Variable Response Time Transient Partial Flow Sampling
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Solution Overview
Problem
Existing partial flow dilution tunnel systems struggle to maintain proportional sampling during transient conditions, especially when dealing with small engines or when exhaust aftertreatment devices are present, leading to potential over-sampling of particulate emissions due to time lags and varying exhaust flow rates.
Innovation Solution
A method is introduced to estimate the time delay for exhaust gases to reach the sampling area, with a controller and computer system adjusting the dilution air flow proportionally based on this estimation, using sensors and algorithms to account for factors like exhaust volumetric flow rate, temperature, and pressure, and incorporating closed-loop strategies for accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the sampling system responds quickly to transient air/fuel supply changes, then the system can accommodate changes in exhaust mass flow rate, but the exhaust may be over or under sampled for a brief duration due to time lag
Solution Approach 1:
The controller predicts future exhaust flow conditions based on current air and fuel supply rates, and preemptively adjusts the sampling system parameters before the actual transient change occurs. This prediction-based preliminary adjustment eliminates the time lag problem by ensuring the sampling system is already configured correctly when the exhaust change arrives, preventing both over-sampling and under-sampling during transient events.
2Reliability
If the probe is located downstream from exhaust aftertreatment devices, then the sampling location is optimal, but the time lag between exhaust changes and probe detection increases
Solution Approach 1:
The controller calculates the expected arrival time of exhaust changes at the downstream probe location based on the known exhaust system volume and flow rates. It then preemptively adjusts the sampling system parameters before the exhaust changes actually reach the probe, compensating for the time lag and ensuring accurate sampling despite the downstream probe location.
Solution Approach 2:
The system continuously monitors actual exhaust parameters and compares them with predicted values, using this feedback to refine the time lag compensation algorithm. This ensures that the controller can accurately predict and compensate for variable time lags under different operating conditions, maintaining sampling reliability at the downstream probe location.
3Productivity
If a fixed response time system is used, then the system operates well when engine displacement relative to exhaust system volume does not change, but particulate emissions over-sampling occurs during accelerations when the ratio is less than 550:1
Solution Approach 1:
The system transitions from a fixed response time configuration to a dynamic, variable response time system. The controller continuously calculates the optimal response time based on real-time measurements of exhaust volumetric flow rate and exhaust system volume, adjusting the sampling parameters dynamically to maintain the appropriate 550:1 ratio under all operating conditions, preventing over-sampling during accelerations while maintaining efficiency during steady-state operation.
Solution Approach 2:
The system changes the response time parameter dynamically based on operating conditions. By monitoring exhaust flow rate and system volume ratios, the controller adjusts the sampling response time parameter to maintain optimal proportional sampling, preventing over-sampling when the ratio is less than 550:1 during accelerations while preserving system efficiency during normal operation.
Data Source
AI summary
A partial flow dilution tunnel in a gas sampling system is connected to the exhaust from an internal combustion engine. More accurate gas sampling results are enabled for accounting for a delay from when the engine produces an exhaust change to when that transient arrives at a probe location. Thus, an estimated time delay is determined, and the gas sampling system is operated at least in part based upon that estimated time delay for the exhaust to arrive at the sampling location.