Bivalent (engine) - AbsoluteAstronomy.com

A bivalent engine is one that can use two fuel types. Examples are petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

/CNG

Compressed natural gas

Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...

or petroleum/LPG which are widely offered in the European passenger vehicle aftermarket. Bivalent engines can also use hydrogen

Hydrogen vehicle

A hydrogen vehicle is a vehicle that uses hydrogen as its onboard fuel for motive power. Hydrogen vehicles include hydrogen fueled space rockets, as well as automobiles and other transportation vehicles...

as demonstrated by the recently introduced BMW

BMW

Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...

'Clean Energy' H7 Series, featuring a V12 bivalent engine and BMW Hydrogen 7

BMW Hydrogen 7

The BMW Hydrogen 7 is a limited production hydrogen vehicle built by German automobile manufacturer BMW. The car is based on BMW’s traditional gasoline powered 7-series line of vehicles, and more specifically the 760Li...

which is more fuel efficient than the standard H7 Series engine.

Petroleum/Hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

is now being researched as a fuel for vehicles because of its ability to be regenerated. The burning of hydrogen fuel also produces no carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

emissions which makes it environmentally friendly. BMW has been the leader in consistent research to develop cars that use hydrogen. Once hydrogen fuel becomes more popular it will be a lot less expensive than other fuels. 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

Liquid hydrogen

Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

fuels. Liquid hydrogen has almost three times as much energy as gasoline in terms of density per unit volume. The liquid hydrogen can be produced in many different ways but many of these methods produce carbon dioxide in the process. The most promising method of hydrogen production is through a process known as electrolysis

Electrolysis

In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

. There are two fuel tanks in the vehicle and it can run on either type of fuel if one is not available. Safety of the hydrogen storage tanks has been investigated in the event of an accident and various tests show that the storage tanks used do not present any problems. The engine itself is similar to a regular gasoline combustion engine with an exception to the fuel injection

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

system. As seen in BMW's Hydrogen 7, when the vehicle is running in gasoline mode the fuel is injected directly into the cylinders, and when the vehicle is running on hydrogen the fuel is injected into the intake manifold. Hydrogen when used as a fuel has a wide range of flammability, and has a low ignition energy. These properties allow hydrogen to be combusted over a wide range of air-fuel mixtures but problems arise with premature ignition. Crankcase ventilation is also very important in burning hydrogen because of the low ignition energy. Proper ventilation should be ensured to prevent ignition in the crankcase

Crankcase

In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

and water forming in the engine oil. Hydrogen and natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

are very similar as fuels, so the differences between parts needed to burn both fuels are trivial, and interoperable systems are easily made.

There are some disadvantages of using liquid hydrogen fuel, most of which have been dealt with decades ago by the LNG vehicle industry. The technology is very new and the infrastructure for liquid hydrogen filling stations is currently very limited. Also, many of the methods commonly used in creating the fuel give off greenhouse gases during the process and the hydrogen typically produced is derived from finite resources. One major problem with these vehicles is in the storage of the liquid hydrogen. 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 the liquid hydrogen warms, it evaporates and the pressure in the fuel tank increases and some of the gas must be released. There are release valves installed on these vehicles so the pressure in the tank does not get too high but a small amount of the fuel is lost in this process.

Compressed/Liquefied Natural Gas (CNG/LNG)/Petroleum

CNG is made by compressing methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

which is extracted from natural gas and stored at high pressures, LNG

Liquefied natural gas

Liquefied natural gas or LNG is natural gas that has been converted temporarily to liquid form for ease of storage or transport....

is made and stored cryogenically, much like liquid hydrogen. The physical properties of natural gas require the compression ratio

Compression ratio

The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...

of the engine to be higher than in normal internal combustion engines, which also makes them more efficient. Natural gas has also got a higher octane rating

Octane rating

Octane rating or octane number is a standard measure of the anti-knock properties of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating...

which allows the fuel to be burned at a higher temperature therefore reducing engine knock. Another advantage of these engines is they produce nearly no carbon dioxide emissions and the fuel can be produced without complicated refinement processes. Since little carbon is produced in the combustion of natural gas, the vehicles engine and oil are kept much cleaner than if just gasoline

Gasoline

Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

was being burned which then increases the engine's life. There are aftermarket conversion kits available for converting vehicles to run on LNG or CNG and gasoline. The cost of natural gas in the United States is cheaper than gasoline but CNG at typical pressures requires more frequent refueling because it contains only a quarter of energy per unit volume when compared to gasoline, while LNG contains only 80%. Although natural gas is a finite resource like petroleum and its reserves can be depleted, natural gas is unique among current fuels in having a net positive EROEI

EROEI

In physics, energy economics and ecological energetics, energy returned on energy invested ; or energy return on investment , is the ratio of the amount of usable energy acquired from a particular energy resource to the amount of energy expended to obtain that energy resource...

, while other fuels such as petroleum are net negative energy sinks.

Liquefied Petroleum Gas (LPG)/Petroleum

LPG is a mixture of several hydrocarbons (mainly propane

Propane

Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

, butane

Butane

Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

and ethane

Ethane

Ethane is a chemical compound with chemical formula C2H6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....

). The gas mixes readily with air which allows for more complete combustion. The fuel costs less than regular gasoline but LPG has lower energy per unit volume which results in lower fuel economy and also is not that fuel efficient. The use of LPG provides a longer engine life due to its clean burning characteristics. The main difference between these vehicles and others is the fuel storage system. LPG is a gas at room temperature but is a liquid when it is pressurized (levels vary depending on composition of mixture) and is usually stored at around 10 bar

Bar (unit)

The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

. One drawback is that these fuel tanks are much heavier than conventional ones, and two tanks would be needed which would increase the vehicle's weight. There are many automobile manufactures that make vehicles that run on LPG and gasoline. Some say that LPG is the least environmentally friendly alternative fuel

Alternative fuel

Alternative fuels, known as non-conventional or advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels...

because it is derived from fossil fuels and one way or another greenhouse gases will be released into the atmosphere.

Future

Reduction of greenhouse gas emissions and preservation of natural resources is becoming more and more important to people around the world due to. Many countries have regulations and restrictions as to the fuel economy of newly manufactured vehicles and many governments offer incentives in the form of tax breaks for vehicle manufactures that use clean burning fuel technologies. All of these issues give vehicle manufacturers motivation for the development of new technologies in internal combustion engines. The bivalent engine allows for an easier transition from fossil fuels to alternative fuels. The future of these engines looks to be promising because of the advancing technology and higher demand for more efficient and cleaner burning engines.

External links

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Petroleum/Hydrogen

Compressed/Liquefied Natural Gas (CNG/LNG)/Petroleum

Liquefied Petroleum Gas (LPG)/Petroleum

Future

See also

External links