Autogas

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A Shell Autogas refuelling station.

Autogas is the common name for liquefied petroleum gas (LPG) 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 it decreases exhaust emissions. In particular, it reduces CO₂ emissions by around 35% compared to petrol. One litre of petrol produces 2.3 kg of CO₂ when burnt, whereas the equivalent amount of autogas produces only 1.5 kg of CO₂ when burnt. It has an octane rating (MON/RON) that is between 90 and 110 and an energy content (higher heating value—HHV) that is between 25.5 megajoules per litre (for pure propane) and 28.7 megajoules per litre (for pure butane) 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 (in ascending order): Turkey, South Korea, Poland, Italy, and Australia.

Terminology variations

In countries where petrol is called petrol rather than gasoline, it is common for autogas to be simply referred to as gas.^{[citation needed]} This can be confusing for people from countries where petrol is called gasoline, as they often use gas as an abbreviation of gasoline.

In the United States, autogas is more commonly known under the name of its primary constituent, propane. The term autogas is used in the United States to refer to automobile petrol, when used in piston-powered small aircraft. Aircraft owners using this fuel in place of the more common aviation fuel or avgas, require a Supplemental Type Certificate issued by the United States Federal Aviation Agency.

In the UK and Australia LPG and autogas are used interchangeably. In Italy and France, GPL (an acronym for gas di petrolio liquefatto and gaz de pétrole liquéfié) is used, and in Spain GLP (gas licuado del petróleo) is used.

In Asian countries, particularly those with historical American influences such as the Philippines, the term autogas is not commonly recognised as a generic term and the use of the terms LPG or autoLPG is more widely used by consumers, especially by taxi drivers many of whom use converted vehicles. The converted vehicles are commonly called LPG vehicles or LPG cars.

Vehicle manufacturers

Toyota made a number of LPG-only engines in their 1970s M, R, and Y engine families.

A number of automobile manufacturers—Citroën, Fiat, Ford, Hyundai, General Motors (including Daewoo, Holden, Opel/Vauxhall, Saab), Maruti Suzuki, Peugeot, Renault (including Dacia), Skoda, Tata Motors, Toyota, Volvo, and more recently Volkswagen —have OEM bi-fuel models that will run equally well on both LPG and petrol. Holden Special Vehicles (HSV) also offer bi-fuel models however the vehicles use a different system to that of their donor vehicles from Holden, with HSV using technology from Orbital Autogas Systems, which injects the autogas into the engine as a liquid instead of a gas for increased efficiency.

Petrol engined cars which have not been fitted with LPG/autogas systems by the manufacturers can usually accept third party systems to enable them to use both LPG or petrol.

Vialle manufacture OEM LPG powered scooters and LPG powered mopeds that run equally well on LPG. Ford Australia have offered an LPG-only variant of their Falcon model since 2000.

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  4.0 litre E-Gas straight-six engine of a 2001 Ford AU Falcon.

• Alloytec V6 (LPG) engine of a 2006-2008 Holden VE Commodore 1.jpg

  3.6 litre Alloytec bi-fuel (petrol and LPG) V6 engine of a 2006–2008 Holden VE Commodore.

Countries

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2008 Global Autogas Consumption graph.

Autogas enjoys great popularity in numerous countries and territories, including Australia, Croatia, Lithuania, the European Union, Hong Kong, India, Philippines, the Republic of Macedonia, South Korea, Serbia, and Turkey. It is also available at larger petrol stations in several countries. In the Republic of Armenia, for example, the transport ministry estimates as many as 20 to 30% of vehicles use autogas, because it offers a very cheap alternative to both diesel and petrol, being less than half the price of petrol and some 40% cheaper than diesel. The recent rises in oil-derived fuel prices has significantly increased the difference.

Algeria

Since the 1980s, the Algerian Government has pursued a policy to promote the use of autogas in Algeria. The two main incentives for the government to put this policy into action was to take advantage of the large LPG production and reduce urban pollution. At the end of 2003, there were approximately 120,000 autogas-powered vehicles on the roads, supported by over 300 refuelling stations, accounting for 14% of the national vehicle fuel network.

