Compressed natural gas is Definition, composition, properties

2024 Author: Howard Calhoun | [email protected]. Last modified: 2024-01-02 13:48

In most cases, modern personal, passenger and freight vehicles run, of course, on petroleum fuel. However, sometimes cars can be filled with compressed natural gas. This fuel has, first of all, the advantage that it can be considered the most economical automobile at the moment.

Definition and what it is

Until 1994, compressed gas was simply called liquefied natural gas. At the moment, among motorists, this type of fuel is quite popular. It is CNG ordinary natural gas methane, compressed on special equipment to a pressure of 20 MPa and filled into cylinders. The latter are further installed directly into the car and included in its fuel system.

Advantages and disadvantages

So compressed natural gas is just liquefied methane. The advantages of this type of fuel, in addition to saving money,has mass. The advantages of CNG, among other things, include:

• increase in engine life due to the absence of soot;
• environmental safety;
• reducing engine noise;
• reliability.

Of course, compressed gas as a fuel has some drawbacks. These include, for example:

• high cost of converting a car to gas;
• large dimensions of CNG tanks;
• some loss of engine power;
• possible smell of gas.

How to receive

Liquefy natural gas methane at stations using special compressors. It is stored and transported in storage tanks of a special design. Actually, natural gas is supplied to CNG filling stations in the usual way - through main pipelines. At such stations, of course, various standards for the transportation, preparation, storage and injection of compressed natural gas must be observed. GOST 27577-2000 is a document according to which all these operations must be carried out.

Composition of CNG

CNG is thus made from conventional methane by compression. Accordingly, it has the same composition. That is, it is a mixture of CnH2n+2 hydrocarbons. The main component of CNG, as already mentioned, is methane CH4. Its content in the compressed gas is about 98%. Also, heavier hydrocarbons can be CNG components:

• ethane C₂N_6;
• butaneS₄N_10;
• propane C₃H_8.

Non-hydrocarbon substances may also be contained in such a gas:

• hydrogen H_2;
• carbon dioxide CO_2;
• helium He;
• nitrogen N_2;
• hydrogen sulfide H_2S.

Natural gas is formed, which is subsequently compressed in CNG, in the bowels of the earth and is the result of anaerobic decomposition of organic matter. Initially, this type of mineral has no color or smell. However, natural gas, including CNG, is an explosive substance. Therefore, before use, special volatile components with a pungent odor are added to it. This is necessary so that people can quickly detect leaks when working with such gas. The smell of CNG prepared in this way is very pungent even at low concentrations.

Performance

Compressed natural gas is a type of fuel characterized, among other things, by a relatively low degree of fire hazard. Its lower ignition threshold is 645°C. For gasoline, this figure, for example, is 550 ° C. The dangerous concentration of CNG in the air is 4-15% of the volume of the latter.

Also natural gas:

1. 1.6 times lighter than air. That is, when it leaks, it simply quickly rises up and dissipates.
2. Not toxic.

According to the regulations, this type of fuel belongs to the 4th class in terms of sensitivity. Tofor example, the same gasoline is considered a more dangerous substance in this regard and belongs to materials of hazard class 3.

Physical and chemical properties

Thus, the compressed gas has an ignition temperature of 640-680 °C and consists mainly of hydrocarbons. Also, such fuel is characterized by the following physical and chemical characteristics:

• molecular weight - 16.4;
• polarity under normal conditions - 0.718 kg/m;
• required amount of air for combustion - 9.52.

When the content in the air in the amount of 5-6%, methane burns at a heat source. At a concentration of 5-16%, the mixture may already explode. If methane in the air contains more than 14-16%, it loses its feature. Explosions of the methane mixture have the greatest force at a gas concentration in the air of 9.5%.

The peculiarities of natural gas, among other things, include the fact that it has a high detonation resistance. This is also attributed to the advantages of this type of fuel. Due to the knock resistance of CNG, car engines run smoother than gasoline.

Also, when throttling such a gas, for example, in a reducer, its temperature drops sharply. This feature of natural gas is called the Joule-Thomson effect. Because of this, CNG requires a high degree of drying, which must be taken into account when operating vehicles using this fuel.

Requirements

Compressed natural gas is primarily a type of fuel used to operate enoughcomplex in design of modern automobile engines. In order to avoid damage to motors and other components, CNG for cars, of course, must be used exclusively pure.

According to regulations, for example, dust and liquid residue are not allowed in such fuel. Compressed natural gas used for automobiles must also have a certain degree of humidity. This requirement is primarily due to the fact that if hydrants fall out in such fuel in a car, blockage of the channels of the fuel system can occur.

At gas-filling stations, in addition to the actual compression supplied through the highways, the fuel can, therefore, be additionally purified. For this purpose, CNG stations usually use special filtration, drying and separation equipment.

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Cars are filled with compressed natural gas most often at CNG filling stations. But, since most of the cars in our time still move on gasoline, there are not too many such stations in the country at the moment. In areas remote from CNG filling stations, refueling of vehicles can be carried out at mobile refueling stations. At such mobile stations, a special three-section gas-cylinder installation is mounted. At the same time, such equipment is supplied with gas charging and dispensing units for the tanker.

Compressed natural gas cylinders requirements

Any equipment designed to store, transport, pump or use CNG,Of course, it must have a large margin of safety. This also applies to cylinders installed on vehicles for such fuel. Such containers are tested for destruction before being delivered for sale:

• when fired from a firearm;
• when falling from a height;
• under the influence of open fire;
• under the influence of extreme temperatures and corrosive environments.

According to statistics, in the 90s and 2000s, out of 1360 collisions in cars, gas cylinders were hit in car accidents. At the same time, such a container has never been significantly damaged during an accident. Therefore, vehicles running on compressed natural gas are currently considered an even safer mode of transport than cars whose engines operate on gasoline or diesel fuel.