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How important is thermal efficiency? How does it affect your car’s gas mileage?
When you walk into a gas station and fill up your tank, have you ever wondered how the energy in that tank is converted into power to propel your car? Thermal efficiency, as a key factor in determining automobile fuel consumption, is the core concept that affects energy conversion efficiency.
The thermal efficiency of an engine is the relationship between the total energy contained in the fuel and the amount of energy that can be converted into useful work.
Automobile engines are mainly divided into two categories: internal combustion engines and external combustion engines. Internal combustion engines include gasoline engines, diesel engines, etc., while external combustion engines are usually used for steam engines and turbines. Different types of engines have unique thermal efficiency characteristics, which affect the fuel consumption of the vehicle.
In general, engine efficiency is calculated based on the ratio of useful work to heat absorbed, so energy losses due to friction, airflow resistance, etc., have a significant impact on fuel consumption. Every time a car drives, it silently loses a considerable amount of energy.
According to data, the maximum thermal efficiency of modern gasoline engines can reach over 50%, but most commercially available models can only reach between 20% and 40%.
With more than 60% of the thermal energy not converted into propulsion, most of the energy is still discharged in the form of heat and noise. This phenomenon undoubtedly makes us feel helpless every time we refuel. Does this mean that the price you pay for filling up your tank actually hides a lot of wasted energy costs?
There are many factors that affect the thermal efficiency of the engine, among which the compression ratio is an important factor affecting the thermal efficiency of the internal combustion engine. The higher the compression ratio, the higher the total effective power in theory, but excessive compression may cause unstable engine operation, so it is necessary to balance performance and practicality.
Increasing the fuel-air mixing ratio to make combustion more complete is one of the important methods to improve thermal efficiency.
Further considering the oxygen supply, about 21% of the air is oxygen. When there is insufficient oxygen, the fuel cannot be completely burned, resulting in reduced efficiency and emission pollutants. To achieve higher thermal efficiency, the intake pressure needs to be increased, which can be achieved through a supercharging system.
Among gasoline engines, many models often use the Otto cycle. However, with the advancement of technology, some new engines combine the Atkinson cycle to focus on improving energy efficiency. This is undoubtedly an important direction for the future development of automobiles.
Diesel engines are generally more thermally efficient because they use a higher compression ratio, which compensates for air pumping losses.
Diesel engines, because they run at a higher compression ratio, can actually outperform many gasoline engines in terms of efficiency. This is undoubtedly the best choice for trucks that need to carry heavy goods.
Finally, we come to external combustion engines, such as steam engines. Although their thermal efficiency is not as good as that of internal combustion engines, they are still used in areas such as shipping in certain specific cases. To sum up, since thermal efficiency plays a vital role in the entire drive chain, the future development of automotive technology will focus more on how to improve this efficiency.
As you further explore the limits of automotive technology, does it make you reflect on the balance between driving comfort and fuel consumption?