The Algerian Government fixes the prices of all automotive fuels. Autogas is priced in Algeria at 61% of the price of diesel, making it an affordable option.

Australia

LPG is popular in Australia, because it is less than half the price of petrol in urban areas (approx A$0.59-0.75 per litre, as opposed to A$1.10-1.35 per litre for unleaded fuel and A$1.15-1.30 per litre for diesel, as of February 2010), and it is locally produced. The three major local manufacturers, (Ford, Holden and Toyota), offer factory fitted autogas in some models of their locally made large cars and commercial vehicles. Mitsubishi Australia formerly manufactured factory-fitted autogas vehicles locally but ceased manufacturing in 2008. All factory autogas vehicles, with the exception of the E-Gas Ford Falcon model, are bi-fuel vehicles, meaning they have the capability to run on either petrol, autogas, or a combination. It should be noted that Holden Special Vehicles offers a different autogas system to its parent, Holden, that injects the autogas into the engine as a liquid, making for efficiency.

There are over 615,000 autogas-powered cars on Australia's roads and over 3,200 refuelling stations. Autogas is especially popular with taxis, except in remote areas where transportation costs make autogas prices uncompetitive.

Whilst autogas is currently excise-free, excise is to be imposed on all vehicle fuels that are not currently subject to excise, being added incrementally from 2011 to 2015. The excise on autogas will start at 2.5 cents per litre in 2011 and reach 12.5 cents per litre by 2015. By comparison, the excise on petrol will remain at its existing 38 cents per litre. The additional excise on autogas is being offset somewhat by a subsidy that was implemented in 2006 for private motorists, paying either A$2000 to convert their existing vehicle to autogas, or A$1000 for purchasing a new vehicle that was manufactured to operate on autogas. The subsidy does not apply to business vehicles or vehicles with a Gross Vehicle Mass of over 3500 kilograms. In addition to the subsidy provided by the Australian federal government, the Western Australian government also provides a A$1000 subsidy under the long-running LPG subsidy scheme.

Belgium

The use of autogas was once very popular in Belgium, thanks to the subsidies given by the government to install conversion kits. Since, 2003, when the subisidies disappeared, the number of cars running in LPG has decreased and the number of cars running on diesel has increased. In recent years, the use of autogas as a vehicle fuel has accounted for less than 2% of vehicle fuel use in Belgium. At the end of 2003, there were an estimated 93,000 autogas-powered vehicles on Belgium, supported by 600 refuelling stations. The price of a litre of autogas is approximately 50% of the price of diesel, thanks to the low taxation on autogas by the Belgian government.

Bulgaria

Autogas consumption in Bulgaria accounted for 14% the total fuel consumption in 2003, an amount which has tripled since 1999. By the end of 2003, there were an estimated 195,000 autogas-powered vehicles on the road, with around 1,500 refuelling stations. Autogas is also very popular with commercial users in Bulgaria, as 90% of minibuses and taxicabs were able to run on the fuel. Vehicles originally manufactured to operate on autogas are virtually non-existent in Bulgaria, so the vast majority of the vehicles are third-party conversions.

Canada

In 2003, there were an estimated 92,000 autogas vehicles on Canada's roads, accounting for 0.8% or the total automotive fuel use. In the late 1980s and early 1990s, autogas enjoyed widespread consumption in Canada, only to decline in the late 1990s.

In the early 1980s, there were few autogas vehicles in Canada. Then, the Canadian Government established a grant to convert petrol vehicles to run on alternative fuels, in an attempt to resolve or improve the country's energy security concerns. The grant was a success, with Autogas becoming Canada's most popular alternative vehicle fuel by a wide margin. Over 5,000 refuelling stations were set up to facilitate the boom, and autogas sales peaked in 1992 with 700,000 tonnes sold. In the mid 1990s, the national conversion grant was dropped and components became more expensive. This resulted in a major decline in autogas sales and vehicles by more than half, with only 310,000 tonnes sold in 2003, equal to 0.8% of the total automotive fuel consumption. In 2005, an estimated 92,000 autogas vehicles survived on Canada's roads, with the majority being owned by commercial users. Many of the previous autogas users have since switched to diesel or CNG.

