Internal Combustion Engine Structure and Working Principle | 内燃机结构及其工作原理

📚 Internal Combustion Engine Structure and Working Principle | 内燃机结构及其工作原理

An internal combustion engine (ICE) is a heat engine in which fuel is burned inside a combustion chamber within the engine itself. The expanding hot gases directly push a piston, converting chemical energy into mechanical work. This topic is essential for understanding thermodynamics, energy conversion, and real-world applications of physics.

内燃机（ICE）是一种在发动机内部的燃烧室内燃烧燃料的热机。膨胀的高温气体直接推动活塞，将化学能转化为机械功。这一主题对于理解热力学、能量转换及其在现实世界中的应用至关重要。

1. Basic Types of Internal Combustion Engines | 内燃机的基本类型

Internal combustion engines can be classified in several ways. The two most common types are the spark-ignition (SI) engine, which uses a spark plug to ignite a fuel-air mixture, and the compression-ignition (CI) engine, which ignites fuel by the heat of compressed air.

内燃机可以通过多种方式进行分类。最常见的两种类型是火花点火（SI）发动机（使用火花塞点燃燃油-空气混合物）和压燃（CI）发动机（利用压缩空气的热量点燃燃油）。

Spark-Ignition (SI) Engine: Runs on petrol/petrol-like fuels; uses an electric spark to initiate combustion.
火花点火（SI）发动机： 使用汽油类燃料；利用电火花引燃。
Compression-Ignition (CI) Engine: Runs on diesel; air is compressed to a high temperature, then fuel is injected and self-ignites.
压燃（CI）发动机： 使用柴油；空气被压缩至高温后喷入燃油，自行着火。

Another classification is by the number of strokes per cycle: four-stroke engines and two-stroke engines. The four-stroke cycle is the most common in automobiles and will be the focus of this article.

另一种分类方式是按照每个循环的冲程数：四冲程发动机和二冲程发动机。四冲程循环在汽车中最常见，本文将重点讲解。

2. Main Components of an Internal Combustion Engine | 内燃机的主要部件

The engine’s structure consists of a series of interconnected components, each with a specific function. Understanding these components is the first step to mastering how the engine operates.

发动机的结构由一系列相互关联的部件组成，每个部件都有特定的功能。理解这些部件是掌握发动机工作原理的第一步。

Component \| 部件	Function \| 功能
Cylinder \| 气缸	Houses the piston; guides its motion. \| 容纳活塞并引导其运动。
Piston \| 活塞	Receives gas pressure and converts it into linear motion. \| 承受气体压力并将其转化为直线运动。
Connecting Rod \| 连杆	Connects the piston to the crankshaft; transmits force. \| 连接活塞与曲轴；传递力。
Crankshaft \| 曲轴	Converts linear piston motion into rotational motion. \| 将活塞的直线运动转化为旋转运动。
Valves \| 气门	Control intake of air/fuel and exhaust of combustion gases. \| 控制空气/燃油的进入和废气的排出。
Spark Plug \| 火花塞	Provides an electric spark to ignite the mixture (SI engines). \| 提供电火花点燃混合气（SI发动机）。
Fuel Injector \| 喷油器	Sprays fuel into the cylinder (modern engines). \| 将燃油喷入气缸（现代发动机）。

The piston moves within the cylinder between two extreme positions. The topmost position is called top dead centre (TDC), and the bottommost is called bottom dead centre (BDC). The distance between TDC and BDC is the stroke, and the volume swept by the piston is the swept volume.

活塞在气缸内在两个极限位置之间移动。最上方的位置称为上止点（TDC），最下方的位置称为下止点（BDC）。TDC与BDC之间的距离称为冲程，活塞扫过的体积称为排量（工作容积）。

3. The Four-Stroke Cycle | 四冲程循环

The four-stroke cycle consists of four distinct phases: intake, compression, power (expansion), and exhaust. One complete cycle requires two full rotations of the crankshaft (720°).

四冲程循环包括四个不同的阶段：进气、压缩、做功（膨胀）和排气。一个完整的循环需要曲轴旋转两圈（720°）。

Stroke 1 – Intake: The piston moves from TDC to BDC. The intake valve opens, and a fresh air-fuel mixture is drawn into the cylinder.

第一冲程 – 进气： 活塞从上止点向下止点移动。进气门打开，新鲜空气-燃油混合物被吸入气缸。

Stroke 2 – Compression: Both valves are closed. The piston moves from BDC to TDC, compressing the mixture to a high pressure and temperature (compression ratio is typically 8:1 to 12:1 for SI engines).

