Internal Combustion Engines (ICE)

Internal Combustion Engines (ICE) – Definition and Classification

Internal Combustion Engines (ICE) are the mechanisms that transform chemical energy obtained from the fuel into mechanical energy by means of burning. The process of combustion is going on in the engine and it is the power to bring the pistons and other mechanical parts which later produce the power needed to propel a vehicle or do other works by the combustion of the process.

Classification of Internal Combustion Engines:

IC engines may be grouped into the following types, depending on the grounds:

1. Based on the Number of Strokes:
   • Two-Stroke Engine
   • Four-Stroke Engine
2. Based on the Type of Ignition:
   • Spark Ignition (SI) Engines
   • Compression Ignition (CI) Engines
3. Based on the Fuel Used:
   • Gasoline Engine
   • Diesel Engine
   • LPG, CNG, or Other Fuels

Two-Stroke Engine

Definition:

A two-stroke engine is an internal combustion engine, which is characterized by four stages: intake, compression, propelling, and exhaust. These stages are completed in two piston strokes, which are equal to one crankshaft revolution.

Working Principle:

In the two-stroke engine, the piston makes only two movements to complete the cycle of increasingly smaller volumes (intake, compression, power, and exhaust) versus four in the four-strokes one. This is a simple version of how it works.

1. First Stroke (Compression and Intake):
   • The fuel-air mixture in the combustion chamber is compressed by the piston, moving up.
   • Concurrently, the exhaust valve is open for gases from the previous cycle to be removed.
   • Fresh fuel-air mixture rushes into the crankcase through the open intake port, and it gets ready for the next cycle.
2. Second Stroke (Power and Exhaust):
   • The spark plug fires compressed fuel-air mixture when the piston is at the top of its stroke creating an explosion which in turn suddenly forces down the piston.
   • When the piston descends, the exhaust port is exposed, through which the exhaust gases are removed.
   • Simultaneously, the intake port is opened, which allows the cranked powdery fuel-air mixture to broker with the intake of the cylinder.

There are no separate intake and exhaust valves in a two-stroke engine. Two piston strokes, which implies one crankshaft revolution, are enough to complete the operation.

Example:

• Motorcycles (especially older models)
• Lawnmowers
• Chainsaws

Four-Stroke Engine

Definition:

A four-stroke engine is an internal combustion engine that goes through a four-stroke cycle accomplished in two crankshaft rotations (piston two times). This type of engine is being used in most of the cars, motorcycles and other machinery.

Working Principle:

Each piston stroke in a four-stroke engine involves the intake, compression, power, and exhaust sequences, completing four different strokes.

1. First Stroke (Intake Stroke):
   • The intake valve opens, and the piston moves down the cylinder, drawing in a fuel-air mixture.
2. Second Stroke (Compression Stroke):
   • The intake valve closes, and the piston moves up, compressing the fuel-air mixture inside the combustion chamber.
3. Third Stroke (Power Stroke):
   • At the top of the stroke, the spark plug ignites the compressed fuel-air mixture, causing an explosion.
   • The force from the explosion pushes the piston downward, generating power.
4. Fourth Stroke (Exhaust Stroke):
   • When the piston moves up once again, the exhaust valve opens with the result that burnt gases will be pushed off the combustion chamber.

Intake, compression, power and exhaust- these are the four-stroke cycle that takes place in the four-stroke engine. Meanwhile, the piston moves twice up and down for each crankshaft revolution.

Example:

• Cars and Trucks
• Motorcycles
• Lawn Tractors

Comparison Between Two-Stroke and Four-Stroke Engines

SI and CI Engines

SI (Spark Ignition) Engines and CI (Compression Ignition) Engines differ mainly in how they ignite the fuel-air mixture in the combustion chamber.

Spark Ignition (SI) Engines

• Definition: In Spark Ignition (SI) engines, the fuel-air mixture is ignited by a spark from a spark plug.
• Working Principle: The fuel-air mixture is compressed in the cylinder, and when the piston reaches the top of its stroke, the spark plug creates a spark, igniting the mixture.
• Fuel Type: SI engines usually run on gasoline or alcohol-based fuels.
• Examples: The majority of cars, motorcycles, and small engines are SI engines.
• Advantages:
  • Quieter and more stable operation.
  • Most often, lower emissions than CI engines.
• Disadvantages:
  • Lower thermal efficiency as compared to CI engines.
  • The engine has limited output relative to its size.

Compression Ignition (CI) Engines

• Definition: In Compression Ignition (CI) engines, the fuel is ignited by the heat generated from compressing the air inside the cylinder. No spark plug is used.
• Working Principle: The air is so compressed that its temperature gets higher. As the fuel is sprayed into the hot, compressed air, the fuel spontaneously starts to burn.
• Fuel Type: CI engines usually have diesel fuel which has a higher energy density than gasoline.
• Examples: Diesel engines in trucks, buses, large machinery, and certain cars are among the most well-known users.
• Advantages:
  • Higher thermal efficiency and fuel economy.
  • Thus, the engine can generate more energy with the same power.
• Disadvantages:
  • Diesel engines are more prone to NOx particles and particulate emissions.
  • They are normally louder and more shakable than the SI engines are.

Key Differences Between SI and CI Engines:

Example for SI and CI Engines:

• SI Engine Example: A Honda Civic car operates on a spark ignition engine. It requires gasoline, and the air-fuel mixture is sparked by a spark plug.
• CI Engine Example: A Ford Super Duty Diesel truck relies on a compression ignition engine. It is fed with diesel, and the fuel is injected into super load, very hot, and compressed air, which leads to it catching on fire.

Indeed, the two engine types mentioned are the most commonly used ones in today’s ground transportation, but they are selected in a way whether their fuel efficiency, fuel economy, and peculiar application conditions are satisfied or not.