What is a Compression Ignition Engine?

The compression ignition engine is an internal combustion engine in which the fuel is ignited with the help of hot compressed air. When air is compressed, it heats up and uses its heat to ignite and burn fuel. In this device, the air is drawn in during the suction stroke and then compressed during the compression stroke. At the end of the compression path, fuel is injected into the cylinder, which ignites with the heat of the compressed air and begins the combustion process. Diesel is used as a fuel for engine operation. The principle of operation is the diesel cycle. Used for heavy vehicles such as buses, trucks, boats, etc.


Construction of Compression Ignition Engine

Combustion ignition engine is used in a variety of commercial and consumer applications around the world to power large ships, locomotives, commercial trucks, construction and agricultural equipment, generators, and even vehicles. Almost exclusively, these applications use diesel fuel for combustion.

Diesel engines depend on the degree of spontaneous combustion of the fuel. Chemical engineers call this characteristic cetane number/index, an index derived from the experience that describes the degree of difficulty of spontaneous combustion of a fuel. Biodiesel is also used in many applications, especially in rural areas and developing countries. Biodiesel is usually made from vegetable oil and is chemically treated to remove glycerin products, leaving esters of methyl (or ethyl) fatty acids (FAME). Biodiesel attempts to mimic the properties of diesel fuel, and although it can be used as an alternative to pure fuel, it is often used as a petroleum diesel blend.

There are two main methods for compression ignition engines:

  1. Two-stroke Engine
  2. Four-stroke Engine

Large IC engines (especially ships and locomotives) are generally two-stroke engines, mainly because the engine speed is limited at low revs. Two-stroke IC engines must have an external air supply, such as a turbocharger or supercharger (or a mixture of the two in some cases) because air enters the cylinder through the ports on the cylinder liner. Exhaust gases are discharged through a series of ports or through a piston valve in the cylinder head.

When the piston is lower than the inlet valve during an electric shock, the inlet valve opens on the cylinder liner and allows cold pressurized air to enter the cylinder. As the piston moves towards the BDC along the power path, the exhaust valve on the cylinder head begins to open and the hot exhaust gas begins to exit the cylinder through the exhaust valve installed at the top. As the piston continues to rise towards the BDC, the inlet valve on the cylinder liner opens to allow fresh air to enter the cylinder, forcing the last exhaust gas out through the top exhaust valve. This washing process continues until the drain valve closes (sometimes close to the BDC piston position). The inlet valve is still open, so fresh air from the blower enters the cylinder until the piston passes over the inlet valve to the cylinder liner, which traps the air in the cylinder. This air is then heated and pressurized to bring the piston closer to TDC. The fuel injector injects high pressure into the hot compressed air, causing combustion and automatic combustion. Then the cycle begins again.

On the other hand, the principle of operation of a four-stroke compression ignition engine is to draw air from the intake manifold from the top dead center to the bottom dead center during the intake path into the cylinder. The intake valve closes and then the piston moves. Return to the top dead center by pressing air at high temperature and pressure. The fuel injector injects fuel into the combustion chamber and combustion takes place. Due to the combustion in the so-called power stroke, the piston sinks under high pressure. Finally, the exhaust valve opens and the piston returns to top dead center, releasing the combustion products of the exhaust gases along the exhaust path. Then repeat the cycle from here.

Components of Compression Ignition Engine

The main components of compression ignition (CI) engine are:

1. Fuel Injector

It is used to inject fuel into the cylinder while compressing the air.

2. Inlet Valve

 Air from the cylinder is drawn in through the inlet valve along the inlet stroke.

3. Exhaust valve

All combustion or exhaust gases discharged from the cylinder are discharged through the exhaust valve.

4. Combustion chamber

This is the chamber in which the fuel burns.

5. Piston

This is the alternate part of the CI engine that travels with the cylinder. Its main task is to transmit the thrust created during the power path through the connecting rod to the crankshaft.

6. Connecting rod

It connects the piston to the crankshaft.

7. Crankshaft

 It uses to convert the reciprocating motion of the piston into rotary motion.


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