China

Autogas consumption in China has grown rapidly since the 1990s, has slowed down in the early 2000s, but has started to grow again in recent years. In 2009, Autogas refuelling stations have spread to 25 cities and has become a major alternative fuel in China. Motorcycles account for a large portion of the autogas, with over 260,000 Autogas motorcycles in Shanghai alone. In Shenyang, the local government is encouraging public transport to convert to autogas, and as of 2009 over 160,000 taxicabs run on the fuel as well as over 2,500 buses. The city of Guangzhou accounted for 46.56% of national autogas consumption in 2009. Only 24% of China's Liquefied Petroleum Gas is produced domestically.

Croatia

As of 2008, approximately 30,000 Croatians drove using autogas, which at the time was available from 90 stations throughout the nation. In 2009, it was estimated that there were 60,000 autogas-powered cars on Croatia's roads, and in 2010, it is estimated that 150,000 drivers in Croatia were using the autogas. This recent increase in popularity has largely been attributed to the lower price of autogas compared to petrol or diesel.

In 2009, Croatia exported 51% of domestically produced Liquefied Petroleum Gas (LPG), leaving only 49% for consumption. Out of that 49%, 45% of domestically sold LPG is used as autogas. Damir Stambuk from the Croatian Ministry of Economy, which is also responsible for energy, said that Croatia is not yet ready for a regular autogas market due to a small network of stations, but in the future it will be.

Czech Republic

At the end of 2003, the roads of the Czech Republic had an estimated 145,000 autogas vehicles with 350 refuelling stations.

Denmark

Autogas is uncommon in Denmark, and as a result there are only around 13 refuelling stations. The stations are run by Shell, YX, OK, Uno-X, Q8 and Statoil.

France

It was estimated that France would have over 62,500 autogas vehicles on the road by the end of 2010. By the end of 2003, there were an estimated 190,000 autogas vehicles in use with almost 1,900 refuelling stations. In 2005, autogas accounted for around 0.4% of the total automotive fuel use.

Hong Kong

In Hong Kong all taxicabs rely on autogas. Many public light buses also rely on autogas.

Italy

Autogas is very popular in Italy. With over 1,000,000 autogas vehicles on the road, it is the second largest autogas market in the European Union, after Poland. Italy was one of the first countries in the world to introduce autogas, which happened in the 1950s. In the first half of 2010 alone, more than 170,000 new autogas cars were registered. General Motors has been especially successful in Italy, with two-thirds of the vehicles sold in 2008 being autogas-capable.

Malta

Autogas was introduced to Malta on 22 May 2012 by Liquigas. The first filling station is located at the Malta International Airport.

Japan

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An autogas-powered forklift in Japan.

Currently, Japan has about 280,000 autogas vehicles on the road, which is less than in recent years. However, the number of autogas vehicles on Japan's roads has been very unstable. The first autogas taxicabs were introduced in Japan in the 1960s/1970s. With a sharp decline in the 1990s, the number started to rise again in 2003. Sometime between 2004 and 2010, the number has dropped. The vast majority of autogas vehicles on Japanese roads are taxicabs or commercial vehicles. This is why, in 2010, the Japan LP Gas Association started an initiative to encourage corporations and motorists alike to switch to autogas vehicles. The initiative involves 27,000 Japanese retailers to introduce an autogas vehicle into their fleet every three years. Many of these corporations already have autogas vehicles, but Makoto Arahata from the Japanese LP Gas Association says that there is still much room for improvement.

