SCR Catalyst NO2:NO Ratio Control via Hydrocarbon Injection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Selective catalytic reduction (SCR) systems face inefficiencies due to varying nitrogen dioxide (NO2) to nitric oxide (NO) concentration ratios in exhaust gases, which can be outside the optimal 1:1 ratio required for optimal performance, especially at higher temperatures, and existing systems like those described in U.S. Patent Application Publication No. 2006/0236680 are not suitable for SCR catalysts.

Innovation Solution

An exhaust treatment system with a controller that determines NO2 and NO concentrations and controls the injection of hydrocarbons upstream of an oxidation catalyst to adjust the NO2:NO ratio to 1:1, ensuring optimal SCR performance by reducing NO2 concentration through catalytic site occupation, thereby maintaining efficient SCR operation across varying engine conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an oxidation catalyst is placed upstream of the SCR catalyst to increase NO2 concentration, then SCR performance at lower temperatures is improved, but SCR performance at higher temperatures becomes markedly less efficient

Engineering Contradiction:

ImproveSCR performanceVSAvoidSCR performance across temperature ranges

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The system dynamically adjusts the NO2:NO ratio by controlling hydrocarbon injection based on exhaust temperature. At lower temperatures, the oxidation catalyst operates normally to convert NO to NO2, improving SCR performance. At higher temperatures, hydrocarbon injection is increased to reduce NO2 concentration and maintain optimal SCR performance, making the system adaptive across different temperature ranges.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the chemical parameters of the exhaust gas by injecting hydrocarbons that react with NO2 to form NO, thereby adjusting the NO2:NO ratio. This parameter change allows the system to maintain optimal SCR performance at higher temperatures while preserving the benefits of the oxidation catalyst at lower temperatures.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the NO2 concentration is increased to improve SCR performance, then the NO2:NO ratio approaches 1:1 at lower temperatures, but the NO2 concentration may exceed the NO concentration at higher temperatures

Engineering Contradiction:

ImproveSCR performanceVSAvoidNO2 concentration

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The control system continuously monitors exhaust temperature and adjusts hydrocarbon injection accordingly. When exhaust temperature increases and NO2 concentration becomes excessive, the system increases hydrocarbon injection to convert NO2 back to NO, maintaining the optimal NO2:NO ratio for SCR performance across varying operating conditions.

Inventive Principle:

Principle #23Feedback

3Reliability

If existing systems like those in U.S. Patent Application Publication No. 2006/0236680 are used to reduce NO2 concentration, then particulate filters can be regenerated, but such systems are not suitable for SCR catalysts

Engineering Contradiction:

Improveparticulate filter regenerationVSAvoidcompatibility with SCR catalyst

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The system applies different control strategies to different parts of the exhaust treatment process. The oxidation catalyst is positioned upstream of the SCR catalyst and is controlled differently - it is not deactivated for particulate filter regeneration but rather is used to maintain optimal NO2:NO ratios specifically for SCR performance, making the system suitable for SCR catalysts while still enabling particulate filter regeneration through separate hydrocarbon injection.

Inventive Principle:

Principle #3Local quality

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

The system effectively maintains optimal NO2:NO ratios for SCR catalysts, enhancing the overall efficiency and reducing emissions by controlling hydrocarbon injection to balance NO2 and NO concentrations, thus improving the performance and reliability of the SCR system.

Implementation Method 1

The oxidation catalyst can operate to convert a portion of NO in the exhaust gas to NO2

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 2

During SCR, a catalyst facilitates a reaction between ammonia and NOx to produce water and nitrogen gas

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 3

selective catalytic reduction (SCR)... a catalyst facilitates a reaction between ammonia and NOx to produce water and nitrogen gas

Methodology Applied

Scientific EffectCatalytic reduction:

Data Source

PatentUS8161731B2Selective catalytic reduction using controlled catalytic deactivation

Publication Date: 2012.04.24 CATERPILLAR INC

AI summary

An exhaust treatment control system includes a controller configured to determine a value representative of a NO2 concentration associated with an exhaust gas upstream of a selective catalytic reduction (SCR) catalyst, and determine a value representative of a NO concentration associated with the exhaust gas upstream of the SCR catalyst. The controller can also be configured to transmit a signal to at least partially control an injection of a hydrocarbon into the exhaust gas, wherein the hydrocarbon injection can occur upstream of an oxidation catalyst to at least partially decrease the NO2 concentration of the exhaust gas downstream of the oxidation catalyst, and wherein the oxidation catalyst can be located upstream of the SCR catalyst.