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 +/xe2x88x920.25% 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 perturbationxe2x80x94or 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 xe2x80x9chigh levelxe2x80x9d 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 xe2x80x9chigh levelxe2x80x9d 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 is a flow measurement device that is not affected by pulsations, is very robust and is in no way degraded by the corrosive elements, particulate matter, heat, and vibration associated with exhaust pipes and exhaust systems.
The present invention introduces a small flow of clean/fresh air into the main exhaust stream. A static pressure drop is created in the main exhaust stream by accelerating all or a portion of the exhaust flow, and the pressure is then recovered downstream. Using Bernoulli""s principle, a tube is connected from the ambient clean atmosphere to the lower static pressure region inside the exhaust pipe. The pressure differential creates a flow of clean air into the exhaust pipe, to be entrained with the exhaust flow. The clean air flow rate is measured by a hot wire anemometer. This clean air flow rate directly corresponds to the total exhaust flow rate; therefore total exhaust flow can be determined by knowing the amount of fresh entrained air flow. Since the hot wire is only exposed to fresh air, it should never foul.
In another embodiment, the known temperatures of the exhaust, diluent, and combined flows are used rather than a hot wire. By knowing the specific heat of the gas, the flow rate can be calculated.
The present invention can be used to measure engine exhaust or any other gaseous flow stream wherein the introduction of a diluent flow is acceptable. The present invention may also be applied to measure the flow of factory processes for monitoring exhaust stacks and oil refineries.
The present invention provides a system to measure the undetermined flow rate of a gaseous stream, such as engine exhaust on a mobile or stationary vehicle or power plant. By introducing and combining a stream of a known flow rate and temperature with the second stream of unknown flow rate and known temperature, and measuring the change in temperature of the mixed and combined streams, the flow rate of the second stream can be accurately determined.
One embodiment of the mass flow measurement device of the present invention depends upon the large thermal gradient between exhaust gases and a diluent gas. By introducing a known mass flow of a cool diluent gas into the exhaust flow within the exhaust pipe, a temperature drop occurs in the exhaust. The extent of temperature drop is a function of the mass flow of the exhaust, temperature of the exhaust, mass flow of the diluent gas and temperature of the diluent gas. If complete mixing occurs without other outside thermal losses, the nature of these physical properties and the thermal characteristics of the exhaust and cool gas combination are well understood. Therefore, by measuring the temperature of both unmixed gases just before mixing, accurately measuring the mass flow of the diluent, and finally, accurately measuring the mixed gas temperature before it exits, the mass flow of the exhaust before mixing can be determined.
Because the temperature of a turbulent gas can be measured very accurately (less than 0.1 degrees Fahrenheit error), and because the mass flow of cool ambient air can be determined with excellent accuracy and precision over a very large range using hot wire or vortex shedding acoustic anemometers or both, the system depends only on good mixing.
The induction of the cool air is accomplished by entraining the diluent gas through the use of an eductor or ejector type device. The greater the flow rate of diluent, the more accurate the system becomes. By optimizing the eductor portion of the system to achieve the highest diluent flow rate and to maintain the overall exhaust backpressure below maximum specifications, a very reliable and accurate system is obtained.
Small ambient temperature mass flow measurement devices are inexpensive, accurate and provide very good durability. Resistance temperature devices (RTD""s) or thermocouple temperature measurement probes are very responsive and accurate with excellent precision. By combining these accurate and precise measurement subsystems, the overall exhaust mass flow rate can be accurately and precisely determined over a very large range of flows.
Another embodiment of a mass flow measurement device of the present invention depends upon the induction of a diluent gas flow into the existing engine exhaust flow. By introducing a known mass flow of a diluent gas into the exhaust flow within the exhaust pipe, a quantitative correlation may be developed between the diluent mass flow and engine exhaust flow. The extent of diluent flow is a function of the mass flow of the exhaust, temperature of the exhaust and temperature of the diluent gas. It is not necessary for complete mixing of the diluent gas and exhaust gas to obtain a measurement of the diluent flow and subsequent exhaust flow. As a result the diluent flow is not significantly impacted by the nature of these physical properties and the thermal characteristics of the exhaust and cool gas combination are well understood. Therefore, by accurately measuring the mass flow of the diluent, and finally, correlating the diluent flow to the exhaust gas flow before it exits, the mass flow of the exhaust can be determined.