Netherlands

Use of autogas has varied in the Netherlands. It went up in the 1980s and has gone down ever since, except for an increase in 2005. In 2010, there are around 220,000 autogas vehicles on the road (total cars being a little less than 8 million).

Autogas is so ubiquitous, there are very few fuel stations that do not have it. The aptly named Dutch Bayonet is the standard filling device used.

The road tax on autogas vehicles can be up to 2 times that of petrol powered vehicles. On the modern G3 autogas systems, the difference on tax is zero for cars up to 850 kg, but increases for heavier cars. (Compare the diesel tax, which is twice the petrol tax.) But because the price of autogas is less than half that of petrol, retrofitting a car with an autogas tank is economically viable after around 10,000 km/year.

Poland

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Polish road sign indicating an Autogas station.

Poland has one of the oldest and most successful autogas markets in Europe. In 2011, there were 6050 autogas refuelling stations and 2,500,000 autogas vehicles on the road. The number of autogas vehicles in Poland increased by 8% in 2011, however autogas sales decreased by 3.7%. This is mostly due to older vehicles being replaced with newer, more fuel efficient ones. Almost half of Poland's LPG comes from Russia. As of 2011, the number of autogas vehicles exceeded 2,500,000.

Russia

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AGZS Kazan

Autogas is widely used in Russia. In its modern form it has been used since the 1970s. There are two types of autogas equipment and autogas stations as well. These are LPG (propane-butane mix) and Pressurised Gas (methane). The main consumer of LPG is commercial transport. Pressurised Gas is losing its positions to LPG and now can be rarely seen on public transport buses.^{[citation needed]}. There are some community supported sources where people post gas station location on the map. gas station on a map. Gaz station on a map 2 (propane) / gas stations on a map 2 (metane). These sources may be used by some travelers going to Russia by car. First limited series of vehicles driven by multifuel including metane has appeared in the middle of 20-th century

Turkey

Turkey has the highest percentage of autogas vehicles in the world. Some 37% of passenger cars run on autogas and autogas consumption now exceeds gasoline consumption. The Turkish government regulated the autogas price to provide consumers with a net economic advantage of 20-35%. As of the end of 2010, there are 8,500 autogas fueling stations around the country and market growth has been supported by a network of 1,000 licensed conversion shops.

According to Turkish Statistics Institute’s—TUIK, a governmental organisation— the nation has over 16,500,000 vehicles in January, 2012. %50.3 are passenger vehicles. 16.2% light weight trucks, 15.7% motorcycles, %9.2 tractors, 4.6% heavy weight trucks, 2.5% mini buses for transportation, 1.4% buses and %0.1 special purpose vehicles.

Right now monthly, average 50.000 new generation cars are sold.

LPG is dominantly used in Turkey as an autogas while CNG converted vehicles is only around 500 cars and there is only 2 CNG filling stations.

In Turkey, nobody has the courage to convert diesel vehicles to LPG after unsucessul applications in the past. For that reason, the conversion workshops don't make installations to light and heavy weight trucks, tractors, bus and mini-buses and motorcycles.

8,3 millions are passenger vehicles. 33% of the passenger cars (2,739.000 ) are diesel powered and 67% are gasoline powered (5.561.000). As there is no conversion to diesel cars, among 5.561.000 gasoline powered passenger cars, According to the reports of MMO ( Chamber of Mechanical Engineer's Department autohorised to deal with the leakage tests and exhause emissions of LPG powered vehicles) declared that LPG powered vehciles are 3.1 million by the end of 2011.

This means more than 55% of gasoline powered passenger vehicles are already converted to LPG.

The converted vehicles were mostly carburated engines. More or less 90% of the old carburated engines has already been converted and day by day, new generation vehicle owners are also choosing LPG as an alternative fuel.

