What is the working principle of a car engine?

introduction

As the core component of modern transportation, the working principle of automobile engines is an outstanding achievement in the field of mechanical engineering. Since the emergence of internal combustion engines in the late 19th century, engine technology has undergone countless innovations and improvements, but its basic principles have remained unchanged. This article will provide a detailed analysis of the working principle of automotive engines, helping readers understand how this complex and sophisticated mechanical system converts fuel into power to drive the vehicle forward.

Basic structure of engine

The automobile engine is mainly composed of components such as cylinders, pistons, connecting rods, crankshafts, valve mechanisms, fuel systems, and ignition systems. Most modern cars use four stroke cycle engines, which are widely adopted due to their high efficiency and reliability. The number of cylinders in an engine can range from single cylinder to sixteen cylinder, with common configurations being four cylinder, six cylinder, and eight cylinder. There are also various cylinder arrangements, including inline, V-shaped, and opposed, each with its own advantages and disadvantages, suitable for different types of vehicle needs.

Detailed explanation of four stroke cycle

The working cycle of a four stroke engine includes four stages: intake, compression, power generation, and exhaust. In each stage, the piston completes an up and down motion in the cylinder, which is called a "stroke".

Intake stroke: The intake valve opens and the exhaust valve closes. As the piston moves downwards from top dead center, negative pressure is generated inside the cylinder, and a mixture of air and fuel is drawn into the cylinder. In modern electronic fuel injection engines, fuel is directly injected into the intake manifold or cylinder through fuel injectors, rather than being pre mixed with air.

Compression stroke: Both the intake and exhaust valves are closed, and the piston moves upward from bottom dead center to compress the mixed gas inside the cylinder. Compression ratio is an important parameter of an engine, indicating the degree to which the mixture is compressed. A higher compression ratio can improve engine efficiency, but it also increases the risk of detonation, thus requiring fuels with higher octane ratings.

Power stroke (also known as power stroke): When the piston approaches top dead center, the spark plug generates an electric spark to ignite the compressed mixture. The high-temperature and high-pressure gas generated by combustion rapidly expands, pushing the piston downward and converting linear motion into rotational motion of the crankshaft through the connecting rod. This is the key stage for the engine to generate power.

Exhaust stroke: The exhaust valve opens and the piston moves upward again, pushing the burned exhaust gas out of the cylinder and out through the exhaust system. Modern engines are typically equipped with turbochargers, which use the energy from the exhaust to compress the intake and increase the engine's power output.

Engine auxiliary system

The normal operation of the engine requires the collaborative work of multiple auxiliary systems:

Lubrication system: Ensure that all moving parts are adequately lubricated to reduce friction and wear. The oil pump delivers oil to various parts of the engine, and then flows back to the oil pan, forming a cycle.

Cooling system: prevents engine overheating. The coolant circulates between the engine waterway and radiator through a water pump, taking away excess heat. The thermostat regulates the coolant flow to maintain the engine at its optimal operating temperature.

Fuel system: Modern electronic fuel injection systems can precisely control fuel quantity, improve combustion efficiency, and reduce emissions. The system consists of a fuel pump, fuel injectors, fuel pressure regulator, and electronic control unit.

Ignition system: Generate high-voltage electric sparks at the appropriate time to ignite the mixture. Modern electronic ignition systems are more precise and reliable than traditional distributor systems.

Emission control system: including catalytic converters, exhaust gas recirculation (EGR) systems, and evaporative emission control systems, aimed at reducing harmful gas emissions and meeting environmental regulations.

Engine performance parameters

The performance of an engine is usually measured by the following key parameters:

Displacement: The total working volume of all cylinders, usually expressed in liters or cubic centimeters, directly affects the power and torque output of the engine.

Compression ratio: The ratio of the maximum volume to the minimum volume of a cylinder, which affects thermal efficiency and fuel adaptability.

Power: The rate at which an engine performs work, expressed in horsepower or kilowatts, determines the maximum speed of a vehicle.

Torque: The rotational force of the engine, expressed in Newton meters, which affects the acceleration and traction of the vehicle.

Thermal efficiency: The proportion of fuel chemical energy converted into mechanical energy, typically between 30-35% for modern gasoline engines.

Development of Modern Engine Technology

With increasingly strict environmental regulations and worsening energy crises, engine manufacturers are constantly developing new technologies to improve efficiency and reduce emissions

Direct injection technology in cylinder: Injecting fuel directly into the combustion chamber to achieve more precise fuel control and higher compression ratio.

Variable valve timing and lift system: optimizes valve opening and closing time and lift based on engine speed and load, improving efficiency across the entire speed range.

Turbocharging and small displacement: Replace large displacement naturally aspirated engines with small displacement turbocharged engines to reduce fuel consumption while maintaining sufficient power.

Hybrid technology: Combining internal combustion engine and electric motor to recover braking energy and optimize engine operating range.

Cylinder deactivation technology: Close some cylinders at low loads to reduce pumping and friction losses.

Lean combustion technology: using a mixture that is thinner than the theoretical air-fuel ratio to improve thermal efficiency.

conclusion

An automobile engine is a complex and sophisticated energy conversion device that drives a vehicle by converting the chemical energy of fuel into mechanical energy. Understanding its working principle not only helps us better use and maintain vehicles, but also allows us to appreciate the brilliant achievements of humanity in the field of mechanical engineering. With technological advancements, future engines will continue to develop towards higher efficiency and lower emissions, while facing challenges and opportunities in electrification. Anyway, the important position of internal combustion engines in the development history of the automotive industry will always be remembered.