DE20115936U1 - Exhaust sample bag - Google Patents

Description

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AVL List GmbH

Hans-List-Platz 1

8020 Graz

AUSTRIA

Abqas sample bag

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The invention relates to a flexible exhaust gas sample bag for collecting, storing and evaluating exhaust gas samples, in particular exhaust gas samples from internal combustion engines.

Nowadays, for example, when measuring the concentration of exhaust gas components from diluted exhaust gases, which is required for type approvals and certifications of engines and vehicles, but also for other similar tasks, these are collected in sample bags and only analyzed accordingly after the samples have been taken, which are usually required at different operating points of the engines. The sample bags in the known designs are made of plastics such as TEDLAR (PVF, polyvinyl fluoride), which are inexpensive, easy to handle and at least to a certain, currently sufficient, degree of gas-tightness and inert. For the concentrations of exhaust gas components that have existed or are to be measured in ranges from around 10 to more than 100 ppm (for example for HC and NO _x ), the adulteration effects caused by the bag material (through outgassing, solubility of exhaust gas components in the material, gas diffusion from the ambient air into the interior of the bag, or the like) are relatively small and mostly negligible. However, it is already apparent that with the lower emission values that are being aimed for in the future, such as those proposed by the European Union (EURO 3, EURO 4, EURO 5 directives) or in the USA for ULEV (Ultra Low Emission Vehicles) and SULEV (Super Ultra Low Emission Vehicles), emissions of HC and NO _x in the range of around 1 to 3 ppm are to be expected, although previous measurement experience already suggests that such secondary influences of the bag material will no longer be negligible.

In particular, the properties of the polymers used are expected to have an impact on the hydrocarbons (HC) through outgassing, solubility in the bag material or gas diffusion from the ambient air. In addition, temporary high pollutant concentrations, such as those released during test operation, can

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Fuels that are released during the combustion process are also dissolved in the polymer material and are only released again at a much later point in time through outgassing, which can have further undesirable effects on the measured values. Reactive gas components such as aldehydes or NO _x can have further effects that change the polymer material and therefore cannot be controlled in the long term.

The object of the present invention is to improve exhaust gas sample bags of the type mentioned at the outset in such a way that the disadvantages of the known bags of this type mentioned above are avoided and that, in particular, future lower emission measurement values can be determined as accurately as possible.

This object is achieved according to the present invention in that the sample bags have wall material consisting at least partially of plastic and built up in layers, with at least one layer consisting of at least largely inert and gas-tight metal. Appropriate tests have shown that the problems mentioned can be easily eliminated by providing at least one layer of inert and gas-tight metal, with the other advantages of this measuring system and the existing associated infrastructure remaining unchanged.

In a preferred embodiment of the invention, it is provided that the innermost layer of the wall material facing the interior of the sample bag consists of at least largely inert and gas-tight metal, which has the advantage that the sample gas only comes into contact with this unproblematic layer, so that the composition of the layers further out becomes uncritical.

For reasons of production and handling of the wall material, however, according to another preferred embodiment of the invention, it can also be provided that this has at least one metallic middle layer and at least one polymer layer on both sides of it. At least one of these middle layers can

according to another preferred embodiment of the invention made of aluminum foil as : ::·· .·: : : : ···. '..: *.:". ! : :

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carrier layer, which is easy to manufacture and produces a sufficiently stable and flexible structure in a cost-effective manner.

According to a particularly preferred further embodiment of the invention, a separate coating of inert and gas-tight metal can be applied to this middle carrier layer on the side facing the interior of the sample bag, which on the one hand facilitates the application of this inert layer and on the other hand improves the properties of the aluminum - pure aluminum, as is currently technically possible and also used for foils, is too reactive towards some components to be measured in the exhaust gas and must be separately coated with inert metal at least on the inside to ensure meaningful measurements in the mentioned range of low emission values.

In a particularly preferred further embodiment of the invention, gold is applied as the innermost, inert and gas-tight metal layer to at least one intermediate layer, preferably made of an at least partially inert material such as Cr-Ni or Al, which is applied to an outer plastic carrier layer to promote adhesion. This enables a relatively simple production of sufficiently flexible layer material.

In a particularly preferred embodiment of the invention, the at least largely inert and gas-tight metal comes from the group: gold, titanium, zirconium, nickel, Ni-Cr alloys, high-alloy stainless steels. These materials are relatively easy to handle and provide sufficient protection against undesirable influences of the type described above on the measurement results.

According to the invention, the layer of at least largely internal and gas-tight metal preferably has a thickness in the range of 50 to 500 nm, preferably in the range of 100 to 200 nm.

