The modern automobile is very easy to get into and drive off. But have you ever wondered how a car works? How is it that just by turning a key a car engine starts? Ever wondered how the engine drives the wheels of the car? Read on to find out.
Everyone knows that all cars powered by fuel have engines. There are many components inside an engine which allows the engine to generate power from fuel to send rotational energy to the wheels of a car to make it move.
Let’s get to know the different components of a petrol engine.
Spark Plug – Provides the spark necessary to ignite the fuel.
Cylinder – The power generator where fuel is ignited and power is generated.
Piston – A cylindrical block of metal which moves up and down the cylinder.
Valves – Control the intake and exhaust of air from the cylinders.
Camshaft – Controls the timings of opening and closing valves.
Piston Rings – Provide a sliding seal between the piston and the cylinder necessary for lubricating the cylinder with oil. Piston rings prevent fuel/air mixture from leaking out of the cylinder.
Connecting rod – It connects the piston to the crankshaft. The connecting rod rotates at both ends so that its angle can rotate the crankshaft as the piston moves up and down.
Crankshaft – It converts the piston’s up and down movement into circular motion to drive the wheels of a car.
Oil Sump – It is located below the crankshaft and collects and circulates oil which lubricates different components in the engine to reduce friction for smooth and efficient operation of the engine.
All engines in cars operate on a four stroke (stage) engine cycle also called the Otto cycle, named after the man who invented the cycle. It is called the four stroke engine.
The Four Strokes are called;
- Intake stroke: The piston is at the top of the cylinder, the intake valves open, the piston moves creating a suction force and sucking in air into the cylinder.
- Compression stroke: The piston moves up to compress the air within the cylinder.
- Combustion stroke: A tiny amount of fuel is injected into the cylinder and the spark plug emits a spark causing an explosion within the cylinder.
- Exhaust stroke: The explosion causes the piston to move down and send kinetic energy to the crankshaft. The exhaust valve opens in the cylinder and the piston moves back up to force the combusted air/fuel mixture out of the cylinder.
Turn the key in the ignition of a car and the starter motor spins the engine a few revolutions so that the combustion process can start. It takes a powerful motor to spin a cold engine. The ignition coil connected to the 12 volt battery in a car produces a high voltage electrical spark and sends it via ignition wires to the distributer. The distributer has one wire coming in from the ignition coil and has multiple wires (the same as the number of cylinders an engine has) flowing out of it to the spark plugs of each cylinder. The ignition wires flowing out of the spark plug carry the electrical charge to fire a spark plug. The distributer allows only one plug to be fired at a point of time. If all cylinders fire at the same time there will be too much unwanted energy which will cause the engine to cease.
So the spark is sent to the appropriate cylinder according to the firing order of an engine (which is different in different engines), the camshaft which is connected by a timing belt to match the motion of the crankshaft opens the intake valve/s on the cylinder. The piston moves down sucking air into the cylinder. The camshaft closes the intake valve/s. The piston moves up to compress the air, meanwhile the oil pump pumps fuel to the fuel injector which adds the right amount of fuel into the cylinder. The spark plug fires to create an explosion within the cylinder which causes the piston to move downward and rotate the connecting rod which rotates the crankshaft. The crankshaft then sends the circular energy to drive the wheels of the car.
This four stroke cycle repeats itself as long as the engine remains on.
The cooling system for the internal combustion engine consists of a radiator and pump. The coolant in a car is circulated by the pump through passages around the cylinders and absorbs heat from the cylinders. The coolant then moves along to the radiator which cools it with air as the car moves along. The pump keeps repeating the cycle as long as the engine is running. This helps maintain an ideal temperature to ensure smooth and efficient operation of the engine. The cooling system is the same for all internal combustion engines except for on smaller engines which can be found on motorcycles, those engines are cooled by air.
Diesel engines
A diesel engine uses a four stroke cycle just like a petrol engine. All the engine components are the same as a petrol engine, except that a diesel engine does not use spark plugs to ignite the air fuel mixture. Instead it uses the heat generated in the compression stage to ignite the air fuel mixture. Because diesel is denser and heavier than petrol mere heat combined with compressed air is enough to ignite the air/fuel mixture.
