Heater Control for Diesel Aftertreatment Systems
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Solution Overview
Problem
The control of heater systems in diesel engine aftertreatment systems faces challenges due to long lead times and large thermal inertia, which can result in inefficient NOx conversion and increased fuel consumption.
Innovation Solution
A control system is implemented that includes a dynamic response system to account for long lead times and thermal inertia, allowing for a faster response without stability issues, by adjusting the heating power setpoint based on feedback and dynamic modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heater system is used to heat the aftertreatment system to operating temperature, then the SCR conversion efficiency is improved, but the fuel consumption increases
Solution Approach 1:
The control system applies preliminary heating action by activating the heater system before the engine reaches operating temperature, ensuring the aftertreatment system is pre-heated to the required level. This preliminary action allows the SCR catalyst to be ready for efficient operation as soon as exhaust flow is sufficient, minimizing the period of low conversion efficiency and reducing the total heating energy required.
Solution Approach 2:
The control system continuously monitors the temperature of the aftertreatment system and adjusts the heater power accordingly. When the target temperature is approached, the heating power is reduced or switched off, preventing overheating and unnecessary fuel consumption. This feedback mechanism ensures optimal balance between achieving sufficient SCR conversion efficiency and minimizing additional fuel usage for heating.
2Device complexity
If the heater system is controlled with conventional PID control, then the control simplicity is maintained, but the response time is slow due to long lead times and thermal inertia
Solution Approach 1:
The control system incorporates a model of the aftertreatment system's thermal behavior that predicts future temperature based on current heating power and system state. This preliminary modeling action allows the controller to anticipate the system's response and adjust heating power proactively, compensating for the inherent delays and thermal inertia without requiring complex adaptive control algorithms.
Solution Approach 2:
An intermediate control model or lookup table is introduced between the simple PID controller and the heater system. This intermediary translates the simple PID error signal into appropriate heating power commands that account for system delays and thermal inertia, effectively decoupling the simplicity of the controller from the complexity of the system dynamics.
3Use of energy by moving object
If the target temperature is set closer to the SCR light-off temperature, then the fuel penalty is reduced, but the control stability becomes more difficult to maintain
Solution Approach 1:
The control system applies different control strategies at different temperature ranges. When the aftertreatment system temperature is below the SCR light-off temperature, aggressive heating is applied to reach the target quickly. Once the target temperature (close to light-off) is approached, the control becomes more conservative with smaller heating steps to prevent overshooting. This localized adaptation of control quality maintains stability while achieving fuel-efficient operation.
Solution Approach 2:
The control system anticipates potential temperature overshoot by reducing heating power in advance before the target temperature is reached. This preliminary anti-action counteracts the thermal inertia that would otherwise cause the temperature to continue rising past the desired setpoint, maintaining control stability even when operating close to the SCR light-off temperature with minimal fuel penalty.
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 enables more efficient control of the heater system, ensuring sufficient SCR conversion while minimizing fuel consumption and maintaining stable operation.
Implementation Method 1
an electrical heater
Implementation Method 2
a fuel burner
Implementation Method 3
a catalytic converter more specifically an SCR (Selective Catalytic Reduction) catalyst that converts NOx into harmless products
Implementation Method 4
SCR (Selective Catalytic Reduction) catalyst that converts NOx into harmless products also known as the deNOx process
Implementation Method 5
a diesel oxidation catalyst (DOC) to (inter alia) increase the deNOX efficiency and oxydize unburned hydrocarbon and CO
Data Source
AI summary
A control system is arranged to control the heater system; wherein the control system is programmed to heat the exhaust after treatment system based on a setpoint value. The control system comprises a controller having an error input and an output; that outputs a heating power setpoint value that is adjusted by a feedback signal, said adjusted setpoint value provided in parallel to a branch including the heater system and a branch including a dynamic response system. The dynamic response system comprises a dynamic response part and a delay part. A first subtractor subtracts a measured heat output and an output of the dynamic response system; an adder adds an output of the dynamic response part and an output of the first subtractor. A second subtractor subtracts a heating power setpoint from the output of the adder to provide a control error signal for the error input of the controller.