Exhaust Nozzle Urea Crystallization Prevention
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Solution Overview
Problem
Conventional exhaust gas purifying apparatuses face clogging issues in injection nozzles due to urea crystallization in urea aqueous solutions used as reducing agents, leading to inefficient NOx purification, as the temperature control within the nozzles is inadequate, especially in air-assisted systems where compressed air cools the nozzle interior below the melting point of urea.
Innovation Solution
An exhaust gas purifying apparatus with a temperature detection system that adjusts the reducing agent supply quantity to maintain the nozzle interior below the crystallization temperature of the reducing agent, and includes a control circuit to compare engine operation state signals with temperature data to ensure adequate cooling, while also using pressure detection to manage compressed air supply and prevent clogging by restarting when the exhaust gas temperature exceeds the melting point of urea.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If compressed air is constantly supplied to atomize the reducing agent, then the reducing agent is effectively atomized and supplied to the exhaust gas, but the compressed air cools the interior of the injection nozzle below the melting point of urea, causing solid urea to attach and clog the nozzle
Solution Approach 1:
The patent implements periodic stopping and resumption of compressed air supply to the injection nozzle. The control unit stops compressed air supply when urea crystallization is detected (via pressure increase or temperature sensor), allowing the nozzle interior temperature to rise above the urea melting point and clear crystallized urea. Then compressed air supply is resumed to continue the atomization function. This periodic action resolves the contradiction by temporarily sacrificing atomization efficiency to prevent clogging and maintain long-term reliability.
2Temperature
If the quantity of reducing agent supplied is reduced to allow nozzle heating, then the nozzle interior temperature can rise above 100°C to prevent urea crystallization, but insufficient reducing agent supply causes inadequate cooling and potential urea crystallization
Solution Approach 1:
The patent dynamically adjusts the reducing agent supply quantity based on detected parameters (exhaust gas temperature, nozzle internal pressure, or nozzle interior temperature). When the exhaust gas temperature is high or nozzle temperature approaches the urea crystallization point, the control unit increases the reducing agent supply quantity to ensure adequate cooling. When exhaust gas temperature is low, the supply quantity is reduced to allow nozzle heating above the urea melting point. This dynamic parameter adjustment resolves the contradiction by balancing cooling requirements with temperature maintenance to prevent crystallization.
3Reliability
If the exhaust gas temperature is raised to melt solid urea and clear nozzle clogging, then clogging is cleared, but this may not be advisable for some engines with temperature constraints
Solution Approach 1:
The patent employs self-service mechanisms where the system uses its own operational parameters to clear clogging without external intervention or engine temperature increase. When clogging is detected via pressure sensor or temperature sensor, the control unit stops compressed air supply, allowing the nozzle interior to heat up using residual heat from the reducing agent and exhaust gas contact. The system monitors until the temperature exceeds the urea melting point, then resumes compressed air supply to clear the clogged urea. This self-service approach clears clogging without requiring increased exhaust gas temperature, resolving the contradiction for temperature-sensitive engines.
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
Prevents clogging of injection nozzles by maintaining the reducing agent in a liquid state, ensuring continuous NOx purification efficiency and effective operation even at lower exhaust gas temperatures.
Implementation Method 1
the urea water supplied from the reservoir tank, (urea water and compressed air in the case of a reducing agent supply system that supplies compressed air with urea water to the injection nozzle), cools the interior of the nozzle
Implementation Method 2
This is because urea water solidifies at 100° C., and hence when the urea water is heated above 100° C. urea crystals form
Implementation Method 3
the urea water supplied from the reservoir tank... cools the interior of the nozzle, so that even if the injection nozzle is heated by the exhaust gas from the engine, the urea water does not reach 100° C. However, in the case where the quantity of urea water supplied is reduced, so that the interior of the nozzle can no longer be cooled, there is a possibility that the urea water inside the nozzle could reach or exceed 100° C., and urea crystals could form
Implementation Method 4
the melting point of solid urea is 132° C. Therefore if the exhaust gas temperature close to the injection nozzle is raised by the exhaust gas from the engine, and the heat input to the injection nozzle is increased, the solid urea will melt and the clogging of the nozzle will be cleared
Implementation Method 5
In the case where a reduction agent supply means is a so-called air assisted type reduction agent supply means that supplies compressed air together with urea water to the injection nozzle to atomize the urea water and eject it, the compressed air that is constantly supplied to the injection nozzle cools the interior of the nozzle. Therefore, the temperature of the interior of the nozzle does not rise above 132° C., and melting of the solid urea is prevented
Data Source
AI summary
Clogging of an injection nozzle which supplies a reducing agent to the exhaust gas on an upstream side of a reduction catalyst in the exhaust gas passage is prevented, and the efficiency of NOx purification processing is improved. A reducing agent supply unit uses a detection signal of the exhaust gas temperature from a temperature detection device to set a supply quantity at or above a lower limit for cooling the interior of an injection nozzle to below the temperature at which urea water crystallizes, for the detected exhaust gas temperature, and supplies urea water to the injection nozzle at the set supply quantity. By such supply of urea water, the interior of the injection nozzle is cooled to below the temperature at which the urea water crystallizes. As a result, the urea water does not crystallize inside the injection nozzle, and clogging of the injection nozzle can be prevented.