In particular, the gold coating mentioned above has several

Advantages: It is chemically inert and therefore no additional

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chen unwanted reactions in the stored exhaust gas samples. The layers are gas-tight and thus prevent the gas diffusion of pollutant components or interfering components from the ambient air into the interior of the bag, in particular ambient air methane or other gaseous air components. On the other hand, this also prevents the loss of exhaust gas samples through gas diffusion from the interior of the bag into the ambient air. The good chemical inertness of the gold also prevents or at least significantly reduces surface adsorption losses or losses through chemical reactions with gas components. The gas-tightness of this metallic barrier layer means that the various exhaust gas components to be measured are not soluble in the wall material, thus eliminating such unwanted influences on the measurement. Another argument in favor of gold is its corrosion resistance to the exhaust gas components to be measured.

Since the measuring technology used also requires the condensation of water vapor (from combustion) or hydrocarbons, the exhaust gas to be measured has previously been diluted with correspondingly large amounts of air in order to ensure that the temperature falls below the dew point. When using the bag materials according to the invention, this fall below the dew point can also be achieved by increasing the temperature of the collection bag to temperatures in the range of greater than 50 ^° C, without affecting the measurement accuracy. This is not possible with the bag materials used to date, since on the one hand the gas diffusion (and also the solubility and permeability) of various exhaust gas components increases significantly, up to several orders of magnitude, at these high temperatures. On the other hand, the reactivity of various exhaust gas components with the polymer materials themselves and with conventional diffusion barriers made of aluminum also increases significantly, so that severe falsifications of the gas composition and concentration values can occur. By using the bag materials according to the invention,

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Bags can significantly minimize or even prevent all of these influences even at high temperatures (for example, above 60 ⁰ C), since neither the gas diffusion through the gold nor the reactivity of gas components with the inert material gold increases significantly with this increase in temperature. By completely thermostatting a measuring system that works with such bags to a temperature above 50 ⁰ C or 60 ⁰ C, complex control mechanisms for diluting the exhaust gas with air, as described for example in PCT WO 98/44332 or EP 0 971 211, can be avoided or these procedures can at least be significantly simplified.

In principle, it is also possible within the scope of the invention to apply several metal layers made of different materials one after the other to a substrate material (polymer or, for example, flexible aluminum foil with thicknesses of up to 50 μm or combinations thereof, for example a pre-coated polymer material). This is particularly advantageous because the inert materials mentioned, such as gold, do not adhere well directly to some polymer materials, so that an additional, usually metallic, adhesive layer is required. On the other hand, gas diffusion can be further reduced by using a middle or intermediate layer made of a different material that is also gas-tight. The material used for this adhesion-promoting intermediate layer is therefore preferably also a relatively inert material, such as Cr-Ni. It must of course be ensured that this intermediate or carrier layer must not significantly reduce the required flexibility of the sample bag overall.

The above-mentioned application of an inert gold layer to a metallic substrate also makes it possible to compact the gold layer by tempering, thereby further improving both the adhesive properties and the tightness. In most cases, however, the entire bag will be coated on the outside with a flexible polymer material in order to prevent mechanical damage to the metallic ·.· ·♦·· ·· ·· · · ;··* .··, . . ....

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This outer polymer coating should be suitable for a temperature range of at least -10 ⁰ C to about 60 ⁰ C - preferably this temperature range should be from -20 ⁰ C to about 200 ⁰ C. PVF, PVC, PVF2, PVC2, Teflon FEP, Teflon PFA, ETFE or ECTFE can be used for an outer (or inner) flexible polymer layer.

Claims (8)

1. Flexible exhaust gas sample bag for the collection, storage and evaluation of exhaust gas samples, in particular exhaust gas samples from internal combustion engines, with a wall material consisting at least partially of plastic and built up in layers, wherein at least one layer consists of at least largely inert and gas-tight metal. 2. Sample bag according to claim 1, characterized in that the innermost layer of the wall material facing the interior of the sample bag consists of at least largely inert and gas-tight metal. 3. Sample bag according to claim 1, characterized in that the wall material has at least one metallic middle layer and on both sides thereof at least one polymer layer. 4. Sample bag according to claim 3, characterized in that at least one middle layer consists of aluminum foil as a carrier layer. 5. Sample bag according to claim 4, characterized in that the carrier layer has a coating of inert metal on the side facing the interior of the sample bag. 6. Sample bag according to claim 1, characterized in that gold is applied as the innermost, inert and gas-tight metal layer to at least one intermediate layer applied to an outer plastic carrier layer for adhesion, preferably made of an at least partially inert material, such as Cr-Ni or Al. 7. Sample bag according to one or more of claims 1 to 6, characterized in that the at least largely inert and gas-tight metal comes from the group: gold, titanium, zirconium, nickel, Ni-Cr alloys, high-alloy stainless steels. 8. Sample bag according to one or more of claims 1 to 7, characterized in that the layer of at least largely inert and gas-tight metal has a thickness in the range of 50-500 nm, preferably in the range of 100-200 nm.