Liquefied Petroleum Gas (LPG) - Autogas
Liquefied petroleum gas (also called LPG, LP Gas, or autogas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to the ozone layer. Autogas is the common name for liquified petroleum gas when it is used as a fuel in internal combustion engines in vehicles. The same equipment is also used for similar engines in stationary applications such as generators (see below). Varieties of LPG bought and sold include mixes that are primarily propane, mixes that are primarily butane, and the more common, mixes including both propane (60%) and butane (40%), depending on the season—in winter more propane, in summer more butane. Propylene and butylenes are usually also present in small concentration. A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. LPG is manufactured during the refining of crude oil, or extracted from oil or gas streams as they emerge from the ground. At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is supplied in pressurised steel bottles. In order to allow for thermal expansion of the contained liquid, these bottles are not filled completely; typically, they are filled to between 80% and 85% of their capacity. The ratio between the volumes of the vaporised gas and the liquefied gas varies depending on composition, pressure and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapor pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) for pure propane at 55 °C (131 °F). LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with.
ProductionLPG is synthesised by refining petroleum or 'wet' natural gas; it was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. It currently provides about 3% of the energy consumed. Usage in vehiclesWhen LPG is used to fuel internal combustion engines, it is often referred to as autogas. In some countries, it has been used since the 1940s as an alternative fuel for spark ignition engines. More recently, it has also been used in diesel engines. Its advantage is that it is non-toxic, non-corrosive and free of tetra-ethyl lead or any additives. It burns more cleanly than petrol or diesel and is especially free of the particulates from the latter. There are two downsides. Firstly it has a lower energy density than either petrol or diesel, so the equivalent m.p.g. is worse, but since many governments impose less tax, it is still usually more cost effective. Secondly, some designs of internal combustion engine require the lubrication of petrol or diesel and LPG's lack thereof can shorten or damage valves. Propane (autogas) is also being used increasingly for vehicle fuels. In the U.S., 190,000 on-road vehicles use propane, and 450,000 forklifts use it for power. It is the third most popular vehicle fuel in America, behind gasoline and diesel. In other parts of the world, propane used in vehicles is known as autogas. About 9 million vehicles worldwide use autogas. The advantage of propane is its liquid state at room temperature and moderate pressure. This allows fast refill times, affordable fuel tank construction, and ranges comparable to (though still less than) gasoline. Meanwhile it is noticeably cleaner (both in handling, and in combustion), results in less engine wear (due to carbon deposits) without diluting engine oil (often extending oil-change intervals), and until recently was a relative bargain in North America. Octane rating is a noticeably higher 110, which could result in more power, though exploiting this extra "octane" requires significant engine modification. However, public filling stations are still rare. Many converted vehicles have provisions for topping off from "barbecue bottles." Purpose-built vehicles are often in commercially-owned fleets, and have private fueling facilities. Propane is generally stored and transported in steel cylinders as a liquid with a vapor space above the liquid. The vapor pressure in the cylinder is a function of temperature. When gaseous propane is drawn at a high rate the latent heat of vaporisation required to create the gas will cause the bottle to cool. (This is why water often condenses on the sides of the bottle and then freezes). In extreme cases this may cause such a large reduction in pressure that the process can no longer be supported. In addition, the lightweight, high-octane compounds vaporize before the heavier, low-octane ones. Thus the ignition properties change as the tank empties. For these reasons, the liquid is often withdrawn using a dip tube. Refrigeration and air conditioningIn highly purified form, various blends of the LPG constituents propane and iso-butane are used to make hydrocarbon refrigerants, which are increasingly being used in refrigeration and air conditioning systems including domestic refrigerators, building air conditioners and vehicle air conditioning. This is partly because of concerns about the greenhouse effect of the widely used HFC 134a. Hydrocarbons are more energy efficient, run at the same or lower pressure and are generally cheaper than HFC 134a. However, a major concern relating to the use of LPG hydrocarbons in HVAC systems is that the hydrofluorocarbon HFC 134a does not present a significant flammability hazard according to the American organization ASHRAE's applicable Standard 34 and addenda. The flammability of LPG hydrocarbons restrict their use to specially designed systems where the risk of ignition is mitigated especially considering leaks and accidents. LPG as cooking fuel
