Abstract
Real Driving Emissions (RDE) regulations require the adoption of stoichiometric operation across the entire engine map for downsized turbocharged gasoline engines, which have been so far generally exploiting spark timing retard and mixture enrichment for knock mitigation. However, stoichiometric operation has a detrimental effect on engine and vehicle performances if no countermeasures are taken, such as alternative approaches for knock mitigation, as the exploitation of Miller cycle and/or powertrain electrification to improve vehicle acceleration performance. This research activity aims, therefore, to assess the potential of 48 V electrification and of the adoption of Miller cycle for a downsized and stoichiometric turbocharged gasoline engine. An integrated vehicle and powertrain model was developed for a reference passenger car, equipped with a EU5 gasoline turbocharged engine. Afterwards, two different 48 V electrified powertrain concepts, one featuring a Belt Starter Generator (BSG) mild-hybrid architecture, the other featuring, in addition to the BSG, a Miller cycle engine combined with an e-supercharger were developed and investigated. Vehicle performances were evaluated both in terms of elasticity maneuvers and of CO2 emissions for type approval and RDE driving cycles. Numerical simulations highlighted potential improvements up to 16% CO2 reduction on RDE driving cycle of a 48 V electrified vehicle featuring a high efficiency powertrain with respect to a EU5 engine and more than 10% of transient performance improvement.
Highlights
The regulatory framework for light-duty vehicles concerning both pollutants emissions and greenhouse gasses has become increasingly demanding in the last decade.As far as pollutant emissions are concerned, the introduction of the Worldwide HarmonizedLight-Duty Vehicles Test Procedure (WLTP) and of Real Driving Emissions (RDE) tests may represent a major challenge for car manufacturers
48 V electrification benefits in terms of fuel economy and vehicle performance for a gasoline passenger and the 48 V electrification benefits in terms of fuel economy and vehicle performance for a gasoline car were investigated through numerical simulation
Vehicle performance and fuel consumption were passenger car were investigated through numerical simulation
Summary
The regulatory framework for light-duty vehicles concerning both pollutants emissions and greenhouse gasses has become increasingly demanding in the last decade.As far as pollutant emissions are concerned, the introduction of the Worldwide HarmonizedLight-Duty Vehicles Test Procedure (WLTP) and of Real Driving Emissions (RDE) tests may represent a major challenge for car manufacturers. The new European Regulation [1] requires the declaration of Auxiliary Emissions Strategies (AES) which may be activated during real driving operation and may have an impact on tailpipe pollutant emissions Among these techniques, the fuel enrichment is a widely used practice in downsized gasoline engine to prevent engine damage from hot exhaust gases. As a matter of fact, downsized and turbocharged engines demonstrated to be an effective solution for fuel consumption reduction on type-approval driving cycles [2], but at the same time they require the exploitation of techniques (as spark timing delay and mixture enrichment) to increase the specific output power without component lifetime deterioration In this context, embracing the strategy of delaying the spark timing for knock mitigation brings the temperature of the exhaust
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