Because the mass flow of the diluent gas can be measured very accurately (less than 1% error), and because the mass flow of cool ambient air can be correlated via laboratory flow bench measurements to the exhaust flow with excellent accuracy and precision over a very large range using hot wire or vortex shedding acoustic anemometers or both, the system depends only on accurate on-board/laboratory measurement of the diluent flow.
The induction of the cool air is accomplished by entraining the diluent gas through the use of an eductor or ejector type device. The greater the flow rate of diluent, the more accurate the system becomes. By optimizing the eductor portion of the system to achieve the highest diluent flow rate and to maintain the overall exhaust backpressure below maximum specifications, a very reliable and accurate system is obtained.
In another embodiment, a highly mobile, telemetry based, unattended, environmentally sealed device measures and records the mass flow of power plant exhaust and intake air, power plant exhaust gaseous speciation and particulate matter quantification, power output, engine speed, fuel consumption, power plant lubricant quality, A/F ratio, performance, geographic location information (such as longitude, latitude, altitude and speed), travel routes, atmospheric conditions (such as but not limited to ambient pressure, ambient temperature and ambient relative humidity) and mobile vehicle as well as power plant performance on a mobile or stationary vehicle or power plant. The device may also be used for real time emissions and performance monitoring. The above-described measurement system is contained in a mobile environmental disclosure that lends itself to secure/antitheft attachment to the test specimen. The device also provides the user with the option of interfacing with and recording data from the power plant computer control module (if one exists) over a publicly available communication protocol.
The device is also capable of controlling the test specimen via data links (such as J1587/J1708/J1939). The device is capable of interpreting and interfacing with the power plant via the data link. The data acquired from the power plant emissions and performance measurement/monitoring devices is stored within an on-board data storage and acquisition system. The information is accessible both on-site and remotely via but not limited to cellular network and other communication devices. The emissions, performance and duty cycle analysis system once installed can be left unattended for extended periods of time, such as but not limited to several days to over a year.
The device is also capable of providing an extremely robust method of attachment to the power plant. A power plant is defined as any device or system that bums, combusts or consumes any type of hydrocarbon-based fuel.
The system may be utilized in the accurate measurement of any type of flowing gases, regardless of the size of the exhausting unit, possibly including but not limited to on-vehicle emissions for cars, trucks (both light and heavy), SUV""s, off-road vehicles including snowmobiles, ATV""s, dirt bikes, construction equipment, stationary and mobile power generation units, airplanes, helicopters, jets, personal water craft, boats, ships, outboard motors, lawnmowers, string trimmers, chain saws, leaf blowers, motorcycles, locomotives, furnaces, flow bench testing equipment, vehicle and engine test cells, heating and cooling ventilation systems, and industrial smokestacks of all types.
The measurement system can be used to help develop power plant preventive maintenance standards and intervals as well as power plant diagnostics.
There are several reasons for measuring exhaust mass flow, including emissions monitoring, performance development, engine development and vehicle development to name a few. With these accurate and precise data, mass specific and, more importantly, brake power specific emissions measurements can be made.
The output from the exhaust flow measurement device provides data relating to a wide variety of gaseous emissions, brake specific emissions and fuel consumption. The exhaust flow measurement and sampling device also provides a mechanism for speciation of the exhaust gas gaseous components as well as exhaust gas particulate matter.
The device of the present invention can be in the form of a module that is either placed partially inside an engine exhaust pipe or added to the end of an existing exhaust stack.
In yet another embodiment, an exhaust probe is used in conjunction with exhaust measurement devices for the measurement of particulate matter, hydrocarbons or other gaseous emitted species. The device is designed for direct placement into an exhaust stack. The shape of the device is such that, at the bottom, the exhaust gas pressure in the stagnation zone is significantly higher than the static pressure of the exhaust in the stack. By routing this unhindered through a tube outside of the stack to ambient air pressure, the maximum possible pressure differential is achieved. This results in the greatest possible flow through the tube without non-passive components such as pumps, ejectors etc.
