posted 02 Jun 2012, 06:46
What is an Engine? We all drive cars and motorbikes. So, we should know what an engine is, right? Okay for those of you who don’t know. An engine is a device which converts one form of energy to another. I will not be going into the details as they may seem very complex, and trust me it is complex stuff; just basic classifications and nomenclature.
A heat engine is a device which converts the chemical energy of a fuel into thermal energy; this thermal energy gets converted to mechanical energy for the purpose of doing work.
Heat engines are classified into two categories:-
1. Internal Combustion Engines (IC Engines)
2. External Combustion Engines (EC Engines)
These two types of engines are the most general categorization of heat engines according to where the combustion takes place: Outside or Inside the engine.
External Combustion engines are rarely used in modern times, what we see inside of automobiles are Internal Combustion Engines.
Internal Combustion Engines (IC Engines) are of two types, if we classify them according to their cycle of operation:-
1. Otto Cycle engine called a Spark Ignition Engine(SI Engine) which runs on Gasoline
2. Diesel Cycle engine called a Compression Ignition Engine(CI Engine) which runs on Diesel
Spark ignition means that the combustion process inside the cylinder (combustion chamber) is initiated by means of a spark plug. A Spark plug has electrodes which generate a spark at timed intervals. These are your basic engines which run on petrol.
Compression Ignition means that the combustion process inside the cylinder (combustion chamber) takes place due to the compression action of the piston and the increase in temperature and pressure inside the cylinder. These are the ones which run on diesel.
Here is a picture of a Spark Ignition Internal Combustion Engine—
img class="lazyjs" src="//kastatic.com/images/blank.gif" data-original="https://kastatic.com/i2/u/1662016/gyANWowv1E.png " />
We see in this figure that it has four cylinders, higher the number of cylinders means the smoother the engine will run. The output of an engine depends on many factors which we will avoid discussing as they may confuse you at the moment.
Here is a working of a Four Stroke Spark Ignition Internal Combustion Engine-
img class="lazyjs" src="//kastatic.com/images/blank.gif" data-original="">https://kastatic.com/i2/u/1662016/UrobBtOQgL.gif" />
The classification of engines according to the number of strokes it takes for them to complete one working cycle will be discussed later. As for now, have fun with the extra knowledge.