The natural gas is a mixture of the hydrocarbons methane СН4, ethane С2Н6, propane С4Н10 and insignificant quantities of other heavier hydrocarbons – pentane С5Н16, hexane С7Н16 and others. Almost all kinds of natural gas contain nitrogen N2 and carbon dioxide СО2, rarely containing hydrogen sulphide Н2S and inert gases. At atmospheric pressure it liquefies at -161°С.
The natural gas is a primary energy source – it is extracted from the bowels of the earth, as opposed to the propane/butane, resulting from the processing of petrol.
Natural gas is lighter than air. At a concentration of natural gas from 5% to 15% in the air the mixture is explosive. The self-ignition temperature of the natural gas is 537°С under atmospheric conditions. The basic combustion products are carbon dioxide and water vapours. The chemical heat of combustion of the natural gas is 7000 – 9000 Kcal/m3.
The natural gas /methane/ is the most attractive fuel. It is environmentally friendly and with the lowest price among fuels. It is one of the alternative fuels, its usage is encouraged by the European Union. Until 2020 10% of the vehicles in the EU should be fuelled by natural gas.
The natural gas finds greater implementation as a basic fuel for motor vehicles with internal combustion engines (ICEs). As a fuel for ICEs mainly the products from processing of oil are used – different kinds of gasoline, diesel fuel and liquefied petroleum gas (LPG) propane/butane. The oil reserves are limited, that's why the tendency is toward constant increase in the prices of oil products. The natural gas deposits are practically limitless because new deposits are yet to be exploited, and the existing oil fields still have enormous quantities of natural gas. A standard cubic metre natural gas (at air temperature 0°С and pressure 760 mm Hg) is equivalent to 1.1-1.2 l gasoline with regard to energy performance. With natural gas a motor vehicle will cover the distance of 100 km with two times less vapours than gasoline and diesel fuel.
Calculator – Insert the fuel and calculate how much kg natural gas you are going to use.
Among all hydrocarbon gases the natural gas contains maximum hydrogen per one hydrogen atom, therefore it has high combustion temperature, wide range of ignition of the gas/air mixture, more complete burning, and lower content of toxic substances.
Among all kinds of fuels for ICEs the natural gas has the highest detonation resistance during burning. Its octane number is between 105-110 units, which allows increasing of the pressure ratio of the internal combustion engine and improvement of their fuel economy. Among all fuels natural gas generates the greatest deal of heat during burning, which results in improvement of the fuel economy of the engines and thermal efficiency.
Due to the identical physical states of air and natural gas, the mixture between them is much better and the burning is considerable more complete. The usage of natural gas allows reducing 3-4 times of the toxic substances, soot and opacity of the exhaust gases. The natural gas (after the hydrogen) is the most environmentally friendly fuel for the machines with ICE.
Due to the higher detonation resistance of the natural gas, the better mixture with air, the more complete burning and the lack of detergent characteristics, the wear of engines is reduced by 1.5 to 2 times!
The suitability of the spark plugs is increased by 40% – 50%, while the period of usage of oils is increased from 1.3 to 1.8 times.
All motor vehicles with gasoline and diesel engines can be reconstructed to work with natural gas along with liquid fuel.
The basic elements of the system for natural gas in the gasoline ICEs are: gas cylinder/s, pipeline, main and charging el. valve, gas-mixer, reducer-evaporator for gas and electrical switch.
In order to have enough fuel reserve for the engines, the natural gas has to be "prepared" in advance. There are three methods:
• by compressing to high pressure to 20-22 MРа
• by liquefying of the natural gas to cooling to -162°С
• by extracting of methanol from the natural gas.
Greatest implementation has found the first method – the natural gas is being compressed through compressors for high pressure up to 20-22 MРа and it is stored in special high-pressure bottles. Basically the bottles are cylinder-shaped, constructed of alloy steel.
When empty, they weigh around 30 kg. In a cylinder with volume 56 l, filled with natural gas, with pressure 20 mРа, can be placed around 9-10kg gas methane.
There already have been developed carbon cylinders, which are characterized by their lightweight and capability to be filled with around 15kg compressed natural gas.
By the gasoline ICEs, natural gas replaces gasoline at a 100%. In Bulgaria there are already available compressed natural gas stations in almost all big cities, which provides opportunity for more and more ICEs of motor vehicles to be reconstructed to work with natural gas in order to achieve savings and better environmental indicators.
The economic efficiency for the owners of motor vehicles as a whole is enormous: for every litre gasoline, replaced with natural gas, they save around 1.20 BGN. Estimates show, that the gas system is paid off for 6-7 months with the achieved savings.
Advantages of the natural gas /methane/:
• Lower price compared to the other fuels
• Its usage reduces the emissions of harmful gases
• The wear of the engine is reduced
• The period for usage of engine oil is increased
• It is possible to be used in gasoline and diesel engines
• Available network of compressed natural gas stations, covering the whole country.