Analysis of the integration of the three-way catalyst thermal management in the on-line supervisory control strategy of a gasoline full hybrid vehicle

Full hybrid electric vehicles have proven to be a midterm viable solution to fulfil stricter regulations, such as those regarding carbon dioxide abatement. Although fuel economy directly benefits from hybridization, the use of the electric machine for propulsion may hinder an appropriate warming of the aftertreatment system, whose temperature is directly related to the emissions conversion efficiency. The present work evaluates the efficacy of a supervisory energy management strategy based on Equivalent Minimization Consumption Strategy (ECMS) which incorporates a temperature-based control for the thermal management of the Three-Way Catalyst (TWC). The impact of using only the midspan temperature of TWC is compared against the case where temperature at three different sampling points along the TWC length are used. Moreover, a penalty term based on TWC temperature has been introduced in the cost functional of the ECMS to allow the control of the TWC temperature operating window. In fact, beyond a certain threshold, the increase of the engine load, requested to speed up TWC warming, does not translate into a better catalyst efficiency, because the TWC gets close to its highest conversion rate. A gasoline P2 parallel full hybrid powertrain has been considered as test case. Results show that the effects of the different calibrations strategies are negligible on the TWC thermal management, as they do not provide any improvements in the fuel economy nor in the emissions abatement of the hybrid powertrain. This effect can be explained by the fact that the charge sustaining condition has a greater weight on the energy management strategy than the effects deriving from the addition of the soft constraints to control the TWC thermal management. These results hence encourage the use of simple setups to deal with the control of the TWC in supervisory control strategies for full hybrid electric vehicles

Analysis of the integration of the three-way catalyst thermal management in the on-line supervisory control strategy of a gasoline full hybrid vehicle

Full hybrid electric vehicles have proven to be a midterm viable solution to fulfil stricter regulations, such as those regarding carbon dioxide abatement. Although fuel economy directly benefits from hybridization, the use of the electric machine for propulsion may hinder an appropriate warming of the aftertreatment system, whose temperature is directly related to the emissions conversion efficiency. The present work evaluates the efficacy of a supervisory energy management strategy based on Equivalent Minimization Consumption Strategy (ECMS) which incorporates a temperature-based control for the thermal management of the Three-Way Catalyst (TWC). The impact of using only the midspan temperature of TWC is compared against the case where temperature at three different sampling points along the TWC length are used. Moreover, a penalty term based on TWC temperature has been introduced in the cost functional of the ECMS to allow the control of the TWC temperature operating window. In fact, beyond a certain threshold, the increase of the engine load, requested to speed up TWC warming, does not translate into a better catalyst efficiency, because the TWC gets close to its highest conversion rate. A gasoline P2 parallel full hybrid powertrain has been considered as test case. Results show that the effects of the different calibrations strategies are negligible on the TWC thermal management, as they do not provide any improvements in the fuel economy nor in the emissions abatement of the hybrid powertrain. This effect can be explained by the fact that the charge sustaining condition has a greater weight on the energy management strategy than the effects deriving from the addition of the soft constraints to control the TWC thermal management. These results hence encourage the use of simple setups to deal with the control of the TWC in supervisory control strategies for full hybrid electric vehicles

Improvement of the Control-Oriented Model for the Engine-Out NOX Estimation Based on In-Cylinder Pressure Measurement

Nowadays, In-Cylinder Pressure Sensors (ICPS) have become a mainstream technology that promises to change the way the enginecontrol is performed. Among all the possible applications, the prediction of raw (engine-out) NOX emissions would allow to eliminate the NOX sensor currently used to manage the aftertreatment systems. In the current study, a semi-physical model already existing in literature for the prediction of engine-out nitric oxide emissions based on in-cylinder pressure measurement has been improved; in particular, the main focus has been to improve nitric oxide prediction accuracy when injection timing is varied. The main modification introduced in the model lies in taking into account the turbulence induced by fuel spray and enhanced by in-cylinder bulk motion. The effectiveness of the new model has been tested with data acquired during an extensive experimental campaign during which a 2.0l 4 cylinders Diesel engine, whose after-treatment system allows to fulfil the EU6 legislation limits, has been operated on the overall engine map. It is shown that, comparing measured and estimated NOX on a wide range of engine settings, the improved model is quite effective in capturing the effect of injection timing on engine-out NOX emissions: the average error between measured and estimated NOX is reduced of about 10% while the correlation coefficient is increased from 0.86 to 0.97

Effect of Incorporating the Thermal Management of the Three-Way Catalyst on Energy Efficiency and Tailpipe Emissions for a P2 Parallel Hybrid Vehicle

The energy management of hybrid electric vehicles (HEVs) is a complex subject that can be addressed with the tools provided by optimal control theory. Optimization algorithms explored so far in the literature, like dynamic programming (DP) or equivalent consumption minimization strategy (ECMS), have systematically analyzed the potential CO2 reduction for different topologies and degree of hybridization. However, the management of engine and electric machine (EM) neglects that the catalyst material in the aftertreatment system needs to reach a certain temperature to properly convert pollutant emissions. In this study, the thermal management of the catalyst in a gasoline HEV has been investigated, and two algorithms have been proposed. Two strategies based on the ECMS are presented: the first one explicitly considers the catalyst temperature; the second one keeps the underlying structure of ECMS, but it adds a high-level rule to indirectly encompass catalyst management. To have a reliable catalyst temperature, a monodimensional model for the three-way catalyst (TWC), incorporating chemical kinetics, has been implemented. Finally, both strategies have been assessed via numerical simulations on two different driving cycles: the Worldwide harmonized Light vehicles Test Cycle (WLTC) and the Transport for London cycle (TfL), an urban driving cycle that is selected as a worst-case scenario for the thermal management of the aftertreatment system. On the WLTC both strategies show a 2% increase in fuel consumption with a potential 60% NOx reduction. On the urban cycle, only the second strategy is able to ensure the catalyst heating in a reasonable timespan. However general trends are still confirmed: when the catalyst thermal management is incorporated into the energy management strategy, since the first ignition, the engine produces extra power and charges the battery so that the TWC reaches the light-off temperature over a time-lapse comparable with a conventional vehicle. The stored energy is exploited at higher power demands to reduce the fuel consumption. The average engine load is hence shifted upwards in comparison to a fuel economy-oriented strategy