第二冲程 – 压缩： 两个气门均关闭。活塞从下止点向上止点移动，将混合气压缩到高压高温（SI发动机的压缩比通常为8:1至12:1）。

Compression Ratio = V_max / V_min | 压缩比 = V_最大 / V_最小

Stroke 3 – Power (Expansion): Just before TDC, the spark plug ignites the compressed mixture. The burning gases expand rapidly, forcing the piston downward. This is the only stroke that produces useful work.

第三冲程 – 做功（膨胀）： 在上止点前，火花塞点燃被压缩的混合气。燃烧气体迅速膨胀，推动活塞向下运动。这是唯一产生有用功的冲程。

Stroke 4 – Exhaust: The exhaust valve opens. The piston moves from BDC to TDC, pushing the spent combustion gases out of the cylinder.

第四冲程 – 排气： 排气门打开。活塞从下止点向上止点移动，将燃烧后的废气推出气缸。

4. The Thermodynamic Cycle: Otto and Diesel | 热力学循环：奥托循环与狄塞尔循环

The SI engine operates on the Otto cycle, while the CI engine operates on the Diesel cycle. Both are idealized thermodynamic models used to analyze engine efficiency.

SI发动机遵循奥托循环，CI发动机遵循狄塞尔循环。两者都是用于分析发动机效率的理想化热力学模型。

Otto Cycle (SI Engine): Consists of two adiabatic processes and two isochoric (constant-volume) processes. Combustion is modeled as instantaneous heat addition at constant volume.

奥托循环（SI发动机）： 包含两个绝热过程和两个等容过程。燃烧被建模为在恒定体积下的瞬时加热。

Diesel Cycle (CI Engine): Consists of two adiabatic processes, one isobaric (constant-pressure) process, and one isochoric process. Combustion is modeled as heat addition at constant pressure.

狄塞尔循环（CI发动机）： 包含两个绝热过程、一个等压过程和一个等容过程。燃烧被建模为在恒定压力下的加热。

For the ideal Otto cycle, thermal efficiency depends only on the compression ratio r:

对于理想奥托循环，热效率仅取决于压缩比 r：

η = 1 − 1 / r^γ−1

where γ is the specific heat ratio (C_p/C_v). Higher compression ratios yield higher theoretical efficiencies, but practical limits exist due to knocking (uncontrolled combustion) in SI engines.

其中γ是比热比（C_p/C_v）。更高的压缩比带来更高的理论效率，但SI发动机中爆震（不受控制的燃烧）限制了实际压缩比的提高。

5. Valve Timing and the Valve Mechanism | 气门正时与气门机构

Proper valve timing is crucial. The intake and exhaust valves must open and close at precise moments relative to piston position to optimize the flow of gases and engine performance.

正确的气门正时至关重要。进气门和排气门必须在相对于活塞位置的精确时刻开闭，以优化气体流动和发动机性能。

Intake valve opens (IVO): Slightly before TDC during exhaust stroke to ensure fresh mixture enters as exhaust exits.
进气门开启（IVO）：在排气冲程中略早于上止点打开，以确保新鲜混合气在废气排出时进入。
Intake valve closes (IVC): Slightly after BDC to use momentum to pack more mixture into the cylinder.
进气门关闭（IVC）： 略晚于下止点关闭，利用惯性使更多混合气进入气缸。
Exhaust valve opens (EVO): Slightly before BDC during power stroke to release pressure before the piston starts its upward exhaust stroke.
排气门开启（EVO）： 在做功冲程中略早于下止点打开，在活塞开始向上排气前释放压力。
Exhaust valve closes (EVC): Slightly after TDC to reduce residual exhaust gas in the cylinder.
排气门关闭（EVC）： 略晚于上止点关闭，以减少气缸内的残余废气。

Valves are typically operated by camshafts. A camshaft is a rotating shaft with lobes (cams) that push on the valves via lifters, pushrods, and rocker arms. In double-overhead-camshaft (DOHC) designs, two camshafts per cylinder head operate the valves directly.

气门通常由凸轮轴驱动。凸轮轴是一种带有凸轮的旋转轴，通过挺杆、推杆和摇臂推动气门。在双顶置凸轮轴（DOHC）设计中，每缸盖有两根凸轮轴直接驱动气门。

6. Energy Conservation and Efficiency | 能量守恒与效率

In an internal combustion engine, the chemical energy stored in fuel (Q_in) is converted into several forms: useful mechanical work (W_out), heat lost to the coolant and exhaust, friction losses, and pumping losses.