In a further embodiment, a gaseous mass flow measurement device may be inserted in any type of gaseous flow stream, from clean air to a stream containing products of combustion, such as the exhaust pipe on an internal combustion engine. The flow measurement device contains an optional sampling port to take a small portion of the flow and redirect it to an analyzer to determine such things as particulate matter or unburned hydrocarbons. The measurement device entrains a flow of clean ambient air by creating a pressure differential between the main flow being measured and the ambient entrained flow. The clean ambient flow rate is determined with a hot wire anemometer, and is calibrated to the total flow through the pipe to be measured. The system has been designed such that the same flow measurement device will work on a wide range of pipe sizes. The system has also been designed so that it is relatively easy to mount on an exhaust pipe. The measurement device may be located eccentric relative to the exhaust pipe. The shape of the device is such that at the bottom, the exhaust gas pressure in the stagnation zone is significantly higher than the static pressure of the exhaust in the stack.
In a still further embodiment, a gaseous mass flow measurement device may be inserted in any type of gaseous flow stream, from clean air to a stream containing products of combustion, such as the exhaust pipe on an internal combustion engine. The flow measurement device contains an optional sampling port to take a small portion of the flow and redirect it to an analyzer to determine such things as NOx, CO2, particulate matter or unburned hydrocarbons. The measurement device entrains a flow of clean ambient air by creating a pressure differential between the main flow being measured and the ambient entrained flow. The clean ambient flow rate is determined with a hot wire anemometer, and is calibrated to the total flow through the pipe to be measured.
The system is designed such that the same flow measurement device will work on a wide range of pipe sizes. The system is also designed so that it is relatively easy to mount on an exhaust pipe. The measurement device may be located eccentric relative to the exhaust pipe. The venturi or eductor accelerates the main flow stream by smoothly reducing the cross-sectional area. At the point where the main gaseous flow is traveling through the reduced cross-sectional area, referred to as the throat region, the total pressure is maintained while the static pressure is reduced due to an increase dynamic pressure caused by the increase in velocity. The pressure drop created at the throat region induces fresh ambient flow in through an opening at the throat which is connected to the fresh air. The downstream side from the throat is designed for pressure recovery. The measurement device may be used with full or partial exhaust flow.
The present invention may be employed on numerous different applications of a gas flowing through a pipe. The flowing gas can flow through an engine exhaust stack and be generated from an internal combustion engine. Throughout the following descriptions, the component creating the reduced pressure region will be referred to as a venturi. The word xe2x80x9ceductorxe2x80x9d may be substituted for the word venturi within any of these embodiments.
The invention comprises, in one form thereof, a method of determining a rate of flow of a first gas in a pipe. A flow-restricting device is placed in the pipe such that the device and/or the pipe define a first channel section and a second channel section. The second channel section is disposed downstream from the first channel section. The first channel section has a first cross-sectional area. The second channel section having a second cross-sectional area less than the first cross-sectional area. A source of a second gas is provided in fluid communication with the second channel section. A rate of a flow of the second gas into said second channel section is measured. A mathematical relationship between the rate of the flow of the second gas into the second channel section and the rate of flow of the first gas in the pipe is ascertained. The rate of flow of the first gas in the pipe is calculated based at least partially upon the rate of flow of the second gas into the second channel section and the ascertained mathematical relationship.
An advantage of the present invention is that the flow measurement device is not affected by pulsations, is very robust and is in no way degraded by the corrosive elements, particulate matter, heat, and vibration associated with exhaust pipes and exhaust systems.
Another advantage is that the relative size of the outer diameter of the flow module to the inner diameter of the exhaust pipe may or may not be similar. That is, the entire module does not need to fit tightly into the exhaust pipe. This attribute allows for the module to be sized smaller than the range of pipes expected to be encountered, thus providing increased ease of installation.
Yet another advantage is that the system is very precise and durable in that the flow measurement device does not get fouled by the exhaust.
A further advantage of the present invention is that it provides the greatest mass flow of exhaust gas through a tube that can be delivered to an external measurement device with the minimum generated unwanted backpressure in the exhaust stack.
A still further advantage of the present invention is that it provides an easily installed gaseous mass flow measurement device that can be utilized on an internal combustion engine without generating unacceptable backpressure.
Another advantage is that the flow device with the integral chemical analyzers can be easily, quickly and reliably inserted into a wide array of exhaust configurations without modifications such as cutting or adapting.