Numerical Investigation of 48 V Electrification Potential in Terms of Fuel Economy and Vehicle Performance for a Lambda-1 Gasoline Passenger Car

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 CO 2 emissions for type approval and RDE driving cycles. Numerical simulations highlighted potential improvements up to 16% CO 2 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.Energies 2019, 12, 2998 2 of 21 gases at a higher level, eliciting a further enrichment of the mixture. What is more, the use of mixture enrichment (i.e., moving from a stoichiometric to rich combustion) while cooling the in-cylinder charge and the exhaust gases, increases the CO emissions during high engine load operation, as highlighted by Clairotte et al. [3]. Moreover, future Regulation may prescribe a conformity factor for CO [4] limiting the exploitation of the fuel enrichment and pushing the development of the gasoline engines towards stoichiometric operation [5,6]. This aim can be achieved with the adoption of different powertrain technologies, like cooled exhaust manifold, high temperature resistant turbine as well as water injection, Miller cycle and advanced turbocharging, as explained by Glahn et al. [6].On the other hand, concerning the greenhouse emissions, the average fleet target value for CO 2 has been set to be 95 g/km from 2021 [7], measured according to the new Worldwide Harmonized Light-Duty Vehicles Test Procedure (WLTP) and correlated to the value of the New European Driving Cycle (NEDC). Moreover, recently the European Parliament and the Council adopted Regulation (EU) 2019/631 [8] setting CO 2 emission performance standards for new passenger cars in the EU for the

Fuel economy improvement and emission reduction of 48 V mild hybrid electric vehicles with P0, P1, and P2 architectures with lithium battery cell experimental data

“…11 The P0 architecture is mainly for engine start/stop function, while with limited motor power assist and regenerative braking due to belt slip, belt durability, and torque capability of the electric machine. [12][13][14] The P1 architecture, Crankshaft-ISG (C-ISG) or Flywheel-Alternator-Starter (FAS), replaces the conventional starter motor and alternator with a larger electric machine located between the engine flywheel and transmission. [15][16][17][18] A P1 architecture typically utilizes conventional transmissions with significant packaging changes to accommodate the increased envelope of the electric machine.…”

Real Driving Emissions—Conception of a Data-Driven Calibration Methodology for Hybrid Powertrains Combining Statistical Analysis and Virtual Calibration Platforms

“…With the potential of increasing the system efficiency and reducing the fuel consumption [9], one of the most common approaches for GHG reduction of passenger vehicles is the hybridization of the powertrains. For the operating strategy of hybrid vehicles, a good compromise between optimum fuel consumption, system efficiency, emission behavior and drivability is required [10].…”

Electric torque assist and supercharging of a downsized gasoline engine in a 48V mild hybrid powertrain

“…Especially with novel 48V power net topologies, the benefits of energy recuperation and torque assist via a BSG have drastically increased compared to previous 12V systems. 2–4 Improvements in electric motor technologies, power electronics, and microprocessors also allow for sufficiently high power output for eCs, enabling a rapid vehicle acceleration despite higher system inertia and making electric boosting a viable option for transient operation assist. 5…”

“…Especially with novel 48V power net topologies, the benefits of energy recuperation and torque assist via a BSG have drastically increased compared to previous 12V systems. [2][3][4] Improvements in electric motor technologies, power electronics, and microprocessors also allow for sufficiently high power output for eCs, enabling a rapid vehicle acceleration despite higher system inertia and making electric boosting a viable option for transient operation assist. 5 In principle, powertrains with electrified boosting systems can benefit from more efficient powertrain design and calibration, which can lead to essential fuel savings in transient driving scenarios in comparison to a conventional base variant.…”