What are the differences between 95 and 98 gasoline? – Explica .co
The cycle shift in favor of gasoline is more than obvious. As an indication, in 2019, nearly twice as many gasoline cars (838 thousand) were registered as diesel (463 thousand), which makes more and more drivers are wondering if it is better to use 95 or 98 octane gasoline. We will clarify what to do and in which case it is better to refuel one or the other.
What is the compression ratio?
First of all, it is convenient to lay a little groundwork and explain two key concepts of the topic being discussed: definition of compression ratio and the problem-malfunction called crank or auto-detonation.
We start with the compression ratio. The volume filled with air and gasoline inside the engine is the sum of two volumes, the shifting and the combustion chamber volume. The first of these is the space that the piston sweeps from PMI (bottom dead center) to TDC (top dead center), and the second is, as the name suggests, that of the combustion chamber, space in which the process of detonation and gasoline explosion takes place. In this way, the air which reaches the cylinder at the time of admission occupies the sum of the two volumes and is compressed until it occupies only that of the combustion chamber. Yes indeed, the compression ratio is the quotient between the total volume and the volume of the combustion chamber, usually expressed as Rc: 1.
The compression ratio indicates the degree of compression of the air entering the cylinders.
This value is generally understood between 8 and 12 for gasoline engines, by placing the most common and the best performing in the upper range of the lower part. Instead of, diesel engines have a higher compression ratio, generally in 16 and 18, making them engines with much higher performance, understanding performance as the amount of useful energy in the form of movement that they can extract from what is theoretically contained in a 1 liter of fuel, at least in theory and taking into account the laws of thermodynamics.
What is knocking or self-knocking?
The phenomenon known as auto-detonation or automatic start It occurs when the gasoline present in the mixture explodes or explodes spontaneously in the upward stroke of the piston in the compression phase and without a spark at the level of the spark plug, that is to say combustion occurs sooner than it should. This explosion “hits” the head of the piston and tries to push it down, contrary to its natural and coordinated movement with the others, which produces a loss of power, deformations in the piston and stresses in the connecting rod, in more than one very characteristic sound by means of a tapping known as connecting rod cut.
The clicking of the connecting rod, auto-ignition or auto-detonation is an advance of combustion.
The causes of this self-detonation of gasoline can be found in a overpressure or temperature, a poor quality fuel or one wrong ignition timing. In the latter case, we would not speak of an auto-detonation strictly if we stick to the lexicon of the word, since the gasoline exploded as a result of the spark provided by the spark plug, only that this spark did not happen at the right time. In practice, the consequences are the same, but not the solution.
To avoid this problem, the engines are equipped with a knock detector, which detects when auto-ignition occurs, and adapts several parameters, such as turbo pressure (if equipped), ignition advance, injection point or even injects a larger quantity of gasoline to cool the cylinder and achieve a decrease in temperature, because when gasoline evaporates, it “steals” heat from the environment.
What is the difference between 95 and 98 octane gasoline?
the The main difference between 95 octane gasoline and 98 octane gasoline is its octane number..
Octane is an index that indicates the anti-rattle power of gasolineThus, the higher the octane number, the lower the possibility of self-detonation problems. In terms of appearance, gasoline 98 has a deep blue, while 95 is duller, but this is due to practicality in identifying them. The other big difference is the price, 98 gasoline costs around 15 cents / l more expensive.
When it comes to chemical composition and additives, oil companies are not very keen on disclosing this data publicly. If we consult the technical sheets we can verify that they retrace all the values of each parameter, except for octane. One of the rare deviations, and only in the case of Cepsa, is in the amount of oxygen, 2.7% m / m in his STAR 95 and 3.7% m / m in his OPTIMA 98. Regarding sulfur content, all oil companies and octane numbers coincide at 10 mg / kg.
On the contrary, and to justify this surcharge, in major oil companies offer a series of additives in their 98 octane gasoline, which indicate that they allow better cleaning, reduce the amount of carbon or optimize consumption. Their effectiveness is another matter.
Which gasoline to use? 95 or 98 octane?
The refueling of petrol with 95 or 98 octane will depend exclusively on the indications of the manufacturer of your car., depending on its engine, its compression ratio and under what specifications it was designed.
To find out which gasoline your car needs, all you need to do is check the sticker on the fuel tank cap. or the instruction manual.
What happens if you put 95 gas instead of 98?
Using 95 octane gasoline in a ready-to-use 98 octane gasoline engine reduces engine performance, increases consumption, the level of emissions and, in the long run, it can lead to failure.
Modern cars have a knock sensor that will force the ECU to adjust its operation and eventually make the engine less smooth and lazy. In the very long term and due to the continued use of a low octane fuel, it is possible that a mechanical problem will occur despite the presence of this knock sensor.
What happens if you put 98 gas instead of 95?
If we refuel 98 gasoline in a ready-to-use 95 octane gasoline engine, that does not signal any benefit to the engine. and you will not feel any improvement in terms of consumption or power. It really is a waste of money. In any case, nothing dangerous happens if you add one essence in place of the other.
Unless your car manufacturer says so, filling up with 98 gasoline will only end up spending more money on you.
Which cars need to fill up with 98 octane gasoline?
In general, cars with compression ratios above 10.5 should use 98 octane gasoline. In them it is advisable to use 98 gasoline. In this way, it is possible to extract the full potential with which the motor was designed.
My car can fill up with 98 or 95 octane gasoline, what should I do?
The manufacturers of some modern turbocharged cars indicate that they can use both types of gasoline: either 98 or 95 octane (see photo). So maybe you are asking yourself the question: is there something wrong with regular use of 95 octane gasoline?
In this specific case, the regular use of 95 octane gasoline would not pose any reliability problems, even in the long term. because the knock sensor forces the ECU to adapt its operation. On the other hand, with 95 octane gasoline, the vehicle offers slightly lower performance and slightly higher consumption.
Diesel also has its “own octane number”: the cetane number
As a final note and curiosity, in case you were wondering, diesel also has another parameter to measure its quality, although unlike gasoline it is not so well known. It is cetane number and indicates the time elapsing between the injection of fuel and the start of combustion. Thus, the higher the cetane number, the shorter the time, which results in a better quality combustion with less waste.
More articles on fuels:
– What happens if I fill my diesel tank with gasoline? What should I do?
– 97 and 100 octane gasoline arrives in Spain: is it worth changing fuel?
– Filling up with diesel in a gasoline car by mistake: what is happening and how to fix it?
– Dismantling myths: my car no longer runs on 98 octane gasoline
– Winter diesel and gasoline: the problems of using fuel at the wrong time
– E10 gasoline: the fuel is not suitable for all engines arrives in Spain