Measuring and testing – Volume or rate of flow – By measuring transit time of tracer or tag
Reexamination Certificate
2001-12-21
2003-12-30
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring transit time of tracer or tag
C073S861950, C073S861630
Reexamination Certificate
active
06668663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow measurement device, and, more particularly, to a gaseous mass flow measurement device.
2. Description of the Related Art
Traditional ways to measure exhaust gas flow rate are either cumbersome or do not work very well. It is known to measure an exhaust gas flow rate by introducing a trace gas with a known concentration and flow rate into the stream to be measured and utilizing an analyzer to measure the final concentration.
In one known method of measuring an exhaust gas flow rate includes making dynamic and static pressure measurements. The difference in static and dynamic pressure corresponds to the velocity of the gas. By knowing the temperature, velocity, and cross-sectional area of the exhaust pipe, the mass flow rate can be calculated. Examples include pitot tube type devices. A problem with these devices is that the dynamic pressure is often very small and highly fluctuating due to pulses in the exhaust. The signal-to-noise ratio is bad, with the noise being generally much greater than the signal.
In another known method of measuring an exhaust gas flow rate, a trace gas is introduced into the stream at a known concentration. The downstream concentration is measured, and thereby the total exhaust flow can be calculated. A problem is that a sophisticated analyzer and cumbersome source of trace gas is required.
In another known method of measuring an exhaust gas flow rate, a hot wire anemometer is used only in clean gaseous flow mediums. If the hot wire becomes fouled through exhaust particle deposition or other cause, the resulting flow rate data is not valid.
Current exhaust flow measurement devices rely upon the use of gas pressure differentials created with pitot tube devices and or reduced pressures generated by vortexes generated around an obstruction in the flow path. These pressures, either relative to atmospheric, absolute or differential are measured with indicating devices such as pressure or differential pressure transducers. The nature of these measurement devices makes it nearly impossible to improve on accuracies better than +/−0.25% of span. For most engine exhaust mass flow measurement systems, there exist specific and stringent specifications for exhaust backpressure measured at the engine. If the exhaust system and any integrated exhaust measurement device together exceed these specifications, then it is deemed that this interference can degrade engine performance and disqualify the test results. In order to satisfy these requirements, generally exhaust pipe sizes are maintained at a size larger than necessary to carry the flow without unwanted restriction. By over-sizing the exhaust pipe, the resultant flow velocity is diminished. Generally, pitot or vortex based systems rely on this velocity to activate the generated pressure, reduced pressure or differential pressure. The small signal therefore generated by the transducer may be only incrementally larger than the noise generated due to the fundamental precision of the instrument. The result is poor signal to noise ratio and therefore poor precision in the overall exhaust mass flow. For all these systems, turbulence only worsens the backpressure.
Another problem with these types of systems is flow perturbation—or otherwise known in the industry as pulsation. Pulses in continuous flow, as would be generated by any reciprocating internal combustion engine, exist in the exhaust pipe. These pulses interact with pitot tube or vortex based systems in such a way that significant errors result. Because engine to engine and exhaust configurations differ greatly among vehicles, these errors cannot be corrected through assumption.
Another problem revolves around fouling. A principal reason why hot wire anemometer based flow measurement systems cannot be used in engine exhaust is particulate fouling. The solid matter, which exists in all engine exhaust eventually, deposits on the hot wire and changes the thermal transfer or electrical properties of the element, resulting in large errors. Correspondingly, pitot tube and even vortex based systems are also greatly affected by particulate fouling. The material impedes the flow of gas into the entrance and exit ports, thus resulting in errors that increase with time and additional fouling.
Another problem with these types of devices is the requirement to place very precise and therefore fragile measurement transducers near the exhaust exit port. The resultant vibration and thermal gradients experienced by the transducer often reduces the accuracy, introduces errors and can greatly detract from the inherent durability of the part.
Hot exhaust gas, by its very nature is a very difficult medium to quantify mass flow because traditional electronic sensors cannot tolerate the temperature, chemistry and/or particulate fouling. Several techniques are used for on-vehicle measurements including pitot tube, averaging anemometer, differential pressure flow measurement devices, etc. All of the existing devices for on-vehicle and most devices for stationary engine mass flow suffer from issues stemming from fouling, poor durability and/or poor precision as a result of one or more of the aforementioned conditions.
Power plant performance, emissions and hot exhaust gas flow are by their very nature very difficult media to quantify, even more so in actual field situations. Quantification is difficult due to the extremely harsh environments in which power plants such as on-road and off-road diesel and spark ignition engines operate. Due to the ever increasingly stringent world wide emissions regulations, it is becoming more and more important to have the capability to remotely measure and remotely monitor power plant performance parameters.
There are several reasons for measuring exhaust mass flow, including emissions monitoring, performance development, engine development and vehicle development to name a few. With the need to accurately measure emissions on a moving vehicle, it is becoming more important to accurately discern the exhaust mass flow. With these accurate and precise data, mass specific and more importantly, brake power specific emissions measurements can be made. With known methods, accurate and highly precise flow and performance measurements are impossible without huge, bulky and awkward instrumentation. This huge, bulky laboratory instrumentation does not lend itself to field, mobile power plant or vehicle testing.
Current systems capable of measuring emissions, power plant performance, duty-cycle monitoring, data storage and retrieval, and providing remote access via, but not limited to cellular networks are large, bulky, environmentally sensitive and require constant on-site engineering and technical support. Some of the current systems are so large that trailers must be towed behind the test article to support all of the measurement equipment. Current emissions measurement systems require daily and sometimes constant calibration and technical attention to acquire accurate data and measurement system uptime.
Many of the exhaust flow measurement techniques of the current systems are prone to fouling when operated in a diesel engine environment. The fouling of the current state of the art exhaust flow measurement device may take place in a relatively short period of time. In addition, the current systems may require “high level” and time-consuming instrumentation to measure all of the required engine performance parameters, such as torque, power, lubricating oil quality, intake air flow and fuel consumption. This “high level” of instrumentation is also typically very intrusive upon the test specimen, resulting in significant power plant downtime and reduced productivity. In summary, some of the current systems may require anywhere from one to several days for installation alone. The current emissions measurement systems are also more prone to failure since they were designed for a laboratory environment rather than a field environment.
What is needed in the art i
Krempel Louis A.
May Angela R.
May David F.
Analytical Engineering, Inc.
Patel Harshad
Taylor & Aust P.C.
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