Gasoline or its vapors are burning. Fuel combustion process

05.03.2020

Salon

Everything about everything. Volume 5 Likum Arkady

Why does gasoline burn?

Gasoline is very important in our life because it is used as a fuel for cars. Gasoline is a liquid fuel. It burns so quickly and with so much heat that it can explode. Gasoline is a mixture of hydrocarbons, substances consisting of carbon and hydrogen. These substances are light liquids boiling at low temperatures. Carbon and oxygen are attracted to each other, like a magnet and iron. When carbon and hydrogen combine, ignition starts. During combustion, a lot of energy is released in the form of heat.

When gasoline burns, hydrogen combines with oxygen to form water vapor. Carbon reacts with oxygen to form carbon dioxide. How does burning gasoline make a car move? Liquid gasoline turns into steam and mixes with air using a carburetor. This mixture enters the cylinder, where it is compressed by a piston moving inside the cylinder.

When the mixture of gasoline and air vapors is compressed, the spark from the spark plug ignites the fuel. A large amount of gas is produced in this small explosion (rapid combustion). The pressure of this gas acts on the piston and moves it inside the cylinder. The piston is connected to a crank that turns easily. The push received from the combustion of gasoline causes the crank arm to turn. This lever, in turn, is connected to the wheels. He moves them. The gasoline we use is made from crude oil. In the process of distillation, oil decomposes into different parts, one of which is gasoline.

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10. Gasoline and oil PETROL As you know, the main difference between gasoline grades is the octane number, which characterizes the combustion rate of gasoline and its detonation resistance. On sale there are mainly gasolines with an octane rating of 80 to 98, probably somewhere

Introduction

To ensure combustion in an internal combustion engine, a small amount of fuel is mixed with the incoming air. Unfortunately, an internal combustion engine cannot burn all the fuel it uses without leaving any residue. As a result, the engine releases combustion by-products in the form of exhaust gases. Some of these by-products are harmful and pollute the air. To combat this problem, car manufacturers have developed so-called emission control devices that limit or eliminate the emission of these harmful substances.

Combustion

During combustion, several chemical reactions take place. Some connections are destroyed, and new connections are formed. Controlling the combustion process is the key to controlling the overall performance and emissions of an internal combustion engine.

The combustion process requires three elements:

1. Air
2. Fuel
3. Ignition spark

These three elements are sometimes referred to as the "combustion triad". If one element of the triad is missing, combustion is impossible. The internal combustion engine is designed to combine these three elements while maintaining complete control over the process.

Air

Air is made up of nitrogen (N), oxygen (O) and other gases. Most of the air is nitrogen, which is an inert, non-flammable gas. Air does not burn, but it contains enough oxygen to support combustion.

Fuel

Gasoline is made up of hydrocarbons that are formed from the refining of crude oil. Hydrocarbons are made up of hydrogen (H) and carbon (C) atoms. Various chemicals are added to gasoline, such as corrosion inhibitors, dyes, and cleaning agents. These chemicals are called additives.
The heat and pressure present in an internal combustion engine can cause gasoline in the combustion chamber to ignite before an ignition spark is generated. This is called pre-ignition and is described in more detail below. The octane number of gasoline indicates how well it resists pre-ignition. Additional cleaning may increase the octane number.
Currently, in regions with extremely high levels of air pollution, a type of fuel called improved (reformed) gasoline (RFG) is used. Such gasoline has special additives called oxidizers that improve combustion, increase octane and reduce exhaust emissions.

Ignition spark

In an internal combustion engine, air and fuel enter the combustion chamber and then an ignition spark is generated to cause combustion. Before the air-fuel mixture is ignited, the engine heats up and compresses the mixture. Heating aids the carburetion process, while compression increases the energy generated by combustion.

combustion process

In an internal combustion engine, combustion occurs within a fraction of a second (approximately 2 milliseconds). At this point, the bonds between the hydrogen and carbon atoms are broken. Breaking the bonds releases energy in the combustion chamber, pushing the piston down and initiating the rotation of the crankshaft.
After the separation of hydrogen and carbon atoms, they combine with oxygen atoms contained in the air. Hydrogen atoms combine with oxygen to form water. Carbon atoms combine with oxygen to form carbon dioxide (carbon dioxide).

