#Chemical Composition of Gasoline and Diesel

25 / October 2023
Chemical Composition of Gasoline and Diesel

Seletron Performance

Chemical Composition of Gasoline and Diesel and Differences in Their Engine Operating Regimes

The most widely used fuels for internal combustion engines, gasoline and diesel, distinguish themselves by their unique chemical composition, which profoundly influences the operation and performance of the engines that use them. Let's first explore how they differ chemically.

Gasoline, Chemical Structure

Gasoline is a lightweight and volatile fuel, primarily composed of short-chain hydrocarbons. Short-chain hydrocarbons are molecules consisting solely of carbon and hydrogen atoms, forming the basic structure of many organic compounds. In this context, "chain" refers to a succession of carbon atoms with single or double chemical bonds between them, along with hydrogen atoms attached to the carbon atoms.

In general, the length of the hydrocarbon chain influences the chemical and physical properties of a molecule. Short-chain hydrocarbons are characterized by relatively short chains of carbon atoms, ranging from one to four or five atoms. These molecules tend to be lighter and more volatile than longer-chain hydrocarbons.

This composition gives gasoline the ability to evaporate rapidly and burn quickly. Short-chain hydrocarbons are less dense and easily ignite when exposed to a spark. This property makes gasoline ideal for spark-ignition engines, which require a spark to initiate combustion.

Diesel, Chemical Structure

In contrast, diesel is primarily composed of long-chain hydrocarbons. These hydrocarbons are heavier and less volatile than those found in gasoline. Due to their higher density, they require higher compression and temperatures to ignite spontaneously. This process is known as compression ignition (or spontaneous ignition) and forms the basis of how diesel engines operate. Diesel's ability to self-ignite makes it ideal for diesel engines, where combustion occurs through compression rather than a spark.

Implications on Performance: Diesel vs. Otto Cycle

Differences in the chemical composition of these two fuels influence engine performance. Gasoline engines are more suitable for rapid acceleration and high speeds due to the quick combustion of the fuel used. Diesel engines are known for their ability to deliver high torque at low RPMs, making them effective for towing and heavy vehicles, although developments in recent decades have made these engines significantly more high-performance and suitable for sports cars.

The different compositions also affect combustion efficiency and fuel consumption. However, as mentioned, recent decades have seen significant innovations in both diesel and gasoline engines that have reduced the performance gap that once clearly distinguished diesel engines from Otto cycle engines. Some important technical developments include:

- The introduction of electronic control in diesel fuel systems

- Widespread use of electronically controlled direct injection systems

- Use of variable geometry turbochargers (VNT)

- Introduction of common-rail injection systems

- Use of variable intake manifold designs

- Adoption of multi-stage forced induction systems (bi-turbo, sequential tri-turbo)

- Further refinement of fuel injection control systems, becoming faster and more precise

- Use of new materials and manufacturing processes


On the other hand, gasoline engines have also seen various developments in recent decades, including:

- The use of direct gasoline injection systems

- Further refinement of fuel injection control systems, becoming faster and more precise

- Adoption of new materials and manufacturing processes

- Use of combined forced induction systems (supercharger + turbocharger)

- Use of twin-scroll hot-side turbochargers


All of this has led to performance improvements and enhanced engine usability in gasoline engines (along with an increase in specific power) and a significant increase in power and specific torque in diesel engines. For example, comparing the power of a 2-liter turbocharged diesel engine from the 1980s (e.g., 82hp for an Alfa Romeo) with a modern 2-liter common-rail engine (e.g., the 245hp Mercedes engine with a displacement of 1950cc and 500Nm of peak torque) highlights the substantial performance improvements.

What's interesting to note, in connection to the chemical aspect of fuel (combustion speed), is that despite the substantial increase in specific power by a factor of three or more, the maximum rotational speed of turbocharged diesel engines has remained nearly constant. The most high-performance common-rail engines of today can, in some cases, reach 5500 RPM, but typically, the rev limiter is set at around 5000 RPM (or even lower) as it was in engines from decades ago. The significant increase in specific power has been made possible by working with much higher boost pressures and the precise management of multiple diesel injections (capabilities enabled by the development of common-rail injection systems and sophisticated electronic controls for injection and forced induction).

In this article, we've discussed the chemical composition of gasoline and diesel and the differences in the operating regimes of their respective engines. If you want to increase the power of your car, you can search for your model in our catalog and see what you can order to increase power and torque by installing a non-invasive and completely removable external kit. Visit the catalog here: >>> https://seletron.com/en/shop/




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