Skip-Fire Cylinder Valve Control for Catalyst Warm-Up
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Solution Overview
Problem
Existing methods for quickly warming up catalysts in internal combustion engine systems, especially when catalysts are located further downstream from the engine, face challenges in minimizing hydrocarbon emissions and noise, vibration, and harshness (NVH) issues during cold starts, due to inadequate control over the ratio of exhaust gas and secondary air.
Innovation Solution
The engine operates in a thermactor mode by selectively deactivating cylinders and adjusting valve timing and lift to provide secondary air, optimizing the ratio of burned gas to secondary air and mixing, thereby expediting catalyst heating while reducing NVH and excess air flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If catalysts are placed closer to the engine to minimize warm-up time, then catalyst warm-up speed is improved, but catalyst degradation during peak power increases
Solution Approach 1:
A thermactor system is introduced as an intermediary device between the engine and the catalyst. This system delivers secondary air to the exhaust system to create exothermic reactions that heat the catalyst, allowing the catalyst to be positioned further downstream while still achieving rapid warm-up. The thermactor acts as a mediator that enables both catalyst protection and efficient warm-up.
2Temperature
If a dedicated thermactor provides secondary air to heat the catalyst, then catalyst warm-up is improved, but device complexity increases
Solution Approach 1:
The engine's own cylinders are made multi-functional: they not only produce power during normal operation but also serve as secondary air sources during cold start by operating in a skip-fire mode. This eliminates the need for a separate dedicated thermactor device, reducing system complexity while maintaining the catalyst heating function.
Solution Approach 2:
The engine system serves itself by using its own cylinders to generate the secondary air needed for catalyst warm-up. Instead of requiring an external thermactor system, the engine utilizes its existing components (cylinders, valves, intake system) to provide the heating function, making the system self-sufficient and simpler.
3Stability of the object's composition
If skip-fire patterns are used to improve mixing of secondary air and exhaust gas, then mixing efficiency is improved, but excessive secondary air causes cooling of the exhaust system
Solution Approach 1:
The valve timing and lift of deactivated cylinders are dynamically adjusted to precisely control the amount of secondary air delivered to the exhaust system. By making the valve characteristics variable rather than fixed, the system can optimize mixing while preventing excessive air intake that would cause cooling, thereby maintaining exhaust temperature.
Solution Approach 2:
The intake valve timing and lift parameters of the deactivated cylinders are modified to control secondary air flow. By changing these parameters, the system achieves optimal mixing of exhaust gas and secondary air while limiting the total secondary air quantity to prevent exhaust system cooling.
4Quantity of substance
If deactivated cylinders provide secondary air without valve adjustments, then secondary air delivery is improved, but NVH issues increase
Solution Approach 1:
The valve timing and lift of deactivated cylinders are dynamically adjusted to control secondary air delivery while minimizing NVH. By optimizing when and how the valves open during deactivation, the system reduces turbulence and pressure fluctuations that cause noise, vibration, and harshness, while still delivering adequate secondary air for catalyst heating.
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 reduces hydrocarbon emissions and accelerates catalyst warm-up, minimizing NVH and operational costs by utilizing deactivated cylinders for secondary air delivery, enhancing emission control device efficiency.
Implementation Method 1
a thermactor provides air to an exhaust system upstream of an emission control device, which exothermically reacted with unburnt fuel in exhaust gas to create an exothermic reaction that will heat the emission control device
Data Source
AI summary
Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include operating an engine in a thermactor mode responsive to a cold start condition, the thermactor mode including skipping a first number of engine cylinders and producing torque via a remaining number of the engine cylinders, and differently adjusting a cylinder valve of at least one of the first number of the engine cylinders relative to the remaining number of the engine cylinders while operating in the thermactor mode. In this way, exotherms may be generated by the secondary air reacting with fuel in exhaust gas, thus increasing a temperature of the catalyst.