Energy Harvesting Technology for turbocompounding automotive engines with waste-gate valve

The reduction of CO2 and, more generally, GHG (Green House Gases) emissions imposed by the European Commission (EC) and the Environmental Protection Agency (EPA) for passenger cars has driven the automotive industry to develop technological solutions to limit exhaust emissions and fuel consumption, without compromising vehicle performance and drivability. In a mid-term scenario, hybrid powertrain and Internal Combustion Engine (ICE) downsizing represent the present trend in vehicle technology to reduce fuel consumption and CO2 emissions. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory for both Spark Ignition (SI) and Diesel engines. Following this aspect, the possibility to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. One method to recover exhaust gas energy from ICEs is the adoption of turbo-compounding technology to recover sensible energy left in the exhaust gas by-passed through the waste-gate valve. In the paper, an innovative option of advanced boosting system is investigated through a bladeless micro expander, promising attractive cost-competitiveness. The numerical activity was developed on the basis of experimental data measured on a waste-gated turbocharger for downsized SI automotive engines. To this aim, mass flow rate through the by-pass valve and the turbine impeller was measured for different waste-gate settings in steady-state conditions at the turbocharger test bench of the University of Genoa. The paper shows that significant electrical power can be harvested from the waste-gate gases, up to 94 % of compressor power, contributing to fuel consumption reduction.