Petrol-paraffin engine
Encyclopedia
A petrol-paraffin engine (aka gasoline-kerosene engine in North America
) is an old-fashioned type of dual-fuel internal combustion engine
with spark-ignition, designed to start on petrol (gasoline
) and then to switch to run on paraffin (kerosene) once the engine is warm.
The advantages of the petrol-paraffin engine are that (compared to petrol):(i) paraffin can be cheaper and/or more readily available ; (ii) being less flammable, paraffin is safer to store; (iii) being less volatile, paraffin is less likely to go "stale" in the tank. Some of these advantages have become illusory since paraffin, once widely available as a cheap fuel, has become rarer and more expensive, particularly in developed countries. Also, while some older vessels still use marine petrol-paraffin engines, most inboard marine engines now tend to be diesels.
A petrol-paraffin engine differs from a single-fuel petrol engine
in that two independent fuel tanks containing petrol and paraffin (respectively) are required, but both fuels may be supplied through the same carburreter(s) or fuel-injection system. Paraffin is less volatile than petrol, and will not normally ignite at ambient temperatures, so the petrol-paraffin engine is started using petrol, and only when the engine has attained a sufficient operating temperature will the engine be switched to paraffin. This switching can be done manually or automatically. The engine may have a provision to warm the paraffin in the fuel tank, using a heat exchanger.
Petrol-paraffin engines are traditionally found in motor boats, small tractors, light railway
locomotive
s, and stationary auxiliary engines
, but not in cars or motorcycles.
Most light aircraft
have piston engines that burn Mogas or Avgas
. In Europe, Avgas is very expensive and is being phased out. Mogas often has an alcohol content that can cause airlocks in fuel lines; and the Civil Aviation Authority
has prohibited Mogas containing alcohol. Jet fuel
, which has similarities to both paraffin and road diesel (DERV), is much cheaper and more widely available than Avgas; and opportunities now arise to develop light aero-engines that can burn jet-fuel.
One approach is to develop aircraft diesel engine
s, as exemplified by the Wilksch Airmotive WAM, the "Diesel-AIr" and the Thielert
Centurions. Alternatively, one may create a petrol-paraffin aero-engine which starts on petrol before switching to jet fuel. A UK firm tried running their MidWest AE series
wankel engine
on jet fuel; but tests were never completed. As Avgas becomes unobtainable, it may prove cost-effective to convert existing gasoline piston aero-engines into petrol-paraffin units.
piston engines and wankel engine
s. A petrol/paraffin engine tends to run hotter whilst burning paraffin, and so the cooling system must be sufficiently robust. Being slower burning, the paraffin requires the combustion longer period that a four-stroke engine engine can provide. Although modern petrol engines may have compression ratios typically between 9:1 and 12:1, a petrol-paraffin engine requires a lower compression ratio
of 8:1 or less, to avoid pre-ignition of the fuel-air mixture which would cause damage from engine knocking
. Most existing petrol aero-engines have low compression ratios, around 8:1 or 9:1, making a dual-fuel conversions viable.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
) is an old-fashioned type of dual-fuel internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
with spark-ignition, designed to start on petrol (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...
) and then to switch to run on paraffin (kerosene) once the engine is warm.
The advantages of the petrol-paraffin engine are that (compared to petrol):(i) paraffin can be cheaper and/or more readily available ; (ii) being less flammable, paraffin is safer to store; (iii) being less volatile, paraffin is less likely to go "stale" in the tank. Some of these advantages have become illusory since paraffin, once widely available as a cheap fuel, has become rarer and more expensive, particularly in developed countries. Also, while some older vessels still use marine petrol-paraffin engines, most inboard marine engines now tend to be diesels.
A petrol-paraffin engine differs from a single-fuel petrol engine
Petrol engine
A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....
in that two independent fuel tanks containing petrol and paraffin (respectively) are required, but both fuels may be supplied through the same carburreter(s) or fuel-injection system. Paraffin is less volatile than petrol, and will not normally ignite at ambient temperatures, so the petrol-paraffin engine is started using petrol, and only when the engine has attained a sufficient operating temperature will the engine be switched to paraffin. This switching can be done manually or automatically. The engine may have a provision to warm the paraffin in the fuel tank, using a heat exchanger.
Applications
- Traditional Applications
Petrol-paraffin engines are traditionally found in motor boats, small tractors, light railway
Light railway
Light railway refers to a railway built at lower costs and to lower standards than typical "heavy rail". This usually means the railway uses lighter weight track, and is more steeply graded and tightly curved to avoid civil engineering costs...
locomotive
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
s, and stationary auxiliary engines
Stationary engine
A stationary engine is an engine whose framework does not move. It is normally used not to propel a vehicle but to drive a piece of immobile equipment such as a pump or power tool. They may be powered by steam; or oil-burning or internal combustion engines....
, but not in cars or motorcycles.
- Future Applications
Most light aircraft
Light aircraft
A light aircraft is an aircraft that has a maximum gross take-off weight of or less.Many aircraft used commercially for freight, sightseeing, photography and scheduled flights are light aircraft.Examples of light aircraft include:...
have piston engines that burn Mogas or Avgas
Avgas
Avgas is an aviation fuel used to power piston-engine aircraft. Avgas is distinguished from mogas , which is the everyday gasoline used in cars and some non-commercial light aircraft...
. In Europe, Avgas is very expensive and is being phased out. Mogas often has an alcohol content that can cause airlocks in fuel lines; and the Civil Aviation Authority
Civil Aviation Authority
This is a list of national and supra-national civil aviation authorities.-See also:* Air route authority between the United States and the People's Republic of China* National Transportation Safety Board -External links:****...
has prohibited Mogas containing alcohol. Jet fuel
Jet fuel
Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...
, which has similarities to both paraffin and road diesel (DERV), is much cheaper and more widely available than Avgas; and opportunities now arise to develop light aero-engines that can burn jet-fuel.
One approach is to develop aircraft diesel engine
Aircraft diesel engine
The aircraft diesel engine or aero diesel has not been widely used as an aircraft engine. Diesel engines were used in airships and were tried in aircraft in the late 1920s and 1930s, but never "caught on" in a major fashion...
s, as exemplified by the Wilksch Airmotive WAM, the "Diesel-AIr" and the Thielert
Thielert
Thielert AG is a German financial holding company which has owned engine development and manufacturing companies. It is headquartered in Hamburg. Companies owned were Thielert Aircraft Engines GmbH with sites in Lichtenstein, Saxony and Altenburg, Thuringia and Superior Air Parts, Inc. in Dallas,...
Centurions. Alternatively, one may create a petrol-paraffin aero-engine which starts on petrol before switching to jet fuel. A UK firm tried running their MidWest AE series
MidWest AE series
| -See also:-External links:*...
wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...
on jet fuel; but tests were never completed. As Avgas becomes unobtainable, it may prove cost-effective to convert existing gasoline piston aero-engines into petrol-paraffin units.
Design
Petrol-paraffin fuelling is suitable for four-stroke cycleFour-stroke cycle
A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.There are two...
piston engines and wankel engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...
s. A petrol/paraffin engine tends to run hotter whilst burning paraffin, and so the cooling system must be sufficiently robust. Being slower burning, the paraffin requires the combustion longer period that a four-stroke engine engine can provide. Although modern petrol engines may have compression ratios typically between 9:1 and 12:1, a petrol-paraffin engine requires a lower 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 8:1 or less, to avoid pre-ignition of the fuel-air mixture which would cause damage from engine knocking
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
. Most existing petrol aero-engines have low compression ratios, around 8:1 or 9:1, making a dual-fuel conversions viable.