Backpressure Supercompensation in a Novel Electrically Assisted Turbo Compound

In the current environmental and political scenario, hybrid vehicles play crucial roles in the transition to sustainable mobility. The role of internal combustion engines (ICEs) is also of utmost importance to comply with the even more stringent emissions regulations. To that end, also considering the need for increased power density in ICEs, turbocharging allows for improved performance and reduced emissions. Within this context, the present paper introduces the novelties of a patented turbo compound layout with supercharging capabilities, i.e., the Turbo Generator Electric Multistage Supercharger (TGEMS) system. The analysis also allowed for providing evidence of a “backpressure supercompensation effect” associated with rising exhaust backpressure in the ICE. TGEMS introduces a novel compressor group decoupled from the turbine. The analyses were carried out on a 2.0 L turbocharged gasoline direct injection engine. The “supercompensation” phenomenon was isolated using a stepwise procedure in which TGEMS was initially applied to the baseline engine to be exploited on a modified configuration featuring a downscaled turbine. The results were analyzed from the perspectives of specific fuel consumption reduction and total power output as well as operating flexibility increase. The results indicate that, in a context like TGEMS, the assumption that rising exhaust backpressure is always penalizing is no longer valid. Under higher backpressure conditions, TGEMS alone achieved −4.92% in specific fuel consumption at 5000 rpm, with +8.75% in maximum power output. Moreover, with the configuration with a downscaled turbine and the possibility to control the engine operating line, specific fuel consumption reductions of −7.93% at 5000 rpm and −6.83% at 3000 rpm were achieved. The maximum power output increment was +11.04%. These outcomes could open up to new downsizing perspectives and a new generation of “super-backpressured engines”.