SCR Catalyst NOx Reduction via Hydrocarbon Adsorption Control
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Solution Overview
Problem
Existing methods for reducing nitrogen dioxide emissions from lean burning internal combustion engines with SCR catalytic converters are ineffective, especially at low exhaust gas temperatures, leading to unreliable reduction of NOx and NO2 emissions.
Innovation Solution
Supplying an exhaust gas enriched with ammonia above an operating temperature to an SCR catalytic converter with adsorption centers, and enriching it with hydrocarbons below the operating temperature to inhibit NOx adsorption and facilitate NO2 reduction, using a device that can add ammonia or generate it from exhaust gas components, and employing a catalytic unit to convert NO2 to NO or N2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the SCR catalytic converter operates below the operating temperature, then the ammonia supply is avoided to prevent unnecessary NOx reduction, but NOx and especially NO2 emissions are not reduced reliably
Solution Approach 1:
The patent changes the chemical composition parameter of the exhaust gas by adding hydrocarbons below operating temperature to modify the adsorption behavior on SCR catalytic converter surfaces. This enables NOx reduction through hydrocarbon-based mechanisms rather than ammonia-based SCR, achieving reliable NOx reduction without ammonia consumption at low temperatures
2Quantity of substance
If the SCR catalytic converter adsorbs NOx at low temperatures, then NOx is temporarily stored, but this leads to undesired NO2 release during temperature increases
Solution Approach 1:
The patent converts the harmful effect of NOx adsorption (which leads to NO2 release during heating) into a beneficial effect by adding hydrocarbons that modify the adsorption mechanism. The hydrocarbons enable NOx to be converted to N2 through alternative pathways, transforming the potential harm of temporary storage into a beneficial permanent removal of NOx without subsequent NO2 release
3Reliability
If the SCR catalytic converter is used for selective NOx reduction with ammonia, then NOx reduction is achieved above operating temperature, but NO2 emissions persist at lower exhaust gas temperatures
Solution Approach 1:
The patent segments the temperature-dependent NOx reduction strategy into two distinct modes: below operating temperature, hydrocarbons are added to enable NOx reduction through hydrocarbon-based mechanisms; above operating temperature, ammonia-based SCR reduction takes over. This segmentation allows each mechanism to operate in its optimal temperature range, eliminating NO2 emissions across the full temperature spectrum
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces NOx and NO2 emissions across a wide range of operating conditions, including low temperatures, by inhibiting adsorption and promoting desorption of NOx, thereby minimizing nitric acid formation and toxic gas emissions, and ensuring a significant decrease in NO2 emission.
Implementation Method 1
an SCR catalytic converter, which has adsorption centers for nitrogen oxides... enabled for the catalyzation of a selective NOx reduction under oxidizing conditions by means of NH3
Implementation Method 2
The SCR catalytic converter, which is enabled for the catalyzation of a selective NOx reduction under oxidizing conditions by means of NH3, has adsorption centers where nitrogen oxides (NOx) can adsorb
Implementation Method 3
converting nitrogen dioxide (NO2) with hydrocarbons stored in the SCR catalytic converter
Implementation Method 4
Due to a thermolysis and/or hydrolysis, NH3 is released from the urea in the exhaust gas at increased temperatures
Implementation Method 5
Due to a thermolysis and/or hydrolysis, NH3 is released from the urea in the exhaust gas at increased temperatures
Data Source
AI summary
In a method for reducing the emission of nitrogen dioxide in a motor vehicle having an exhaust gas purification system having an SCR catalytic converter with adsorption centers for nitrogen oxides, an exhaust gas enriched with ammonia is supplied to the SCR catalytic converter above an operating temperature. Below the operating temperature, the exhaust gas supplied to the SCR catalytic converter is enriched with a material such that an adsorption of nitrogen oxides is inhibited at corresponding adsorption centers of the SCR catalytic converter. In order to reduce the overall NOx emissions below a first, predeterminable amount, an exhaust gas enriched with ammonia is supplied to the SCR catalytic converter and the NO2 portion of the total NOx emissions is reduced below a second, predeterminable amount in that NO2 is converted with hydrocarbons stored in the SCR catalytic converter.