Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2001-11-20
2004-04-13
Dolinar, Andrew M. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C073S023310, C340S632000, C060S276000
Reexamination Certificate
active
06721649
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and portable apparatus for testing engine exhaust, particularly the exhaust from large industrial engines.
BACKGROUND OF THE INVENTION
Large, industrial engines are used for a variety of purposes, including: to generate electrical power; to drive pumps; and to drive compressors for the compression of natural gas in pipelines. In use, these engines emit a variety of gases, including carbon monoxide (“CO”), carbon dioxide (“CO
2
”) and nitrogen/oxygen compounds (“NO” and “NO
2
”) Concern about the environmental effect of the exhaust from these engines has resulted in widespread regulation of the operation of these engines, and particularly regulation of exhaust emissions. In many countries, these engines may not be operated without a permit granted by the relevant regulatory body.
Typically, such permits set out maximum emission limits for specified gases. The permit for a particular engine may merely set out a maximum emission rate for each specified gas or it may specify a maximum emission rate for each specified gas at a specified engine load. To ensure that the engine complies with the permitted emission rate, such permits also typically require that the engine emissions be monitored using a specified testing protocol. The permit may require that the emissions be monitored continuously, but more commonly, such permits require that the engine be tested periodically, such as every year.
The test protocols for periodic engine emission testing typically require that a series of tests of set duration be conducted. As well, the test protocols typically specify pre-test and post-test calibration procedures for the gas sensors used to measure the concentration of the test gases. Typically, when an industrial engine is tested for compliance with the permitted emission rate, neither the emission rates of the test gases nor the engine load can be easily measured directly. Rather, the test protocols provide for a variety of different measurements to be taken so as to enable the testers to estimate the emission rates of the test gases and the engine load.
It is difficult to measure the weight per unit time of a given regulated effluent gas (test gas) directly, so it is conventional to measure the concentration of the test gas in the exhaust and the volume of the exhaust gas and from those measurements compute the rate of emission of the test gas in pounds per hour (lbs/hr) or other designated units of measurement. In simple terms, the emission rate of a test gas is determined by: measuring the concentration of the test gas, typically in parts per million; determining or at least estimating the exhaust gas volumetric flow (that is, the rate of exhaust gas emission as indicated by a unit of volume over a unit of time); and using these two numbers to estimate the emission rate of the test gas.
It is, however, further difficult to accurately directly measure the volumetric flow of the hot, turbulent exhaust gas. Therefore, conventionally, the exhaust gas volumetric flow is also estimated. For an engine powered by natural gas, the exhaust gas volumetric flow can be estimated from: the volumetric flow of the fuel gas; a fuel factor constant; and the concentration of oxygen (O
2
) in the exhaust gas. The volumetric flow of the fuel gas can be measured directly with a flowmeter, but it must be corrected for temperature and pressure to be of use in estimating the exhaust gas volumetric flow. The fuel factor constant is determined from the concentrations of the constituent compounds of the fuel gas. In simple terms, the exhaust gas volumetric flow is estimated by determining the corrected volume of fuel gas and calculating, on the basis of the fuel gas composition, what the volume will be after combustion, with a correction for the concentration of O
2
in the exhaust gas.
As well, using previously known procedures and conventional portable apparatus for engine emission testing, the engine load is usually estimated from the work done by whatever equipment the engine is driving. For example, if the engine is driving a compressor, the work done by the compressor may be determined by measuring the pressure and volumetric flow of gas upstream of the compressor, and the pressure of the gas downstream of the compressor. Such measurements can be used to determine the work done by the compressor, but, due to power losses in the compressor, and in the linkage between the engine and the compressor, they may not be an accurate indicator of the engine load. Depending on these power losses, the actual engine load may be up to 12% greater than the engine load estimated by this method, resulting in errors in the emission test results. While some tolerance for such errors can be taken into account when the regulatory authority sets emission standards, it would be preferable to obtain more accurate measurements of engine load.
The concentrations of the test gases can be measured directly with any of a variety of commercially available gas analyzers, including electrochemical, non-dispersive infrared and chemiluminescence gas analyzers. Typically, these gas analyzers contain sensors (also referred to in the trade as “cells”) for measuring the concentration (in parts per million) of the gases specified in the engine permit (usually CO, CO
2
, NO and NO
2
) As well, the gas analyzers typically also measure the concentration of O
2
. In the known procedures for analyzing engine emissions, the O
2
measurements are used as indicators of whether the engine is running in a rich or lean combustion state.
The sensors may be cross-sensitive in that their accuracy may be affected by the presence of non-target gases (referred to as “interfering gases”). Cross-sensitivity is also referred to as the interference response. A sensor's cross-sensitivity to a particular interference gas is tested by exposing the sensor and a sensor targeted to the interference gas, to a test gas containing the interference gas but not containing the target gas of the sensor being tested for cross-sensitivity. For example, a NO
2
sensor's cross-sensitivity to NO would be tested for by exposing the NO
2
sensor and a NO sensor to a test gas containing NO but not containing NO
2
. Any response by the NO
2
sensor to the test gas would be due to cross-sensitivity. Cross-sensitivity may be quantified by comparing the interference response of the sensor being tested (the NO
2
sensor in the example) with the response of the interference-gas-targeted sensor (the NO sensor in the example).
The measurements from the gas sensors may not be stable, in that they may have a tendency to drift over time when the sensor is exposed to a gas with a constant concentration of the relevant test gas. This quality of the sensors is referred to as stability or sensor drift, the two terms implying opposite characteristics. Sensor drift may be evaluated by exposing the sensor to a calibration gas and noting how the sensor measurements vary over time. The extent of sensor drift is often stated as the maximum absolute percentage deviation from an average measurement recorded shortly after the measured response time of the sensor.
Further, the accuracy of the measurements from a sensor may not be consistent over a range of concentrations, particularly when the sensor is subject to rapidly changing concentrations of the test gas. This quality of a sensor is referred to as degree of linearity of the sensor, or simply “linearity”. Linearity is tested by first exposing a sensor to at least two gases having different concentration of the test gas, one after the other, and observing the response of the sensor over time to the different concentrations of the test gas.
The test protocols typically require that the sensors be calibrated within a specified period before and after the relevant test. The test protocols typically require that the sensors be tested for calibration error and cross-sensitivity before and after each test run. The calibration error test results may be used to correct the sensor's measurem
Knott Christopher Norman
Knott Norman Sydney
Barrigar Robert H.
Dolinar Andrew M.
Oasis Emission Consultants Inc.
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