Emission system, apparatus, and method

An engine system, comprising:

• an engine having an intake manifold and an exhaust manifold;
• an exhaust conduit connected to the exhaust manifold to convey an exhaust gas away from the engine;
• a turbocharger having a turbine and a compressor driven by the turbine, wherein the turbine is connected to the exhaust conduit to receive the exhaust gas from the exhaust manifold, and wherein the compressor is positioned upstream of, and connected to, the intake manifold;
• and
• an exhaust gas recirculation (EGR) system connected to the exhaust conduit to receive at least a portion of the exhaust gas therefrom, the EGR system comprising:
• an EGR conduit connected to the exhaust conduit to receive the at least a portion of the exhaust gas;
• an expander connected to the EGR conduit and configured to expand the at least a portion of the exhaust gas and reduce a pressure thereof;
• a heat exchanger connected to the EGR conduit downstream of the expander to cool the at least a portion of the exhaust gas;
• and
• an EGR compressor connected to the EGR conduit downstream of the heat exchanger and configured to compress the at least a portion of the exhaust gas for recirculation to the intake manifold of the engine.

A method, comprising:

• conveying exhaust gas from an exhaust manifold of an internal combustion engine to an exhaust gas recirculation (EGR) system;
• expanding the exhaust gas in an expansion turbine in the EGR system to lower a temperature and to generate a mechanical power output;
• selectively transferring the expanded exhaust gas to an EGR compressor in the EGR system positioned downstream from the expansion turbine;
• compressing the exhaust gas in the EGR compressor to a desired pressure independently of the mechanical power output of the expansion turbine;
• and
• recirculating the compressed exhaust gas to an intake manifold of the internal combustion engine.