Four Brazilian full flex-fuel automoviles 05 2008

Multifuel, sometimes spelled multi-fuel, is any type of

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centra ...

, or

heater Heating, ventilation, and air conditioning (HVAC ) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...

or other fuel-burning device which is designed to burn multiple types of

fuels 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 ...

in its operation. One common application of multifuel technology is in military settings, where the normally-used diesel or gas turbine fuel might not be available during combat operations for vehicles or heating units. Multifuel engines and boilers have a long history, but the growing need to establish fuel sources other than

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

for

transportation Transport (in British English) or transportation (in American English) is the intentional Motion, movement of humans, animals, and cargo, goods from one location to another. Mode of transport, Modes of transport include aviation, air, land tr ...

heating In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, atom ...

, and other uses has led to increased development of multifuel technology for non-military use as well, leading to many

flexible-fuel vehicle A flexible-fuel vehicle (FFV) or dual-fuel vehicle (colloquially called a flex-fuel vehicle) is an alternative fuel vehicle with an internal combustion engine designed to run on more than one fuel, usually gasoline blended with either ethanol f ...

designs in recent decades. A multifuel engine is constructed so that its

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

permits firing the lowest

octane Octane is a hydrocarbon and also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...

fuel of the various accepted alternative fuels. A strengthening of the engine is necessary in order to meet these higher demands. Multifuel engines sometimes have switch settings that are set manually to take different octanes, or types, of fuel.Dunstan, S., ''Chieftain Main Battle Tank 1965–2003'', p. 8.

Types

Multifuel systems can be classified by the fuel-burning appliance it is based on. For

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

s there are: * Multifuel

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s. * Multifuel

gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...

s. * Flexible-fuel

petrol engine A petrol engine (gasoline engine in American and Canadian English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends ...

s. Limited to fuels that can be spark-ignited. For heaters, see

multi-fuel stove A multi-fuel stove is similar to a wood-burning stove in appearance and design. Multifuel refers to the capability of the stove to burn wood and also coal, wood pellets, or peat. Stoves that have a grate for the fire to burn on and a removable ash ...

Military multifuel engines

One common use of this technology is in

military vehicles A military vehicle is any vehicle for land-based military transport and activity, including combat vehicles, both specifically designed for or significantly used by military. Most military vehicles require off-road capabilities and/or vehicle a ...

, so that they may run a wide range of alternative fuels such as gasoline or jet fuel. This is seen as desirable in a military setting as enemy action or unit isolation may limit the available fuel supply, and conversely enemy fuel sources, or civilian sources, may become available for usage. One large use of a military multifuel engine was the LD series used in the US M35 -ton and M54 5-ton trucks built between 1963 and 1970. A military standard design using M.A.N. technology, it was able to use different fuels without preparation. Its primary fuel was

Diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engine ...

#1, #2, or AP, but 70% to 90% of other fuels could be mixed with diesel, depending on how smooth the engine would run. Low octane

commercial Commercial may refer to: * (adjective for) commerce, a system of voluntary exchange of products and services ** (adjective for) trade, the trading of something of economic value such as goods, services, information or money * a dose of advertising ...

and

aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' include fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air aircraft such as h ...

gasoline could be used if engine oil was added,

jet fuel Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by Gas turbine, gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for ...

Jet A, B, JP-4, 5, 7, and 8 could be used, as well as

fuel oil Fuel oil is any of various fractions obtained from the distillation of petroleum (crude oil). Such oils include distillates (the lighter fractions) and residues (the heavier fractions). Fuel oils include heavy fuel oil (bunker fuel), marine f ...

#1 and #2. In practice, they only used diesel fuel, their tactical advantage was never needed, and in time they were replaced with commercial diesel engines. Another use of multifuel engines is the American

M1 Abrams The M1 Abrams () is a third-generation American main battle tank designed by Chrysler Defense (now General Dynamics Land Systems) and named for General Creighton Abrams. Conceived for modern armored ground warfare, it is one of the heavies ...

Main battle tank A main battle tank (MBT), also known as a battle tank or universal tank or simply tank,Ogorkiewicz 2018 p222 is a tank that fills the role of armour-protected direct fire and maneuver in many modern armies. Cold War-era development of more po ...

, which uses a multifuel gas turbine engine. Currently, a wide range of Russian military vehicles employ multifuel engines, such as the

T-72 The T-72 is a family of Soviet Union, Soviet main battle tanks that entered production in 1973. The T-72 was a development based on the T-64 using thought and design of the previous Object 167M. About 25,000 T-72 tanks have been built, and refu ...

tank (multifuel diesel) and the

T-80 The T-80 is a main battle tank (MBT) that was designed and manufactured in the former Soviet Union and manufactured in Russia. The T-80 is based on the T-64, while incorporating features from the later T-72 and changing the engine to a gas turbi ...

(multifuel gas turbine).

Non-military usage

Many other types of engines and other heat-generating machinery are designed to burn more than one type of fuel. For instance, some heaters and boilers designed for home use can burn wood, pellets, and other fuel sources. These offer fuel flexibility and security, but are more expensive than are standard single fuel engines. Portable stoves are sometimes designed with multifuel functionality, in order to burn whatever fuel is found during an outing. Innovative industrial heaters or burners were the subject of multi-fuel research at a Shell plant in 2014. The movement to establish alternatives to automobiles running solely on

gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...

has greatly increased the number of automobiles available which use multifuel engines, such vehicles generally being termed a

bi-fuel vehicle 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 gasolin ...

Underperformance issues

Multifuel engines are not necessarily underpowered, but in practice some engines have had issues with power due to design compromises necessary to burn multiple types of fuel in the same engine. Perhaps the most notorious example from a military perspective is the L60 engine used by the British Chieftain Main Battle Tank, which resulted in a very sluggish performance – in fact, the Mark I Chieftain (used only for training and similar activities) was so underpowered that some were incapable of mounting a

tank transporter A tank transporter is a combination of a heavy tractor unit or a ballast tractor and a mating Trailer (vehicle)#Full trailer, full trailer, hydraulic modular trailer or semi-trailer (typically of the Lowboy (trailer), "lowboy" type), used for t ...

. An equally serious issue was that changing from one fuel to another often required hours of preparation. The US LD series had a power output comparable to commercial diesels of the time. It was underpowered for the 5-ton trucks, but that was due the engine size itself; the replacement diesel was much larger and more powerful. The LD engines did burn diesel fuel poorly and were very smokey. The final LDT-465 model received a turbocharger largely to clean up the exhaust, there was little power increase.Doyle (2003), pp. 128.

Footnotes

References