In most cases, modern personal, passenger and freight vehicles, of course, run on petroleum fuel. However, sometimes cars can be refueled with compressed natural gas. This fuel primarily has the advantage that it can be considered the most economical automobile at the moment.
Definition and what constitutes
Until 1994, compressed gas was simply called liquefied natural gas. At the moment, this type of fuel is quite popular among motorists. CNG is an ordinary natural methane gas, compressed on special equipment to a pressure of 20 MPa and filled into cylinders. The latter are then installed directly in the car and are included in its fuel system.
Advantages and disadvantages
Thus, compressed natural gas is simply liquefied methane. In addition to saving money, this type of fuel has a lot of advantages. The advantages of CNG, among other things, include:
- increased engine life due to the lack of soot;
- environmental safety;
- reduction in engine noise;
- reliability.
Of course, compressed gas as a fuel has some drawbacks. These may include, for example:
- the high cost of remaking the car for gas;
- large tank sizes for CNG;
- some loss of engine power;
- the possibility of a gas odor.
How to get
They liquefy natural gas methane at stations using special compressors. Store and transport it in drives of a special design. Actually, natural gas is supplied to CNG filling stations in the usual way - via trunk 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 - a document according to which all these operations should be carried out.
CNG composition
CNG is thus made from conventional methane by compression. Accordingly, it has the same composition. That is, it is a mixture of hydrocarbons CnH2n + 2. The main component of CNG, as already mentioned, is methane CH4. Its composition of compressed gas is about 98%. Heavier hydrocarbons can also be components of CNG:
- ethane C 2 H 6 ;
- butane C 4 H 10 ;
- propane C 3 H 8 .
Also, non-hydrocarbon substances may be contained in such a gas:
- hydrogen H 2 ;
- carbon dioxide CO 2 ;
- helium He;
- nitrogen N 2 ;
- hydrogen sulfide H 2 S.
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 substances. Initially, this type of mineral has neither color nor 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 when working with such gas can quickly detect its leaks. The smell prepared in this way CNG is very sharp even in low concentrations.
Operational properties
Compressed natural gas is a type of fuel characterized, among other things, by a relatively low degree of fire hazard. The lower threshold for its ignition 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:
- 1.6 times lighter than air. That is, with a leak, it simply rises quickly and dissipates.
- No toxicity.
According to the regulations, this type of fuel belongs to class 4 in terms of sensitivity. For example, the same gasoline is considered to be a more dangerous substance in this regard and belongs to hazard class 3 materials.
Physiochemical properties
Thus, the compressed gas has a flash point of 640-680 ° C and consists mainly of hydrocarbons. Also, such fuel is characterized by the following physico-chemical characteristics:
- molecular weight 16.4;
- polarity under normal conditions - 0.718 kg / m;
- the required amount of air for combustion is 9.52.
When contained in air in an 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 such a feature. The explosions of the methane mixture have the greatest force at a gas concentration of 9.5% in air.
Among the features of natural gas, among other things, include the fact that it has a high knock resistance. This also applies to the advantages of this type of fuel. Due to the detonation resistance of CNG, car engines are softer than when using gasoline.
Also, when throttling such a gas, for example, in a reducer, its temperature drops sharply. Such a 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 cars using such fuel.
Requirements
Compressed natural gas is primarily a type of fuel used to operate modern automobile engines that are quite complex in design. In order to avoid damage to motors and other components, CNG for cars, of course, must be used exclusively clean.
According to the regulations, for example, dust and liquid residue are not allowed in such fuel. Compressed natural gas also used for automobiles must have a certain degree of humidity. This requirement is primarily due to the fact that when hydrants occur in such fuel in the car, the channels of the fuel system may become clogged.
At gas filling stations, in addition to actually compressing the fuel supplied along the mains, it can thus be additionally cleaned. For this purpose, a special filtration, drainage and separation equipment is usually used at CNG filling stations.
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Car refueling with compressed natural gas is most often done at CNG filling stations. But, since most of the cars in our time still move on gasoline, there are currently not too many such stations in the country. In areas remote from CNG filling stations, refueling of cars can be carried out on mobile PAGZ. At such mobile stations, a special three-section gas cylinder installation is mounted. At the same time, such equipment is supplied with refueling gas units and its distribution units.
Compressed natural gas cylinders: requirements
Any equipment intended for storage, transportation, injection or use of CNG, of course, must have a large margin of safety. This also applies to cylinders mounted on vehicles for such fuel. Such containers before delivery for sale are tested for destruction:
- when fired from a firearm;
- when falling from a height;
- under the influence of open flame;
- under the influence of extreme temperatures and aggressive environments.
According to statistics, in the 90s and 2000s during an accident of 1360 collisions, the blow in the cars fell on gas cylinders. In this case, even during an accident, such a capacity was not significantly damaged. Therefore, cars operating on compressed natural gas are currently considered to be even safer means of transport than cars whose engines operate on gasoline or diesel fuel.