In the language of chemistry, complete combustion in an internal combustion engine is expressed by the formula:

HC + O2 = H2 O + CO2

In other words:

fuel + oxygen = water and carbon dioxide

A perfectly efficient internal combustion engine would have only water (HO) and carbon dioxide (CO) at the exhaust, which corresponds to the chemical formula given above. This would mean that all hydrocarbons decomposed during the combustion process. Unfortunately, this is not the case.

Inefficient combustion is the main reason for the presence of harmful substances in the exhaust of a car. Efficient combustion leads to the lowest emissions. Combustion efficiency is increased by adjusting the air/fuel ratio.

Air/fuel ratio

Automotive engineers have determined that vehicle emissions can be reduced by running a gasoline engine at an air/fuel ratio of 14.7:1. The technical term is known as "stoichiometric ratio". The stoichiometric ratio means the chemically correct air-fuel mixture that produces the desired chemical reaction, the input of which is the complete combustion of the fuel with the desired exhaust toxicity.
The 14.7:1 air/fuel ratio provides the best control of all three components (hydrocarbons, carbon monoxide and oxides of nitrogen) in exhaust under almost all conditions. The air/fuel ratio also increases the efficiency of the catalytic converter, which is part of the vehicle's exhaust system.

Lean air-fuel mixture

A lean air-fuel mixture is usually caused by a malfunction in the engine. Leaning is a condition where the engine is getting too much air or oxygen. Too high oxygen levels can be caused by vacuum leaks or a faulty fuel supply system.

Rich air-fuel mixture

A rich air/fuel mixture is also an indication of an engine problem. Rich is a condition where the engine cannot burn all the fuel that has entered the combustion chambers. An enriched condition can result from high fuel pressure, ignition timing problems, or low compression.

abnormal combustion

There are two types of abnormal combustion that can occur in an engine: detonation and pre-ignition.
Knocking is an intermittent combustion process that can cause head gasket failure and other engine damage. Detonation occurs when there is overheating and increased pressure in the combustion chamber. When this happens, an explosive force is created, which initiates a sharp increase in pressure in the cylinders, accompanied by a strong metallic knock. Hammer-like shock waves generated by detonation subject the cylinder head gasket, piston, rings, spark plug and connecting rod bearings to severe stress.
Preignition is another abnormal combustion condition that is sometimes confused with detonation. Preignition occurs when a point in the combustion chamber becomes so hot that it becomes an ignition source and causes the fuel to ignite before an ignition spark is generated. It can contribute to detonation or even cause it.
Instead of igniting the fuel at the right time to give the crankshaft a gentle push in the right direction, the fuel ignites prematurely. This causes instant kickback as the piston tries to turn the crankshaft in the wrong direction. This impact, due to the stresses it creates, can be very destructive. In addition, pre-ignition can localize heat to the extent that it can partially melt or burn through a hole in the piston head.

Exhaust toxicity

The stoichiometric air/fuel mixture provides the best compromise between performance, economy and emissions.
With a rich air-fuel mixture, all the fuel does not burn. Therefore, the level of emissions of hydrocarbons and carbon monoxide increases. A lean air/fuel mixture can generate excessive heat when burned. Therefore, the content of nitrogen oxides increases. An excessively lean air/fuel mixture results in misfiring. This increases the emission of hydrocarbons.
Catalytic converters, which chemically neutralize toxic exhaust gases, are most effective in a very narrow range, close to the stoichiometric ratio.

by-products of combustion

Since an internal combustion engine is not of absolute efficiency, three undesirable by-products are generated during the combustion process:
1. Hydrocarbons (HC)
2. Carbon monoxide (CO)
3. Nitrogen oxides (N0 X)

Incomplete combustion causes the release of hydrocarbon and carbon monoxide. Hydrocarbon emissions are hydrocarbons that have not been destroyed during the combustion process. Carbon monoxide is formed because there are not enough oxygen atoms to bind the carbon.

Ideally, nitrogen should pass through the combustion chamber unchanged. But when the temperature in the combustion chamber reaches approximately 1,371 °C (2,500 °F), the nitrogen and oxygen atoms bond to form (N0 X)

The chemical formula of the combustion process in which nitrogen oxides are formed is as follows:

HC + O2 + N2 = H2 O + CO + N0x

The formula "NO" is used for oxides of nitrogen because OHci represents a combination of a nitrogen atom and any number of oxygen atoms. For example, nitric oxide (N0) is made up of one nitrogen atom and one oxygen atom, while nitrogen dioxide (N0) is made up of one nitrogen atom and two oxygen atoms.

