Ammonia occlusion amount estimation device and method, and purification control apparatus and method

An ammonia occlusion amount estimation method for estimating the amount of ammonia occluded in a selective catalytic reduction catalyst as an ammonia occlusion amount, the selective catalytic reduction catalyst being arranged in an exhaust pipe of an internal combustion engine so as to purify NOx in an exhaust gas of the internal combustion engine,

• the ammonia occlusion amount estimation method comprising:
• a first data acquisition step of acquiring first concentration identification data identifying the concentrations of NO and NO2 in the exhaust gas flowing into the selective catalytic reduction catalyst as an upstream NO concentration and an upstream NO2 concentration, respectively, and identifying the concentration of NO, NO2 and ammonia in the exhaust gas flowing out of the selective catalytic reduction catalyst as a downstream NO concentration, a downstream NO2 concentration and a downstream ammonia concentration, respectively;
• a second data acquisition step of acquiring second concentration identification data identifying the concentration of ammonia flowing into the selective catalytic reduction catalyst as an upstream ammonia concentration;
• and
• an occlusion amount estimation step of estimating the ammonia occlusion amount based on the first concentration identification data acquired by the first data acquisition step and the second concentration identification data acquired by the second data acquisition step by subtracting a purification usage amount and a slipped ammonia amount from an acquired urea injection amount, wherein
• the purification usage amount is calculated on the basis of the following reaction formulas (1), (2) and (3) for reduction of NOx with the selective catalytic reduction catalyst,
• 2NH3+NO+NO2→2N2+3H2O (1)
• 4NH3−4NO+O2→4N2+6H2O (2)
• 8NH3+6NO2→7N2+12H2O (3)
• an upstream NOx concentration is acquired from an upstream NOx sensor;
• the upstream NO2 concentration is acquired from an upstream NO2 sensor;
• the upstream NO concentration is determined based on the upstream NOx concentration and the upstream NO2 concentration;
• a downstream NOx concentration is acquired from a downstream NOx sensor;
• the downstream ammonia concentration is acquired from a downstream ammonia sensor;
• and
• the downstream NO concentration and the downstream NO2 concentration are determined based on the downstream NOx concentration and the downstream ammonia concentration.

A purification control method for controlling an urea supply unit to supply urea as a reducing agent to a selective catalytic reduction catalyst, the selective catalytic reduction catalyst being arranged in an exhaust pipe of an internal combustion engine so as to purify NOx in an exhaust gas of the internal combustion engine,

• the purification control method comprising:
• a first data acquisition step of acquiring first concentration identification data identifying the concentrations of NO and NO2 in the exhaust gas flowing into the selective catalytic reduction catalyst as an upstream NO concentration and an upstream NO2 concentration, respectively, and identifying the concentration of NO, NO2 and ammonia in the exhaust gas flowing out of the selective catalytic reduction catalyst as a downstream NO concentration, a downstream NO2 concentration and a downstream ammonia concentration, respectively;
• a second data acquisition step of acquiring second concentration identification data identifying the concentration of ammonia flowing into the selective catalytic reduction catalyst as an upstream ammonia concentration;
• and
• an occlusion amount estimation step of estimating, as ammonia occlusion amount, the amount of ammonia occluded in the selective catalytic reduction catalyst based on the first concentration identification data acquired by the first data acquisition step and the second concentration identification data acquired by the second data acquisition step by subtracting a purification usage amount and a slipped ammonia amount from an acquired urea injection amount,
• wherein the purification usage amount is calculated on the basis of the following reaction formulas (1), (2) and (3) for reduction of NOx with the selective catalytic reduction catalyst;
• and
• a supply control step of controlling the supply of the urea from the urea supply unit based on the ammonia occlusion amount estimated by the ammonia occlusion amount estimation step,
• 2NH3+NO+NO2→2N2+3H2O (1)
• 4NH3+4NO+O2→4N2+6H2O (2)
• 8NH3+6NO2→7N2+12H2O (3)
• wherein an upstream NOx concentration is acquired from an upstream NOx sensor;
• the upstream NO2 concentration is acquired from an upstream NO2 sensor;
• the upstream NO concentration is determined based on the upstream NOx concentration and the upstream NO2 concentration;
• a downstream NOx concentration is acquired from a downstream NOx sensor;
• the downstream ammonia concentration is acquired from a downstream ammonia sensor;
• and
• the downstream NO concentration and the downstream NO2 concentration are determined based on the downstream NOx concentration and the downstream ammonia concentration.