Energy recovery potential by replacing the exhaust gases recirculation valve with an additional turbocharger in a heavy-duty engine

A simulation-based assessment of different twin-turbocharging configurations allowing energy recovery from the exhaust gas recirculation flow is performed in a heavy-duty engine from the basis of a single-stage turbocharging architecture. This baseline configuration consists of a single stage turbocharged engine with a low-pressure exhaust gas recirculation system. Experimental data from the baseline engine tests are used to calibrate the model. The novelty of this study is to evaluate the energy recovery potential from the low-pressure exhaust gas recirculation flow by replacing its control valve with a turbine so that the flow energy is not lost due to the expansion across the valve. This additional turbine is coupled to a compressor placed in the intake line so that the turbocharging system is converted into a twin-turbocharging architecture. Different twin-turbocharging con-figurations are tested to attain maximum exhaust gas recirculation rates at 1100, 1500, and 2200 rpm engine speeds with boost pressures ranging from 1.8 to 2.6 bar. Fuel consumption calculations have been performed at constant exhaust gas recirculation rates for all three speeds as well as 1500 rpm partial load operation to attain 11.5 bar of brake mean effective pressure. The results in 8 engine running conditions show that twin-turbocharging with the compressors in series configuration with the exhaust gas recirculation turbine dis-charging after the first stage benefits, in average, from increasing about 5% maximum exhaust gas recirculation rates and saves up to 7% in fuel economy compared to the single-stage turbocharging layout.