The car's engine is the brain and the muscles, the central component that transforms a simple gesture (turning the key or pressing a button) into the movement that drives you forward.
But have you ever wondered what exactly happens under the hood at that precise moment? From the moment you turn the ignition to when you feel the vibration of power beneath your feet, a complex sequence of events takes place with millimetric precision.
You'd better pay attention, because whether you need to check the car or are considering buying a second-hand engine, you need to fully understand the fascinating process that brings your car to life, from the first spark to the roar of the engine.
Why is it important for you to know how a car engine works?
Understanding how your car's engine works is important for several reasons, both safety-related and practical:
Maintenance and breakdowns
By understanding the basic principles, you'll be able to understand why certain maintenance tasks are carried out, gaining experience that will allow you to identify unusual noises or behaviours that could indicate an emerging problem, enabling you to act in time and avoid major breakdowns.
Save money
By understanding how it works, you'll be able to make more informed decisions about your vehicle's maintenance.
This way, you'll be able to tell whether the workshop is offering you the necessary repairs or is trying to get more money out of you, or understand why it is consuming more fuel than it should.
Driving safety
If you understand how power is transmitted, or how a failure can affect performance, you'll be better prepared to react to an unexpected situation on the road.
Making the right decision when buying
Whether you're buying a new car, replacing the entire engine, or just a single part, you'll understand how the whole process works so you can make the right decision at the time of purchase.
Self-confidence
You will no longer have to rely on what the workshop tells you; instead, you will have a sense of control and be able to make the right decision.
How does a car engine work? Here's the process!
Next, we are going to look, step by step, at the entire process from the moment you activate the circuit until the engine starts roaring and you can set off on your journey. Pay attention!
Activation of the Main Electrical Circuit
What is commonly known as "ignition" is activated when we insert and turn the key, or, in more modern models, when we press the start button without pressing the brake/clutch.
With this simple action, the car's main electrical circuit is closed, sending power from the battery to essential systems such as the dashboard, the fuel injection system….
Ignition
In the next step, the starting phase begins, also known as ignition. In this phase, the current from the battery is directed to a key component: the starter solenoid, which acts as a power switch.
Activation of the starter motor
Also known as the starter motor, once the solenoid receives the current, it carries out two actions:
- It moves a small gear, called a pinion, forward.
- Completes the high-current electrical connection from the battery directly to the starter motor.
Crankshaft movement
The crankshaft is the main shaft of the engine. Two phases take place at this stage:
- First, the starter motor's pinion gear meshes with the teeth of the main engine's flywheel ring gear, which is directly connected to the crankshaft.
- When the starter motor turns, it rotates the flywheel and, consequently, the main engine's crankshaft, which makes the engine's first mechanical movement.
Intake and compression cycle
As the crankshaft rotates, the engine's pistons begin to move up and down inside their cylinders. You've probably seen this process in many animations.
The intake stroke then takes place, in which the intake valve of one of the cylinders opens and the piston descends, creating a vacuum that draws a mixture of air and fuel into the cylinder.
Within milliseconds the intake valve closes and the piston rises, compressing this mixture of air and fuel into a very small space at the top of the cylinder.
Combustion
In this phase, a process occurs in which the cylinder's spark plug generates a high-intensity electrical spark, which ignites the compressed air-fuel mixture. It is a rapid and controlled explosion.
Power stroke
This stage, also known as the power stroke, is the phase in which the combustion generates an enormous amount of high-pressure gases that violently push the piston downward.
With this movement, the piston descends, generating the engine's force and energy, transmitting it to the crankshaft.
Exhaust cycle and continuity
We have reached the final phase of the entire process. When the piston has descended due to the combustion, an exhaust valve opens, allowing the piston to rise again. This pushes the exhaust gases out of the cylinder, directing them to the vehicle's exhaust system.
This entire process is known as the four-stroke cycle, although there are engines that do it in two strokes. It repeats continuously in each cylinder of the engine in a sequential manner. When one or two cylinders have completed their cycle and have generated enough energy for the engine to continue turning on its own, the starter motor disengages and the main engine begins to operate autonomously.
How long does the whole process take?
It is a process that takes place in a matter of seconds, so it sometimes feels almost imperceptible to us. Of course, that is always under normal conditions.
As a general rule, it usually takes between 1–4 seconds, but sometimes it can take a little longer, for example:
- The battery not having much energy or being weak, which will prolong the process.
- Outside temperature also affects a car's ignition, as in cold climates the engine oil is denser and the battery performs less efficiently.
- The condition of the engine also matters, because if it has not been properly cared for and you haven't carried out the appropriate maintenance, it may take longer to start.
- Does the type of engine matter? Yes, in fact diesel engines usually take a few more seconds to start than petrol engines, which start almost instantly.
As a small tip, once the engine has started it is advisable to wait 30–60 seconds at idle, especially in winter, before starting to drive. This allows the oil to distribute properly through all the internal parts, and the engine reaches its optimal operating temperature.
And how does an electric motor work? Is it really that different from a petrol one?
The truth is yes, as it has different components from a petrol or diesel one. Let's see what the process looks like:
System ignition
To start the car, an electronic key is used or the Power button is pressed, which activates the car's low-voltage systems, such as the lights, the screen, and the battery management system (BMS), which performs a quick check to ensure everything is in order.
If everything is OK, the vehicle enters a ready-to-drive state, indicated by a light on the dashboard or a soft sound. In other words, the engine does not need to start, as it is always ready.
Movement request
With the vehicle already activated, it is necessary to press the accelerator pedal, or power/demand pedal, to send a signal to the vehicle control unit (VCU), which acts as the central brain.
It interprets the intensity with which you press the pedal and determines how much power is needed.
Energy management by the inverter
The VCU sends a signal to the inverter, also known as a power converter, which transforms the high-voltage direct current stored in the battery into alternating current of variable voltage and controlled frequency.
Electric motor power supply
The alternating current generated by the inverter is sent to the electric traction motor.
Transmission of power to the wheels
When the electric motor receives the energy, it begins to rotate. Most models have a single-speed transmission, which directly transmits the motor's movement to the axles, and from there to the wheels.
Unlike a manual combustion vehicle, multiple gears are not needed for the car to start moving at its maximum torque.
Movement and regeneration
When the wheels receive the torque, the vehicle begins to move smoothly and silently.
When the driver releases the accelerator or applies the brake, the electric motor often acts as a generator, converting the kinetic energy of the car's movement into electricity that is fed back to recharge the battery.