According to the 2001 Census of India, 17.5% of Indian households or 33.6 million Indian households used LPG as cooking fuel in 2001.[1] 76.64% of such households were from urban India making up 48% of urban Indian households as compared to a usage of 5.7% only in rural Indian households. LPG is subsidised by the government. Increase in LPG prices has been a politically sensitive matter in India as it potentially affects the urban middle class voting pattern. LPG was once a popular cooking fuel in Hong Kong; however, the continued expansion of town gas to buildings has reduced LPG usage to less than 24% of residential units. LPG is the most common cooking fuel in Brazilian urban areas, being used in virtually all households. Poor families receive a government grant ("Vale Gás") used exclusively for the acquisition of LPG. LPG and SNGLPG has a higher calorific value (94 MJ/m³ equivalent to 26.1kWh/m³) than natural gas (methane) (38 MJ/m³ equivalent to 10.6kWh/m³), which means that LPG can not simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the LPG. The method for determining the mixing ratios is by calculating the Wobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable. LPG-based SNG is used in emergency backup systems for many public, industrial, and military installations, and many utilities use LPG peak shaving plants in times of high demand to make up shortages in natural gas supplied to their distributions systems. LPG-SNG installations are also used during initial gas system introductions, when the distribution infrastructure is in place before gas supplies can be connected. Developing markets in India and China (among others) use LPG-SNG systems to build up customer bases prior to expanding existing natural gas systems... Fire risk and mitigation
LPG containers that are subjected to fire of sufficient duration and intensity can undergo a boiling liquid expanding vapour explosion (BLEVE). Due to the destructive nature of LPG explosions, the substance is classified as a dangerous good.[2] This is typically a concern for large refineries and petrochemical plants that maintain very large containers. The remedy is to equip such containers with a measure to provide a fire-resistance rating. If the containers are cylindrical and horizontal, they are referred to as "cigars", whereas circular ones are "spheres". Large, spherical LPG containers may have up to a 15 cm steel wall thickness. Ordinarily, they are equipped with an approved pressure relief valve on the top, in the centre. One of the main dangers is that accidental spills of hydrocarbons may ignite and heat an LPG container, which increases its temperature and pressure, following the basic gas laws. The relief valve on the top is designed to vent off excess pressure in order to prevent the rupture of the tank itself. Given a fire of sufficient duration and intensity, the pressure being generated by the boiling and expanding gas can exceed the ability of the valve to vent the excess. When that occurs, an overexposed tank may rupture violently, launching pieces at high velocity, while the released products can ignite as well, potentially causing catastrophic damage to anything nearby, including other tanks. In the case of "cigars", a midway rupture may send two "rockets" going off each way, with plenty of fuel in each to propel each segment at high speed until the fuel is spent. Mitigation measures include separating LPG tanks from potential sources of fire. In the case of rail transport, for instance, LPG tanks can be staggered, so that other goods are put in between them. This is not always done, but it does represent a low-cost remedy to the problem. LPG rail cars are easy to spot from the relief valves on top, typically with railings all around. In the case of new LPG containers, one may simply bury them, only leaving valves and armatures exposed, for easy maintenance. Great care must be taken there though, as mechanical damage can occur to the primers, which can result in hazardous corrosion of the containers. For the buried container, only the exposed parts need to be treated with approved fireproofing materials, such as intumescent and or endothermic coatings, or even fireproofing plasters. The rest are amply protected by soil. Speciality removable covers exist for easy access to the dials and components that must be accessed for proper maintenance and operation of the