CNG Engine Valve Timing for Methane Slip Reduction
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Solution Overview
Problem
Compressed natural gas (CNG) engines face challenges in reducing methane slip and improving volumetric efficiency due to improper timing of intake and exhaust valve operations, leading to reduced performance and non-compliance with emission regulations.
Innovation Solution
A CNG engine design that simultaneously opens the intake and exhaust valves within a specific rotation angle of the crankshaft, with a phase difference between the intake and exhaust cams, optimizing valve timings to minimize overlap and enhance fuel efficiency and emission control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the intake valve is quickly closed, then the exhaust valve can close earlier to improve exhaust efficiency, but the amount of intake air decreases and volumetric efficiency is reduced
Solution Approach 1:
The patent applies dynamic valve timing control by independently adjusting the opening and closing times of the intake and exhaust valves. The intake valve closing time is set to occur before the exhaust valve closing time, creating a dynamic sequence that optimizes both exhaust efficiency and volumetric efficiency. This dynamic timing adjustment allows the system to achieve early exhaust valve closure for better exhaust efficiency while maintaining adequate intake air charge for volumetric efficiency.
2Quantity of substance
If the intake valve is closed lately, then more intake air can be retained in the cylinder, but the mixture flows backwardly toward the intake port reducing volumetric efficiency
Solution Approach 1:
The patent implements preliminary action by closing the intake valve before the exhaust valve closes. This sequencing ensures that the intake valve is already closed and sealed before any potential backward flow of mixture toward the intake port can occur. By taking this preliminary closing action, the system prevents mixture backflow while still retaining adequate intake air quantity in the cylinder, thus maintaining volumetric efficiency.
3Quantity of substance
If the exhaust valve is quickly closed, then exhaust gas can be retained in the cylinder for better combustion, but the exhaust gas is not sufficiently exhausted
Solution Approach 1:
The patent applies dynamic timing control by setting the exhaust valve closing time to occur after the intake valve closing time. This dynamic sequencing allows the exhaust valve to remain open longer, ensuring sufficient exhaust gas is expelled from the cylinder. The delayed exhaust valve closure, occurring after intake valve closure, prevents premature trapping of exhaust gas while still achieving adequate exhaust efficiency through the extended open duration.
4Reliability
If the exhaust valve is closed late, then more exhaust gas can be exhausted, but the exhaust gas flows backwardly from the exhaust port to the cylinder reducing volumetric efficiency
Solution Approach 1:
The patent implements preliminary action by closing the intake valve before the exhaust valve closes. This creates a protective sequence where the intake port is already sealed before the exhaust valve remains open late to maximize exhaust gas expulsion. The preliminary intake valve closure prevents any potential backward flow of exhaust gas into the cylinder from the exhaust port, thus maintaining volumetric efficiency while still achieving high exhaust efficiency through the delayed exhaust valve closure.
5Object-generated harmful factors
If the overlap between intake and exhaust valves is increased, then internal EGR can be controlled to reduce emissions, but the mixture flow backwardly reduces volumetric efficiency
Solution Approach 1:
The patent implements preliminary action by closing the intake valve before the exhaust valve closes, creating a controlled overlap sequence. This timing arrangement allows for limited internal EGR (exhaust gas recirculation) during the brief overlap period, which can help control emissions. However, by closing the intake valve first, the system prevents excessive backward flow of mixture toward the intake port, thus maintaining volumetric efficiency while still achieving emission control benefits from the controlled overlap.
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
The optimized valve timing reduces methane slip and improves volumetric efficiency, leading to enhanced engine performance and compliance with emission regulations by ensuring efficient combustion and exhaust processes.
Implementation Method 1
an intake valve configured to introduce an air and a fuel into the cylinder bore; a piston slidably arranged in the cylinder bore to convert an explosive force, which is generated by combusting the fuel, into a linear driving force
Implementation Method 2
The camshaft is configured to operate the intake valve and the exhaust valve. An intake cam combined with the camshaft is provided to open/close the intake valve and an exhaust cam combined with the camshaft is provided to open/ close the exhaust valve
Implementation Method 3
a crankshaft connected with the piston to convert the linear driving force into a rotational driving force
Data Source
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AI summary
An engine may include a cylinder, an intake valve, a piston, an exhaust valve and a crankshaft. The cylinder may include a cylinder bore. The intake valve may be configured to introduce a fuel and an air into the cylinder bore. The piston may be slidably arranged in the cylinder bore. The piston may be configured to convert an explosive power of an exhaust gas, which may be generated by combusting the fuel, into a linear driving force. The exhaust valve may be configured to exhaust the exhaust gas from the cylinder bore. The crankshaft may be connected with the piston to convert the linear driving force into a rotary driving force. The intake valve and the exhaust valve may be simultaneously opened within a rotation angle of about 3° to about 12° of the crankshaft. Thus, the engine may have improved volumetric efficiency of the engine and fuel efficiency of the engine. Further, the engine may satisfy emission regulations with respect to a CH4 gas.