Method and apparatus for providing diluent gas to exhaust emission analyzer

A method for preparing a diluted sample of exhaust gas from the exhaust system of an engine for analysis, said method including the steps of:

• extracting an exhaust gas sample from the exhaust system of an engine and passing said exhaust gas sample through an exhaust gas sampling line having an orifice;
• extracting a diluent gas from a diluent gas source and passing said diluent gas through a diluent line having an orifice;
• fitting a pressure regulator to said diluent line and in connection with said exhaust gas sampling line;
• controlling pressure such that said exhaust gas sampling line orifice produce substantially equal pressure drops thereacross, to maintain a substantially constant volumetric ratio of said exhaust gas sample and said diluent gas;
• introducing said diluent gas into said exhaust gas sample to create a diluted exhaust gas sample;
• establishing a dilution ratio between said diluent gas and said exhaust gas sample;
• directing said diluted exhaust gas sample to an exhaust emission analyzer at a flow rate sufficient for analysis;
• and
• analyzing said diluted exhaust gas sample.

An apparatus for controlling the dilution of an exhaust gas sample from the exhaust system of an engine for analysis, the apparatus comprising:

• an exhaust gas sampling line having first and second ends, said first end being fluidly connected to the exhaust system;
• an exhaust gas sampling line orifice fitted to said exhaust gas sampling line, said exhaust gas sampling line orifice having an inlet;
• a source of substantially pollutant-free diluent gas;
• a diluent line having first and second ends, said first end being connected to said source of substantially pollutant-free diluent gas;
• a diluent line orifice fitted to said diluent line, said diluent line orifice having an inlet;
• a diluent pressure regulator fitted to said diluent line and connected to said exhaust gas sampling line for controlling pressure such that said exhaust gas sampling line orifice and said diluent line orifice are configured so as to produce substantially equal pressure drops thereacross;
• a diluted gas outlet line having first and second ends, said first end being connected to an exhaust emission analyzer;
• a fluid junction, said second ends of said exhaust gas sampling line, said diluent line, and said diluted gas outlet line being connected to said fluid junction;
• and
• a system for drawing diluted exhaust gas sample through said diluted gas outlet line.