EGR for a Two-Stroke Cycle Engine without a Supercharger

Abstract

A two-stroke cycle, turbo-driven, opposed-piston engine with one or more ported cylinders and uniflow scavenging has no supercharger. The engine includes a high pressure EGR loop and a pump in the EGR loop to boost the pressure of the recirculated exhaust products.

I claim: 
     
         1 . A uniflow-scavenged, two-stroke cycle engine including at least one cylinder with piston-controlled exhaust and intake ports and a charge air channel coupled to at least one intake port of the engine, in which the engine has no supercharger and comprises:
 a high pressure exhaust gas recirculation (EGR) loop having a loop input coupled to an exhaust port of the cylinder and a loop output coupled to the charge air channel;   a pump in the EGR loop to pump exhaust gas through the EGR loop into the charge air channel; and,   a turbocharger with a charge air output coupled to the charge air channel, a turbine input coupled to the exhaust port, and a turbine output coupled to an exhaust output.   
     
     
         2 . The uniflow-scavenged, two-stroke cycle engine of  claim 1 , in which the charge air channel includes at least one cooler, wherein the loop output is coupled in series with the at least one cooler. 
     
     
         3 . The uniflow-scavenged, two-stroke cycle engine of  claim 2 , in which the EGR loop includes a variable valve between the loop input and the pump. 
     
     
         4 . The uniflow-scavenged, two-stroke cycle engine of  claim 3 , in which the pump is a variable capacity pump. 
     
     
         5 . The uniflow-scavenged, two-stroke cycle engine of  claim 1 , further including a turbocharger with a charge air output coupled to the charge air channel and a turbine input coupled to the exhaust port. 
     
     
         6 . The uniflow-scavenged, two-stroke cycle engine of  claim 5 , in which the turbocharger includes a power-assist system. 
     
     
         7 . The uniflow-scavenged, two-stroke cycle engine of  claim 1 , further including a power-assist system coupled to the turbocharger. 
     
     
         8 . A uniflow-scavenged, opposed-piston engine including at least one cylinder with piston-controlled exhaust and intake ports, an exhaust channel coupled to at least one exhaust port of the engine, and a charge air channel coupled to at least one intake port of the engine, in which the engine has no supercharger and comprises:
 a power-assisted turbocharger with a compressor output coupled to the charge air channel, a turbine input coupled to the exhaust channel, and a turbine output coupled to an exhaust output   an exhaust gas recirculation (EGR) loop having a loop input coupled to the exhaust channel upstream of the turbine input and a loop output coupled to the charge air channel downstream of the compressor output;   an electrically-driven pump in the EGR loop to pump exhaust gas through the EGR loop into the charge air channel;   an electrically-controlled variable valve in the EGR loop between the loop input and the pump; and,   a control unit connected to provide control signals for the power-assisted turbocharger, the pump, and the valve.   
     
     
         9 . The uniflow-scavenged, opposed-piston engine of  claim 8 , in which the EGR loop further includes an EGR cooler in series with the pump. 
     
     
         10 . A method of operating a non-supercharged, uniflow-scavenged, opposed-piston engine with one or more cylinders, in which charge air is pressurized and then cooled in at least one cooler and provided to an intake port of each of the one or more cylinders, by pumping engine exhaust gas in a high pressure exhaust gas recirculation (EGR) loop to an input of the at least one air charge cooler.