Fuel saving devices
Encyclopedia
Fuel saving devices are sold on the aftermarket
with claims to improve the fuel economy
and/or the exhaust emissions
of a vehicle. There are numerous different types of device; many purport to optimize ignition, air flow, or fuel flow in some way. An early example of such a device sold with difficult-to-justify claims is the 200 mpg carburetor
designed by Canadian inventor Charles Nelson Pogue
.
The US EPA
is required by Section 511 of the Motor Vehicle Information and Cost Savings Act to test many of these devices and to provide public reports on their efficacy; the agency finds most devices do not improve fuel economy to any measurable degree. Tests by Popular Mechanics
magazine also found these types of devices yield no measurable improvements in fuel consumption or power, and in some cases actually decrease both power and fuel economy.
Other organizations generally considered reputable, such as the American Automobile Association
and Consumer Reports
have performed studies with the same result.
One reason that ineffective fuel saving gadgets are popular is the difficulty of accurately measuring small changes in the fuel economy of a vehicle. This is because of the high level of variance in the fuel consumption of a vehicle under normal driving conditions. Due to selective perception
and confirmation bias
, the buyer of a device can perceive an improvement where none actually exists. For this reason, regulatory bodies have developed standardized drive cycles
for consistent, accurate testing of vehicle fuel consumption. Where fuel economy does improve after the fitment of a device, it is usually due to the tune-up procedure that is conducted as part of the installation. In older systems with distributor ignitions, device manufacturers would specify timing advance
beyond that recommended by the manufacturer, which by itself could boost fuel economy while potentially increasing emissions of some combustion products, at the risk of possible engine damage
.
modify the amount of engine power that can be drawn by accessory devices. Such alterations to the drive systems for alternator
s or air conditioning
compressors (rather than the power steering pump, for example) can be detrimental to vehicle usability, but will not impair safety.
sold for addition to the vehicle's fuel may include tin
, magnesium
and platinum
. The claimed purpose of these is generally to
improve the energy density
of the fuel. Additives for addition to the engine oil, sometimes marketed as "engine treatments", contain teflon, zinc
, or chlorine
compounds; none of these is appropriate or helpful when added to an engine's crankcase, and they can in fact damage the engine. The US Federal Trade Commission
has aggressively pursued marketers of oil additives falsely claimed to improve fuel economy.
, no such alignment or other magnetic effect on the fuel is possible. When tested, typical magnet devices had no effect on vehicle performance or economy.
. These include fuel heaters and devices to increase or decrease turbulence
in the intake manifold
. These do not work because the principle is already applied to the design of the engine, and because intake tract flow dynamics are highly specific to each engine design, no universal device could have any given effect on more than one kind of engine.
magazine found that the device contains nothing but "a simple circuit board for the LED lights", and disassembly and circuit analysis reaches the same conclusion. The maker disputed claims that the device has no effect, and proposed changes to the Consumer Reports testing procedure, which when implemented made no difference to the results.
Another device described as 'electronic' is the 'Electronic Engine Ionizer Fuel Saver'. Testing of this device resulted in a loss of power and an engine compartment fire.
There are also genuinely useful 'emissions-control defeat devices' that operate by allowing a vehicle's engine to operate outside government-imposed tailpipe emissions parameters. These government standards force factory engines to operate outside their most efficient range of operation. Either engine control units are reprogrammed to operate more efficiently, or sensors that influence the ECU's operation are modified or 'simulated' to cause it to operate in a more efficient manner. Oxygen sensor simulators allow fuel-economy reducing catalytic converter
s to be removed. Such devices are often sold for "off-road use only".
. This formula expresses the theoretical efficiency of an engine:
where h is efficiency, rv is the compression ratio
, and g is the ratio of the specific heats of the gases before and after combustion.
Assuming an ideal engine with no friction, perfect insulation, perfect combustion, a compression ratio of 10:1, and a g of 1.27 (for gasoline-air combustion), the theoretical efficiency of the engine would be 46%.
For example, if an automobile typically gets 20 miles per gallon with a 20% efficient engine that has a 10:1 compression ratio, a carburetor claiming 100MPG would have to increase the efficiency by a factor of 5, to 100%. This is clearly beyond what is theoretically or practically possible. A similar claim of 300MPG for any vehicle would require the engine (in this particular case) that is 300% efficient, which violates the Second Law of Thermodynamics
.
