 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(August 2012) |
A bivalent engine is an engine that can use two different types of fuel. Examples are petroleum/CNG and petroleum/LPG engines, which are widely available in the European passenger vehicle aftermarket.[ citation needed ]
Engines that can use either alcohol (often produced as a biofuel) or standard gasoline are variants of flex fuel vehicles. Such vehicles are in production and commonly available for sale in the United States and other countries.
Compressed natural gas (CNG) is made by compressing methane to store it at high pressures. Liquefied natural gas (LNG) is made and stored cryogenically, much like liquid hydrogen. The physical properties of natural gas require the compression ratio of the engine to be higher than in normal internal combustion engines, and the higher compression makes for greater efficiency. Natural gas also has a higher octane rating, so it can be burned at a higher temperature, reducing engine knock, and the fuel can be produced without complicated refinement processes. Since little unburned carbon is produced in the combustion of natural gas, the engine and oil are kept much cleaner than would be the case if gasoline alone was being burned, and the engine's life is thus increased. Aftermarket kits are available to convert vehicles to run on LNG or CNG and gasoline. In the United States, natural gas is cheaper than gasoline. Still, CNG at typical pressures requires more frequent refueling because it contains only a quarter of the energy per unit volume of gasoline, [1] whereas LNG contains only 80%. Although natural gas is a finite resource and its reserves can be depleted, it is unique among current fuels in having a net positive EROEI (energy returned on energy invested), while petroleum and other fuels are net energy sinks.[ citation needed ]
Liquefied petroleum gas (LPG) is a mixture of several hydrocarbons, mainly propane, butane, and ethane. The gas mixes readily with air, allowing for more complete combustion. The fuel costs less than regular gasoline, but LPG has lower energy per unit volume, so its fuel economy and efficiency are lower. LPG gives a longer engine life due to its clean-burning characteristics. The main difference between these vehicles and others is in their fuel storage systems. LPG is a gas at room temperature, but a liquid when pressurized (the required pressure varies according to the composition of the mixture). It is usually stored at around 10 bar. One drawback is that LPG fuel tanks are much heavier than conventional ones, hence two tanks would be needed, which would increase the vehicle's weight. Many automobile manufacturers make vehicles that run on LPG and gasoline. [2] Some[ who? ] say that LPG is the least environmentally friendly alternative fuel because it is derived from fossil fuels so that greenhouse gases will inevitably be released into the atmosphere. [3]
Bivalent engines can also use hydrogen fuel, as demonstrated by the BMW Hydrogen 7 using a bivalent V12 H7 Series engine. The engine itself is similar to a regular gasoline combustion engine, except for the fuel injection system. When a BMW Hydrogen 7 is running in gasoline mode, the fuel is injected directly into the cylinders, but when the vehicle is running on hydrogen, the fuel is injected into the intake manifold. BMW claims the Hydrogen 7 is the "world's first production-ready hydrogen vehicle", although only 100 total vehicles have been produced, and no more are planned to be produced. [4]
Reduction of greenhouse gas emissions and preservation of natural resources are becoming increasingly important to people worldwide. Many countries have regulations on the fuel economy of newly manufactured vehicles, and many governments offer tax breaks for vehicle manufacturers that use clean-burning fuels. Vehicle manufacturers are thus motivated to develop new internal combustion engine technologies. The bivalent engine allows for an easier transition from fossil fuels to alternative fuels. The technology is advancing and there is increasing demand for more efficient and cleaner burning engines.
Hydrogen is being researched as a fuel for vehicles because it produces no carbon dioxide emissions. If hydrogen fuel becomes more popular, it has the potential to be less expensive than other fuels, if low-cost production via electrolysis can be implemented.[ citation needed ] Hydrogen can be used and created in fuel cells to power electric motors or burnt directly in combustion engines. BMW has developed a bivalent internal combustion engine that can switch between petroleum and liquid hydrogen fuels. In gaseous form, hydrogen is difficult to store and has a low volumetric energy density. It can be produced in many different ways, but many of the methods produce carbon dioxide. The most promising method is electrolysis. The safety of the hydrogen storage tanks in the event of an accident has been investigated, and various tests show that they do not present any problems. [5] When used as a fuel, hydrogen has a wide range of flammability and low ignition energy. These properties allow hydrogen to be burned using a wide range of air-fuel mixtures, but problems arise with premature ignition. Crankcase ventilation is very important when burning hydrogen, because of the low ignition energy. Proper ventilation is needed to prevent ignition in the crankcase and the formation of water in the engine oil. [6] Hydrogen and natural gas are very similar fuels, so the differences between the components needed to burn them are trivial, and interoperable systems are easily made.
The volumetric energy density can be increased if hydrogen is stored as a cryogenic liquid. Liquid hydrogen provides almost a third as much energy per unit volume as gasoline.
Liquid hydrogen fuel has some disadvantages. The technology is very new and the infrastructure for liquid hydrogen filling stations is currently very limited. Many of the processes commonly used in creating the fuel give off greenhouse gases, and the hydrogen produced is usually derived from finite resources. The storage of the liquid hydrogen is a major problem. Since the boiling point of liquid hydrogen is very low (-252.88 °C), it is difficult to keep the fuel cold enough to maintain its liquid form. When it warms, it evaporates. The pressure in the fuel tank then increases, and some gas must be released. Release valves are installed in these vehicles so that the pressure in the tank does not get too high, but a small amount of fuel is lost.