High HC content

High CO content

High CO content can be caused by factors such as:
. Excessively rich air-fuel mixture
. Air filter dirty
. Failure of the PCV valve
. Fuel oil contamination
. Seized or leaking fuel injector
On a serviceable vehicle with a catalytic converter, carbon monoxide emissions will usually approach zero. The content of carbon monoxide is measured as a percentage of the total volume in the air.

NOx are generated at high combustion temperatures (above approximately 1371°C (2500°F)) and are usually formed if the combustion temperature is not controlled. Nitrogen oxides are measured in parts per million.

In my previous article and video about octane and compression ratio (by the way, I recommend that you watch the video below), many people began to ask me an interesting question - “what kind of gasoline burns faster? Say 92 or 95?” There were also not so common options - “which is longer” or “better”. Personally, they seemed interesting to me, and I decided to think about it in detail. As usual, there will be a video version at the end. So let's read and watch...

At the very beginning, I would like to say - that not always the rapid burning of gasoline speaks of its quality! Now it’s rather the opposite, but I won’t reveal the cards right away, read the information below.

normal ignition front

Any gasoline, for any type of fuel, has its own normal ignition front. It usually ranges from 10 to 30 m/s. With properly selected fuel, the full potential of mechanical and thermal energy is used to the maximum, the internal combustion engine can be said to work with and its resource is not reduced.

The ignition front depends on various parameters, such as: - octane number (OC), compression ratio, ignition (now it can be electronic or analog), fuel supply ().

Ideally, for each engine design, the recommended fuel is selected. This was especially true on analog carburetor engines (after all, the ignition there could not be automatically adjusted), unlike modern “injector” units, where the electronics themselves can deduce everything based on various sensors (detonation, lambda probes, etc.)

Destructive ignition

I already talked about it, it's still. If any of the parameters is not correctly selected, for example, the engine is designed for the 95th gasoline, and you filled in the 80th. Electronics, namely the "knock sensor" will no longer be able to cope with the destructive processes inside.

During detonation processes, the flame propagation front is about 2000 m / s, which is a lot, such loads simply destroy the internal combustion engine from the inside

This is very bad. In our case, we have the wrong fuel. It's just that 80th gasoline will ignite faster from compression than 95th.

What is modern gasoline?

Modern types of gasoline are made using other technologies, and they are not the same as they were before. Previously, 30-50 years ago, the only type of production was only one - the direct distillation method. If you walk, this is something reminiscent of a moonshine still, only instead of "mash", crude oil was poured in and light fractions came out first - namely gasoline. Then kerosene and the heaviest fraction -.

This method has long been abandoned, the thing is that with such production, the octane number was only 50 - 60 units. You need to add a lot of additives to bring the final product to the desired octane, at least up to AI 76 - 80! YES and additives used to be used on tetraethyl lead etc. they are very effective but very harmful to humans and the environment.

Now everything has changed, the direct distillation method is practically not used, refineries are being updated, and now the main method is various kinds of cracking - thermal, catalytic, etc. (we will not go deep, I already have an article - for those who are interested, read it).

Here the essence is a little different here, oil is laid out with the help of pressure, temperatures, as it were, into layers, and the topmost layer - gasoline - is drained. There are many advantages to these methods:

This is a larger OC - approximately 80 - 85 units. And ideally, you need to get rid of additives altogether
More gasoline per liter of oil

BUT 80 - 85 units for a modern motor is VERY SMALL! Need at least .

BUT the additives that were used before are NOW FORBIDDEN! Again, if you don't go too far currently only ETHERS and ALCOHOLS are allowed . It is they who practically do not harm the environment and humans (such norms are recommended to us through the EURO standards).

BUT alcohols and ethers, having a high OC (approximately 113 - 130), do not burn as fast as we would like! Here we come to the most interesting

What determines the burning rate of gasoline?

We think logically - it is additives, the more of them in gasoline, the slower, but longer the final product burns!

In simple words, if you take 92nd it ignites faster but burns out quickly . Its ignition is similar to a flash.

