Six-Stroke Engine Valve Activation for NOx Reduction
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Solution Overview
Problem
Internal combustion engines operating on a six-stroke cycle face increased emissions, particularly nitrous oxides (NOx), due to high cylinder temperatures during re-compression and re-combustion processes.
Innovation Solution
The engine employs a valve activation system that opens the intake valve during the recompression stroke to allow a portion of the products from the first combustion stroke to exit and enter the intake collector, and includes a recirculation passage to segregate blowdown exhaust gases from the main exhaust stream, mixing them with incoming air to reduce emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the six-stroke cycle is implemented with re-compression and re-combustion of combustion products, then engine productivity is improved, but emissions (particularly NOx) increase due to high cylinder temperatures
Solution Approach 1:
The exhaust system is segmented into two separate paths: a blowdown passage that directs high-temperature combustion products away from the main exhaust stream, and a main exhaust passage for normal exhaust gases. This segmentation prevents the high-temperature blowdown gases from contributing to NOx emissions in the main exhaust stream, thereby resolving the contradiction between maintaining six-stroke productivity and reducing harmful emissions.
Solution Approach 2:
The harmful high-temperature combustion products are extracted and removed from the main exhaust stream through a dedicated blowdown passage. By taking out these high-temperature gases that would otherwise generate NOx emissions, the system maintains the productivity benefits of the six-stroke cycle while eliminating the harmful emission component.
2Stress or pressure
If exhaust valves remain closed during recompression stroke to assist cylinder recompression, then compression efficiency is improved, but exhaust gas evacuation is delayed
Solution Approach 1:
The blowdown valve opens during the recompression stroke to preliminarily evacuate high-temperature combustion products before the exhaust stroke begins. This preliminary action reduces the volume and temperature of gases remaining in the cylinder, allowing the exhaust valve to remain closed longer for better compression while still ensuring timely exhaust gas evacuation through the blowdown passage.
Solution Approach 2:
The blowdown valve acts as an intermediary mechanism that provides a separate evacuation path for combustion products during the recompression stroke. This mediator allows the exhaust valve to remain closed for compression efficiency while the blowdown valve handles the evacuation of hot gases, resolving the timing conflict between compression and exhaust evacuation.
Data Source
AI summary
An engine combustion cylinder is fluidly connectable to an intake system through an intake valve and to an exhaust system through an exhaust valve. A valve activation system is to activate the intake valve and the exhaust valve. The valve activation system is responsive to a controller providing command signals to the valve activation system such that, when the engine operates in a six-stroke combustion cycle, the intake valve is opened during a recompression stroke to allow a portion of the products from the first combustion stroke to exit the combustion cylinder and enter into the intake system.