equipment. LPG containers are subject to significant motion due to expansion, contraction, filling and emptying; even with very thick steel walls. This operational motion makes the burial option less attractive in the long run because it is difficult to detect mechanical damage to the outer waterproofing of the vessel through soil. A small stone scraping back and forth across the epoxy-painted hull can jeopardise the waterproofing and be the cause for corrosion. Whilst one may calculate and justify on paper the use of inorganic plasters to cover entire spheres, it can be difficult to keep plasters operable for extended periods of time. Major errors have also been made in the past in this field, as the presumption was that the steel substrate would be adequately protected from rusting through the use of alkaline plasters. The alkalinity in such plasters is due to the presence of cement stone. This alkalinity, however, does not typically have a permanent character, which means that waterproofing with high quality epoxy primers is very important. Also, exterior waterproofing of the plaster is required by some fireproofing plaster vendors, as reduced alkalinity in exposed plasters can have a deleterious effect on the cement stone, which binds the plaster in the first place. By contrast, the intumescent and endothermic coatings are usually epoxy based to begin with, meaning that corrosion of the substrate is no problem whatsoever. Fireproofing, not unlike all passive fire protection products, is subject to stringent Listing and approval use and compliance. The problem with this is though, that exterior structures of this nature are not subject to the building code or the fire code, meaning that one still sees the majority of LPG containers without any fireproofing at all, as there are often no local regulations, let alone any Authority Having Jurisdiction, apart from an insurance inspector, to force owners to use the proper mitigation methods. Insurance companies are also in a competitive quandary, where such items are concerned, as they compete not only on the basis of rates, but also on the strictness of the demands by their inspectors. LPG vessel fireproofing tests are varied. The only realistic exposure offered is done at the Braunschweig test facility of "BAM" Berlin. BAM's procedure is to expose a small LPG container to the hydrocarbon test curve and to quantify the results. North American methods are based on UL1709. While UL1709 uses the correct time/temperature curve for testing, it is limited to testing steel columns (not even beams), whereas BAM actually exposes a real LPG container that has been fireproofed. No matter the fireproofing method one uses, it is very important to pay close attention to listing and approval use and compliance and to be sure that the product one chooses has undergone product certification, whereby the original test included the environmental exposures that the product will be exposed to during operations. Particularly with organic products, such as the endothermic and intumescent ones, one must closely review the ageing criteria and be able to quantify how long the product is expected to be operable for. This is where UL1709 "shines". Anything that can withstand the full battery of environmental exposures prior to the actual fire test, is a very tough product indeed. The idea is to rule out conditions that may render the product inoperable before it is ever exposed to a fire. By using products that have received the appropriate environmental tests FIRST, and the fire expose afterwards, using the very same test sample with all the applicable exposures, one can then demonstrate due diligence, but not otherwise. Likewise, the DIBt ageing qualifications for intumescents have proven to be very reliable. With close attention to the bounding and coverage of ageing and environmental exposures, it is absolutely possible to buy a lot of time for firefighting measures to relieve the LPG containers of the energy exposure from accidental fires and thus reduce the likelihood of a BLEVE to the maximum possible extent. See also
ReferencesExternal links
Autogas is the common name for liquified petroleum gas when it is used as a fuel in internal combustion engines in vehicles. The same equipment is also used for similar engines in stationary applications such as generators. Autogas is widely used as a "green" fuel as it decreases exhaust emissions. In particular, it reduces CO2 emissions by around 20% compared to petrol. 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. In countries where petrol is called petrol (UK) rather than gasoline, it is common for autogas to be simply referred to as gas. This can be confusing for people from countries where petrol is called gasoline, as they often use the abbreviation gas to refer to petrol. In the United States, autogas is more commonly known under the name of its primary constituent, propane.
