Diesel Engine Cold Start EGR and Combustion Control
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Solution Overview
Problem
Diesel engines face challenges in catalyst light-off due to lower exhaust gas temperatures and heat extraction by turbochargers, leading to longer warm-up times and increased emissions.
Innovation Solution
Implementing an engine operating method that adjusts exhaust gas recirculation (EGR) levels and combustion phasing, particularly using higher EGR at idle conditions and retarding combustion timing, aided by a hybrid powertrain to increase engine temperature and reduce emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If higher EGR is used at idle conditions to increase exhaust gas temperature, then catalyst light-off time is reduced, but engine emissions may increase due to higher EGR levels
Solution Approach 1:
The system dynamically adjusts EGR levels based on engine temperature conditions. During cold start, higher EGR is applied to accelerate catalyst heating. Once the catalyst reaches light-off temperature, EGR is reduced to minimize emissions. This dynamic adaptation resolves the contradiction by applying high EGR only temporarily when needed for catalyst heating.
Solution Approach 2:
The system changes the EGR parameter based on engine operating conditions and temperature thresholds. By monitoring engine temperature and adjusting EGR percentage accordingly, the system optimizes between catalyst heating efficiency and emissions control, resolving the trade-off between fast catalyst light-off and emissions generation.
2Loss of time
If combustion phasing is retarded to increase engine temperature, then warm-up time is reduced, but engine efficiency may decrease
Solution Approach 1:
Combustion phasing is dynamically adjusted based on engine temperature. During cold start, combustion is retarded to direct more heat to the exhaust system for rapid warming. Once operating temperature is reached, combustion phasing is optimized for maximum efficiency. This dynamic control resolves the contradiction between warm-up speed and efficiency.
Solution Approach 2:
The system periodically adjusts combustion phasing during the warm-up phase to maximize heat transfer to the exhaust system. By implementing periodic retardation strategies during specific temperature ranges, the system achieves rapid warm-up while maintaining acceptable efficiency, resolving the time-efficiency trade-off.
3Temperature
If engine load is increased to tolerate higher EGR percentages, then catalyst heating is improved, but vehicle drivability may be affected
Solution Approach 1:
The hybrid powertrain acts as an intermediary, allowing the engine to operate at higher loads for catalyst heating while the electric motor compensates for any drivability impacts. The electric motor can provide auxiliary power during high EGR conditions, enabling the engine to run at optimal temperatures for catalyst heating without compromising vehicle performance or drivability.
Solution Approach 2:
The system changes engine operating parameters (load, speed, EGR percentage) in a coordinated manner to achieve catalyst heating while maintaining drivability. By adjusting multiple parameters simultaneously rather than isolating EGR changes, the system resolves the contradiction between exhaust temperature and drivability.
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 catalyst light-off time, decreases engine warm-up time, and improves vehicle drivability by directing more combustion heat to the engine and exhaust system, thereby lowering emissions.
Implementation Method 1
directing more combustion heat to the engine and exhaust system
Implementation Method 2
combustion heat to the engine and exhaust system
Implementation Method 3
retarding combustion phasing (e.g., location of peak cylinder pressure) can increase engine temperature
Data Source
AI summary
An engine starting method is disclosed. In one example, engine operation is adjusted to reduce catalyst light off time. Exhaust temperatures may be increased until a threshold engine temperature is reached.