Delayed Exhaust Engine Cycle for Cold Start Warm-Up
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Solution Overview
Problem
Conventional four-stroke engine cycles during light load conditions and cold start conditions lead to extended warm-up times due to cool in-cylinder temperatures, limited heat transfer to engine coolant, and inefficient exhaust gas flow, especially in diesel engines with unthrottled air flow.
Innovation Solution
Implementing a delayed exhaust engine cycle where intake and exhaust valves are closed during specific strokes to allow for additional combustion events, injecting fuel during closed valve positions, and maintaining the valves in a closed position until the engine reaches a predetermined temperature or oxygen concentration, thereby optimizing combustion and heat retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional four-stroke cycle is used during cold start conditions, then the engine operates with standard intake and exhaust valve timing, but the warm-up time is extended due to cool in-cylinder temperatures
Solution Approach 1:
The exhaust valve is closed earlier than conventional timing (e.g., at 10-20 degrees before bottom dead center) to trap hot exhaust gases in the combustion chamber before the next intake stroke. This preliminary action of retaining heat builds up in-cylinder temperature faster during cold start conditions, reducing warm-up time without requiring additional heating components.
Solution Approach 2:
The valve timing parameters are dynamically adjusted during cold start conditions. The exhaust valve closure timing is advanced (changed from conventional after bottom dead center to before bottom dead center), and the intake valve opening timing is also modified. These parameter changes optimize heat retention and combustion temperature during the warm-up phase.
2Temperature
If the exhaust valve is opened early to clear combustion chamber, then exhaust aftertreatment components receive cooler gas flow, but if delayed, heat transfer to coolant is reduced
Solution Approach 1:
The exhaust valve is closed earlier in the cycle to allow combustion to complete and build higher exhaust gas temperatures before the valve opens. This preliminary heat buildup ensures that when the exhaust valve does open, hotter gas flows to the aftertreatment components, improving their heating and activation during cold start conditions.
Solution Approach 2:
The exhaust valve timing is made dynamic rather than fixed. During cold start conditions, the exhaust valve closure timing is advanced to maximize heat retention and exhaust temperature. As the engine warms up, the timing reverts to conventional settings, allowing flexible optimization of both heat retention and heat transfer to coolant based on operating conditions.
3Productivity
If additional combustion events are enabled during light load conditions, then engine efficiency improves, but residual oxygen levels must be carefully managed
Solution Approach 1:
The control system monitors residual oxygen levels in the combustion chamber and uses this feedback to determine when to enable additional combustion events. Oxygen sensors detect the oxygen concentration, and based on this feedback, the engine control unit adjusts fuel injection timing and valve timing to optimize multiple combustion events while maintaining proper oxygen levels for continued combustion.
Solution Approach 2:
The engine operates with dynamic valve timing that adjusts based on load and oxygen conditions. During light load conditions with sufficient residual oxygen, the intake and exhaust valve timing is optimized to enable multiple combustion events. When oxygen levels drop below thresholds, the timing reverts to conventional operation, allowing the system to adaptively maximize efficiency when conditions permit.
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 reduces engine warm-up times, enhances exhaust gas temperatures, and accelerates vehicle cabin heating while improving emission control through faster exhaust aftertreatment component heating and internal exhaust gas recirculation.
Implementation Method 1
maintaining the valves in a closed position until the engine reaches a predetermined temperature or oxygen concentration, thereby optimizing combustion and heat retention
Implementation Method 2
A first fuel mass may be provided to the combustion chamber between an end portion of a second stroke immediately subsequent to the first stroke and a beginning portion of a third stroke immediately subsequent to the second stroke
Implementation Method 3
These relatively cool in-cylinder temperatures may provided limited heat transfer to engine coolant which is used for vehicle cabin heating
Implementation Method 4
may also provide a relatively cool exhaust gas flow to exhaust aftertreatment components
Data Source
AI summary
A method of operating an engine in a delayed exhaust engine cycle may include opening an intake valve of the engine during a first stroke to form an intake stroke. The method may further include closing the intake valve and determining an engine operating temperature. The engine operating temperature may be compared to a predetermined temperature limit. A first fuel mass may be provided to the combustion chamber between an end portion of a second stroke and a beginning portion of a third stroke. The third stroke may form a first power stroke and the intake valve and an exhaust valve in communication with the combustion chamber may be closed during the second and third strokes. The exhaust valve may be maintained in a closed position during a fourth stroke when the engine operating temperature is less than the predetermined temperature limit.