A adsorber or trap (also called Lean trap, abbr. LNT) is a device that is used to reduce

oxides of nitrogen Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide *Nitrogen dioxide (), nitrogen(IV) oxide * Nitrogen trioxide (), or n ...

(NO and NO₂) emissions from a lean burn

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 co ...

by means of

adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...

Purpose and function of a adsorber

A adsorber is designed to reduce oxides of nitrogen emitted in the exhaust gas of a lean burn

. Lean burn engines, particularly

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 engi ...

s, present a special challenge to emission control system designers because of the relatively high levels of O₂ (atmospheric

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

) in the exhaust gas. The 3-way

catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usual ...

that has been successfully used since the 1980s on

stoichiometric Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equ ...

engines (such as fueled by

petrol 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 organic c ...

, LPG, CNG, or

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

) will not function at O₂ levels in excess of 1.0%, and does not function well at levels above 0.5%. Because of the increasing need to limit emissions from diesel engines, technologies such as

exhaust gas recirculation In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide () emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust ...

(EGR) and

selective catalytic reduction Selective catalytic reduction (SCR) is a means of converting nitrogen oxides, also referred to as with the aid of a catalyst into diatomic nitrogen (), and water (). A reductant, typically anhydrous ammonia (), aqueous ammonia (), or a urea () s ...

(SCR) have been used, however EGR is of limited effectiveness and SCR requires a continuous supply of reductant to the exhaust. The adsorber was designed to avoid the problems that EGR and SCR experienced. An adsorbant such as

zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These p ...

traps the NO and NO₂ molecules — acting as a molecular sponge. Once the trap is full (like a sponge full of water) no more can be absorbed. Various schemes have been designed to "purge" or "regenerate" the trap. One of possible reactants used to this aim is diesel fuel. Injection of diesel fuel before the adsorber can purge it — the is made to desorb and react with

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

s under rich conditions to produce

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

and

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

. Also

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

is a good reductant, but is dangerous and difficult to store. Some experimental systems have used fuel reformers for on-board hydrogen generation.

Market use

A trap is used on the

Volkswagen Jetta The Volkswagen Jetta () is a compact car/ small family car manufactured and marketed by Volkswagen since 1979. Positioned to fill a sedan niche above the firm's Golf hatchback, it has been marketed over seven generations, variously as the Atl ...

TDI and the

Volkswagen Tiguan The Volkswagen Tiguan () is a car produced by German manufacturer Volkswagen since 2007, sitting between the smaller T-Roc and the larger Touareg in the company's crossover SUV range. The first generation is based on the PQ46 platform, while ...

concepts. Both are projected to be introduced into the American market by 2008. They were to be marketed as part of the BlueTec program from Audi, Daimler-Chrysler, and Volkswagen. In 2015 an

ADAC ADAC, officially the Allgemeiner Deutscher Automobil-Club (), is Europe's largest motoring association. ADAC is the largest club (Verein) in Germany with around 21 million members. It would be more aptly described today as an individual mo ...

study (ordered by ICCT) of 32

Euro6 The European emission standards are vehicle emission standards for pollution from the use of new land surface vehicles sold in the European Union and EEA member states and the UK, and ships in EU waters. The standards are defined in a seri ...

cars showed that few complied with on-road emission limits, and LNT cars had the highest emissions.NOx control technologies for Euro 6 diesel passenger cars
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Technical details

The adsorber is based on a monolithic catalyst support that has been coated with a adsorbing washcoat such as one containing

zeolites Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These p ...

. Alkali/alkaline oxide (carbonate) can also be used as the adsorbant. Traps are gradually poisoned by SO_''x'' which adsorbs more strongly than . It necessitates a periodic high temperature regeneration that tends to reduce the adsorber's operating life.{{cite web, last1=Hu, first1=Horan, title=Eaton Aftertreatment System (EAS) For On-Highway Vehicles, url=http://energy.gov/sites/prod/files/2014/03/f9/2006_deer_hu.pdf, publisher=12th Diesel Engine-Efficiency and Emissions, accessdate=24 September 2015

References

Engine technology Gas technologies