Diesel engines and petrol engines draw their energy from liquid fuels, but they differ substantially. The function of the engines also differs significantly between petrol and diesel. While the petrol engine ignites the gas compressed by the piston in the cylinders by means of a spark plug, the diesel works by self-ignition at high compression. Get an overview of the different fuels and the state of the art now.

Different fuels – diesel and petrol in comparison

The fuels diesel and petrol are both derived from crude oil, yet there are sometimes far-reaching differences. For example, diesel is produced from the heavier components of the oil, while petrol is produced from the lighter components. Both fuels are produced in a refinery, and other types of fuel are also produced.

Different composition of petrol and diesel

Diesel contains a higher proportion of carbons and is heavier and oilier than petrol. Petrol, on the other hand, is lighter and also more flammable. Compared to petrol, diesel only vaporises at a much higher temperature, which is why it is more difficult to ignite. Another fundamental difference is that diesel contains more energy than petrol.

Advantages and disadvantages of diesel or petrol

Depending on the type of fuel, there are advantages and disadvantages. For a long time, the low price of diesel compared to petrol was one of the advantages in Germany. The reason for this is the different taxation of this type of fuel. However, this price difference at the pump has now almost disappeared, so that diesel is only slightly cheaper than petrol.

Differences in fuel consumption and purchase

Diesel offers a major advantage in terms of fuel consumption. Due to its high energy content, the diesel engine can draw more power from the same amount of fuel than a petrol engine. This is why diesels are more economical than petrol engines. However, the lower consumption is more noticeable on long journeys; on short journeys, the diesel engine cannot always exploit its advantage.

When it comes to buying a new car, fuel sometimes affects the cost of the purchase. Cars with petrol engines are generally cheaper to buy than comparable diesel vehicles. On the one hand, a diesel engine is more complex in design, and on the other hand, the cleaning of exhaust gases is often more complicated due to strict regulations. This affects the purchase price of the vehicles.

Taxes and insurance depending on fuel

Advantages and disadvantages also arise in terms of taxes and insurance. The motor vehicle tax for diesel vehicles in Germany is generally higher than for vehicles that use petrol as fuel. Among other things, a difference is made in the calculation based on engine capacity and pollutant emissions. This puts diesel engines at a disadvantage. In motor vehicle insurance, too, diesels are at a disadvantage compared to petrol engines, partly because diesel vehicles are more expensive.

Advantages of the petrol engine

• Acquisition is cheaper
• Engine is considered more refined
• Insurance and tax are cheaper

Advantages of the diesel engine

• Consumption is lower
• Torque is higher
• Tax advantages on fuel

Ignition for diesel engines and petrol engines

When it comes to ignition, diesel engines and petrol engines differ significantly. Diesel engines are so-called self-ignition engines that do not require actual ignition. Instead, the air in the cylinder is strongly compressed via the piston, causing it to heat up. The diesel injected into the cylinder then ignites itself in the form of a self-ignition.

To start the cold engine, manual preheating by means of a preheating system is still necessary, especially with older diesel engines, but diesel engines do not have an ignition system. The petrol engine is quite different. In order for the mixture of air and petrol introduced into the cylinder to be combusted, spark ignition is necessary. This ignition takes place in petrol engines by means of an ignition system and spark plugs for each cylinder.

Compression ratio for petrol and diesel

Diesel engines have a much higher compression ratio than petrol engines. One of the reasons for this is that, unlike petrol, diesel only ignites itself at much higher pressure. The mixture in the cylinders is compressed much more in the diesel engine, which leads, among other things, to a higher torque compared to the petrol engine. However, the higher pressure requires a more robust construction, which makes the diesel engine heavier.

Power and torque

Diesel engines are known for their high torque. This in turn results from the higher compression ratio and the higher and narrower cylinder shape. This results, for example, in better acceleration with diesel. And this even if the diesel has a lower engine power compared to the petrol engine. On the other hand, the diesel engine operates at a lower speed and runs less smoothly than a petrol engine.

Repair and spare parts for diesel and petrol engines

Depending on whether an engine is designed for diesel or petrol, there can be differences in terms of maintenance and repair. For example, many diesels have a more complicated exhaust system, and there is also a difference in injection compared to petrol engines. In addition, diesel engines have an exhaust gas aftertreatment system that uses injected urea to effectively reduce the level of harmful nitrogen oxides. It is not uncommon for diesel engines to require more parts to be disassembled, or for assembly and disassembly to be generally more complicated. This can result in higher costs for the purchase, repair and spare parts of diesel engines.

Maintenance costs – difference petrol and diesel engines

The costs for maintenance can be quite different for cars with a petrol engine than for a vehicle with a diesel engine. Often the maintenance of a petrol engine is cheaper because there are fewer parts in the engine and exhaust tract than in a diesel. In addition, diesel engines often have urea injection in the exhaust tract, which also requires maintenance. However, some petrol engine models have shorter maintenance intervals than the same model with a diesel engine. Therefore, maintenance timing and costs should always be compared.

Costs for spare parts – diesel versus petrol engine

Due to the different design and mixture formation in the engine, the cost of spare parts can vary between petrol and diesel engines. Although some spare parts, such as the spark plug, are omitted in the diesel, other components are additional to the petrol engine. This applies, for example, to numerous components from the area of exhaust gas recirculation and exhaust gas purification. In addition, components such as injectors for diesel engines often cost a considerable amount per unit. However, spare parts for the engine and drive are readily available second-hand for both petrol and diesel.

Buy spare parts for diesel and petrol engines

For diesels and petrol engines, special spare parts are required for the car depending on the fuel. When buying parts, you should always note whether the corresponding component is designed for the respective diesel engine or petrol engine. The air supply can differ, as can components of the vehicle electronics. Cylinders and pistons are designed completely differently for diesel engines compared to petrol engines. There are also differences between a car for petrol and a model for diesel with regard to the discharge of exhaust gases.