The reason of this high LPG application is because of the Turkish government's application of an unbelaivable high fuel taxes + OTV (special consumption tax) especially upon the petrol and diesel prices and due to that reason Turkish people are using the most expensive fuel in the world for almost 50 years. (Even though Turkey has borders with OPEC countries exporting crude oil and petroleum to the world and has the lowest transportation costs ) Turkish people found the only solution to save money from their road expenses by converting their cars to autogas which gives them an advantage of 35% up to 40% saving.

This big conversion is the success of Turkish Autogas Kits and Autogas Tanks manufacturers starting from 1995, even though autogas use became legal in 2000. At the same time, Italian companies also supplied systems through their several companies.

United Kingdom

According to the LPG trade association in the UK there are about 1500 refuelling stations that cater for the 160,000 LPG powered vehicles on UK roads. This represents less than 1% of vehicles. The only Government incentive to use LPG is the lower road fuel tax applied to LPG compared to petrol. As of January 2012, the saving of about 60 pence per litre is the highest it has ever been and that combined with conversion prices being an historic low should result in an increase in LPG conversions. Technology has reached the point where almost all conversions are 'Sequential Vapour Injection', and in the UK there is a large number of kits with various price and quality ranges to choose from, resulting in a very competitive market.

United States

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Propane-powered Ford van Wayne, Michigan

Autogas is on the rise in the United States. As of February 2012, the United States has more than 270,000 autogas vehicles on the road, accounting for just 2% of the world’s total and as of 2011, the United States has more than 2,600 autogas fueling stations, making it easier for drivers to refuel across the country. The U.S. Department of Energy has a website that autogas drivers can easily locate autogas fueling stations near them as well as other alternative fuels. The cost of converting a car to use gasoline or autogas at a turn of a knob starts from US$3,000. Autogas use by car drivers can help the United States to reduce dependence on foreign oil as 90% of all U.S. Autogas is produced in the U.S. In 2005, a provision was enacted that placed a 50 cent per gallon tax credit on propane autogas as part of H.R. 4853, making it $1 per gallon cheaper than petrol on average. The alternative fuel credit was extended in 2010 and remains in effect until the end of 2011.

Autogas for America claims to be the unified voice of the autogas industry in the United States. Composed of autogas experts, transportation industry specialists and environmental advocates, Autogas for America says it "leverages industry cooperation to widen recognition of autogas among the US public, media and government."

System types

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Vialle LPI liquid injection on a 2003 Lexus IS 300 2JZ-GE.

The different autogas systems generally use the same type of filler, tanks, lines and fittings but use different components in the engine bay. Liquid injection systems use special tanks with circulation pumps and return lines similar to petrol fuel injection systems.

There are three basic types of autogas system. The oldest of these is the conventional converter-and-mixer system, which has existed since the 1940s and is still widely used today. The other two types are known as injection systems, but there are significant differences between the two.

A converter-mixer system uses a converter to change liquid fuel from the tank into vapour, then feeds that vapour to the mixer where it is mixed with the intake air. This is also known as a venturi system or "single point" system.

Vapour phase injection systems also use a converter, but unlike the mixer system, the gas exits the converter at a regulated pressure. The gas is then injected into the air intake manifold via a series of electrically controlled injectors. The injector opening times are controlled by the autogas control unit. This unit works in much the same way as a petrol fuel injection control unit. This allows much more accurate metering of fuel to the engine than is possible with mixers, improving economy and/or power while reducing emissions. Liquid phase injection systems do not use a converter, but instead deliver the liquid fuel into a fuel rail in much the same manner as a petrol injection system. These systems are still very much in their infancy. Because the fuel vaporises in the intake, the air around it is cooled significantly. This increases the density of the intake air and can potentially lead to substantial increases in engine power output, to the extent that such systems are usually de-tuned to avoid damaging other parts of the engine. Liquid phase injection has the potential to achieve much better economy and power plus lower emission levels than are possible using mixers or vapour phase injectors.

System components

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Fuel filler in E-Gas Ford Falcon

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Filler with mounting and cover removed

Filler

The fuel is transferred into a vehicle tank as liquid by connecting the bowser at the filling station to the filler fitting on the vehicle.

