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 ...

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, centr ...

, 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 mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

for

transportation Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline, ...

heating A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning (short: HVAC) systems, which can both cool and warm interior spaces. ...

, 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 fu ...

designs in recent decades. A multifuel engine is constructed so that its compression ratio permits firing the lowest octane 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.

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 c ...

s there are: * Multifuel

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-ca ...

s. * Multifuel

gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

s. * Flexible-fuel

petrol engine A petrol engine (gasoline engine in American 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 (such as ' ...

s. Limited to fuels that can be spark-ignited.

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 and armed forces. Most military vehicles require off-road capabilit ...

, 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 multi-fuel 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 #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: * a dose of advertising conveyed through media (such as - for example - radio or television) ** Radio advertisement ** Television advertisement * (adjective for:) commerce, a system of voluntary exchange of products and s ...

and

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

gasoline could be used if engine oil was added, jet fuel Jet A, B, JP-4, 5, 7, and 8 could be used, as well as fuel oil #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

Main battle tank A main battle tank (MBT), also known as a battle tank or universal tank, is a tank that fills the role of armor-protected direct fire and maneuver in many modern armies. Cold War-era development of more powerful engines, better suspension sys ...

, 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/Russian main battle tanks that entered production in 1969. The T-72 was a development of the T-64, which was troubled by high costs and its reliance on immature developmental technology. About 25,000 T-72 tanks h ...

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. The chief designer of the T-80 was S ...

(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. The movement to establish alternatives to automobiles running solely on

gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...

has greatly increased the number of automobiles available which use multifuel engines, such vehicles generally being termed a bi-fuel vehicle or

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 and a mating full trailer or semi-trailer (typically of the "lowboy" type), used for transporting tanks and other armoured fighting vehicles. Some also function as tank recovery vehi ...

. An equally serious issue was that changing from one fuel to another often required hours of preparation.Dunstan, ''Chieftain'', p. 13 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