Exhaust Gas Burner Lambda Control for Catalyst Light-Off
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Solution Overview
Problem
Existing exhaust gas aftertreatment systems face challenges in quickly heating catalytic converters to light-off temperature with minimal emissions, particularly in underbody positions where heat losses are significant, and the combustion air ratio of exhaust gas burners can lead to high raw emissions.
Innovation Solution
The method involves an exhaust gas burner with an oxygen storage device and lambda sensors to alternately operate at substoichiometric and superstoichiometric combustion air ratios, ensuring rapid heating of catalytic converters while minimizing emissions, using lambda sensors to control the combustion air ratios of both the internal combustion engine and the exhaust gas burner, and adjusting fuel and air quantities for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an exhaust gas burner is used to heat the catalytic converter, then the heating speed and light-off temperature are improved, but the raw emissions from the burner increase
Solution Approach 1:
The exhaust gas burner operates in periodic cycles, alternating between substoichiometric and superstoichiometric combustion air ratios. During the substoichiometric phase, the burner provides maximum heating output. During the superstoichiometric phase, excess oxygen is supplied to oxidize accumulated unburned hydrocarbons and carbon monoxide, thereby reducing raw emissions while maintaining effective catalyst heating.
Solution Approach 2:
The combustion air ratio (lambda) is dynamically changed between substoichiometric (lambda < 1) and superstoichiometric (lambda > 1) conditions. This parameter variation allows the system to optimize between heating efficiency and emission reduction, with the lambda probe providing feedback for precise control of the air-fuel mixture.
2Volume of moving object
If the catalytic converter is placed in the underbody position, then the catalytically effective volume is improved, but the heating time to reach light-off temperature increases
Solution Approach 1:
The exhaust gas burner is activated during the cold start phase to preheat the catalytic converter before the exhaust gas temperature is sufficient for effective catalytic conversion. This preliminary heating action ensures that the catalyst reaches its light-off temperature quickly, enabling efficient emissions conversion as soon as possible despite the long exhaust path to the underbody position.
Solution Approach 2:
The exhaust gas burner acts as an intermediary heating device between the engine exhaust and the catalytic converter. It introduces additional hot gases into the exhaust stream, providing the necessary thermal energy to heat the large-volume underbody catalyst to operating temperature more rapidly than engine exhaust alone could achieve.
3Object-generated harmful factors
If lambda control is implemented for the exhaust gas burner, then emissions are reduced, but the device complexity increases
Solution Approach 1:
A lambda probe is installed downstream of the exhaust gas burner to measure the oxygen content in the exhaust gas. This measurement provides feedback to the control system, which adjusts the combustion air ratio of the burner to maintain optimal lambda values. This feedback mechanism enables effective emissions control through a relatively simple and proven technology approach.
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 enables rapid and efficient heating of catalytic converters with reduced emissions, ensuring quick light-off temperatures and minimizing breakthroughs of pollutants, thus optimizing the heating phase and reducing tailpipe emissions.
Implementation Method 1
an exhaust gas burner with which hot exhaust gas can be introduced into the exhaust system
Implementation Method 2
heating a catalyst (30, 38) in an exhaust system (20) of an internal combustion engine (10)
Implementation Method 3
catalysts coated with precious metals are installed in the exhaust system to convert the pollutants
Implementation Method 4
A lambda probe (34) is arranged immediately downstream of the inlet point (32) and upstream of the catalyst (30, 38) with which the combustion air ratio of the exhaust gas burner (28) can be controlled
Data Source
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AI summary
The invention relates to a method for heating a catalyst (30, 38, 40) in an exhaust system (20) of an internal combustion engine (10). An exhaust gas burner (28) for heating the catalyst is arranged in the exhaust system (20) upstream of the catalyst (30). A lambda sensor (34) for controlling the combustion air ratio of the exhaust gas burner (28) is arranged immediately downstream of the exhaust gas burner (28) and upstream of the catalyst (30, 38, 40).The method comprises the following steps: - operating the internal combustion engine (10) with a stoichiometric air-fuel ratio (λE=1), - activating the exhaust gas burner (28), wherein the exhaust gas burner (28) is operated alternately with a substoichiometric air-fuel ratio (λB<1) and a superstoichiometric air-fuel ratio (λB>1), wherein - switching from the substoichiometric air-fuel ratio (λB<1) to the superstoichiometric air-fuel ratio (λB>1) occurs as soon as a rich mixture is detected by the lambda sensor (34), and wherein - switching from the superstoichiometric air-fuel ratio (λB>1) to the substoichiometric air-fuel ratio (λB<1) occurs as soon as a lean mixture is detected by the lambda sensor (34). The invention further comprises an exhaust gas aftertreatment system for carrying out such a method.