Spark-Ignition Engine Emissions Control via Secondary Air Injection
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Solution Overview
Problem
Existing systems for controlling emissions in spark-ignition internal combustion engines fail to maintain low noxious emissions at high engine loads and speeds, leading to increased engine component and catalytic converter temperatures, and do not effectively reduce fuel consumption while preventing particulate accumulation.
Innovation Solution
A system with a secondary air feeding system controlled by an electronic controller, which adjusts air/fuel ratio and secondary air introduction based on engine load and speed, using two catalytic converters positioned to reduce exhaust gas temperature and maintain stoichiometric conditions except at high loads/speeds, where a slightly rich mixture is allowed to enhance combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the engine is operated with a rich air/fuel mixture at high loads and speeds to protect engine components, then engine component temperatures are reduced, but noxious emissions increase
Solution Approach 1:
The exhaust gas treatment system is divided into two separate catalytic converters: a first converter (downstream) that handles reduction reactions for NOx, and a second converter (upstream) that handles oxidation reactions for CO and unburned hydrocarbons. This segmentation allows each converter to specialize in specific emission components, enabling the engine to operate with rich mixtures at high loads while maintaining low overall emissions through coordinated action of both converters.
Solution Approach 2:
A secondary air feeding system is introduced as an intermediary mechanism that injects additional air between the two catalytic converters. This secondary air serves as a mediator to provide the necessary oxygen for oxidation reactions in the second converter, enabling it to effectively treat CO and hydrocarbons from rich mixture combustion without compromising the reduction function of the first converter.
2Speed
If conventional secondary air feeding is used to warm-up the catalytic converter, then the catalytic converter activation is accelerated, but the system complexity increases
Solution Approach 1:
The second catalytic converter is positioned upstream in the exhaust flow path, before the first converter. This preliminary positioning allows the second converter to perform oxidation reactions first, generating heat that warms up the exhaust gases before they reach the first converter. This preliminary heating action accelerates the overall system warm-up without requiring complex additional heating mechanisms.
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 achieves reduced noxious emissions across all operating conditions, lowers engine and catalytic converter temperatures, improves fuel efficiency, and prevents particulate accumulation in the gasoline particulate filter, meeting future emission regulations while maintaining engine performance.
Implementation Method 1
The second converter is an oxidation converter, which is used for oxidizing HCs and COs
Implementation Method 2
a first exhaust gas treatment device, interposed in the exhaust gas conduit and a second exhaust gas treatment device, interposed in the exhaust gas conduit
Implementation Method 3
providing a quicker warm-up of the catalytic converter due to the exothermic reactions which are generated
Data Source
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AI summary
A system for controlling the emissions of a spark-ignition internal combustion engine of a motor-vehicle comprises first and second exhaust gas treatment devices (12, 13) and a secondary air feeding system (14; 20) for feeding secondary air into the exhaust gas conduit (11), between the first and second exhaust gas treatment devices (12, 13). The secondary air feeding system (14; 20) is activated only when the load of the engine is greater than a predetermined load value and/or when the engine rotational speed is greater than a predetermined speed value. In this condition the air/fuel ratio of the engine is kept at a value lower than the stoichiometric value, so as to feed the engine with a rich mixture. In one example an electronic controller (E) is programmed for controlling the activation of the secondary air feeding system on the basis of a map, as a function of values of the engine load and the engine rotational speed. The map is predetermined depending upon the specific characteristics of the engine.