Diesel engines directly inject fuel into the cylinder. The injector has to be able to withstand the temperatures inside the cylinder and still be able to spray a fine mist of fuel within the cylinder. The fuel has to be sprayed evenly all over the cylinder, before the compression stage is completed in the cylinder when combustion takes place. Before direct injection was invented in diesel engines a glow plug or heat plug (an electrically heated wire wrapped around the outside of the cylinder) was used to heat the combustion chamber from the outside to increase the air temperature within the cylinder so that the fuel/air mixture could ignite.
Today Common Rail Direct Injection is used in diesel engines to reduce emissions and ensure smoother operation of the engine. Common Rail means same fuel line for all cylinders. It ensures that there is virtually no loss of pressure in the fuel line when fuel is injected a particular cylinder. This in turn means that there is always adequate pressure available for fuel injection. Common rail technology makes use of 2 pumps in order to bring the fuel up to high pressures.
The first pump, an electronic pump draws the required amount of fuel. The speed of drawing fuel by the pump is determined by driver inputs and other information obtained from sensors. The second pump, which is a mechanical pump is coupled with the crankshaft and geared in order that it may rotate at half engine speed. The fuel goes to an accumulating duct (rail), where these pressures are maintained. This tank allows for the maintaining of this constant pressure even during the injection.
The whole system is monitored by the Electronic Combustion Unit (ECU).
Each fuel injector is mounted directly above the piston within the cylinder head and is connected to the fuel rail by rigid steel lines that can withstand the high pressure. This high pressure allows for a very fine spread of fuel by the injector. Like the fuel pump, the injectors are also controlled by the engine computer and can be fired in rapid succession several times during the injection cycle. With this precise control over injector firings, smaller, staggered quantities of fuel delivery can be timed over the course of the power stroke to promote complete and accurate combustion.
The development of the modern common rail direct injection diesel engine has made diesel engines quieter, more fuel efficient, cleaner, and more powerful than the indirect mechanical injection units they have replaced.
Rotary Engines
Also called the Wankel Rotary Engine, named after the inventor Dr. Felix Wankel works on the basic principles of a normal engine and even has the same four stroke cycle but everything else just blows your mind. Even the name of the shape of the engine spins your head. It is called epitrochoid which in short is oval like.
The different components of a rotary engine are;
- Rotor: The rotor has three convex faces which has grooves on them (deeper the groves more the displacement of the engine) which act like a piston.
- Housing: The oval shape of the combustion chamber is designed so that the three tips of the rotor are always in touch with the walls of the housing forming three sealed volumes of gas. Each part of the housing is dedicated to one of the four cycles of a four stroke engine cycle. There are no valves in the intake and exhaust located in the housing. \
- Output shaft: The output shaft is located band in the middle of the engine and is connected to the centre of the piston. It spins due to the rotational energy from the rotor/piston which creates torque.
Even though a rotary engine uses the same four stroke cycle as a regular internal combustion engine the cycle is very different and amusing. Here is how it functions.
At the heart of the engine is a rotor (roughly equivalent to a piston in a piston engine). The rotor is mounted on a large circular lobe connected to the output shaft. As the rotor orbits inside the housing, it pushes the lobe around in tight circles, turning three times for every one revolution of the rotor. As the rotor moves its edges sweep along the walls of the housing and because of the shape of the rotor and the housing the size of each chamber changes as the rotor performs revolutions.
Combustion Process
The intake process starts as one of the tips of the rotor passes the intake port drawing air into it. The size of the chamber reduces as the rotor passes the intake chamber and compresses the air in it.
Most rotary engines have two spark plugs because the combustion chamber is longitudinal. One spark plug may fail to spread the flame evenly throughout the chamber. When the spark plugs ignite the fuel/air mixture in the combustion chamber the explosion causes the rotor to move in the direction which will make the chamber grow in volume. As the gases continue to expand it causes the rotor to move towards the exhaust port. As the tip of the rotor passes the exhaust port the gases flow out of it due to the movement of the rotor which contracts the size of the chamber and forces the remaining gases to flow out of the chamber.
The rotor then moves along and passes the intake port and the whole process starts again.
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