Patent ID: 7571608

Claim:
A method of operating an engine system, comprising: routing a first portion of exhaust gases from an internal combustion engine to drive a variable geometry high pressure turbine of a high pressure turbocharger; routing a second portion of the exhaust gases to drive a variable geometry low pressure turbine of a low pressure turbocharger; routing a third portion of the exhaust gases to a low pressure compressor of the low pressure turbocharger to compress the third portion of exhaust gases for intake into the internal combustion engine, wherein the first and second portions of exhaust gases are different from one another, wherein the first and second portions of the exhaust gases are introduced simultaneously into the high pressure and low pressure turbines, respectively, wherein the exhaust gases do not pass from one turbine to another turbine of the respective turbochargers, and wherein the third portion includes at least some of the first portion of exhaust gases output from the high pressure turbine; and controlling operating parameters comprising varying flow of the third portion to change an amount of exhaust gas recirculation to reduce nitrogen oxide (NOx) emissions and to achieve a desired specific fuel consumption (SFC).