Types of Diesel engine

Two types of diesel engines are available

1. Two stroke/Two stroke cycle engine
2. Four stroke/Four stroke cycle engine

Two stroke engine is, one working stroke occurs in (in each cylinder) for every revolution of the engine crankshaft. That is every alternate stroke is a firing stroke.


Four stroke engine is, one working stroke offers(in each cylinder) for every two revolutions of the engine crankshaft, that is one firing or working stroke and three idling strokes for every two revolutions of the crankshaft.


Fundamental Difference between Two stroke and Four stroke
In the two stroke engine, a separate pump or blower is required to recharge the cylinder with air, whilst in the four stroke engine the working cylinder itself performs that duty.

What are the Compression Ratios for Diesel Engine?

Compression ratios for diesel engines vary between 12.5:1 to 19:1. Generally speaking,compression ratios are high in smaller high speed diesel engines than in large low speed diesel engines. This is chiefly due to the far greater rate of heat loss in the smaller cylinders,necessitating the use of a higher ratio in order to achieve the necessary temperatures for ignition purposes.

Compression ratio of an Engine

The compression ratio of an engine is the ratio of the sum of the swept and clearance volumes in each cylinder to the clearance volume.
if,For example, the cylinder holds 64cm3 of air when the piston is at the bottom of its stroke,and there is only a 4 cm3 space left when the piston is at the top of its stroke,the engine has a compression ratio of 16:1

Usual Compression ratios for petrol engine

Between 7:1 and 10:1

Clearence Volume Definition

This is the space or Volume remaining in the cylinder and or cylinder head where the air charge is compressed by the piston.

Swept Volume or Capacity of a Cylinder

This is the space or volume swept out in the cylinder by the piston,and is equal to the product of the piston stroke and its cross-sectional area.

Difference between Diesel and Petrol Engines

In the petrol engine,mixture of air and petrol vapour is drawn into the cylinder during the suction(Induction) stroke of the piston and is ignited towards the end of the compression stroke by means of a sparking plug.
In the diesel engines,only air enters the cylinder during the suction stroke.It may enter by suction or by blowing in under pressure. The fuel oil,in the form of a fine spray or mist,is injected into the cylinder towards the end of the compression stroke and is spontaneously ignited by the tempreture of the highly compressed air.

Diesel engines classed as an internal-combustion engine.Why?

The diesel engine,like the petrol engine,converts the latent heat energy of the fuel into mechanical work. The heat in the fuel is released by combustion, and is transferred to a working substance. The diesel engine is classified as an internel combustion engine because this working substance actually takes part in the process of combustion ; it is,in fact,air.

In the steam engine,the working fluid does not take part in the combustion of the fuel,and it cannot therefore be classed as "Internal combustion"

Types of Fuel oil used in Diesel Engines

The choice of the fuel oil is mainly governed by the design and speed of the engine.
In high speed engines, the most important fuel is gas oil.shale oils are also used as they very much akin to gas oils.
Medium sized engines,especially in the larger sizes,run satisfactorily on diesel oil. This may be a heavier distillate than gas oils,or may be a blend of gas oil and selected residual fuel.
For marine engines,Heavily distillate or selected furnace oil may be used.

First Diesel Engine

Diesel engine was invented by Dr.R.Diesel in year 1893. The heavy oil fuel was injected into the engine cylinder mixed with a jet of compressed air. This air-blast injection priciple id now seldom used today.
In the engine invented by Ackroyd Stuart,two years earlier than Dr.Diesel filed his first patent, the oil was injected into the cylinder without and compressed air, that is as a spray or mist of oil particles. A hot bulb or other external source of heat was used for ignition. This airless or solid injection priciple is now used on the majority of modern diesel engines.

What is Meant By the Term Diesel or Oil Engine?

An internal combustion engine which uses a heavy or gas-oil distillate as fuel, the fuel being fired in the cylinder by heat of compression.It is,therefore , also known as a compression ignition engine.