Extremely efficient vehicle designs capable of achieving 100MPG+ (such as the VW 1l
) do not have substantially greater engine efficiency, but instead focus on better aerodynamics
, reduced vehicle weight, and using energy that would otherwise be dissipated as heat during braking.
about an inventor who creates a 100 mpg (2.35 L/100 km) or even 200 mpg carburetor
, but after demonstrating it for the major vehicle manufacturers, the inventor mysteriously disappears. In some versions of the story, he is claimed to have been killed by the government. This fiction is thought to have started after Canadian Charles Nelson Pogue
filed in 1930 for such a device, followed by others.
investigated several fuel-saving devices using gasoline- and diesel-powered fuel-injected
cars under controlled circumstances. Fuel line magnets, which supposedly align the fuel molecules so they burn better, were tested and found to make no difference in fuel consumption. The debunked notion that adding acetone
to gasoline improves efficiency by making the gasoline burn more completely without damaging the plastic parts of the fuel system was tested, and although there was no apparent damage the fuel system, the vehicle's fuel economy was actually worsened.
The show tested the hypothesis that a diesel-powered car can run on hydrogen
gas alone, which was confirmed as viable, although the high cost of hydrogen gas currently prohibits widespread adoption. They also tested a device that supposedly produces sufficient hydrogen to power a car by hydrolysis
(running an electric current through water to split its molecules into hydrogen and oxygen). Although some hydrogen was produced, the amount was minuscule compared to the quantity necessary to run a car for even a few seconds.
The show also tested a carburetor
that, according to its manufacturer, could improve fuel efficiency to 300 miles per gallon. However, the device actually made the car less fuel efficient. They also determined that a diesel
-powered car can run on used cooking oil
though they did not check whether it damaged the engine.
The show noted that out of 104 fuel efficiency devices tested by the EPA, only seven showed any improvement in efficiency, and even then, the improvement was never more than six percent. The show also noted that if any of the devices they tested actually worked to the extent they were supposed to, the episode would have been one of the most legendary hours of television.
Aftermarket (automotive)
The automotive aftermarket is the secondary market of the automotive industry, concerned with the manufacturing, remanufacturing, distribution, retailing, and installation of all vehicle parts, chemicals, tools, equipment and accessories for light and heavy vehicles, after the sale of the...
with claims to improve the fuel economy
Fuel economy in automobiles
Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....
and/or the exhaust emissions
Automobile emissions control
Vehicle emissions control is the study and practice of reducing the motor vehicle emissions -- emissions produced by motor vehicles, especially internal combustion engines....
of a vehicle. There are numerous different types of device; many purport to optimize ignition, air flow, or fuel flow in some way. An early example of such a device sold with difficult-to-justify claims is the 200 mpg carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
designed by Canadian inventor Charles Nelson Pogue
Charles Nelson Pogue
Charles Nelson Pogue was a Canadian mechanic and inventor who in the 1930s filed a series of US patents for a miracle carburettor that would enable a car to attain 200 mpg, and described as a vapourising or sometimes a catalytic carburettor...
.
The US EPA
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
is required by Section 511 of the Motor Vehicle Information and Cost Savings Act to test many of these devices and to provide public reports on their efficacy; the agency finds most devices do not improve fuel economy to any measurable degree. Tests by Popular Mechanics
Popular Mechanics
Popular Mechanics is an American magazine first published January 11, 1902 by H. H. Windsor, and has been owned since 1958 by the Hearst Corporation...
magazine also found these types of devices yield no measurable improvements in fuel consumption or power, and in some cases actually decrease both power and fuel economy.
Other organizations generally considered reputable, such as the American Automobile Association
American Automobile Association
AAA , formerly known as the American Automobile Association, is a federation of 51 independently operated motor clubs throughout North America. AAA is a not-for-profit member service organization with more than 51 million members. AAA provides services to its members such as travel, automotive,...
and Consumer Reports
Consumer Reports
Consumer Reports is an American magazine published monthly by Consumers Union since 1936. It publishes reviews and comparisons of consumer products and services based on reporting and results from its in-house testing laboratory. It also publishes cleaning and general buying guides...
have performed studies with the same result.
One reason that ineffective fuel saving gadgets are popular is the difficulty of accurately measuring small changes in the fuel economy of a vehicle. This is because of the high level of variance in the fuel consumption of a vehicle under normal driving conditions. Due to selective perception
Selective perception
Selective perception may refer to any number of cognitive biases in psychology related to the way expectations affect perception.For instance, several studies have shown that students who were told they were consuming alcoholic beverages perceived themselves as being "drunk", exhibited fewer...
and confirmation bias
Confirmation bias
Confirmation bias is a tendency for people to favor information that confirms their preconceptions or hypotheses regardless of whether the information is true.David Perkins, a geneticist, coined the term "myside bias" referring to a preference for "my" side of an issue...
