Modeling catalyst exotherm due to blowthrough

A method of operating an internal combustion engine having a turbocharger and a catalyst, the method comprising:

• boosting engine intake air;
• adjusting one or more of intake valve and exhaust valve timing to generate positive valve overlap between the intake valve and the exhaust valve in response to a driver tip-in, the boosting generating blowthrough air from an intake manifold to an exhaust manifold of the engine;
• fueling the internal combustion engine for rich combustion during the boosting with positive valve overlap such that an air-fuel mixture in the exhaust of the rich combustion and blowthrough air is stoichiometric;
• determining a base temperature of the catalyst in response to exhaust temperature;
• determining an additional temperature rise of the catalyst during boosted positive valve overlap conditions based on an amount of blowthrough air and based on exhaust temperature, the additional temperature rise being determined to be smaller as exhaust temperature increases;
• and
• determining an estimate of catalyst temperature based on the base temperature and the additional temperature rise.

A method of operating an internal combustion engine having a turbocharger and a catalyst based on determination of a catalyst exotherm and blowthrough air, the method comprising:

• performing a boosting operation by generating valve overlap between an intake valve and an exhaust valve in response to a driver tip-in, the boosting operation generating blowthrough air;
• fueling a cylinder of the internal combustion engine for rich combustion during the boosting operation such that an air-fuel mixture in the exhaust is stoichiometric;
• determining a temperature of the exhaust;
• determining a base exotherm based on air and fuel trapped in the cylinder;
• determining a potential exotherm due to blowthrough based on a total heat released from an oxidization of the fuel in the exhaust and a total exhaust flow;
• adjusting the potential exotherm to account for energy loss due to port oxidation where chemical energy is converted to heat in an exhaust port, the potential exotherm decreasing as a temperature of an exhaust port flange increases;
• determining the catalyst exotherm based on the base exotherm and the adjusted potential exotherm;
• adjusting the determined temperature of the exhaust based on the determined catalyst exotherm;
• and
• if the determined temperature of the exhaust is greater than a threshold value, then performing a control action.