Innovation and Technology

A comparison of combustion technologies

The diesel engine has always outscored its gasoline counterpart with its lower
fuel consumption. In its combustion process, energy stored in the fuel is far better
utilized. Admittedly, diesel combustion generates more pollutants, necessitating
additional elaborate exhaust gas treatment measures.

Gasoline and diesel

The diesel engine has always outscored its gasoline counterpart with its lower fuel consumption. In its combustion process, energy stored in the fuel is far better utilized. Admittedly, diesel combustion generates more pollutants, necessitating additional elaborate exhaust gas treatment measures. The dynamic tension between fuel consumption, emissions, driving performance and vehicle costs sees dieseland gasoline-powered vehicles pitting their respective strengths against each other in different vehicle classes: A modern gasoline engine makes compact cars with moderate annual mileage affordable, whereas an advanced diesel with a tendency for higher mileage delivers lower fuel consumption. The ability to choose between gasoline and diesel helps to accommodate customers’ individual needs – especially in terms of cost. It is no coincidence that the diesel engine business fleets, including those of the skilled trades.

Diesel scores in terms of fuel consumption

A diesel engine’s fuel consumption advantage relative to a comparable gasoline engine is around 20 percent. CO2 emissions are a function of fuel consumption. Because CO2 is given off when a fossil fuel such as diesel or gasoline is burned. Despite a higher carbon content, diesel persists because of its efficient combustion with an ultimate CO2 advantage of up to 15 percent. 

Their lower CO2 emissions make diesel vehicles an indispensable building block in implementing European climate protection targets. This is illustrated by an example: in 2015, 48 percent of all newly registered cars in Germany featured a diesel engine. Based on this distribution, average emissions per car were 128 g/km CO2. If all diesel cars were now replaced by corresponding gasoline cars, then significantly higher emissions of about 135 g/km CO2 would result. Conversely, the emissions would be approximately 121 g/km CO2 if all gasoline cars were replaced by diesel cars. This is where the advantage of the diesel becomes apparent: With an average mileage of over 15,000 kilometers and a volume of 3.2 million new car registrations, this represents a savings of over 630,000 tons of CO2 per year. That is the same as a small town of 70,000 inhabitants emits each year.

Hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate matter (PM) pollutants are generated from fuel combustion. In particular, the relatively high NOx emissions are a challenge for the diesel engine. They result, alongside low fuel consumption, from the specific combustion process of diesel. Light and dark are close bedfellows here. The better the combustion, the higher the temperature and the more NOx is produced. This gives rise to conflicting interests: measures to reduce CO2 often result in higher nitrous oxide formation, whereas combustion optimized for less nitrous oxide means higher CO2 emissions. In Euro 6 vehicles, this trade-off is achieved by active DeNOx exhaust gas treatment (also see “Exhaust technology for reducing nitrogen oxides”).

The German automotive industry is the leader in diesel

Because of its technical advantages, the economic importance of the diesel engine to the German automotive industry has also steadily increased. In 2015 alone, at 2.7 million vehicles, 48 percent of all cars produced in Germany had diesel motors. Of this, 2 million vehicles were exported, of which almost 1.5 million went to EU member states. Due to the leading position of the German automotive industry in diesel technology, a significant share of the currently approximately 800,000 jobs in the automotive industry in Germany depend directly and indirectly upon the diesel engine. This applies to manufacturers, but also, and above all, to the German automotive suppliers. Currently, approximately every other newly registered car, both in Germany and Western Europe, is a diesel. And every other diesel car sold in Western Europe bears a German brand name. For medium and heavy commercial vehicles, the diesel engine has traditionally had a strong position because of its cost effectiveness. In production, and of course also in exports, its share is nearly 100 percent.

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