Engine Exhaust Port Secondary Air Injection Timing
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Solution Overview
Problem
Conventional engines using internal EGR techniques face reduced combustion efficiency and incomplete exhaust gas purification due to increased CO2 and water vapor, leading to inadequate output characteristics and excessive HC and CO emissions.
Innovation Solution
An engine design that includes an air supply mechanism which supplies air to the exhaust port only after the exhaust valve reaches half its maximum lift, allowing air to flow into the combustion chamber via pressure fluctuations, thereby improving charging efficiency and purifying exhaust gases by mixing with exhaust gases before they reach the catalyst device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If exhaust gas is taken into the cylinder using internal EGR technique, then combustion temperature is decreased and heat loss is minimized, but combustion efficiency is lowered and output characteristics cannot be sufficiently improved
Solution Approach 1:
The exhaust gas recirculation process is segmented into two distinct stages: (1) internal EGR where exhaust gas is recirculated to control combustion temperature, and (2) secondary air injection where fresh air is introduced to improve combustion efficiency. This segmentation allows the system to achieve both low combustion temperature and high output characteristics by separating the temperature control function from the efficiency enhancement function.
Solution Approach 2:
Fresh air acts as an intermediary substance that is introduced between the exhaust gas recirculation process and the combustion chamber. This intermediary air supply mechanism allows the system to maintain the benefits of exhaust gas recirculation (temperature control) while adding the benefits of fresh air (combustion efficiency and output improvement) without directly conflicting with the EGR process.
2Loss of energy
If exhaust gas is taken into the cylinder, then pumping loss is decreased, but HC and CO in the cylinder are increased and exhaust gas cannot be sufficiently purified
Solution Approach 1:
The secondary air injection system performs preliminary purification action by introducing fresh air into the exhaust port before the exhaust gas reaches the catalyst device. This preliminary action starts the oxidation process of HC and CO in the exhaust port, reducing the burden on the catalyst device and improving overall purification efficiency while maintaining the pumping loss benefits of exhaust gas recirculation.
Solution Approach 2:
Fresh air serves as an intermediary that facilitates the purification of harmful emissions (HC and CO) in the exhaust stream. By introducing this intermediary air into the exhaust port, the system enables oxidation reactions that convert harmful emissions into less harmful substances, thereby reducing emissions while maintaining the pumping loss advantages of EGR.
3Productivity
If air is supplied to the exhaust port continuously, then combustion efficiency is improved, but excessive air flows into the catalyst device reducing purification efficiency
Solution Approach 1:
The air supply mechanism operates periodically rather than continuously, synchronizing air injection with specific phases of the engine cycle. Air is supplied to the exhaust port during periods when the exhaust valve is open and pressure conditions are favorable, while avoiding continuous supply that would cause excessive air to reach the catalyst device. This periodic action optimizes both combustion efficiency and catalyst purification efficiency.
Solution Approach 2:
The air supply system dynamically adjusts the timing and amount of air supplied to the exhaust port based on real-time engine operating conditions. By making the air supply dynamic rather than static, the system can optimize the balance between improving combustion efficiency and preventing excessive air from reaching the catalyst device, thereby maintaining high purification efficiency across varying operating conditions.
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 combustion efficiency, reduces HC and CO emissions, and improves exhaust gas purification efficiency while preventing excessive air from entering the catalyst device, thus stabilizing engine output and enhancing vehicle performance.
Implementation Method 1
air flows from the exhaust port into the combustion chamber by pulsation caused by pressure fluctuations in the exhaust port
Implementation Method 2
HC and CO in the exhaust gas can be efficiently oxidized
Data Source
AI summary
An engine includes a cylinder, an exhaust port, an exhaust valve, a secondary air supply pipe, and an electromagnetic valve. The electromagnetic valve is opened in a predetermined time period after a point in time when a lift amount of the exhaust valve reaches about half a maximum value during a time period in which an opening of the exhaust port is opened. This causes air to be supplied from a secondary air supply pipe to the exhaust port.