific or gross calorific value per liter higher.

An important quality criterion for diesel fuel is Cetane number, a measure of the fuel's ignitability. Diesel fuel has had to have a cetane number of at least 51 since 2000 (before that, at least 49). Of course, higher quality fuels achieve higher values ​​of z. B. 60 or in special cases (synthetic fuels) even up to 80. A high ignitability is important for use in engines (especially high-speed ones) in order to be able to achieve even and complete combustion.

Another quality criterion is the sulfur content. Unfortunately, crude oil contains significant amounts of sulfur and its removal at the refinery costs money. However, sulfur is undesirable in diesel fuel because it leads to toxic sulfur dioxide (SO2) in the exhaust of the engines. Sulfur is also harmful to some types of catalytic converters.

Varieties of diesel fuel

The variety of grades is less for diesel fuel than for gasoline. Usually only one type of diesel is available at petrol stations, but in some places certain types of premium diesel are also offered with special additives. B. cause a higher cetane number (higher ignitability). Also, in winter, a somewhat thinner diesel fuel (Winter diesel) without being specially marked.

Marine diesel based on heavy oil with a high sulfur content is very harmful to the environment.

Much heavier grades are often used for large engines. In particular, ship diesel (marine diesel oil) is a heavy (dense), less ignitable but inexpensive variant that often has a high sulfur content (→Heavy fuel oil). Such particularly environmentally harmful diesel fuels are often forbidden for use in coastal areas and especially in ports. International efforts are under way to greatly reduce the sulfur content of marine diesel in general. In recent years, the sulfur content of marine diesel has been increased in some cases, since lower-sulfur oil is preferred for motor vehicles and therefore more sulfur-rich (“acidic”) oil is left for marine diesel.

In some cases, diesel fuel is not used in its pure form, but in a mixture (an emulsion) with water, which is used as Water diesel referred to as. This approach is explained in the article on water injection. Water diesel is not filled up in this form, but produced shortly before it is used in the vehicle.

Similarity to heating oil

Gone are the days when heating oil could be used as a substitute for diesel fuel without any technical problems (albeit illegally).

In terms of its composition, diesel fuel is similar to light heating oil (although less today than in the past). Since it is subject to the mineral oil tax significantly higher than heating oil, there is in principle an incentive to use heating oil in diesel engines, but this is punishable as tax evasion. Heating oil in the tank can be recognized by a red dye and an additional marker.

From a technical point of view, it would have been relatively problem-free in the past to use heating oil instead of diesel fuel. In the meantime, however, the differences between diesel fuel and heating oil have become much greater:

  • Diesel fuel is optimized for engine use with various additives, e.g. B. small amounts of amyl nitrate or ethyl hexyl nitrate (EHN) for a sufficiently high ignitability (cetane number). In addition, detergents are used to keep injection nozzles clean, flow improvers for operational safety at low ambient temperatures and to enable higher contents of paraffinic components with a high cetane number, lubricating substances to reduce the wear and tear of injection pumps, silicone oils to suppress foam formation when refueling and other substances for corrosion protection in the Fuel system and storage.
  • The proportion of heavy hydrocarbons is limited for diesel fuels because they contribute significantly to the formation of soot.
  • The sulfur content is also much more strictly limited than with heating oil. Since 2009, only 10 ppm (i.e. 10 mg per kg of fuel) have been allowed in the EU, which is why the sulfur dioxide emissions from diesel vehicles are practically no longer of any ecological importance. (Even low-sulfur heating oil can contain up to 50 ppm sulfur, i.e. five times more.) Particulate emissions are also lower with sulfur-free fuel, and the use of so-called SCR catalytic converters to reduce nitrogen oxide emissions also requires fuel that is practically sulfur-free. However, this requires additional additives to reduce the wear and tear on injection pumps (which have benefited from the lubricating effect of the sulfur content).

For these reasons, the use of heating oil in a diesel engine can significantly worsen the exhaust gas values ​​and even cause engine damage. In particular, downstream exhaust gas cleaning systems such as exhaust gas catalytic converters are also at risk.

For similar reasons, the use of vegetable oil, especially in modern diesel engines, is questionable; even if the engine is currently running, severe damage can result.

