Unlock new possibilities of the best-in-class performance and fuel economy with SC-VNT
This innovation in turbocharger architecture pairs split compression and a variable geometry turbine on the same shaft to optimize the Brake Thermal Efficiency of heavily Millerized gasoline engines in HEV and PHEV passenger cars. The result is significantly improved Brake Specific Fuel Consumption (BSFC) and reduced CO2.
Enhancing the Value of Millerization
High degrees of Millerization allow for better knock resistance, earlier combustion phasing, and increased engine geometrical compression ratios. These all lead to enhanced Brake Thermal Efficiency (BTE).
Garrett’s VNT turbochargers enable Millerized gasoline engines to run in stoichiometric conditions across the whole engine map. However, the performance potential of a single compression stage turbine is limited to around 90 kW/l and a minimum BSFC circa 225 g/kWh. At such performance levels, the turbocharger is running close to its maximum limits in terms of speed and compressor outlet temperature.
With the Split Compression Variable Nozzle Geometry Turbo (SC-VNT) system developed by Garrett, two compressors are combined on the same shaft with a single VNT turbine wheel.
When the compressors are arranged in series with an external interstage cooler the configuration can generate compression ratios up to 6:1 without over-speeding the turbo. At the same time, the system maintains a wide composite compressor map with excellent overall efficiency.
Combining this technology with ultra Millerization can deliver BSFC levels approaching 200 g/kWh at 100-120 kW/L.
It’s a technology that can be applied to all spark ignition engines limited in BMEP by the phenomenon of “knock”.
Turbocharging a hybridized future
Garrett’s SC-VNT turbo optimizes the synergies and exploits the best potential of multiple components in a single turbo application. The technology is proven to enable ultra-high levels of Millerization in gasoline engines within hybrid powertrains, leading to significant benefits. These include:
- Delivering efficiency gains of up to 6.5% in Worldwide Harmonized Light Vehicles Test Cycle (WLTC) and 8% in Real Driving Emissions in a P2 48V MHEV
- Facilitating Brake Thermal Efficiencies (BTE) of up to 42.5% at over 100kW/L
- Enabling PR~6 (pressure ratio) through a single turbine, along with better thermal management and warm-up
SC-VNT has already demonstrated BSFC below 220 g/kWh across an extremely broad operating range of speeds and loads, with the potential to go further with the addition of EGR. It’s a technology perfectly in tune with leveraging the environmental benefits of electrified and hybridized powertrains. It offers manufacturers a route to high-efficiency engine performance – with no significant reduction in specific power – required to meet WLTC CO2 reductions of 15% by 2025 and 37.5% by 2030 (over NEDC targets).