The engine is one of the essential elements of an automobile. In fact, it’s probably the most important part of the whole car. And even though most car owners know what an engine looks like, rare are the ones who know how it works or the different components needed to make their vehicle move. Understanding how an engine works and the various processes needed to transform air and fuel into a moving force can help you to save money or at least prevent you from getting ripped off the next time you go to an auto repair shop.
We have created this article with this specific objective in mind. Read on to learn everything you need to know about how a car engine works and how it does its thing.
Table of Contents
- 1 What Is A Car Engine?
- 2 Main Components
- 3 Different Types Of Car Engines
- 4 Fundamental Working Principles
- 5 Different Internal System And Their Uses
- 6 To Wrap It All Up
What Is A Car Engine?
An engine is a mechanical element transforming energy created from the combustion of fuel into mechanical movement. The main types of engines that can be found on cars are called “internal combustion” or “explosion” engines. A typical internal combustion engine burns fuel creating an explosion in a closed space, creating pressure then used to make various components turn, ultimately making the wheels move.
A car engine is a complex machine composed of a multitude of elements, each having a different form and function. The main components of an automotive internal combustion engine are as follows:
- Valve springs
- Head gasket
- Connecting rods
- Spark plugs
- Thrust bearings
- Oil Pan
- Water pump
- Timing belt or chain
The components listed above are only the most important components because an engine also relies on a wide array of sensors and electrical motors to do its job properly. Newer engines are also filled with small electronic parts and control modules to ensure the engine is as fuel-efficient as possible but we’ll leave them aside for the time being. Let’s just concentrate on the main ones, for now, to make sure we correctly grasp the basics of how an engine works before going any further.
Different Types Of Car Engines
Car engines come in all shapes and forms. Each of them has its own advantages and inconveniences. Some are built for speed while others provide better fuel efficiency. Certain types are easier to maintain but less-reliable which is often why they are everywhere while others are a lot less frequently seen in mass-market vehicles. Car manufacturers tend to select a specific engine size and configuration based on the targeted customers, their needs and their budget. Let’s explore the different types of engines and what they are typically used for.
The easiest way to classify car engines is based on their total number of cylinders. The most common number of cylinders is 4 but 6 and 8-cylinder engines are frequently found on SUVs, sports cars and pickup trucks. Most small, entry-level cars are equipped with 4-cylinder engines because of the reduced manufacturing cost from the dealer’s point-of-view but also because 4 cylinders typically burn less fuel than 8. Faster cars and heavy-hauling trucks obviously burn more fuel than a small sedan.
Luxury cars sometimes feature 10, 12 and even 16 cylinders but these are a lot less frequent and also a lot more expensive to maintain. The higher the number of cylinders, the higher the number of moving parts needed to make it work. And moving parts eventually wear out and need service or replacement. Simple as that.
Engines with inline cylinders are the most common type of automotive engine. All the cylinders are configured in a single line and arranged on one side of the crankshaft.
This is, by far, the simplest engine set up which makes it quite inexpensive when compared to other engine configurations. Although it takes up little space in terms of width, this engine, however, requires a lot of space in length, especially in the case of inline 6s and 8s.
The main disadvantage of inline engines lies in the imbalance caused by the arrangement of the cylinders on a single line. Engine imbalance can lead to severe vibrations if not correctly controlled. To avoid this, car manufacturers often add a balancer shaft connected to the crankshaft working as a counterweight.
As their name implied V-shaped engines are, indeed, shaped like a V. The cylinders are arranged in two rows, all hooked to the same crankshaft and they are fired up alternatively. Such a configuration allows car manufacturers to use a shorter and lighter crankshaft typically creates more power while also reducing the vibrations. V-shaped engines usually offer significantly more torque at low rpm when compared to inline engines.
However, the V-shape also brings its limitations and result in a very complex engine often requiring more maintenance which, in turn, result in a higher operating and maintenance cost.
