Hydrogen Engine Exhaust Control Using H2 for Cold-Start NOx Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing hydrogen combustion engines face challenges in effectively reducing NOx emissions, particularly during cold-start conditions when the SCR catalyst is not operating at its full capacity, necessitating an improved exhaust aftertreatment system.
Innovation Solution
Implementing a method that determines the temperatures of the SCR and ASC catalysts, and operates the hydrogen combustion engine in an H2 exhaust excess mode, using unburnt H2 as a reductant in the ASC to convert NOx, even when the SCR catalyst is below its operating threshold temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the SCR catalyst is used for NOx reduction, then NOx emissions are reduced under optimal conditions, but the system fails to effectively reduce NOx during cold-start conditions when catalyst temperature is below threshold
Solution Approach 1:
The system uses unburnt hydrogen from the engine exhaust itself as the reductant for NOx conversion in the ASC, eliminating the need for external reductant injection systems. The hydrogen that would otherwise be wasted is now utilized to reduce NOx emissions during cold-start conditions when the SCR catalyst is not yet at operating temperature.
Solution Approach 2:
Instead of relying on the SCR catalyst to reduce NOx (the conventional approach), the patent inverts the approach by using the ASC downstream to reduce NOx using unburnt hydrogen as reductant. This reverse strategy allows effective NOx reduction to occur even when the primary SCR catalyst is not yet at operating temperature.
2Object-generated harmful factors
If unburnt H2 is increased in exhausts to serve as reductant for ASC, then NOx conversion is improved during cold-start, but engine efficiency may be reduced due to excess fuel consumption
Solution Approach 1:
The patent converts the harmful effect of unburnt hydrogen (which represents wasted fuel and energy loss) into a beneficial effect by using it as a reductant for NOx reduction in the ASC. The unburnt hydrogen that would otherwise contribute to inefficiency is now utilized to reduce NOx emissions, transforming a waste product into a useful reductant.
Solution Approach 2:
The system dynamically adjusts the amount of unburnt hydrogen in the exhaust by controlling engine operation parameters, specifically maintaining an air-to-fuel ratio that allows 0.1-10% unburnt hydrogen to pass through to the ASC. This parameter optimization ensures sufficient hydrogen is available for NOx reduction while minimizing unnecessary fuel consumption.
3Object-generated harmful factors
If the EATS is cold during cold-start, then the SCR catalyst cannot effectively reduce NOx, but adding complex heating systems increases device complexity and cost
Solution Approach 1:
The system uses the chemical energy already present in the unburnt hydrogen fuel to provide the necessary heat for NOx conversion in the ASC, eliminating the need for separate external heating systems. The exothermic reaction between hydrogen and oxygen in the ASC provides self-heating, allowing the catalyst to reach and maintain operating temperature without additional complex heating infrastructure.
Solution Approach 2:
The unburnt hydrogen acts as an intermediary that bridges the gap between the cold exhaust gases and the requirements of the ASC. By introducing this combustible substance, the system creates an intermediate exothermic reaction that generates the necessary heat to activate the catalyst, avoiding the need for direct external heating systems.
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 enhances NOx reduction efficiency by leveraging the ASC's capabilities with unburnt H2, ensuring effective emissions control during cold-starts and sub-optimal operating conditions.
Implementation Method 1
using the unburnt H2 in the engine exhausts as a reductant for NOx conversion in the ASC
Implementation Method 2
an exhaust aftertreatment system, EATS, configured to reduce emissions of the engine exhausts. The invention further relates to a hydrogen combustion engine system
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A hydrogen combustion engine system (10) comprises a hydrogen combustion engine (15, 15') and an exhaust aftertreatment system, EATS, (20) configured to reduce emissions in the engine exhausts. The EATS comprises a selective catalyst reduction, SCR, catalyst (40) and an ammonia slip catalyst, ASC, (50) arranged downstream of the SCR catalyst (40). The method comprises: determining (S10) the temperature of the SCR catalyst (40); determining (S20) the temperature of the ASC (50); in response of determining that the temperature of the SCR catalyst (40) is below a predetermined SCR temperature threshold value, and that the temperature of the ASC (50) is below a predetermined ASC temperature threshold value, operating (S30) the hydrogen combustion engine (15, 15') 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 (S40) the unburnt H2 in the engine exhausts as a reductant for NOx conversion in the ASC (50).