The type of filler used varies from country to country and in some cases different types are used within the same country.

The three types are:

• ACME thread. This type has a threaded fitting onto which the bowser nozzle is screwed before the trigger is pulled to establish a seal before fuel transfer. This type is used in Australia, USA, Germany, Austria, Belgium, Republic of Ireland.
• 'Dutch' Bayonet. This type establishes a gas proof seal by a push and twist action. This type is used in the United Kingdom, Netherlands and Switzerland.
• 'Italian' Dish. This type is used in Italy, France, Poland, Scandinavia and Portugal.

Adaptors that allow a vehicle fitted with a particular system to refuel at a station equipped with another system are available.

The fill valve contains a check valve so that the liquid in the line between the filler and the tank(s) does not escape when the bowser nozzle is disconnected.

In installations where more than one tank is fitted, T-fittings may be used to connect the tanks to one filler so that the tanks are filled simultaneously. In some applications, more than one filler may be fitted, such as on opposite sides of the vehicle. These may be connected to separate tanks, or may be connected to the same tanks using T-fittings in the same manner as for connecting multiple tanks to one filler.

Fillers are typically made of brass to avoid the possibility of sparks when attaching or removing the bowser that might occur if steel fittings were used.

Hoses, pipes and fittings

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Gas lines and fittings. Containment hose, liquid hose, copper pipe with flared end plus brass elbows and T fitting

The hose between the filler and tank(s) is called the fill hose or fill line. The hose or pipe between the tank(s) and the converter is called the service line. These both carry liquid under pressure.

The flexible hose between the converter and mixer is called the vapour hose or vapour line. This line carries vapour at low pressure and has a much larger diameter to suit.

Where the tank valves are located inside an enclosed space such as the boot of a sedan, a plastic containment hose is used to provide a gas-tight seal between the gas components and the inside of the vehicle.

Liquid hoses for LPG are specifically designed and rated for the pressures that exist in LPG systems, and are made from materials designed to be compatible with the fuel. Some hoses are made with crimped fittings, while others are made using re-usable fittings that are pressed or screwed onto the end of the hose.

Rigid sections of liquid line are usually made using copper tubing, although in some applications, steel pipes are used instead. The ends of the pipes are always double-flared and fitted with flare nuts to secure them to the fittings.

Liquid line fittings are mostly made from brass. The fittings typically adapt from a thread in a component, such as a BSP or NPT threaded hole on a tank, to an SAE flare fitting to suit the ends of pipes or hoses.

Tank

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Autogas tank in boot of Volvo sedan

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Tank valves. From left, relief valve (with red cap), service valve, gauge and fill valve

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Autogas tank inside spare wheel recess

Further information: Gas tank, Gas cylinder, Storage tank, and Pressure vessel

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 mounted in the boot of the vehicle or a toroidal tank 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.

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 into the tank shell.

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Fill valve and AFL

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.

Valves

There are a number of types of valve used in autogas systems. The most common ones are shut-off or filter-lock valves, which are used to stop flow in the service line. These may be operated by vacuum or electricity. On bi-fuel systems with a petrol carburettor, a similar shut-off valve is usually fitted in the petrol line between the pump and carburettor.

Check valves are fitted in the filler and on the fill input to the fuel tank to prevent fuel flowing back the wrong way.

Service valves are fitted to the outlet from the tank to the service line. These have a tap to turn the fuel on and off. The tap is usually only closed when the tank is being worked on. In some countries, an electrical shut-off valve is built into the service valve.

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Two Sherwood valves. 1995 on left, 1989 on right

Where multiple tanks are fitted, a combination of check valves and a hydrostatic relief valve are usually installed to prevent fuel from flowing from one tank to another. In Australia, there is a common assembly designed for this purpose. It is a combined twin check valve and hydrostatic relief valve assembly built in the form of a T-fitting, such that the lines from the tanks come into the sides of the valve and the outlet to the converter comes out the end. Because there is only one common brand of these valves, they are known colloquially as a Sherwood valve.