W-shaped engines are identical and work exactly like the “V” models, with the difference that they are doubled with the cylinders aligned in staggered rows.
Cylinders in a W configuration can be presented in two ways:
- Arranged in “joined” double V resulting in 3 rows of cylinders
- Disposed in “separate” double V resulting in 4 rows of cylinders
The main advantage of the W-shaped engines is that a large number of cylinders can be fitted within a minimum amount of space, allowing the use of an even shorter crankshaft than on a V engine. On the other hand, the engine ends up being a lot wider than usual.
This type of engine is much more complicated than inline and v-shaped engines, especially when looking at the engine head and the valvetrain. That’s probably one of the reasons why this type of engine is mainly used in aviation or high-end cars only.
Flat engine, also called Boxter engines, are completely flat: all the pistons are on one plane, usually horizontal. The cylinders are always even in number and are located on each side of the crankshaft.
This engine configuration is very practical since it takes up very little height. Flat engines can thus be positioned very low on the car’s chassis, inducing a very low center of gravity, which will greatly improve the handling of the vehicle.
Also, the fact that the pistons are opposed to each other on both sides of the crankshaft causes a better balance of the engine, which also results in fewer vibrations and a better overall balance of the vehicle on the road.
On the other hand, flat engines are often quite difficult to maintain. Typical maintenance jobs classified as “quick and easy” on other types of engine are frequently much more complicated to perform on a flat engine. Spark plugs replacement is a good example. What would take less than an hour to perform on any other inline 4 engine can easily take up to 4-5 hours on a Boxter engine?
Flat engines are frequently found in vehicles with a high maintenance cost reputation like Subarus, Porsches, and Westfalias, just to name a few.
Direct Injection Or Not
Direct injection is the most common fuel injection method used by car manufacturers today as it greatly increases a vehicle’s fuel efficiency to meet newer environmental standards. This system also limits pollutant emissions and increases torque at low rpm.
The principle of this system is relatively simple: the fuel is directly injected into the combustion chamber right before the spark. This type of injection helps to keep the intake and throttle body cleaner as there are no fuel deposits at all. The amount of fuel injected can be controlled by the PCM on a per cylinder basis instead of the same injections times for all cylinders.
With conventional fuel injection systems, on the other hand, the injectors are placed before the intake valve or incorporated into the intake manifold. Such a system allows the admission of the air/fuel mixture into the engine as the intake valve opens and can’t be controlled individually.
Diesel engines work similarly to gasoline engines, but the ignition system is much simpler. In a gasoline engine, the air/fuel mixture is usually compressed 10 times. In a diesel engine, however, it’s not rare that the air ends up being compressed as much as 25 times. When compressed to that extent, the air inside the combustion chambers can reach temperatures up to 500 ° C (1000 ° F) and sometimes more.
Once the air is compressed, diesel is sprayed into the cylinder. At this point, the temperature inside the combustion chambers is so high that the fuel ignites instantly without the need for a spark. The rest of the cycle is pretty similar to any other fuel-powered engine.
A rotary engine is an internal combustion engine rotating around a fixed crankshaft. This type of engine was very common at the beginning of aviation when the power-to-weight ratio was the main criterion for consumption and reliability.
Rotary engines don’t use the crankshaft-connecting rod system since the piston itself produces a rotary motion. The stroke cycle works pretty much like any other 4 stroke engine but the way the pistons work is totally different.
Sadly, even though rotary engine equipped vehicles like the legendary Mazda RX-7 were amazing to drive, car manufacturers never really got on board with it and those who did eventually abandoned it after a couple of tries, mainly because of the high maintenance costs and relative reliability.
Fundamental Working Principles
The general operating principle of a car engine is quite simple. The objective is to exploit the energy produced by the combustion of an oxidizer/fuel mixture in a closed chamber. When the air/fuel mixture burns, a significant expansion of the gases occur which is in turn used to make the pistons go up and down and make the crankshaft turn. Everything happens in a loop cycle and starts over and over.