Problems at low temperatures

In severe frost, diesel fuel can become viscous and eventually even so go wrongthat it can no longer be pumped through a fuel filter. This can then lead to the failure of a diesel engine until the lines and the filter are sufficiently heated again. If the fuel has absorbed water, similar problems can arise from freezing.

Diesel fuel with a thinner consistency is offered at petrol stations in winter. This Winter diesel also contains special additives (Flow improver), which are supposed to prevent paraffins from flocculating. Certain premium diesel fuel types can even be used well below −30 ° C without any problems. In some regions of Northern Europe there are Polar dieselwhich can still be used even at −40 ° C.

In the past, diesel drivers sometimes added a little gasoline to the diesel fuel in winter to counteract the threat of gulmination. This is not advisable, however, as it can lead to serious engine damage, especially in modern engines (e.g. to the fuel injection system). The winter diesel fuel sold at the filling stations today should normally be sufficient.

Production of diesel fuel

Embodied energy and emissions

Diesel fuel is usually obtained in petroleum refineries. The resulting climate-damaging emissions from crude oil extraction, transport and refineries amount to around 10% of the CO2-Emissions that are later caused by the combustion of the fuel. (However, when using non-conventionally obtained crude oil, the emissions can be much higher.) Essentially, production involves distillation to obtain hydrocarbons in a certain range of molecular sizes. Certain additives are also used, e.g. B. Flow improver to improve flowability, cetane number improver to increase ignitability and other substances to improve lubricity, avoid deposits, reduce soot formation in the engine and reduce corrosion of metal parts.

There is also biodiesel, which can be made from plant materials such as rapeseed and palm oil. Although its chemical composition is completely different from that of petroleum diesel fuel, its combustion properties are quite similar. Otherwise, particularly high-quality diesel fuel can also be produced synthetically from natural gas.

The addition of biodiesel from palm oil is justified with climate protection, although it damages the climate considerably!

In Germany, diesel fuel is usually mixed with a few percent biodiesel; The majority, however, comes from the middle distillate fractions of petroleum. The addition of biodiesel is officially carried out as a climate protection measure, although it has long been known that this tends to damage the climate. In particular, the use of palm oil is extremely problematic because it promotes the destruction of rainforests (mainly in Indonesia). A sustainability certification system has been developed, but it does not seem to be working properly. Even if the certification of palm oil that is extracted from former rainforest areas were consistently prevented, the problem would remain that the demand would also encourage the extraction of non-certified palm oil (possibly by other actors). Although this problem has now been recognized and identified at EU level, z. For example, the German federal government is committed to promoting the use of palm oil, which is extremely harmful to the environment, for the time being.

The transport of fuel z. B. from the refinery to a gas station, but even the transport of the crude oil to the refinery leads to further emissions, which can be very different depending on the case. As a rule, however, the energy consumption in the refinery should predominate.

Problems due to high diesel content

The high proportion of diesel in vehicles in Europe is causing increasing problems in oil refineries.

In Europe (especially in Germany) the proportion of diesel engines in motor vehicles is relatively high, not least because of the low taxation of diesel fuel compared to petrol (see above). While in 1975 the quantities of diesel fuel sold in Germany were only about half as large as those of petrol (petrol), they were already about the same in 2000, and they are even higher today. This not only leads to higher nitrogen oxide and particle emissions from vehicles, but also to increasing problems (including increased energy consumption) in European oil refineries. There is a shortage of diesel there, which would actually require higher refinery capacities, but at the same time an excess of petroleum which threatens the profitability of the refineries. So far, the problem has been alleviated by the fact that surplus gasoline can be exported to the US while diesel fuel is imported from there at the same time. As the US is likely to reduce its gasoline imports, the problem will be exacerbated and could also lead to the closure of European refineries.

For these reasons, efforts are being made to abolish or at least reduce the tax preferential treatment of diesel fuels (see below), although diesel engines can theoretically make a certain contribution to climate protection due to their higher energy efficiency. Another strategy would be to meet the demand for heating oil e.g. B. through increased building renovation and substitution z. B. by natural gas, since light heating oil is made from the same fraction as diesel fuel.

