Method and apparatus to determine flow rate with the introduction of ambient air

A method of determining a rate of flow of an exhaust gas in a pipe, said method comprising the steps of:

• placing a flow-restricting device in the pipe such that at least one of said device and the pipe define a first channel section and a second channel section, said second channel section being disposed downstream from said first channel section, said first channel section having a first crass-sectional area, said second channel section having a second cross-sectional area less than the first cross-sectional area, said second channel section defining a pressure drop section relative to the exhaust gas;
• providing a source of ambient air in fluid communication with said second channel section;
• measuring a rate of a flow of the ambient air into said second channel section;
• ascertaining a mathematical relationship between the rate of the flow of the ambient air into the second channel section and the rate of flow of the exhaust gas in the pipe;
• and
• calculating the rate of flow of the exhaust gas in the pipe based at least partially upon the rate of flow of the ambient air into the second channel section and the ascertained mathematical relationship.

An apparatus for determining a rate of flow of an exhaust gas in a pipe, said apparatus comprising:

• a flow-restricting device configured for being placed in to pipe such that at least one of said device and the pipe define a first channel section and a second channel section, said second channel section being disposed downstream from said first channel section, said first channel section having a first cross-sectional area, said second channel section having a second cross-sectional area less than the first cross-sectional area, said second channel section defining a pressure drop section relative to the exhaust gas;
• a source of ambient air in fluid communication with said second channel section;
• a measuring device configured for measuring a characteristic of a flow of the ambient air into said second channel section;
• and
• a processor configured for calculating the rate of flow of the exhaust gas in the pipe based at least partially upon the measured characteristic of the flow of the ambient air into said second channel section.