Converter

The converter (also known as vaporiser) is a device designed to change the fuel from a pressurised liquid to a vapour at around atmospheric pressure for delivery to the mixer or vapour phase injectors. Because of the refrigerant characteristic of the fuel, heat must be put into the fuel by the converter. This is usually achieved by having engine coolant circulated through a heat exchanger that transfers heat from that coolant to the LPG.

There are two distinctly different basic types of converter for use with mixer type systems. The European style of converter is a more complex device that incorporates an idle circuit and is designed to be used with a simple fixed venturi mixer. The American style of converter is a simpler design which is intended to be used with a variable venturi mixer that incorporates an idle circuit.

Engines with a low power output such as; scooters, quad bikes and generators can use a simpler type of converter (also known as governor or regulator). These converters are fed with fuel in vapour form. Evaporation takes place in the tank where refrigeration occurs as the liquid fuel boils. The tanks large surface area exposed to the ambient air temperature combined with the low power output (fuel requirement) of the engine make this type of system viable. The refrigeration of the fuel tank is proportional to fuel demand hence this arrangement is only used on smaller engines. This type of converter can either be fed with vapour at tank pressure (called a 2 stage regulator) or be fed via a tank mounted regulator at a fixed reduced pressure (called a single stage regulator).

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OHG X-450 mixer showing air valve open to full load position

Mixer

The mixer is the device that mixes the fuel into the air flowing to the engine. The mixer incorporates a venturi designed to draw the fuel into the airflow due to the movement of the air.

Mixer type systems have existed since the 1940s and some designs have changed little over that time. Mixers are now being increasingly superseded by injectors.

Vapour phase injectors

Most vapour phase injection systems mount the solenoids in a manifold block or injector rail, then run hoses to the nozzles, which are screwed into holes drilled and tapped into the runners of the intake manifold. There is usually one nozzle for each cylinder. Some vapour injection systems resemble petrol injection, having separate injectors that fit into the manifold or head in the same manner as petrol injectors, and are fed fuel through a fuel rail.

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Vapour phase injectors

Liquid phase injectors

Liquid phase injectors are mounted onto the engine in a manner similar to petrol injectors, being mounted directly at the inlet manifold and fed liquid fuel from a fuel rail.

Electrical and electronic controls

There are four distinct electrical systems that may be used in autogas systems - fuel gauge sender, fuel shut-off, closed loop feedback mixture control and injection control.

In some installations, the fuel gauge sender fitted to the autogas tank is matched to the original fuel gauge in the vehicle. In others, an additional gauge is added to display the level of fuel in the autogas tank separately from the existing petrol gauge.

In most modern installations, an electronic device called a tachometric relay or safety switch is used to operate electrical shut-off solenoids. These work by sensing that the engine is running by detecting ignition pulses. Some systems use an engine oil pressure sensor instead. In all installations, there is a filterlock (consisting of a filter assembly and a vacuum or electric solenoid operated shut-off valve) located at the input to the converter. In European converters, there is also a solenoid in the converter to shut off the idle circuit. These valves are usually both connected to the output of the tachometric relay or oil pressure switch. Where solenoids are fitted to the outputs of fuel tanks, these are also connected to the output of the tachometric relay or oil pressure switch. In installations with multiple tanks, a switch or changeover relay may be fitted to allow the driver to select which tank to use fuel from. On bi-fuel, the switch used to change between fuels is used to turn off the tachometric relay.

Closed loop feedback systems use an electronic controller that operates in much the same way as in a petrol fuel injection systems, using an oxygen sensor to effectively measure the air/fuel mixture by measuring the oxygen content of the exhaust and control valve on the converter or in the vapour line to adjust the mixture. Mixer type systems that do not have a closed loop feedback fitted are sometimes referred to as open loop systems.

Injection systems use a computerised control system which is very similar to that used in petrol injection systems. In virtually all systems, the injection control system integrates the tachometric relay and closed loop feedback functions.