Comparison of diesel and gasoline

Diesel fuel and gasoline differ in many ways. Their use in combustion engines also has many advantages and disadvantages that make the comparison relatively complex:

The fact that diesel contains approx. 13% more energy per liter than petrol should be taken into account when comparing the liter consumption of diesel and petrol engines.
  • Diesel fuel (in the types customary for motor vehicles) has an approx. 13% higher density. Also the energy content and the CO produced during combustion2-Quantities per liter of diesel are higher by this amount. A proper comparison of the energy efficiency of diesel and gasoline engines must take this into account.
Diesel engines are more efficient than gasoline engines, especially in the partial load range.
  • The efficiency of diesel engines is usually a few percentage points higher, especially in partial load operation. This, together with the higher energy content of diesel per liter, leads to a significantly lower consumption (measured in liters per 100 km - but less in the much more meaningful comparison by kilograms).
  • The exhaust quality of modern diesel engines is far better than that of old diesel engines (with some very high particulate matter emissions), but on the other hand it is usually significantly worse than that of today's gasoline engines. This applies to diesel engines with a particle filter (against soot and other substances), but without special measures against nitrogen oxides, compared to gasoline engines with a three-way catalytic converter (at least as long as no direct injection is used). Further technical improvements (especially SCR catalytic converters against nitrogen oxides) can largely compensate for these differences. However, it has been shown that the exhaust gas cleaning systems of many diesel cars are by far not as effective against nitrogen oxides as they should be in accordance with modern emissions standards, due to the manufacturer's manipulation.
  • Diesel fuel is less volatile and therefore has a significantly less strong smell than gasoline. This also leads to much lower evaporative emissions. However, it also takes a correspondingly longer time for the smell of spilled diesel fuel to dissipate.
  • Another consequence of the lower volatility of diesel fuel is its significantly higher flash point of at least 55 ° C. Since this is well above the typical storage temperatures, diesel fuel is not considered to be very dangerous in terms of its flammability - in contrast to gasoline.


In general, fuels are burdened by the mineral oil tax much higher than fuels such. B. for heating. This is why the tax burden on diesel fuel is much higher than that on heating oil.

In many countries, however, diesel fuel is taxed much less heavily than petrol. Corresponding legal regulations have, however, often been greatly changed, as the energy policy discussion about them is influenced by many different aspects that can gain or lose influence depending on the current situation. In Germany in particular, there have been various adjustments to the mineral oil tax for diesel fuel. However, there has always been a clear tax preference for diesel fuels: The tax burden per liter of fuel is lower, although the energy content and CO2-Emissions are slightly higher. One often tries to justify this by saying that the CO2-The emissions of diesel cars are still lower because of the higher efficiency of the engines, and thus promoting the diesel share would serve to protect the climate. However, there are several arguments against this tax benefit:

The tax preference for diesel fuel due to an alleged climate protection effect is not factually founded!
  • First of all, the CO2-The advantage is significantly lower than is often assumed. It is often overlooked that the fuel consumption benefit measured in liters is partly offset by the higher carbon content of diesel fuel.
  • In addition, rebound effects further reduce the consumption advantage: Because buyers also usually overestimate the consumption advantage, they tend to buy a heavier and more motorized vehicle (e.g. SUV) and possibly to use the vehicle more often. Thus, comparative calculations that implicitly assume equally heavy, equally powerful and equally frequently used vehicles with gasoline or diesel engines are not realistic. It can be assumed that taking these factors into account will reduce the alleged CO2-The advantage of diesel offsets or even overcompensates.
  • The “dieselization” of the European vehicle fleet means that, in relation to gasoline, more diesel fuel is required than the oil refineries can produce. As a result, diesel fuel is imported from the USA and gasoline is exported there. The considerable additional transport effort worsens the CO2-Balance of Diesel continues. The energy consumption in the refineries also increases as a result.
  • Another factor is the significantly higher pollutant emissions from diesel engines. Today, soot particle filters largely solve the problem of particulate matter emissions from engines, and the nitrogen oxide emission limit values ​​have now been brought into line with those for gasoline engines. However, the nitrogen oxide emissions in practice are much higher in most vehicles, as manufacturers have widely used so-called shutdown devices for exhaust gas purification, which usually massively reduce the effectiveness of denitrification. This is why the high proportion of diesel in the passenger car fleet makes a major contribution to air pollution, especially in busy cities.

