The naturally aspirated engine is a classic engine design. This type of unit is now rarely part of the standard equipment in new cars. In principle, this works without additional units such as turbochargers, so that there is no additional air compression. The basis is usually a four-stroke work cycle, which first begins with the intake of the necessary air. In most cases, a turbocharger is used these days. This is because such engines often have higher fuel consumption efficiencies. Nevertheless, there are still vehicles today that are deliberately equipped with them. This includes sports cars, because this is how a so-called turbo lag can be avoided. Some of the less powerful engines are still sold as naturally aspirated engines. It should also be mentioned that in the past the term referred more to the supply of fuel, but today it is primarily about the supply of intake air due to fuel injection.
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What is a naturally aspirated engine?
Even if the designation usually refers to a diesel engine, there are also Otto engines that work according to this principle. The first intake stroke belongs to the four strokes. During this stroke, the piston moves down the cylinder to increase volume. In this way, a negative pressure is generated which is sufficient to suck air into the engine from the outside. Of course, this is achieved by keeping the intake valve open. The intake air is roughly cleaned by the engine air filter. Before the beginning of the next second stroke, the intake valve is closed so that the upward movement of the piston compresses the intake air. This compression to around a twentieth of the original volume heats it up to around 600°C in the car's naturally aspirated engine. In the diesel engine, the fuel injection takes place at this point, i.e. shortly before the piston reaches its highest point in the cylinder. The required pressure is hundreds to thousands of bars. This allows the fuel to be atomized and then the air-fuel mixture to be compressed a little further. This immediately ignites itself and the powerful downward movement of the piston in the cylinder begins. This is therefore also referred to as the so-called working cycle. After opening what is known as the exhaust gas outlet valve, the piston moves upwards so that the exhaust gases produced can be pushed out into the exhaust manifold. Appropriately, this fourth and last bar is also referred to as the so-called exhaust bar.
There are slight deviations when it comes to a petrol engine, which was not designed as a turbo but as a naturally aspirated engine. The explanation of the naturally aspirated engine also applies here because there are also four strokes. However, you must note that no petrol is injected during the power stroke, but that a ready-to-use air-fuel mixture is already introduced into the cylinder as part of the intake stroke. Another difference, of course, is that this compressed mixture is actively ignited and burned by a spark discharge from the spark plug belonging to the cylinder.
The advantages of a naturally aspirated engine
There are a whole range of positive properties of this type of engine, so that even in racing there is sometimes a battle between naturally aspirated and turbocharged engines. But first, let's talk about the general pros and cons of this technology. A disadvantage why a naturally aspirated engine is no longer the standard engine design is its comparatively poor efficiency. The so-called power-to-weight ratio also speaks against such a simple vehicle engine.
One of the most important design-related advantages is that there is no turbo lag. So the gas is accepted almost immediately. If you look at the differences between naturally aspirated and turbo, turbo lag means that supercharging (i.e. compression) can only be effective if the turbocharger reaches a sufficient speed. As a result, the engine is less powerful, especially in the lower speed range. But even when the engine is already operating at a higher power band, throttle response can feel delayed. This is because the turbo turbine wheels first have to be accelerated. However, there are now strategies to minimize these problems, so the performance of the naturally aspirated engine is only really superior in specific areas of application. Turbo performance improvements include variable vanes, accumulators, but also a reduction in turbocharger inertia. In addition, particularly powerful engines usually even have two turbochargers, which is why they are sometimes also referred to as biturbo. Another possibility is an additional drive for the turbo – for example with the help of an electric motor.
Vacuum versus Turbo – who offers more power
In general, an engine with a turbocharger achieves higher performance. On the one hand, of course, this is due to the fact that a certain increase in efficiency is already achieved through the higher efficiency. The real reason, however, is that with the same engine design, more fuel can be burned and converted into mechanical energy in a shorter period of time. This is because there is more air in the combustion chamber when the diesel is injected. In addition, it has a higher density and also a higher temperature. A result of this is an increased engine mean effective pressure, which in turn leads to more engine torque. In petrol engines, the compression may have to be reduced so that the air-fuel mixture does not self-ignite at an unfavorable time. In technical terms, this is also known as engine knocking.
Conclusion
Whether you prefer a naturally aspirated engine or a turbo depends primarily on your personal taste. In principle, however, it can be said that turbo engines offer a number of advantages, which means that this type of engine is the most popular engine design today. Purely naturally aspirated engines, on the other hand, are primarily used in special applications. This includes, for example, motorsport, where direct throttle response can be very important. You will also find this engine technology in exceptional cases in very small car engines.
A tip from CarTipsandmore:
Even if it's tuning Although it is less easy to do with a classic naturally aspirated engine than with an engine with an additional turbocharger, it is still possible. It is important that chip tuning is not usually sufficient, but that several individual measures must be sensibly combined with one another. Exceptions are engines that have only been throttled electronically by the manufacturer. Other useful individual measures include, for example, optimizing the intake air flow or using an individual throttle system or a modified camshaft. It is best to get advice from an experienced expert.