Method for easily measuring nitrogen oxide concentration of an engine vehicle emission

A method for easily measuring nitrogen oxide concentration of an engine exhaust gas, comprising:

• providing a first air-fuel ratio sensor, a second air-fuel ratio sensor, and a lean state NOx sensor for measuring the exhaust gas;
• disposing the first air-fuel ratio sensor, the second air-fuel ratio sensor, and the lean state NOx sensor on an exhaust pipe connected to an engine, the first air-fuel ratio sensor positioned upstream of the second air-fuel ratio sensor, and the second air-fuel ratio sensor positioned upstream of the lean state NOx sensor;
• introducing air into the exhaust pipe between the first air-fuel ratio sensor and the second air-fuel ratio sensor to dilute the exhaust gas;
• measuring a first air-fuel ratio of the exhaust gas prior to dilution with said first air ration sensor and using the second air-fuel ratio sensor to measure a second air-fuel ratio of the exhaust gas after dilution;
• measuring the concentration of lean state NOx within the diluted exhaust gas from a stoichiometrical region to a rich region using the lean state NOx sensor;
• and
• determining the NOx concentration prior to dilution by using the measured concentration of NOx after dilution and a ratio of the second air-fuel ratio and the first air-fuel ratio.

A method for easily measuring nitrogen oxide concentration of an engine exhaust gas, comprising:

• providing a first λ sensor, a second λ sensor, and a lean state NOx sensor for measuring the exhaust gas;
• disposing the first λ sensor, the second λ sensor, and lean state NOx sensor on an exhaust pipe connected to an engine, the first λ sensor positioned upstream of the second λ sensor, and the second λ sensor positioned upstream of the lean state NOx sensor;
• introducing air into the exhaust between the first λ sensor and the second λ sensor, wherein the first λ sensor determines a first air-fuel ratio in the exhaust gas prior to air dilution and the second λ sensor determines a second air-fuel ratio in the exhaust gas after air dilution;
• and
• determining the NOx concentration prior to dilution by using the measured concentration of NOx from a stoichiometrical region to a rich region using said lean state NOx sensor after dilution and multiplying the measured concentration of NOx by the ratio of the second and first air-fuel ratios.