OPERATING PRINCIPLE OF 4-CYCLE DIESEL ENGINE

1. Intake Stroke
During the intake stroke the exhaust valve are closed and only the inlet valve is open. As the piston moves down from the top dead center (TDC), air sucked in from the inlet manifold through the inlet valve.

2. Compression Stroke
When the intake stroke ends, piston begins to move upward again from bottom dead center (BDC). The inlet valve closes and air flow stop. The air in the cylinder is compressed as the piston moves up. As the air is compressed, its temperature rises as well as its pressure. Since a diesel engine burns fuel using the compression heat of air, the air must be compressed until its temperature reaches at least the self ignition temperature of the fuel.
The ignition temperature of the fuel decreases the higher the air pressure becomes. Theoritically, the compression pressure is determined by the compression ratio, so it is not directly related to the rotational speed. in reality, the compression pressure depend depends on various condition, such as rotational speed and leakage from the clearence betwen the piston and the cylinder. The compression pressure is heavily dependent on rotational speed in the low speed range, but not in the high speed range.

3. Combustion Stroke
Near the end of the compression stroke, fuel is injected from a nozzle in the form of high pressure mist. The compression heat of the air makes the fuel self ignite and burn. As a result, the pressure in the cylinder rises suddenly and the piston is pushed down. This force becomes the power that generates a turning force (torque) on the crankshaft.

4. Exhaust Stroke
When combustion ends and piston approaches bottom dead center, the exhaust valve opens. The combustion gas, which added work to the piston during the combustion stroke, is discharged into the atmosphere from the exhaust valve by the ascent of the piston. When the piston reaches top dead center, the intake stroke begins again and the same cycle is repeated.
An engine with a cycle consisting o these 4 strokes is called a 4- cycle engine

OUTLINE OF DIESEL ENGINE II

(5) Classification by Cooling Method
1) Water Cooled type
This cooling method is used for ordinary automobile
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 cylinder. This design is not used for high speed diesel engines.
2) Overhead valve type (OHV type)
The valve are located on the top of the cyliner, that is, on the cylinder head. This design is used or high-speed diesel engines.
3) Overhead camshaft (OHC type)
Both the valve and the camshaft are located on the cylinder head.

(7) Classification by Number and Arrangement of Cylinders
Engines are classified both by number of cylinders and by the arrangement of cylinders :
1) In- Line (Straight) type
2) Horizontal type
3) Horizontal opposed type
4) V type
As the number of cylinders increases, the rotational force (torque) of the engines becomes more balanced, and the high and low limit on the speed of the engine are extended. As a result the range of the enginen speed can be enlarged. It is widely known that a multi engine cylinder generates less vibration than a single cylinder engine.

1) In-Line type
The cylinders are arranged in a straight line. This type of engine encounters dimensional limits when attempting to produce a large output by increasing the number of cylinders. However, these engines are easy to maintain and their production cost is relatively low.

2) Horizontal type
The cylinders are arranged horizontally in this kind of engine. The engine height can be decreased using this design. For example, the engine may be mounted under the floor of a bus to increase the passenger room area.

3) Horizontal opposed area

The cylinders are arranged so that they are opposed in the horizontal direction. This type o engine has a larger capacity and produces a higher output than the horizontal type. In Japan, these have been used as underfloor engines in high-speed buses. However, the engines is rarely manufactured now because of its high manufacturing cost and large weight. This type is superior to then in-line type and the horizontal type from the viewpoint of engine balance.

4) V type
As the capacity of an in-line engine is increased, physical restrictions (length and weight) arise. This is why V-type engine are used for large capacity engines. The boundary betwen the in-line type and the V-type seems to be a displacement of about 13 - 14 l. Selection betwen the two types is made based on consideration of their relative advantages and disadvantages.
Basically, a V-type engine is structurally the same as in-line type engine. However, the cylinder block manufacturing cost tends to be height.
V6, V8, V10 and V12 types are used. The V8 type is used most widely.
The angle of V shape is generally 90 degree V, which is the best angle for obtaining equal interval ignition.

HISTORY OF DIESEL ENGINE

In 1892, Rudolf Diesel, a German engineer, announced a new type of engine which fuel is injected into compressed air and ignited. This engine came to be known as the diesel engine.
By 1897, diesel engine that used heavy oil as fuel had been developed for practical use in Germany. (Low speed diesel engine)
Betwen 1924 and 1926, the development of the injection pump by Robert Bosch (from Germany) led to the development of high-speed diesel engines.
In Japan, research and development into diesel engines started around in 1930. By 1936, 6-cylinder air-cooled diesel engine with a total displacement of 8l had been developed and put to use.
In 1939, 5.1l-6-cylinder water-cooled automotive diesel engine began to be utilized, and diesel engine research and improvements have been continually pursued since then.



The history of diesel engines was briefly explained above. Research and development on diesel engines has been promoted in two separate areas; low-speed diesel engines for boats using heavy oil as fuel and high-speed diesel engine for automobiles such us Truck using light oil as fuel. In Japan research and develpoment on low-speed diesel engine has a longer history than hig-speed diesel engines. Low speed diesel engines have been used for boats and agricultural machinery and as power sources in industry.