Optional valve protection

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INTEC electronic valve protection system

Many LPG equipment installers recommend the installation of so-called valve protection systems. These can consist in the most simple case of a bottle containing valve protection liquid. The liquid is drawn into the air intake system and distributed into the engines' cylinders along with the fuel and air.

More sophisticated systems can consist of a piggyback ECU that is synchronised with the LPG injector ECU. This results in a more precise injection of valve protection fluid.^{[citation needed]}

Converter-and-mixer system operation

The designs of converters and mixers are matched to each other by matching sizes and shapes of components within the two.

In most areas of the world the word "converter" is not commonly used. The LPG REGULATOR - REDUCER - or VAPORIZER are more popular.

Because it has 3 main functions:

1- REDUCER : It reduces the high pressure of incoming liquid phase LPG down to atmospheric pressure.

2- REGULATOR : It regulates the gas flow according to the requirement of the engine.

3- VAPORIZER : It vaporizes the liquid form LPG into gas form by using the hot coolant circulation of the engine.

In European style systems, the size and shape of the venturi is designed to match the converter. In American style systems, the air valve and metering pins in the mixer are sized to match the diaphragm size and spring stiffness in the converter. In both cases, the components are matched by the manufacturers and only basic adjustments are needed during installation and tuning.

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Autogas carburettor consisting of OHG X-450 mixer, adapter and Rochester throttlebody

An autogas carburettor may simply consist of a throttlebody and a mixer, sometimes fitted together using an adapter.

Cold start enrichment is achieved by the fact that the engine coolant is cold when the engine is cold. This causes denser vapour to be delivered to the mixer. As the engine warms up, the coolant temperature rises until the engine is at operating temperature and the mixture has leaned off to the normal running mixture. Depending on the system, the throttle may need to be held open further when the engine is cold in the same manner as with a petrol carburettor. On others, the normal mixture is intended to be somewhat lean and no cold-start throttle increase is needed. Because of the way enrichment is achieved, no additional choke butterfly is required for cold starting with LPG.

The temperature of the engine is critical to the tuning of an autogas system. The engine thermostat effectively controls the temperature of the converter, thus directly affecting the mixture. A faulty thermostat, or a thermostat of the wrong temperature range for the design of the system may not operate correctly.

The power output capacity of a system is limited by the ability of the converter to deliver a stable flow of vapour. A coolant temperature lower than intended will reduce the maximum power output possible, as will an air bubble trapped in the cooling circuit or complete loss of coolant. All converters have a limit, beyond which mixtures become unstable. Unstable mixtures typically contain tiny droplets of liquid fuel that were not heated enough in the converter and will vaporise in the mixer or intake to form an excessively rich mixture. When this occurs, the mixture will become so rich that the engine will flood and stall. Because the outside of the converter will be at or below 0°C when this happens, water vapour from the air will freeze onto the outside of the converter, forming an icy white layer. Some converters are very susceptible to cracking when this happens.

LPG injection for diesel vehicles

LPG may be used for a supplemental fuel for diesels of all sizes. A gallon of diesel contains 128,700 BTU per US gallon, where propane contains 91,690 BTU per US gallon. If LPG is 30-40% less expensive, there may very well be a saving. Any actual savings are dependent on the relative cost of diesel versus LPG. In Australia, where diesel costs substantially more than LPG, savings of 10 to 20% are claimed.

The above systems add small quantities of LPG with the primary aim of improving economy, but much larger quantities of LPG can be injected in order to increase power. Even at full output a diesel engine runs about 50% lean of stoichiometric to avoid black smoke production, so there is a substantial amount of oxygen in the intake charge which is not consumed in the combustion process. This oxygen is therefore available for the combustion of a substantial addition of LPG resulting in a large increase in power output.

See also

• Hybrid vehicle
• Fuel injection
• Gas engine

External links

• European LPG Association
• World LP Gas Association
• LPG Information

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