DIESEL ENGINES
Introduction
The internal combustion (IC) engine has been used for many decades in developing countries
playing a very important role in providing power for rural communities. Many stand-alone units
are used for milling, small-scale electricity production, water pumping, etc. They are readily
available, off-the-shelf in most major towns and cities in a range of sizes to suit various
applications. There is usually a well-established spare parts and maintenance network, both at
urban and rural centres.
There are two main types of IC engine
defined by the type of fuel used; petrol
(gasoline) or diesel. The petrol engine is
widely used for small vehicles and light
applications whereas diesel engines are
more suited to continuous running for
lengthy periods at higher load ratings and
are therefore used more widely for
stationary applications and commercial
vehicles.
Principles of operation
The combustion process in the petrol
engine and the diesel engine differ in the
following ways.
In the petrol engine the petrol and air
mixture is drawn into the cylinder,
compressed (compression ratio ranging
from 4:1 to 10:1), and ignited by a spark
introduced by an electrical system.
In the diesel engine, air alone is drawn
into the cylinder and is compressed to a
Figure 1: One of the owner’s family with a diesel
much higher ratio (14:1 to 25:1) than in
electricity generator in Wau Nur, Kassala. Kenya.
the petrol engine. As a result of this
Photo: Practical Action / Lucy Stevens.
compression the air is heated to a
temperature of 700 – 900 oC. Only then
is a certain quantity of diesel fuel
injected in to the cylinder and the fuel ignites because of the high temperature. Hence the petrol
engine is often referred to as the spark ignition (SI) engine and the diesel as the compression
ignition (CI) engine.
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