Internal Combustion Engine

An Internal Combustion Engine (ICE) is a power unit that mixes liquid or gaseous fuel with air, burns it directly within the engine chambers, and converts the thermal energy generated by combustion into mechanical energy. It serves as the primary powertrain for modern motor vehicles, where the term "car engine" typically refers to a reciprocating piston ICE.

⚙️ Working Principle

The vast majority of automotive internal combustion engines operate on a four-stroke cycle, where the piston completes four distinct strokes to execute one full energy conversion cycle:

Intake Stroke: The piston moves downwards, the intake valve opens, and the air-fuel mixture (petrol engines) or fresh air (diesel engines) is drawn into the cylinder.
Compression Stroke: The piston travels upwards with the valves closed, compressing the charge and causing both temperature and pressure to rise rapidly.
Power Stroke: The spark plug ignites the compressed air-fuel mixture in a petrol engine (spark ignition), or injected fuel auto-ignites in high-temperature compressed air in a diesel engine (compression ignition); the resulting high-pressure combustion gases force the piston downwards to deliver mechanical power.
Exhaust Stroke: The exhaust valve opens as the piston moves upwards, expelling the spent combustion gases out of the cylinder.

🏗️ Main Classifications

Internal combustion engines can be categorised based on several key characteristics:

Classification	Common Types	Overview
Fuel Type	Petrol, diesel, compressed natural gas (CNG), ethanol, etc.	The fuel type determines the ignition method, combustion characteristics, and thermal efficiency.
Ignition Method	Spark Ignition (SI) (typical in petrol engines, ignited via spark plugs) Compression Ignition (CI) (typical in diesel engines, ignited via high compression heat)	This is one of the fundamental engineering differences between petrol and diesel powerplants.
Stroke Count	Four-stroke (industry mainstream) Two-stroke (completes a power cycle in every crankshaft revolution)	The vast majority of passenger and commercial vehicles utilise four-stroke engines.
Cylinder Layout	Inline (Straight), V-engine, Horizontally Opposed (Boxer), W-engine, etc.	Dictates overall engine dimensions, vehicle centre of gravity, and packaging layout.
Cooling Method	Water-cooled (relies on coolant circulation) Air-cooled (relies on airflow and cooling fins)	Modern production cars almost exclusively employ higher-efficiency liquid cooling systems.
Induction Method	Naturally Aspirated (NA) Forced Induction (turbocharged or supercharged)	Forced induction significantly enhances power output and volumetric efficiency from smaller displacements.

🔥 Latest Developments

Amid the accelerating shift towards electrification, the internal combustion engine is far from obsolete, currently undergoing a major technological transformation.

Continuous Efficiency Breakthroughs: The thermal efficiency of mass-produced petrol engines in China has now surpassed 43%, with dedicated hybrid engines exceeding 45%, and future petrol units projected to breach the 50% brake thermal efficiency milestone.
Hybridisation as the Primary Trend: According to the "Technology Roadmap for Energy Saving and New Energy Vehicles 3.0", ICEs will remain an essential automotive powertrain over the next 5 to 15 years, with conventional internal combustion passenger cars moving towards comprehensive hybridisation. Hybrid technology has become the vital catalyst for ICE advancement and lower emissions.
Exploration of Zero-Carbon Fuels: The integration of low-carbon and zero-carbon fuels such as hydrogen, methanol, and ammonia into combustion engines has emerged as a crucial development path, granting the ICE a sustainable new lease of life. Automakers such as Geely have already achieved industry-leading thermal efficiency benchmarks with their methanol-hydrogen powertrains.