Outline of Diesel Engine

[1] Engine Classifications

A diesel engine is a type of internal combustion engine, which is in turn a type of combustion engine. A combustion engine changes thermal energy generated by fuel combustion into mechanical work. Combustion engines can be classified into internal combustion engines and external combustion engines.
An internal combustion engine burns fuel within the engine and changes this energy directly into mechanical work. An external combustion engine gives externally generated thermal energy by heat transfer to water, a working fluid (see note), changing the water into steam which it then uses to turn the thermal energy into mechanical work. A steam locomotive is an example of an external combustion engine.Combustion engines can be classified as follows.

Note: A working fluid means a fluid that functions as a medium to change heat into work in a combustion engine.

[2] Classification of Reciprocating Internal Combustion Engines

Internal combustion engines can be classified by ignition method, combustion cycle, fuel type, fuel feed method, operation cycle, cooling method, valve type, and number and arrangement of cylinders.

(1) Classification by Ignition Method : 1) Spark ignition engine
A gas mixture consisting of compressed fuel and air is ignited and burnt by electrical sparks. Gasoline engines belong to this group. 2) Compression ignition engine
Air is heated (450 – 550 OC) by compression and fuel is injected into the compressed air in the form of high pressure atomized fuel. The atomized fuel is ignited and burnt by the compression heat of the air. Diesel engines belong to this group.

(2) Classification by Combustion Method (Thermodynamic Classification) : Internal combustion engines can be classified into three types by fuel combustion process.
1) Otto cycle (Constant volume cycle)
Combustion takes place under a constant volume. Gasoline engines belong to this group.
2) Diesel cycle (Constant pressure cycle)
Combustion takes place under a constant pressure. This combustion method is called the diesel cycle because the first engine built by Rudolf Diesel, however, current-day high-speed diesel engines (for automobiles) do not belong to this category.
3) Sabathe cycle (Mixed cycle)
In the Sabathe cycle, the above two cycles are combined. Current high-speed diesel engines (for automobiles, general power units and small boats) belong to this category.

(3) Classification by Fuel Type and Fuel Feed Method
Fuels used for internal combustion engines can be broadly classified into the following types:
1) Gasoline, 2) Kerosene, 3) Light oil, 4) Heavy oil, 5) Liquefied-petroleum gas (LPG). 6) Compressed Natural Gas

Fuel feed methods can be classified as follows:
1) Fuel is charged into the engine together with air, using a carburetor.
2) Fuel is injected into the cylinder using an injection pump.

(4) Classification by Operation Technique
1) 4-cycle engine
One cycle (suction, compression, combustion and exhaust) of the engine requires two rotations of the crankshaft, that is, four strokes.
2) 2-cycle engine
One cycle of the engine requires one rotation of the crankshaft, that is, two strokes.

(5) Classification by Cooling Method
Engines can be classified into water-cooled engines and air-cooled engines according to the cooling method.
1) Water-cooled type
This cooling method is used for ordinary automobiles.
2) Air-cooled type
This cooling method is used for motor bicycles and some small cars.

(6) Classification by Valve Type
1) Side valve type (SV type)
The valves are located on the side of the cylinder. This design is not used for high-speed diesel engines.
2) Overhead valve type (OHV type)
This design is used for R series, P series and FE series Engines.
3) Overhead camshaft type (OHC type)
This design is used for GE13 Engines.
4) Double overhead camshaft type (DOHC type)

* Source : Nissan Text Book ( Automotive Engineering )