, the buyer of a device can perceive an improvement where none actually exists. For this reason, regulatory bodies have developed standardized drive cycles
Driving cycle
A driving cycle is a series of data points representing the speed of a vehicle versus time.Driving cycles are produced by different countries and organizations to assess the performance of vehicles in various ways, as for example fuel consumption and polluting emissions.Fuel consumption and...
for consistent, accurate testing of vehicle fuel consumption. Where fuel economy does improve after the fitment of a device, it is usually due to the tune-up procedure that is conducted as part of the installation. In older systems with distributor ignitions, device manufacturers would specify timing advance
Ignition timing
Ignition timing, in a spark ignition internal combustion engine , is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke...
beyond that recommended by the manufacturer, which by itself could boost fuel economy while potentially increasing emissions of some combustion products, at the risk of possible engine damage
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...
.
Accessory drive modifications
Modifying the accessory drive system can increase fuel economy and performance to some extent. Underdrive pulleysUnderdrive pulleys
An Underdrive pulley refers to an aftermarket crankshaft or accessory pulley that is designed to drive a vehicle's accessories at a slower rate than stock. Underdrive in general means the input rate of rotation in a system is greater than the output rate of rotation...
modify the amount of engine power that can be drawn by accessory devices. Such alterations to the drive systems for alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
s or air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...
compressors (rather than the power steering pump, for example) can be detrimental to vehicle usability, but will not impair safety.
Fuel & oil additives
CompoundsChemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
sold for addition to the vehicle's fuel may include tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
and platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
. The claimed purpose of these is generally to
improve the energy density
Energy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
of the fuel. Additives for addition to the engine oil, sometimes marketed as "engine treatments", contain teflon, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, or chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
compounds; none of these is appropriate or helpful when added to an engine's crankcase, and they can in fact damage the engine. The US Federal Trade Commission
Federal Trade Commission
The Federal Trade Commission is an independent agency of the United States government, established in 1914 by the Federal Trade Commission Act...
has aggressively pursued marketers of oil additives falsely claimed to improve fuel economy.
Magnets
Magnets attached to a vehicle's fuel line have been claimed to improve fuel economy by aligning fuel molecules, but because motor fuels are non-polarChemical polarity
In chemistry, polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in...
, no such alignment or other magnetic effect on the fuel is possible. When tested, typical magnet devices had no effect on vehicle performance or economy.
Vapor devices
Some devices claim to improve efficiency by changing the way that liquid fuel is converted to vaporVapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
. These include fuel heaters and devices to increase or decrease turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
in the intake manifold
Inlet manifold
In automotive engineering, an inlet manifold or intake manifold is the part of an engine that supplies the fuel/air mixture to the cylinders...
. These do not work because the principle is already applied to the design of the engine, and because intake tract flow dynamics are highly specific to each engine design, no universal device could have any given effect on more than one kind of engine.
Electronic devices
Some electronic devices are marketed as fuel savers. The Fuel Doctor FD-47, for example, plugs into the vehicle's cigarette lighter and displays several LEDs. It is claimed to increase vehicle fuel economy by up to 25% through "power conditioning of the vehicle's electrical systems", but Consumer Reports detected no difference in economy or power in tests on ten separate vehicles, finding that the device did nothing but light up. Car and DriverCar and Driver
Car and Driver is an American automotive enthusiast magazine. Its total circulation is 1.31 million. It is owned by Hearst Magazines, who purchased prior owner Hachette Filipacchi Media U.S. in 2011...
magazine found that the device contains nothing but "a simple circuit board for the LED lights", and disassembly and circuit analysis reaches the same conclusion. The maker disputed claims that the device has no effect, and proposed changes to the Consumer Reports testing procedure, which when implemented made no difference to the results.
Another device described as 'electronic' is the 'Electronic Engine Ionizer Fuel Saver'. Testing of this device resulted in a loss of power and an engine compartment fire.
There are also genuinely useful 'emissions-control defeat devices' that operate by allowing a vehicle's engine to operate outside government-imposed tailpipe emissions parameters. These government standards force factory engines to operate outside their most efficient range of operation. Either engine control units are reprogrammed to operate more efficiently, or sensors that influence the ECU's operation are modified or 'simulated' to cause it to operate in a more efficient manner. Oxygen sensor simulators allow fuel-economy reducing catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...
s to be removed. Such devices are often sold for "off-road use only".
Thermodynamic Efficiency
The reason why most devices are not capable of producing the claimed improvements is based in thermodynamicsThermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
. This formula expresses the theoretical efficiency of an engine:
where h is efficiency, rv is 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...
