page_title: Autogas
section_title: Tank
hierarchical_section_title: Autogas / System components / Tank
caption_attribution_description: Autogas tank in the boot (trunk) of Volvo 264 Sedan
context_page_description: Autogas is the common name for liquefied petroleum gas when it is used as a fuel in internal combustion engines in vehicles as well as in stationary applications such as generators. It is a mixture of propane and butane.
  Autogas is widely used as a "green" fuel, as its use reduces CO
  2 exhaust emissions by around 15% compared to petrol. One litre of petrol produces 2.3 kg of CO
  2 when burnt, whereas the equivalent amount of autogas produces only 1.5 * 1.33 = 2 kg of CO
  2 when burnt. CO emissions are 30% lower, compared to petrol and NO
  x by 50%. It has an octane rating that is between 90 and 110 and an energy content that is between 25.5 megajoules per litre and 28.7 megajoules per litre depending upon the actual fuel composition.
  Autogas is the third most popular automotive fuel in the world, with approximately 16 million of 600 million passenger cars powered using the fuel, representing less than 3% of the total market share. Approximately half of all autogas-fueled passenger vehicles are in the five largest markets: Turkey, South Korea, Poland, Italy, and Australia.
context_section_description: Vehicles are often fitted with only one tank, but multiple tanks are used in a some applications. In passenger car applications, the tank is typically either a cylindrical tank, made from steel, mounted in the boot of the vehicle or a toroidal tank (also steel) or set of permanently interconnected cylinders placed in the spare wheel well. In commercial vehicle applications, the tanks are generally cylindrical tanks mounted either in the cargo space or on the chassis underneath the body. Increasingly, the tank is an aluminium Conformable Tank, which is lighter, has more capacity and cannot rust.
  The tanks have fittings for filling, liquid outlet, emergency relief of excess pressure, fuel level gauge and sometimes a vapour outlet. These may be separate valves mounted into a series of 3 to 5 holes in a plate welded into the tank shell, or may be assembled onto a multi-valve unit which is bolted into one large hole on a boss welded, or in the case of an aluminium tank, extruded as part of the tank shell.
  Modern fill valves are usually fitted with an automatic fill limiter (AFL) to prevent overfilling. The AFL has a float arm which restricts the flow significantly but does not shut it off entirely. This is intended to cause the pressure in the line to rise enough to tell the bowser to stop pumping but not cause dangerously high pressures. Before AFLs were introduced, it was common for the filler (with integral check valve) to be screwed directly into the tank, as the operator had to open an ullage valve at the tank while filling, allowing vapour out of the top of the tank and stopping filling when liquid started coming out of the ullage valve to indicate that the tank was full. Modern tanks are not fitted with ullage valves.
  The liquid outlet is usually used to supply fuel to the engine, and is usually referred to as the service valve. Modern service valves incorporate an electric shut-off solenoid. In applications using very small engines such as small generators, vapour may be withdrawn from the top of the tank instead of liquid from the bottom of the tank.
  The emergency pressure relief valve in the tank is called a hydrostatic pressure relief valve. It is designed to open if the pressure in the tank is dangerously high, thus releasing some vapour to the atmosphere to reduce the pressure in the tank. The release of a small quantity of vapour reduces the pressure in the tank, which causes some of the liquid in the tank to vaporise to re-establish equilibrium between liquid and vapour. The latent heat of vaporisation causes the tank to cool, which reduces pressure even further.
  The gauge sender is usually a magnetically coupled arrangement, with a float arm inside the tank rotating a magnet, which rotates an external gauge. The external gauge is usually readable directly, and most also incorporate an electronic sender to operate a fuel gauge on the dashboard.
caption: Autogas tank in boot of Volvo sedan
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