Vehicle manufacturers
Toyota made a number of LPG-only engines in their 1970s M, R, and Y engine families. mrak young is gay Currently, a number of automobile manufacturers—Citroën, Fiat, Ford, Hyundai, General Motors (including Daewoo, Holden, Opel/Vauxhall, Saab),Maruti Suzuki, Peugeot, Renault, Toyota and Volvo—have OEM bi-fuel (dual fuel) models that will run equally well on both LPG and petrol. Vialli 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. CountriesAutogas enjoys great popularity in numerous countries including Australia, Belgium, Bulgaria, Germany, Hong Kong, India, Italy, Korea, The Netherlands, Poland, Serbia and Turkey. It is also available at larger petrol stations in Czech Republic, France and United Kingdom in the larger urban areas. The former Soviet republic of Armenia may, however, be the world leader in autogas use. The Armenian transport ministry estimates as much as 20 to 30% of vehicles use autogas compared with traditional gasoline, once again due to the fact that 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 fuels has sharply raised the difference. AustraliaLPG is popular in Australia, in part due to it being less than half the price of petrol in urban areas. The four major local manufacturers (Ford, Holden, Mitsubishi and Toyota) offer factory fitted autogas in some models of their locally made large cars. All factory autogas vehicles are dual fuel vehicles, with the exception of the E-Gas Ford Falcon model, which runs on autogas only. 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 AU$2000 to convert their existing vehicle to autogas, or AU$1000 for purchasing a new vehicle that was manufactured to operate on autogas.[1] 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 AU$1000 subsidy under the long-running LPG subsidy scheme. System typesThe different autogas systems generally use the same type of filler, tanks, lines and fittings but use different components in the engine bay. Some 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. Vapour phase injection systems use a converter in much the same way as with a mixer, but have a series of electrical shutoff solenoids and nozzles (collectively referred to as injectors) that are controlled by a computer. The computer works in much the same way as a petrol fuel injection computer. 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 vapourises 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
FillerThe 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.[2] The three types are:
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. Hoses, pipes and fittings
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
Vehicles are often fitted with only one tank, but multiple tanks are used in a some applications. 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. 
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 shutoff 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 vapourise to re-establish equilibrium between liquid and vapour. The latent heat of vapourisation 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. ValvesThere are a number of types of valve used in autogas systems. The most common ones are shutoff or filterlock valves, which are used to stop flow in the service line. These may be operated by vacuum or electricity. On dual-fuel systems with a petrol carburettor, a similar shutoff 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 shutoff valve is built into the service valve. 
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. ConverterThe 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 setup is only used on smaller engines. This type of converter can either 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). 
MixerThe 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 injectorsMost 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. 
Liquid phase injectorsLiquid 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 controlsThe are four distinct electrical systems that may be used in autogas systems - fuel gauge sender, fuel shutoff, 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 shutoff 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 shutoff 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 dual-fuel systems, 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. Converter-and-mixer system operationThe designs of converters and mixers are matched to each other by matching sizes and shapes of components within the two. 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 sizes and spring stiffnesses in the converter. In both cases, the components are matched by the manufacturers and only basic adjustments are needed during installation and tuning. 
An autogas carburettor simply consists 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 carburetor. 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 vapourise 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 zero degrees Celsius 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 suceptible to cracking when this happens. LPG injection for diesel vehiclesThe performance, economy and emission profile of diesel engines can be improved by injecting a small quantity of LPG into the inlet manifold. It is claimed that the LPG increases the burning efficiency of the diesel fuel from typically 75-85%, to 95-98%.[3] The systems typically operate by metering a small quantity of LPG, at a pressure slightly above atmospheric, into the intake manifold, where it enters the combustion chamber and is ignited with the diesel. LPG flow is regulated to ensure smooth operation, and will typically only deliver LPG under power. Some companies claim a 10% to 20% increase in power and torque,[4][3] and a reduction in overall fuel costs. 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. [5] See alsoReferencesExternal links
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Liquefied Petroleum Gas" |
