Check out the frequently asked questions
On this page, you will find several frequently asked questions (FAQS) that can help answer your questions.
Vehicle natural gas (NVG) is a fuel made available in gaseous (CNG) or liquid (LNG) form, increasingly used in transport as an alternative to conventional fuels.
NGC differs from liquefied petroleum gas (LPG) in that it consists of hydrocarbons in the range of methane and ethane, while LPG has in its formation hydrocarbons in the propane and butane range.
This type of gas is non-toxic and cannot be adulterated, does not condense, as it is a gas that is much more easily processed by the engine than liquid fuel, being cheaper than gasoline and diesel.
In heavy vehicles, LNG is stored at low pressure in thermally insulated tanks and with capacities that can vary between 174 to 511 litres. LNG gets stored in a liquid state at the evaporating temperature. In the case of boiling water (100ºC), the temperature remains constant during the change from liquid to the gaseous phase even if heat still is supplied, which is due to evaporation. Similarly, LNG remains practically at a constant temperature (-162ºC) is maintained at the same pressure and as long as the steam (natural gas in the gaseous phase) gets released from the reservoir. Therefore, the fuel system of an LNG vehicle is, essentially, constituted by a reservoir and a vaporizer in which the secondary fluid is the engine’s coolant and a reservoir level indicator. The system is configured to receive and store LNG, and supply it to the engine in gaseous form.
The only difference between a gasoline vehicle and a CNG vehicle is the fuel system:
1. The CNG is injected into the vehicle through a valve that takes it to the storage cylinders.
2. In these cylinders, the gas is initially stored at about 200 bar. As the gas gets consumed, the pressure goes down, and below 15 bar, it is necessary to refuel.
3. If the vehicle is bi-fuel, a switch must be installed on the dashboard, allowing the driver to select from natural gas or gasoline. When the driver chooses natural gas, it leaves the cylinders and flows through high-pressure rigid piping to the engine compartment.
4. The gas accesses the pressure regulator, a device that reduces the pressure to values that allow overcoming the pressure losses until the engine admission (the pressure close to atmospheric).
5. The gas outlet, from the pressure regulator to the injection system, is controlled by an electro valve. It also stops the gas flow when the driver switches over to gasoline.
6. Natural gas mixes with the air in the injection system and enters the combustion chambers.
Economy: The use of vehicular natural gas vehicles (NVGs) provides significant savings at two levels. According to data from the Portuguese Association of Natural Gas Vehicles (APVGN), based on an equivalent litre, natural gas costs about 70% less than diesel. On the other hand, NVGs consume clean-burning fuel, which reduces the need for maintenance when it comes to oil changes or spark plugs for example.
Environment: Natural gas is the cleanest of the alternative fossil fuels used today. Carbon dioxide exhaust emissions from VGNs are about 20% lower, emissions from non-methane hydrocarbons are 80% lower, and nitrogen oxides emissions are 40% lower than those from gasoline-powered vehicles. In addition, NVGs emit significantly lower amounts of greenhouse gases and toxins. Still, it is not corrosive and does not contaminate soils.
Safety: VNGs are as safe as vehicles that run on conventional fuels. The excellent safety record of VGNs is fundamentally due to the structural integrity of the fuel system and the physical qualities of natural gas. The safety requirements of vehicles powered by natural gas are demanding, which guarantees unquestionable levels of safety.
Abundance: The world reserves of natural gas are practically double that of oil, according to official information available on the website Association for the Study of Peak Oil and Gas. Another important argument of this energy source is that it can be obtained through systems extractors applied in dumps and landfills, extracting biomethane (also known as biogas). Biomethane can be transformed into natural gas and compressed to usage as an energy source in vehicles. In this way, it presents itself as renewable energy.
The big difference between NVG and liquefied petroleum gas (LPG) lies in its constitution. NVG is composed of methane and ethane, while LPG originates from oil refining, being essentially constituted by propane and butane.
According to the main national association of vehicles powered by natural gas (APVGN), the installation in light vehicles is around € 2000, with a higher value for heavy vehicles. A heavy natural gas vehicle, on the other hand, has a cost of about 25% higher than a diesel counterpart. It should be noted that, although in Portugal there is no official table for compressed natural gas, APVGN advances with an estimate of 70% savings compared to the price per litre of diesel, which refers to a quick recovery of the initial investment.
Dourogás GNV offers filling stations for heavy and light vehicles in several locations. See here where we are.
If you have doubts about the filling at Dourogás NVG filling stations, consult our guide here.
In the past, gasoline vehicles converted to natural gas were subject to small power losses, which is no longer the case due to electronic control units. Vehicles designed specifically to run on natural gas do not show any loss of power because they are optimized at the source. In addition, natural gas has high octane rating (about 120), allowing the engine to run at higher compression ratios than gasoline engines (octane rating between 95 and 98), increasing the effective power of the engine
Decree-law no. 40/93, of February 18, article 1, no. 12 and 13, benefits, with exemptions of 50% of the Automobile Tax (IA), light vehicles that use exclusively natural gas; and with 40% exemption for those that use natural gas and another fuel (bi-fuel). The referred legislation is available on the website of the Directorate-General for Customs and Excise.
The European Union has been focusing its efforts on the “Blue Corridors” project. This project aims to establish liquefied natural gas (LNG) as an effective alternative to conventional fuels for medium and long-distance transportation. To this end, the project has defined a route for LNG filling stations, creating four corridors covering the Atlantic, the Mediterranean and connecting the south with northern Europe, the west with the east.