在内燃机中，燃料中储存的化学能（Q_in）被转化为多种形式：有用机械功（W_out）、传递给冷却液和废气的热量、摩擦损耗和泵气损耗。

Q_in = W_out + Q_lost | 输入热量 = 有用功 + 损失热量

Typical brake thermal efficiency (BTE) for modern SI engines is around 25–30%. CI engines achieve 35–45% due to higher compression ratios and leaner combustion. Some turbo-diesel engines can exceed 50% in specific operating conditions.

现代SI发动机的制动热效率（BTE）约为25–30%。CI发动机因压缩比更高、燃烧更稀，可达到35–45%。部分涡轮增压柴油发动机在特定工况下可超过50%。

To maximize efficiency, engineers strive to:

为提高效率，工程师通常努力做到：

Increase compression ratio | 提高压缩比
Reduce friction between moving parts | 减少运动部件之间的摩擦
Recover exhaust heat (turbocharging, thermoelectric generators) | 回收废气热量（涡轮增压、热电发电）
Optimize combustion timing and fuel injection | 优化燃烧时刻和燃油喷射

7. Turbocharging and Supercharging | 涡轮增压与机械增压

To increase the power output of an engine without increasing its displacement, forced induction can be used. A turbocharger uses the kinetic energy of exhaust gases to spin a turbine, which drives a compressor to force more air into the cylinders. A supercharger is mechanically driven by the crankshaft via a belt.

为在不增加排量情况下提高发动机功率输出，可采用强制进气。涡轮增压器利用废气的动能驱动涡轮旋转，涡轮带动压缩机将更多空气压入气缸。机械增压器则通过皮带由曲轴机械驱动。

P = η_v × ρ_air × V_swept × N × (fuel energy per cycle)

Forcing more air into the cylinder allows more fuel to be burned per cycle, increasing power density. However, higher temperatures and pressures also increase the thermal load on the engine, often requiring intercoolers to cool the compressed air.

将更多空气压入气缸，使每个循环能燃烧更多燃料，从而提高了功率密度。然而，更高的温度和压力也增加了发动机的热负荷，通常需要中冷器来冷却压缩后的空气。

8. Real-World Applications and Environmental Considerations | 实际应用与环境考量

Internal combustion engines are widely used in cars, motorcycles, trucks, ships, and small generators. However, they produce carbon dioxide (CO₂), nitrogen oxides (NOₓ), carbon monoxide (CO), and particulate matter, which contribute to climate change and air pollution.

内燃机广泛应用于汽车、摩托车、卡车、船舶和小型发电机中。然而，它们排放二氧化碳（CO₂）、氮氧化物（NOₓ）、一氧化碳（CO）和颗粒物，导致气候变化和空气污染。

Modern solutions to reduce emissions include:

减少排放的现代解决方案包括：

Three-way catalytic converters | 三元催化转化器
Exhaust gas recirculation (EGR) | 废气再循环（EGR）
Particulate filters | 颗粒捕集器
Hybrid electric systems that switch to electric power at low loads | 混合动力系统在低负荷时切换至电力驱动

As governments tighten regulations, the internal combustion engine is evolving. However, its basic structure and thermodynamic principles remain a fundamental part of physics education and engineering practice.

随着各国政府收紧法规，内燃机正在不断进化。然而，其基本结构和热力学原理仍然是物理教育和工程实践中的基础内容。

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Component \| 部件	Function \| 功能
Cylinder \| 气缸	Houses the piston; guides its motion. \| 容纳活塞并引导其运动。
Piston \| 活塞	Receives gas pressure and converts it into linear motion. \| 承受气体压力并将其转化为直线运动。
Connecting Rod \| 连杆	Connects the piston to the crankshaft; transmits force. \| 连接活塞与曲轴；传递力。
Crankshaft \| 曲轴	Converts linear piston motion into rotational motion. \| 将活塞的直线运动转化为旋转运动。
Valves \| 气门	Control intake of air/fuel and exhaust of combustion gases. \| 控制空气/燃油的进入和废气的排出。
Spark Plug \| 火花塞	Provides an electric spark to ignite the mixture (SI engines). \| 提供电火花点燃混合气（SI发动机）。
Fuel Injector \| 喷油器	Sprays fuel into the cylinder (modern engines). \| 将燃油喷入气缸（现代发动机）。

Internal Combustion Engine Structure and Working Principle | 内燃机结构及其工作原理