, and g is the ratio of the specific heats of the gases before and after combustion.
Assuming an ideal engine with no friction, perfect insulation, perfect combustion, a compression ratio of 10:1, and a g of 1.27 (for gasoline-air combustion), the theoretical efficiency of the engine would be 46%.
For example, if an automobile typically gets 20 miles per gallon with a 20% efficient engine that has a 10:1 compression ratio, a carburetor claiming 100MPG would have to increase the efficiency by a factor of 5, to 100%. This is clearly beyond what is theoretically or practically possible. A similar claim of 300MPG for any vehicle would require the engine (in this particular case) that is 300% efficient, which violates the Second Law of Thermodynamics
Second law of thermodynamics
The second law of thermodynamics is an expression of the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. From the state of thermodynamic equilibrium, the law deduced the principle of the increase of entropy and...
.
Extremely efficient vehicle designs capable of achieving 100MPG+ (such as the VW 1l
Volkswagen 1-litre car
The Volkswagen 1-litre car is a two-person diesel concept car produced by Volkswagen. The 1-litre car was designed to be able to travel 100 km on 1 litre of diesel fuel, , while being both roadworthy and practical...
) do not have substantially greater engine efficiency, but instead focus on better aerodynamics
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
, reduced vehicle weight, and using energy that would otherwise be dissipated as heat during braking.
Urban legend
There is a debunked urban legendUrban legend
An urban legend, urban myth, urban tale, or contemporary legend, is a form of modern folklore consisting of stories that may or may not have been believed by their tellers to be true...
about an inventor who creates a 100 mpg (2.35 L/100 km) or even 200 mpg carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
, but after demonstrating it for the major vehicle manufacturers, the inventor mysteriously disappears. In some versions of the story, he is claimed to have been killed by the government. This fiction is thought to have started after Canadian Charles Nelson Pogue
Charles Nelson Pogue
Charles Nelson Pogue was a Canadian mechanic and inventor who in the 1930s filed a series of US patents for a miracle carburettor that would enable a car to attain 200 mpg, and described as a vapourising or sometimes a catalytic carburettor...
filed in 1930 for such a device, followed by others.
MythBusters
The popular U.S. television show MythBustersMythBusters
MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...
investigated several fuel-saving devices using gasoline- and diesel-powered fuel-injected
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....
cars under controlled circumstances. Fuel line magnets, which supposedly align the fuel molecules so they burn better, were tested and found to make no difference in fuel consumption. The debunked notion that adding acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
to gasoline improves efficiency by making the gasoline burn more completely without damaging the plastic parts of the fuel system was tested, and although there was no apparent damage the fuel system, the vehicle's fuel economy was actually worsened.
The show tested the hypothesis that a diesel-powered car can run on 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...
gas alone, which was confirmed as viable, although the high cost of hydrogen gas currently prohibits widespread adoption. They also tested a device that supposedly produces sufficient hydrogen to power a car by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
(running an electric current through water to split its molecules into hydrogen and oxygen). Although some hydrogen was produced, the amount was minuscule compared to the quantity necessary to run a car for even a few seconds.
The show also tested a carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
that, according to its manufacturer, could improve fuel efficiency to 300 miles per gallon. However, the device actually made the car less fuel efficient. They also determined that a diesel
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
-powered car can run on used cooking oil
Cooking oil
Cooking oil is purified fat of plant origin, which is usually liquid at room temperature ....
though they did not check whether it damaged the engine.
The show noted that out of 104 fuel efficiency devices tested by the EPA, only seven showed any improvement in efficiency, and even then, the improvement was never more than six percent. The show also noted that if any of the devices they tested actually worked to the extent they were supposed to, the episode would have been one of the most legendary hours of television.
See also
- TelematicsTelematicsTelematics typically is any integrated use of telecommunications and informatics, also known as ICT...
- History of perpetual motion machinesHistory of perpetual motion machinesThe history of perpetual motion machines dates back to the Middle Ages. For millennia, it was not clear whether perpetual motion devices were possible or not, but the development of modern theories of thermodynamics has indicated that they are impossible. Despite this, many attempts have been made...
- Corporate Average Fuel EconomyCorporate Average Fuel EconomyThe Corporate Average Fuel Economy are regulations in the United States, first enacted by the U.S. Congress in 1975, and intended to improve the average fuel economy of cars and light trucks sold in the US in the wake of the 1973 Arab Oil Embargo...
- Emission standardEmission standardEmission standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...
External links
- Tony's Guide to Fuel Saving Gadgets including a case study on Vaporate
- FCIC warning on fuel saving devices