Components Related To The Explosion Cycle
Car engines are what’s called “4-strokes” engines. To fully understand how each stroke works, here are some of the components directly related to the explosion happening inside the engine.
- The spark plugs – They’re the ones creating the spark, triggering the explosion inside the combustion chambers.
- The cylinders – As their name implies, these are cylinders containing the explosion and guiding the pistons in a vertical movement.
- The pistons – They have 2 roles; compressing the explosive mixture and transmitting the resulting energy to the connecting rods.
- The piston rings – These are seals placed around the pistons allowing them to compress the air contained in the cylinders as well as lubricating the cylinder walls as they go up and down.
- The connecting rods – They transmit the energy of the explosion from the pistons to the crankshaft and contribute to the transformation of the vertical motion into rotary motion.
- The crankshaft – This is the part supporting the connecting rods and transmitting the rotary motion to the flywheel.
- The valves – An engine has two different types of valves: intake valves and exhaust valves. Both work the same way but serve opposite purposes. They open under the work of the rockers following the movement of the camshaft and close automatically thanks to their dedicated valve springs. The intake valves allow the air/fuel mixture to enter the combustion chamber while the exhaust valves release the burnt gases.
- The camshaft – This is the component allowing the valves to open and close in sync with the position of the pistons.
The 4 Strokes And How They Work
The first stroke is the intake stroke. The piston is at top dead center and the exhaust valve is closed. The intake valve opens allowing air to enter the combustion chambers. Pulled down by the crankshaft, the piston lowers, creating a vacuum, sucking the air/fuel mixture.
The compression stroke begins as the piston reaches the bottom dead center and the intake valve closes. Both valves are now tightly closed. The piston, under the action of the crankshaft, begins to move up the cylinder, compressing the air/fuel mixture in the combustion chamber.
When the piston is at the highest point, the spark plug will produce a spark, igniting the air/fuel mixture. The combustion of the air/fuel mixture creates a huge increase in pressure inside the cylinder, forcing the piston downward and making the crankshaft turn.
When the piston reaches the bottom dead center, the exhaust valves will open and will allow the burnt fumes to be pushed out of the cylinder as the piston rises again. Just before the piston reaches the top dead center, the intake valve opens and the exhaust valve remains open a few moments.
On some vehicles, engineers may have used a technique to increase the amount of fresh air sucked back into the combustion chambers. To achieve this, both intake and exhaust valves will stay open for a short amount of time at the end of the exhaust stroke, right before the piston reaches top dead center again. This process is called valve overlapping and is not as frequently employed as it used to be, now that most newer cars are equipped with variable valve timing systems.
Different Internal System And Their Uses
To burn efficiently, fuel has to be mixed with air in the correct proportion; 14:1 to be exact. This specific air/fuel ratio is called stoichiometric and is the most fuel-efficient ratio to be used in modern internal combustion engines.
The correct air/fuel mixture is created inside the air intake. The air starts its journey by going through the air filter to be cleaned and make sure no debris can enter the combustion chambers. Even the smallest dust particles or metal flakes could seriously damage the engine and cause oil consumption problems.
Fuel, on the other hand, is sprayed directly into the intake while it waits for the intake valves to open. The air/fuel mixture is controlled by the oxygen sensors, measuring the amount of fuel left in the exhaust gases. If too much fuel is found in the exhaust fumes, the powertrain control module will reduce the amount of fuel sprayed in the intake and vice-versa. Such a process ensures that the air/fuel mixture is always as optimal as possible.
Note that on newer engines, air and fuel are mixed directly into the combustion chamber allowing for a more precise mix for each of the cylinders. These engines are called direct-injection engines and their popularity is growing every year because of the better fuel-efficiency they can achieve.
It’s important to mention that, in some cases, some of the exhaust fumes can be recirculated into the intake to reduce the amount of NOx, a dangerous atmospheric pollutant, produced by the engine or as a way to cool down the combustion chambers.