Natural gas is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane (95%) in addition to various smaller amounts of other higher alkanes. Traces of carbon dioxide, nitrogen, hydrogen sulfide, and helium are also usually present. Methane is colorless and odorless, and the second largest greenhouse gas contributor to global climate change after carbon dioxide. Because natural gas is odorless, odorizers such as mercaptan are commonly added to it for safety so that leaks can be readily detected.
Propane is a three-carbon alkane with the molecular formula C3H8. It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is often a constituent of liquefied petroleum gas (LPG), which is commonly used as a fuel in domestic and industrial applications and in low-emissions public transportation; other constituents of LPG may include propylene, butane, butylene, butadiene, and isobutylene. Discovered in 1857 by the French chemist Marcellin Berthelot, it became commercially available in the US by 1911. Propane has lower volumetric energy density than gasoline or coal, but has higher gravimetric energy density than them and burns more cleanly.
Liquid hydrogen (H2(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
Liquefied petroleum gas, also referred to as liquid petroleum gas, is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, n-butane and isobutane. It can sometimes contain some propylene, butylene, and isobutene.
Alternative fuels, also known as non-conventional and advanced fuels, are fuels derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; biofuels like biodiesel, bioalcohol, and refuse-derived fuel; and other renewable fuels like hydrogen and electricity.
Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable instead of the fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are several types, such as hydrogen fuel, ethanol, and biodiesel, which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.
Cryogenic fuels are fuels that require storage at extremely low temperatures in order to maintain them in a liquid state. These fuels are used in machinery that operates in space where ordinary fuel cannot be used, due to the very low temperatures often encountered in space, and the absence of an environment that supports combustion. Cryogenic fuels most often constitute liquefied gases such as liquid hydrogen.
Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volume of natural gas in the gaseous state at standard conditions for temperature and pressure.
Compressed natural gas (CNG) is a fuel gas mainly composed of methane (CH4), compressed to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 20–25 megapascals (2,900–3,600 psi; 200–250 atm), usually in cylindrical or spherical shapes.
A natural gas vehicle (NGV) utilizes compressed natural gas (CNG) or liquefied natural gas (LNG) as an alternative fuel source. Distinguished from autogas vehicles fueled by liquefied petroleum gas (LPG), NGVs rely on methane combustion, resulting in cleaner emissions due to the removal of contaminants from the natural gas source.
Autogas or LPG is liquefied petroleum gas (LPG) 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.
A fuel gas-powered scooter is a scooter powered by fuel gas. Fuel gases include such fuels such as liquefied petroleum gas (LPG), compressed natural gas (CNG), biogas and hydrogen (HICE). Hydrogen use in two-wheelers has only recently being started to be looked into, mainly by developing countries, to decrease local pollution at an affordable cost.
The BMW Hydrogen 7 is a limited production hydrogen internal combustion engine vehicle built from 2005–2007 by German automobile manufacturer BMW. The car is based on BMW’s traditional petrol-powered BMW 7 Series (E65) line of vehicles, and more specifically the 760Li. It uses the same 6-litre V-12 motor as does the 760i and 760Li; however, it has been modified to also allow for the combustion of hydrogen as well as petrol, making it a bivalent engine.
An alternative fuel vehicle is a motor vehicle that runs on alternative fuel rather than traditional petroleum-based fossil fuels such as gasoline, petrodiesel or liquefied petroleum gas (autogas). The term typically refers to internal combustion engine vehicles or fuel cell vehicles that utilize synthetic renewable fuels such as biofuels, hydrogen fuel or so-called "Electrofuel". The term can also be used to describe an electric vehicle, which should be more appropriately called an "alternative energy vehicle" or "new energy vehicle" as its propulsion actually rely on electricity rather than motor fuel.
Bi-fuel vehicles are vehicles with multifuel engines capable of running on two fuels. The two fuels are stored in separate tanks and the engine runs on one fuel at a time. On internal combustion engines, a bi-fuel engine typically burns gasoline and a volatile alternate fuel such as natural gas (CNG), LPG, or hydrogen. Bi-fuel vehicles switch between gasoline and the other fuel, manually or automatically. A related concept is the dual-fuel vehicle which must burn both fuels in combination. Diesel engines converted to use gaseous fuels fall into this class due to the different ignition system.
A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has since also been applied to other sources of heat energy, such as nuclear energy.
Compressed natural gas (CNG) carrier ships are those designed for transportation of natural gas under high pressure. CNG carrier technology relies on high pressure, typically over 250 bar (2900 psi), to increase the density of the gas, but it is still 2.4 times less than that of LNG (426 kg/m3). CNG carriers may find their place abreast with the well established technology of liquefied natural gas by LNG carriers as it is economical for medium distance marine transport. Most of the energy consumed for the gas pressurisation can be recovered as electricity using turboexpander while delivering CNG to the inland piping network at unloading jetty/harbour. CNG carriers are also alternate solutions to the undersea pipelines as they have less complicated fast loading and unloading features.
Westport Innovations is a company that develops alternative fuel, low-emissions technologies to allow engines to operate on clean-burning fuels such as compressed natural gas (CNG), liquefied natural gas (LNG), hydrogen and biofuels such as landfill gas. Headquartered in Vancouver, British Columbia, Canada, where the company was founded, Westport also has facilities in France, Sweden, Italy, China, Australia and the United States.
A gas carrier, gas tanker, LPG carrier, or LPG tanker is a ship designed to transport LPG, LNG, CNG, or liquefied chemical gases in bulk.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.