If you take 95th it ignites slower but burns longer .

98 ignites even slower but burns even longer

ou and s 100th you got me .

How is more power and fuel economy achieved with high octane gasolines?

YES, everything is simple - the longer gasoline burns, the longer it pushes the piston, here you are - saving fuel and increasing power. That is, the 92nd burns out faster, pushes the piston less. 95 burns slower, pushes longer. 98 is even longer, and so on.

Of course, you should not expect a GLOBAL increase in power, here it is most likely a matter of an error of 2 - 5%. Which you may not feel. After all, the octane number directly depends on the amount of additives added to gasoline, but the difference between 92 and 95 is only 3%! Do you think it's a lot or a little?

Now watch the video version

Prompt response and use of the correct ones is the key to minimizing the negative consequences of an emergency.

Gasoline is a fairly widely used flammable liquid.

It can be found in garages, small workshops, even in the home where it is used as a solvent.

Knowing how to extinguish burning gasoline and how to do it correctly is important for everyone.

Features of burning gasoline

Gasoline burns with the release of a sufficiently large amount of heat.

Its ignition can occur:

as a result of the action of an open flame source;
when the temperature rises above the spontaneous combustion limit;
as a result of explosive ignition of saturated vapors;
when exposed to an electric spark, including that arising from the accumulation of static voltage on the walls of a metal container.

The considered flammable liquid cannot sustain combustion without access to oxygen. This feature immediately shows several possible ways to extinguish spilled gasoline (or in a container) both with the help and with improvised means.

What is the best way to extinguish a burning gasoline

The main thing worth mentioning is how not to extinguish gasoline. Water, which is most often at hand, will not help to suppress the source of ignition.

Compared to gasoline, it has a lower density. Therefore, it will always float, preserving the area of \u200b\u200bthe spread of fire and maintaining the temperature inside the hearth.

Due to the action of the latter, the water boils. This process is often explosive, causing the gasoline to splatter and spread the flame over an even larger area.

In addition, under the influence of high temperature, water begins to decompose into oxygen and hydrogen. The combination of these gases in a fire causes a sharp increase in temperature and intensity of fire.

Knowing how you can extinguish gasoline, you can quickly and simply suppress the source of ignition and minimize the negative consequences. This is easy to do even with the help of improvised means.

Sand

Sand is an effective means of dealing with spilled and ignited gasoline.

With his help:

stop the expansion of the burning spot;
Suppress the flame throughout the fire area.

Sand is easy to use. By pouring a rim around the perimeter of the burning spot, they prevent the liquid from spreading. After the flame is localized, it is possible to suppress combustion in the area. To do this, the stain is carefully covered until the flame disappears.

Another means of extinguishing gasoline is soil and other non-combustible bulk substances. Like sand, they must be used carefully. It is required to fill up the fire gradually, avoiding splashing of the burning liquid.

thick fabric

Dense fabric is another effective means of extinguishing gasoline. It covers the source of ignition, blocking the access of oxygen.

The fabric works even better if it is moistened with water to prevent fire due to high temperature.

This primary extinguishing agent will help if the fuel in the tank catches fire. In this case, it is enough to cover it.

Also, the fabric is effective in suppressing fire on a person's clothes, on a car seat, in any case, when maximum efficiency is required in the absence of other fire extinguishing means.

Suitable types of fire extinguishers

To understand what kind of fire extinguisher you can extinguish gasoline - you can use it on its body.

The ignition of liquids is class B fires. Flames with such a source are suppressed:

powder fire extinguishers (OP);
carbon dioxide devices (OU).

All vehicles are equipped with powder fire extinguishers without fail. The extinguishing agent combines the mechanics of sand and an oxygen blocker.

However, in domestic conditions, the use of a powder device necessarily causes significant secondary consequences. Removing the remnants of the fire extinguishing agent is very problematic. The powder is not only very fine, but can get into the smallest cracks and spoil the finish of some types of materials.

Carbon dioxide fire extinguishers are able to quickly displace oxygen from the combustion area of gasoline. At the same time, this type of device sharply reduces the temperature in the center of flame propagation.

Carbon dioxide fire extinguishers are convenient in domestic conditions, because they not only effectively fight fire, but also do not create short circuits in electrical wiring and pollution.