Pressure-Based Liquid Reducing Agent Flow Measurement
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Solution Overview
Problem
Existing methods for determining the amount of liquid reducing agent in a tank for exhaust gas treatment systems are imprecise, especially in dynamic conditions like moving vehicles or sloping surfaces, and fail to accurately measure transient flow rates, leading to inaccuracies in liquid supply to the exhaust gas.
Innovation Solution
A method involving pressure sensors at two points in the injection line, downstream of an intermediate store, to detect time-dependent pressures and calculate the quantity of reducing agent supplied per unit of time, allowing for precise determination of liquid flow rates and tank content using unsteady flow equations for compressible media.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If level indicator is used to determine filling level, then tank content can be monitored, but measurement precision deteriorates under dynamic conditions (vehicle motion, sloping surfaces)
Solution Approach 1:
The patent replaces the mechanical level indicator system with a pressure-based measurement system. Pressure sensors measure the pressure of the liquid reducing agent in the injection line, and from this pressure data, the quantity of liquid supplied is calculated. This substitution eliminates the problem of mechanical indicators being inaccurate under dynamic conditions, as pressure measurements are not affected by vehicle motion or sloping surfaces in the same way visual level indicators are.
Solution Approach 2:
The patent introduces an intermediate store in the injection line between the pump and the point of injection. This intermediate store allows for stable pressure measurements to be taken downstream, serving as a mediator that decouples the measurement process from the dynamic pumping action and injection process, thereby improving measurement precision under transient flow conditions.
2Measurement precision
If mechanically moved counting or measuring devices are used for flow measurement, then flow quantity can be measured, but measurement precision deteriorates in highly transient flow rates
Solution Approach 1:
The patent replaces mechanical flow measurement devices with a pressure-based measurement system. By measuring pressure at two different points in the injection line and using the pressure difference along with unsteady flow equations for compressible media, the system can accurately determine flow rates even during highly transient conditions. This eliminates the inertia and response time limitations of mechanical measuring devices.
Solution Approach 2:
The patent employs dynamic pressure measurements taken at multiple points in the injection line. By continuously monitoring pressure changes over time and using unsteady flow equations, the system adapts to rapidly changing flow conditions. This dynamic measurement approach allows accurate flow rate determination during transient operations, unlike static or mechanically moved devices.
3Measurement precision
If pump parameters are monitored to determine pumped quantity, then liquid supply can be tracked, but measurement precision deteriorates without additional parameters (pressure, density, temperature)
Solution Approach 1:
The patent replaces direct pump parameter monitoring with pressure sensor measurements in the injection line. By measuring pressure at two points and using the pressure difference with unsteady flow equations, the system determines liquid quantity without needing to directly measure pump parameters or additional liquid properties. This substitution simplifies the system while maintaining or improving measurement precision.
Solution Approach 2:
The pressure sensors in the injection line serve dual purposes: they monitor the pressure for proper system operation and simultaneously provide the data needed to calculate liquid quantity. The system uses existing pressure measurements, intended for operational monitoring, to also determine flow rates, eliminating the need for separate measurement systems and reducing overall complexity.
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
Enables precise and continuous monitoring of liquid supply to the exhaust gas, preventing inaccuracies due to vehicle motion or transient flow rates, ensuring optimal nitrogen oxide reduction and allowing for timely refilling and recalibration of the tank.
Implementation Method 1
detecting time-dependent pressures simultaneously at at least two points downstream from the intermediate store in the injection line
Implementation Method 2
the intermediate store being pressurized by a pump with liquid from the tank
Implementation Method 3
at least one injector can be arranged, which enables the liquid to be atomized into the exhaust gas
Implementation Method 4
a liquid reducing agent is preferably injected into the exhaust gas flow in order to convert the nitrogen oxides contained in the exhaust gas flow into elemental nitrogen (N2) and water (H2O) using a catalyst
Data Source
Figure 1
AI summary
The invention relates to a method for determining the amount of a liquid removed from a tank (1) per unit of time, wherein the liquid (2) is discontinuously fed to an exhaust gas train (19) of an internal combustion machine. The method comprises at least the following steps: Feeding the liquid (2) into the exhaust gas train (19) by means of an injection line (12), detecting pressures simultaneously at at least two points (28, 29) in the injection line (12), determining from the detected pressures the amount of liquid fed in per unit of time. The amount of liquid (Fx) removed between a first point in time (t1) and second point in time (t2) is further derived by integrating the amounts of liquid removed per unit of time over the period of time from the first point in time (t1) to the second point in time (t2). The method according to the invention allows the precise consumption of the liquid (2) to be calculated, and the remaining amount of liquid in the tank (2) to be additionally determined. On-board diagnosis is further possible by means of the method according to the invention.