EGR constructions for opposed-piston engines
View Patent ↗A two-stroke, opposed-piston engine with one or more ported cylinders and uniflow scavenging includes an exhaust gas recirculation (EGR) construction that provides a portion of the exhaust gasses produced by the engine for mixture with charge air to control the production of NOx during combustion.
1. A ported, uniflow-scavenged, opposed-piston engine including at least one cylinder with a bore and piston-controlled exhaust and intake ports, a pair of pistons disposed in opposition in the bore, each piston being coupled to a crankshaft, and a charge air channel to provide charge air to at least one intake port of the engine, in which an exhaust gas recirculation (EGR) loop has a loop input coupled to an exhaust port of the cylinder and a loop output coupled to the charge air channel, and the engine includes a pump in communication with the EGR loop to pump exhaust gas through the EGR loop into the charge air channel.
2. The ported, uniflow-scavenged, opposed-piston engine of claim 1 , in which the charge air channel includes at least one charge air cooler, wherein the loop output is coupled in series with the at least one charge air cooler.
3. The ported, uniflow-scavenged, opposed-piston engine of claim 2 , in which the EGR loop includes a valve settable to a first state or to a second state, wherein the first state couples the loop output to a charge air input of the at least one charge air cooler for increased cooling of recirculated exhaust gas and the second state couples the loop output to a charge air output of the at least one charge air cooler for decreased cooling of recirculated exhaust gas.
4. The ported, uniflow-scavenged, opposed-piston engine of claim 3 , in which the pump includes a supercharger and the at least one charge air cooler includes a charge air cooler with an input coupled to the compressor output of a turbo-charger and an output coupled to the input of the supercharger, in which the first state couples the loop output to the input of the charge air cooler and the second state couples the loop output to the input of the supercharger.
5. The ported, uniflow-scavenged, opposed-piston engine of claim 2 , further including a charge air source with a charge air output coupled to the input of the at least one charge air cooler, in which the loop output includes a valve settable to a first state or to a second state and a mixer with an exhaust gas input, a charge air input, and a mixer output coupled to the input of the at least one charge air cooler, in which the first state of the valve couples the loop output to the exhaust gas input of the mixer and the second state of the valve uncouples the loop output from the exhaust gas input of the mixer.
6. The ported, uniflow-scavenged, opposed-piston engine of claim 2 , in which the pump includes a supercharger with a supercharger input and a charge air output coupled to the charge air input of the at least one charge air cooler and a valve in parallel with the supercharger, in which the valve is settable to a first state in which the supercharger input is coupled through the valve to the charge air output of the supercharger and to a second state in which the supercharger input is uncoupled through the valve from the charge air output of the supercharger.
7. The ported, uniflow-scavenged, opposed-piston engine of claim 1 , further including a turbo-charger with a charge air output coupled to the charge air channel and a turbine input coupled to the exhaust port, and a back pressure valve in series between the turbine input and the exhaust port, in which the back pressure valve is settable to a state causing a back pressure acting upon the exhaust port.
8. The ported, uniflow-scavenged, opposed-piston engine of claim 7 , in which the turbo-charger includes a variable-geometry turbine.
9. The ported, uniflow-scavenged, opposed-piston engine of claim 1 , further including a turbo-charger with a charge air output coupled to the charge air channel, a turbine input coupled to the exhaust port, a turbine output coupled to an exhaust output, and a back pressure valve in series between the turbine output and the exhaust output, in which the back pressure valve is settable to a state causing a back pressure acting upon the exhaust port.
10. The ported, uniflow-scavenged, opposed-piston engine of claim 9 , in which the turbo-charger includes a variable-geometry turbine.
11. The ported, uniflow-scavenged, opposed-piston engine of claim 1 , further including a turbo-charger with a charge air output coupled to the charge air channel and a turbine with an input coupled to the exhaust port and a turbine bypass valve in parallel with the turbine, in which the turbine bypass valve is settable to a first state in which the turbine input is coupled through the valve to a turbine output and to a second state in which the turbine input is uncoupled through the valve from the turbine output.
12. The ported, uniflow-scavenged, opposed-piston engine of claim 11 , in which the turbo-charger includes a variable-geometry turbine.