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The secret of the heat engine: How do you convert the energy of fuel into power?
In daily life, we often hear the word "fuel economy", especially in automobiles and various mechanical equipment, it is undoubtedly an important indicator of performance and environmental protection. However, how exactly does the efficiency of a heat engine work? This article will explore the basic concepts of heat engines, how they work, and the secrets behind them.
Basic operating principles of heat engines
A heat engine is a mechanical device that generates power by burning fuel. Its working principle can be simply summarized as: converting the chemical energy of fuel into mechanical energy or electrical energy. Heat engines can be divided into two categories: internal combustion engines and external combustion engines. Internal combustion engines, mainly including gasoline engines, diesel engines and gas turbines, all complete fuel combustion inside the engine; while external combustion engines, such as steam engines and Stirling engines, complete fuel combustion outside and then convert the generated heat into mechanical energy.
The efficiency of an engine is the ratio of useful work to heat absorbed.
Factors that affect engine efficiency
Many factors affect the efficiency of a heat engine, the most important of which include compression ratio, friction losses and oxygen supply. The compression ratio is an important parameter of an internal combustion engine, which directly affects the power that can be extracted. Generally speaking, a higher compression ratio improves engine efficiency, but this may also result in increased engine noise and emissions.
Friction loss and energy conversion
Friction among engine components causes energy loss. For example, the lateral friction of the piston increases as the engine speed increases, which prevents some of the energy from being converted into power. In addition, the amount of work required to move air into and out of the engine increases as engine speed increases, which is also a factor that reduces efficiency.
The role of oxygen
An adequate supply of oxygen is essential to the combustion process. Air is about 21% oxygen, and without enough oxygen, the fuel will burn incompletely, reducing power output. Therefore, an effective air-fuel mixture ratio is another key to achieving high efficiency.
Under insufficient oxygen conditions, the fuel cannot be completely burned, thereby reducing the energy conversion efficiency.
Efficiency analysis of different types of heat engines
Different types of heat engines have their own unique efficiency performance. For example, diesel engines are generally more efficient due to their higher compression ratios, reaching a ratio of 45%. The efficiency of a gasoline engine is generally between 20% and 40%. In addition, the gas turbine also exhibits high efficiency at maximum power output, approximately 46% and 61%.
Efficiency of internal combustion engines
Take petrol engines as an example. Modern petrol engines can have a thermal efficiency of over 50%, but many road-legal vehicles have an efficiency of only between 20% and 40%. This means that a considerable portion of the heat, up to 80%, is wasted as thermal energy and fails to be effectively converted into power.
Efficiency of external combustion engines
Relative to internal combustion engines, the efficiency of external combustion engines is generally limited by the steam temperature and pressure. Steam engines and steam turbines have an efficiency of around 40%, but ideally can achieve a Carnot efficiency of 63%. This requires continuous improvement in technology to achieve.
The latest technologies contribute to improving thermal engine efficiency
With the advancement of technology, many new technologies have been introduced to improve the efficiency of thermal engines, including variable compression technology, cylinder change system and electronically controlled fuel injection technology. For example, modern diesel engines use electronically controlled common rail injection system. To increase efficiency.
ConclusionUnderstanding how a thermal engine works and the factors that affect its efficiency not only helps improve vehicle performance, but is also an important step in meeting today's environmental requirements. How will future new energy technologies and engine designs affect the energy conversion efficiency of fuels?
