Kang, J., Lee, J., Song, H., and Lee, D., "Enhancing Power Density with Two-Stage Turbochargers," SAE Technical Paper 2012-01-0709, 2012, doi:10.4271/2012-01-0709.
For passenger car diesel engines, higher air density or higher boost pressure is essential to enhance power density and meet stringent emission regulations. However, single variable geometry turbines (VGT) are limited to eliminate the inherent drawbacks of turbochargers; low-end torque and rated power are hard to reconcile.With a serial two-stage turbocharger, outstanding power density - rated power of 165kW and low-end torque of 350Nm - was obtained from Hyundai Motor's R2.2l engine. Also, it was possible to maintain the maximum torque of 500Nm evenly from 1250rpm up to 2250rpm. Compared to the current R2.2l engine with a single VGT turbocharger, more than 12% of power density increased.The fuel economy of the two-stage turbocharged engine was slightly better than the current R2.2l engine, which resulted in further reduction of fuel consumption compared to a 3.0l single VGT engine. Vehicle test results also showed that the R2.2l engine with two-stage turbocharger could substitute the 3.0l single VGT engine without any deterioration of drivability.