Questions and comments from readers


As part of a study project at my university, I balanced the transport of diesel fuel from the refinery to the tank of a vehicle.

Result for the transport from the refinery to the gas station: approx. 0.04 kWh / l

Refueling the vehicle at the pump: 0.000008 kWh / l diesel

(More details provided later :)

As part of this work, I also balanced the transport and distribution of the fuel in order to determine how large the energy expenditure is until one liter is in the vehicle's tank. We assumed that the fuel was produced in Germany. We had data from a carrier. Based on the data, we were able to determine the monthly mileage of the tractor, fuel consumption and how much fuel was delivered. We then calculated that down to one liter of transported fuel.

Answer from the author:

Such statements say little as long as one does not know the assumptions made. (At least some details were delivered later, see above.)

If z. For example, if diesel fuel is refined in the US and shipped to us, it is probably a lot more gray energy. And it actually happens.


I would like to initiate a direct comparison from the point of view of a normal user between e-mobility and combustion engines:

1 liter of diesel has an energy content of approx. 10 kWh / l. A lithium battery in the Tesla has approx. 100 kWh - that is, equivalent to 10 liters of diesel.

This tells me this with the generally available information from the WWW:

1) E-mobility is significantly more effective than combustion (range for vehicles of comparable size is approx. 5: 1 per e-mobility. Comparison: Passat Diesel / Tesla S)

2) The absolute maximum range of today's vehicles (even with 5: 1 poorer efficiency) is still clearly ahead (range> 1000 km for the Passat versus approx. 450 km for the Tesla S).

3) Charging time / refueling time for an 80% filling (max. Charging speed, e.g. with Tesla), diesel is still a factor of 10 ahead of e-mobility.

For me, I draw the following conclusion from these facts:

a) In the future, environmentally friendly mobility can only be achieved through hybrid concepts. The advantages of regeneration (recuperation) that is possible “online” must be supplemented by the high availability of energy in the vehicle (diesel tank).

b) The effectiveness of e-mobility must be transferred to current vehicle concepts: high torque when accelerating and braking, and the associated recovery of kinetic energy.

c) Continuous output can only be achieved with efficient combustion engines in diesel: Consumption of <3 l of diesel / 100 km of driving distance can already be achieved at any time with constant load. Acceleration and a lack of energy recovery spoil the consumption values ​​of current combustion vehicles.

d) The additional components for e-mobility must be integrated into the necessary units of the combustion engine. Development is required here. It is conceivable to ban all electrical systems from a combustion engine and to replace them with universal machines (generator and motor in one) with the lowest possible weight.

e) Electrical energy storage devices must be able to be exchanged quickly; if necessary, several blocks with lower capacities must be exchangeable within seconds. A plug-in system with an automated changeover at the “gas station” should make this possible with the means that can be realized today.

f) It must also be possible to retrofit existing combustion engines: electric motors in rims, batteries in spare wheel wells. Then only the control with connection to the modern (combustion) engine electronics is missing.

g) It has to be affordable.

Answer from the author:

The comparison in point 1 is weird: The primary energy consumption for charging the battery is not that much lower than that for the petrol tank.

Some things seem over-optimistic to me, e.g. B. regarding retrofitting. You don't even get a larger Adblue tank installed later ... And how is that supposed to be affordable?

Above all, however, the concept is unfortunately not sufficient for the necessary progress. Hybrid drives bring about a 20% reduction in fuel consumption and CO2Emissions, but we need a lot more. So: The development of highly efficient hybrid vehicles makes sense, but we have to fundamentally reorganize our mobility - e. B. not build and use cars for long distances. Even non-electric: hundreds of kilograms of batteries are constantly being driven around, just to be able to cover longer distances. We need other concepts, e.g. B. an optimized public transport system in a clever connection with electric cars for the first and last few kilometers. This with timetable and operating concepts that are no longer as tedious as before.

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See also: fuel, diesel engine, biodiesel, hydrocarbons, ignitability, heavy fuel oil, gasoline, petroleum refinery, mineral oil tax, tank tourism
as well as other items in the categories of energy carriers, vehicles, engines and power plants