Characteristics of petrol, diesel, and hybrid engines

In direct comparison to the gasoline engine, the diesel engine scores with its lower fuel consumption. Thanks to its combustion process, the use of the energy in the fuel is much greater. The so-called thermodynamic efficiency of the diesel engine is higher than that of the gasoline engine. This is why the diesel is so economical. This advantage is due to the higher compression and the higher peak temperatures in the cylinder of the diesel engine.  These extreme conditions in the combustion chamber, however, also produce more pollutants, which then require additional, complex exhaust after-treatment measures.

As a consequence, current-generation diesel engines all have a so-called SCR catalytic converter as well as a diesel particulate filter, which subsequently removes the pollutants produced during combustion. Exhaust gas after-treatment reduces emissions by 90 to 99.9%, and even the strictest Euro 6d limits can be safely met using these technologies.

Under current Euro 6d emissions legislation, vehicles and their drives must be proven to meet the legally prescribed limit values on the road and under all normal driving conditions. The strict requirements require compliance with emissions even under intensified conditions – for example, when navigating Alpine passes in winter. Vehicle drives are developed with extreme conditions of this kind in mind so as to meet and withstand the legal requirements, including in the field. The result is that modern vehicles – and diesel vehicles are explicitly included here – are almost pollutant-free in normal operation.

This is confirmed by independent tests carried out by Emissions Analytics as well as by independent car magazines (see QR code). Even under extreme driving and external conditions, for example, emission values of between 9 and 19 milligrams of NOx per kilometer were measured on the road in new passenger car models from German manufacturers. This is about 80% below the applicable Euro 6 limit.

The ADAC (the German automotive society) also gives the Euro 6d diesels good ratings. In independent tests, the ADAC certified Euro 6d diesels as having very low emissions even at low temperatures: An average of 20 milligrams of NOx per kilometer. A select few German models even had an emission of only one milligram of NOx per kilometer. The emissions are therefore just above the detection limit. The ADAC has confirmed that all vehicles of the Euro 6d standard also comply with the legal limit value on the road.

The German automotive industry has done its homework in this area. The discussion, with reference to air quality, about banning the combustion engine is therefore outdated and cannot be objectively, ecologically, or economically justified. Despite the clear electrification strategy of the German automotive industry, the modern and efficient combustion engine still represents an important cornerstone of mobility.

Since 2021, all newly registered passenger cars in the European Union have had to comply with the average CO₂ limit value of 95 grams per kilometer: A major challenge that requires the optimization of the drive system, from the combustion to power transmission on the road. Every percentage point of improved efficiency must be used to achieve this goal. The diesel emits about 10 to 15% less CO₂ than a comparable gasoline engine, and thus makes an important contribution to complying with the European CO₂ limit.

The modern gasoline engine is approaching the efficiency rates of the diesel engine because it is increasing its efficiency, by adopting the direct injection principles of the diesel engine. The engine and exhaust gas after-treatment technology of the petrol engine, however, is less complex. Its economy and cleanliness are particularly effective in the small car segment, and at lower and medium mileage. The gasoline engine is also particularly suitable for the hybridization of the powertrain. This is a partial electrification of the drive, and constitutes a combination of the classic combustion engine with an electric drive. As a result, the efficiency advantages of the electric drive can be combined with the combustion engine and optimized. Depending on the degree of electrification, efficiency advantages of around 25% are possible.

Classic hybrid drives usually have a high-voltage supply in the range of 200 volts and more. While powerful drives are possible, high-voltage technology is complex and cost-intensive. As a result, it is often not economical for price-sensitive drive segments. The 48-V technology offers an alternative; it not only allows the replacement of the classic 12-V electrical system with a modern, powerful vehicle electrical system, but also enables the use of electric drives in the range of several kilowatts of drive power at this low voltage level.

Thus, the principle of the hybrid drive can be cost-effectively used in combination with a modern vehicle electrical system. The ull hybrid has high electric mileage and a powerful battery. The plug-in hybrid – a powerful full hybrid with built-in socket and enlarged battery – represents the bridge between the full hybrid and the electric vehicle. When it comes to the plug-in hybrid, the built-in combustion engine is increasingly losing importance; thanks to the electric socket, a substantial portion of the driving energy no longer comes from the combustion engine. A plug-in hybrid usually has an all-electric range of about 60 to 100 kilometers – ideal for the typical commuter and short-distance journeys.