Due to stringent emission requirements, such as Californian “Low Emission Vehicle - Ultra Low Emission Vehicle” or European “EURO2000”, as well as increased mileage requirement for vehicle emission durability, the catalyst aging process needs to be better understood.
Beside contamination (by silicon, phosphorus, lead,…), a concern for catalyst durability is thermal stress due, for instance, to engine misfiring, poor air-fuel mixture distribution or poor cylinder combustion during deceleration mode.
Uncontrolled lambda during engine acceleration mode gives alternately lean and rich mixtures. This will increase the concentration of oxygen and carbon monoxide in the exhaust gas.
Deceleration modes are generally calibrated for efficient engine braking with spark retard. This may lead to poor combustion when the pedal is released, with an increase of hydrocarbons and oxygen concentration in the exhaust. The emitted pollutants will be oxidized in the catalyst.
The exothermal reaction induced by the oxidation of hydrocarbons and carbon monoxide is not easily measurable in terms of catalyst overheating.
Lambda control deviation during acceleration or unburned fuel during deceleration may give, for a short period of time, high temperature peaks in the catalyst brick. The repetition of this process will have significant impact on catalyst aging.
Siemens has developed advanced software algorithms in order to better predict cylinder air intake efficiency and to better compensate for the fuel wall wetting evolution. This more precise air-fuel ratio control significantly improves engine emissions during transient mode. The improved software algorithms provide better control of the catalyst temperature fluctuations.
The conventional temperature measurement technique based on thermocouples is not fast enough and gives only limited concerning temperature peaks and distribution in the catalyst brick. This is the reason why Siemens applies a measurement technique based on catalyst surface area visualization with an infrared camera.
The proposed temperature visualization method allows a complete system approach in terms of transient control optimization for better catalyst overheating protection.