Hydrogen Engine Exhaust Control Using H2 for Low-Temp NOx Reduction

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Solution Overview

Problem

Existing hydrogen combustion engines face challenges in effectively reducing NOx emissions, particularly during cold-start conditions, as conventional exhaust aftertreatment systems are not optimized for low temperatures.

Innovation Solution

Implementing a method that operates the hydrogen combustion engine in an H2 exhaust excess mode, using unburnt hydrogen as a reductant in an ammonia slip catalyst (ASC) when the SCR catalyst is below its operating temperature threshold, alongside a selective catalyst reduction (SCR) system to enhance NOx conversion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the SCR catalyst is used for NOx reduction, then NOx emissions are reduced at high temperatures, but the SCR catalyst cannot effectively reduce NOx at low temperatures during cold-start

Engineering Contradiction:

ImproveNOx reduction capabilityVSAvoidcatalyst operating temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent introduces an ammonia slip catalyst (ASC) as an intermediary component downstream of the SCR catalyst. The ASC contains metal sites that can activate molecular nitrogen to form nitride intermediates, which then react with incoming NOx molecules to facilitate reduction. This intermediary mechanism enables NOx reduction to proceed at lower temperatures where conventional SCR catalysts are ineffective, as the ASC provides an alternative reaction pathway that does not rely on high-temperature conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If conventional exhaust aftertreatment systems are used, then the system structure is simple, but NOx emissions cannot be effectively reduced during cold-start conditions

Engineering Contradiction:

ImproveNOx emission controlVSAvoidexhaust aftertreatment system structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the functions of the SCR catalyst and the ammonia slip catalyst into a integrated exhaust aftertreatment system. The SCR catalyst handles NOx reduction at high temperatures, while the ASC downstream provides NOx reduction capability at low temperatures. By combining these two catalysts in series, the system achieves comprehensive NOx control across the full temperature range, from cold-start to hot operating conditions, without requiring separate independent systems.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The ammonia slip catalyst serves multiple functions: it acts as an ammonia slip catalyst to oxidize excess ammonia from the SCR process, and simultaneously functions as a low-temperature NOx reduction catalyst through its metal sites that can activate nitrogen and reduce NOx. This multi-functionality allows a single catalyst component to address multiple emission control needs, reducing the overall system complexity while improving reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If the engine operates in H2 exhaust excess mode with unburnt H2, then NOx conversion is enhanced in the ASC, but the engine efficiency may be reduced due to unburnt fuel

Engineering Contradiction:

ImproveNOx conversion efficiencyVSAvoidunburnt hydrogen in exhaust

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent converts the harmful unburnt hydrogen in the exhaust into a beneficial reducing agent for NOx conversion. By operating the engine in H2 exhaust excess mode, unburnt hydrogen is intentionally allowed to pass into the exhaust stream where it serves as a reductant in the ASC, facilitating the reduction of NOx to nitrogen. This approach transforms what would normally be wasted energy (unburnt fuel) into a useful chemical resource for emission control.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach effectively reduces NOx emissions by leveraging unburnt hydrogen as a reductant in the ASC, even at low temperatures, ensuring efficient NOx conversion and emission control during cold-starts and other low-temperature operations.

Implementation Method 1

using the unburnt H2 in the engine exhausts as a reductant for NOx conversion in the ASC

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 2

NOx conversion in the ASC

Methodology Applied

Scientific EffectReduction: Reduction

Data Source

PatentUS12540568B2Method for controlling the operation of a hydrogen combustion engine system

Publication Date: 2026.02.03 VOLVO TRUCK CORP

AI summary

A method for controlling the operation of a hydrogen combustion engine system of a vehicle. The hydrogen combustion engine system has a hydrogen combustion engine and an EATS to reduce emissions in the engine exhausts. The EATS has a selective catalyst reduction, SCR, catalyst and an ammonia slip catalyst, ASC, arranged downstream of the SCR catalyst. The method comprises: determining the temperature of the SCR catalyst; determining the temperature of the ASC; in response of determining that the temperature of the SCR catalyst is below a predetermined SCR temperature threshold value, and that the temperature of the ASC is below a predetermined ASC temperature threshold value, operating the hydrogen combustion engine in an H2 exhaust excess mode defined by an amount of unburnt H2 of at least 0.2 mol % in the engine exhausts, and using the unburnt H2 in the engine exhausts as a reductant for NOx conversion in the ASC.