Variable Valve Timing for Cold Start Hydrocarbon Reduction
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Solution Overview
Problem
During engine start-up, especially in cold conditions, the low temperature of intake valves and intake ports leads to incomplete fuel atomization, resulting in excessive fuel supply and increased unburned hydrocarbon emissions, particularly when using heavy fuel components, due to the formation of wall flow.
Innovation Solution
A control system that dynamically adjusts the lift amount and opening/closing timing of the intake valve, and promotes valve overlap between the intake and exhaust valves, based on the temperature of the intake valve and intake port, to enhance fuel atomization and reduce wall flow, while optimizing ignition timing and throttle opening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the fuel injection amount is increased to compensate for wall flow during cold start, then the fuel supply to the combustion chamber is sufficient, but the air/fuel ratio becomes excessively rich and unburned hydrocarbon emissions increase
Solution Approach 1:
The invention changes the physical parameters of the intake valve operation (lift amount and opening/closing timing) to modify the flow characteristics of intake air. By reducing the lift amount and retarding the timing, the velocity of intake air increases, which enhances fuel atomization and reduces wall flow formation, thereby optimizing the air/fuel ratio without excessive enrichment
Solution Approach 2:
The invention dynamically adjusts the intake valve lift amount and timing based on operating conditions (cold start vs. warm operation). The valve operation characteristics are made variable rather than fixed, allowing optimization of fuel atomization and wall flow control under different temperature conditions
2Manufacturing precision
If the lift amount of the intake valve is reduced to decrease wall flow, then the velocity of intake air increases and fuel atomization is promoted, but the flow area of the intake valve is reduced
Solution Approach 1:
The invention changes multiple parameters simultaneously - not only the lift amount but also the opening/closing timing of the intake valve. This multi-parameter adjustment allows the system to achieve high fuel atomization quality through increased air velocity while compensating for the reduced flow area by optimizing the timing characteristics
3Temperature
If the ignition timing is retarded to promote exhaust gas temperature increase and catalyst activation, then the exhaust gas temperature rises and catalyst activation is accelerated, but stable combustion becomes more difficult to achieve
Solution Approach 1:
The invention performs preliminary actions to ensure stable combustion before retarded ignition timing is applied. By reducing wall flow and enhancing fuel atomization through optimized intake valve operation, the fuel is better prepared and distributed in the combustion chamber, creating favorable conditions for stable combustion even when ignition timing is retarded for catalyst activation
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 effectively minimizes unburned hydrocarbon emissions by ensuring stable combustion and early catalyst activation, regardless of fuel type, by increasing intake air velocity and promoting valve overlap to enhance fuel atomization and mixing.
Implementation Method 1
The increased velocity of the intake air promotes atomization of the fuel adhered to the intake valve and the walls of the intake port
Implementation Method 2
a blow-back of the combustion gas to the intake port occurs, and atomization of the injected fuel is promoted by the heat of the combustion gas
Data Source
Figure 1
Figure 2
Figure 3A~3K
AI summary
A variable valve mechanism (12a, 12b) varies a lift amount and an opening/closing timing of an intake valve (10) of an internal combustion engine (1). During a first period in an engine start operation, wall flow is suppressed by setting the lift amount of the intake valve (10) to be smaller so as to increase the intake air velocity. During a second period, which starts after the first period ends, the atomization of injected fuel is enhanced by increasing a valve overlap amount between the intake valve (10) and an exhaust valve (11) so as to promote blow-back of the combustion gas to an intake port (4). By sequentially applying a process for increasing the intake air velocity and a process for increasing the valve overlap amount, the emission of unburned hydrocarbon during the engine start is effectively reduced.