Capillary Diluter for Constant Exhaust Gas Sampling Ratio
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Solution Overview
Problem
Existing exhaust gas dilution systems, particularly full flow and partial flow sampling systems, face challenges in maintaining a constant dilution ratio during transient conditions due to varying exhaust gas backpressure, which affects accurate characterization of emissions, especially particulate matter, and introduce variable particle nucleation and condensation.
Innovation Solution
A capillary-based diluter system that samples a small fraction of exhaust gas, maintaining a regulated underpressure at the capillary outlet to achieve a constant dilution ratio, with optional cascaded stabilization chambers for adjustable dilution ratios, and no moving parts, ensuring the capillary inlet is at ambient pressure regardless of exhaust pressure variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If partial flow sampling systems are used to maintain a fixed dilution ratio, then the dilution ratio is constant under steady state conditions, but the dilution ratio varies significantly during transient conditions due to exhaust gas pressure variation
Solution Approach 1:
The patent replaces mechanical pressure regulators with a capillary-based flow resistance system. The capillary tube creates a pressure-independent flow regime where the sampling flow rate is determined by the capillary dimensions and the pressure difference between ambient and stabilization chamber, rather than by mechanical regulation that is sensitive to exhaust pressure variations.
Solution Approach 2:
The patent changes the operating parameters by creating a large pressure difference (ambient pressure vs. stabilized negative pressure) across the capillary. This parameter change ensures that the sampling flow remains relatively constant despite variations in exhaust gas pressure, as the capillary flow is dominated by the stabilized chamber pressure rather than exhaust pressure fluctuations.
2Adaptability or versatility
If pressure regulators are used to adjust dilution ratio, then the dilution ratio can be adjusted for steady state tests, but the system cannot maintain constant dilution during transient tests
Solution Approach 1:
The patent substitutes mechanical pressure regulators with a capillary flow resistance system combined with a stabilization chamber maintained at controlled negative pressure. This substitution eliminates the sensitivity to exhaust pressure variations while maintaining dilution ratio control capability through the stabilization chamber pressure control.
Solution Approach 2:
The stabilization chamber acts as an intermediary between the capillary sampling system and the analysis instrumentation. It buffers the sampling flow from exhaust pressure variations while allowing controlled dilution, serving as a mediator that decouples the sampling process from exhaust condition fluctuations.
3Temperature
If full flow diluters are used to mix exhaust with dilution air, then temperature and humidity are reduced, but the dilution ratio varies over transient tests due to changing flow rates
Solution Approach 1:
The patent extracts only a small fraction of the exhaust gas flow through the capillary tube for sampling and analysis, rather than processing the entire exhaust flow. This extraction approach allows for controlled dilution with constant flow rate, independent of the total exhaust flow variations during transient conditions.
Solution Approach 2:
The stabilization chamber serves as an intermediary that receives the capillary sample flow and mixes it with dilution air under controlled negative pressure. This intermediary system ensures constant dilution ratio by maintaining stable pressure conditions, while still achieving temperature and humidity reduction through the dilution process.
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 solution allows for a consistent dilution ratio during transient conditions, reducing particle nucleation and condensation variability, and enabling precise emission characterization without the need for moving parts, suitable for various engine configurations and aftertreatment devices.
Implementation Method 1
The sample flowrate through the capillary is achieved by maintaining a regulated underpressure at the capillary outlet
Implementation Method 2
The proposed diluter utilizes a very small fraction of the exhaust gas (of the order of 0,5 lpm), which is sampled through a capillary duct
Implementation Method 3
where it mixes with ambient filtered air before analysis
Implementation Method 4
where temperature, humidity and residence time may be adjusted to condition the collected aerosol at will
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a device used for the dilution of exhaust gas (diluter) and in particular for engines or vehicules. More particularly, the invention relates to a device and a method which may maintain a constant dilution ratio regardless of the exhaust gas backpressure in the exhaust line, without using any moving parts. The proposed diluter utilizes a very small fraction of the exhaust gas, sampled through a capillary duct, simply immersed to the exhaust flow, which is otherwise freely exhausting to the atmosphere. The sample flowrate through the capillary is achieved by maintaining a regulated underpressure at the capillary outlet. The diluted exhaust is then collected in a stabilization chamber, where temperature, humidity and residence time may be adjusted to condition the collected aerosol at will. Multiple capillaries and stabilization chambers may be cascaded to increase the dilution ratios. After the final dilution stage, particle samples may be collected on a filter for gravimetric determination or analyzed by number counters, surface monitors or any other technique utilized for the physical or chemical characterization of particles. In a preferred embodiment the capillary duct is realized with a hypodermic needle and two cascaded hypodermic needles/stabilization chambers are combined to provide the desired dilution ratio. In another embodiment, exhaust gas may be led to the diluter's capillary duct by means of two probes, located respectively upstream and downstream of any aftertreatment device, which needs to be characterized. By means of shut-off valves, exhaust gas may be fed to the diluter's capillary by either the upstream or the downstream probe, thus providing an estimate of the filtration efficiency of the device.