In a vehicle, the exhaust system designates the circuit used to redirect all the combustion gases from the engine, usually located in front of the vehicle, towards the rear of the vehicle, to safely release these fumes into the air.
The exhaust system begins at the rear of the engine block. The exhaust manifold is attached to the cylinder head and receives the exhaust fumes from the engine. The manifold directs the heat and the fumes towards the rear of the vehicle to amplify the oxidation of the unburnt hydrocarbons and carbon monoxide.
The exhaust fumes will then reach the catalytic converter which is specially designed to turn toxic exhaust fumes into carbon dioxide, which is a lot less toxic than carbon monoxide, and into the water using a chemical reaction.
An O2 sensor is located right before and right after the catalytic converter to ensure that the air/fuel ratio is maintained at all time to save on fuel cost and minimize the pollutants produced as much as possible.
The last component in the system is the muffler whose job is to reduce the noise created by the explosions inside the engine by directing the fumes into compartments called Helmholtz resonance chambers before releasing them into the atmosphere. The whole exhaust system often seems like nothing but bent metal piping but it’s a lot more technically advanced than you would think.
In the case of old engines, the carburetor used to deal with the air/fuel mixture before sending it into the intake manifold. On recent engines, however, the carburetor is replaced by injectors which are small high-pressure jets spraying fuel into the intake or directly into the combustion chambers.
The fuel needs to be pressurized to be sprayed in small enough droplets to be able to easily vaporize when entering the combustion chambers. It’s the fuel pump’s job to build up the pressure in the fuel system. For the same reason an air filter is used in the intake system, a fuel filter is often used on the fuel system too.
During the combustion process, the engine creates a lot of heat, which could quickly result in overheating if not correctly regulated. This is when the cooling system comes to the rescue. To keep the heat under control, the cylinders are surrounded by passages filled with coolant. The coolant runs around all the engine’s main component and then flows through the radiator. Thanks to the radiator fan blowing fresh air through the fins of the radiator, the coolant fluid is cooled to an acceptable level before being returned into the engine.
The objective of supercharging an engine using a turbocharger or a supercharger is to increase the power output and to reduce its fuel consumption. To significantly increase the power output of an engine, one can either act on its speed of rotation or its torque. However, the possible rpm increase is quickly limited by the inertia of the moving parts and the limit of the frictional resistance of the metal components. One can’t simply keep pushing the rpm of an engine to gain power without severely compromising its long-term efficiency.
The only solution left is to act on the torque output. The engine torque depends on the angle between the connecting rod and the crankshaft, the pressure of the gas inside the cylinder and the amount of fuel burnt. When increasing the amount of fuel introduced into the cylinder, it is also necessary to proportionally increase the air volume to ensure the air/fuel ratio stays the same.
It is, therefore, possible to increase the engine torque by adding a turbocharger or a turbocharger to pump more air in the system, consequently allowing to spray more fuel into it resulting in higher power output to the wheels.
The air volume contained in a given cylinder is proportional to the pressure and, vice versa, also proportional to its absolute temperature. When air is pressurized, its temperature increases and its density is modified. Colder air contains more oxygen, simple as that. It is therefore advisable to install an air cooler to cool down the air before it enters the engine and thus recovers an optimum oxygen density for peak performances. To achieve this goal, car manufacturers use an intercooler system to cool the air before it’s admitted into the air intake.
The video about the working of car engine:
To Wrap It All Up
Even though every car manufacturer has their way of doing things, the fundamental working principles are the same with all internal combustion engines. Recent cars may come equipped with advanced timing systems and electronic modules but the basics stay the same. Learning how an engine works is not that hard once you get to know the main components and what they do. All you need is to learn the key elements and put in some elbow grease. As with most other things in life, it’s always easier to master a skill by doing it.
So go get your wrenches, put in some practice and you should be able to learn how engines work in no time!
Read more: Cold Air Intake: Pros and Cons for your Car