Driving is considered by many to be a great source of pleasure. Many vehicles can be driven, including cars, buses and even trains. These forms of transport have revolutionised our modes of travelling over the last hundred years.
It was in the year 1885, in the last few years before the turn of the 20th century, that Carl Benz developed and made the first automobile, with a two stroke engine. Little did he know that these contraptions would soon rule the roadways. Thanks to him, many of us can travel in style, nowadays. But do you know how an engine works ? Read on to find out …
Since we are talking about Automobiles, we shall talk about only Internal Combustion Engines exclusively. Used widely, the Otto Engine / 4 Stroke Engine comprises of a cylinder in which a piston moves up and down.
A Four - Stroke Engine.
The bottom of the piston is connected to a crankshaft, which is connected to the gearbox, which in turn spins and moves the wheels of the vehicle. The gearbox, which moves the wheels, also has an outer rim, which is connected to a belt. This is connected to two crankshafts installed on top, that control the intake and axle valves. The ratio of upper crankshaft rotation to lower crankshaft rotation is 2 : 1, which means that for every two turns of the smaller crankshafts, the larger one will turn only once. This helps in moderating the frequency at which the axle and intake valves will open.
So, how is the engine powered ? Well, the intake valve allows a mixture of air and petrol to enter the cylinder, during the first stroke of the piston. During the first stroke, the Oxygen and petrol mixture reaches its highest volume, before the piston reaches the top dead centre. The second stroke is known as the compression stroke, as the mixture is compressed. The more the compression, the higher the mechanical energy that is pent up. The pressure and temperature causes the Oxygen and petrol mixture to ignite and combust. A spark plug may also be used to ignite the mixture. This produces power, hence the name of the third stroke - "the power stroke". This "powers" the piston down, creating the rotational movement on the crankshaft necessary to turn the gearbox, and thus the wheels. Finally, the fourth stroke of the piston clears away any left - over gas from the reaction, via the axle valve. Modern cars usually have more than one cylinder, in order to create more rotational movement and faster models. Different cylinder arrangements and 2 / 4 stroke piston cycles give rise to different engines. In 2 stroke piston systems, the piston only moves up and down once. It also uses a system of low pressure to suck Oxygen and petrol mixture into the ignition chamber. Below, you can view the 2 Stroke Engine.
A Two-Stroke Engine.
Diesel Engines work in a similar fashion, with both engines incorporating the intake, compression, power and exhaust stroke, in terms of piston movement. But there are some inherent differences. In a Petrol Engine, a spark plug is used to ignite the mixture, which is pre - mixed. Diesel Engines do not have a spark plug. Ignition takes place due to immense pressure and heat. Furthermore, in the Diesel Engine, the diesel and air only mix during combustion, via the fuel injector.
This leads to Diesel Engines being noisier, as in Petrol Engines the combustion reaction is smooth due to a pre - mixed mixture which propagates well. In the Diesel Engine, the combustion reaction can happen anywhere above the top dead centre, and so the reaction is irregular and uncontrolled. This means that the Diesel Engine must have a more rigid structure, in order to support these vibrations and pressures. Finally, the Diesel Engine has a higher compression ratio resulting in a better fuel economy. This is not possible for a Petrol Engine, as a higher compression ratio could lead to self - ignition and a detonation. The injector is depicted below.
A third type of Engine is the Wankel / Rotary Engine, as shown below. It also follows the basic principles of a piston engine, yet there are no pistons. Instead a single Metal Reuleaux Triangle, which moves a crankshaft, via cog teeth, provides the rotational movement, while all around it the four processes - detailed previously - take place.
A Wankel / Rotary Engine.
Do note that all the above Engines are Internal Combustion Engines. Examples of External Combustion Engines include coal fires to boil steam in power stations or on steam trains. As you can imagine, such engines cannot be used for cars or buses !
I hope this was an interesting read, providing insight on how the cars and buses we see all the time, work.