EGR for a two-stroke cycle engine without a supercharger
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.
1. A uniflow-scavenged, two-stroke cycle, opposed-piston engine comprising:
at least one cylinder with piston-controlled exhaust and intake ports, the exhaust and intake ports being longitudinally spaced so as to be disposed near respective ends of the at least one cylinder;
two crankshafts, in which each exhaust piston couples to a first crankshaft and each intake piston couples to a second crankshaft;
an exhaust channel coupled to at least one exhaust port of the engine; a charge air channel coupled to at least one intake port of the engine;
a power-assisted turbocharger with:
a compressor output coupled to the charge air channel;
a turbine coupled to the exhaust channel for being rotated by exhaust gas passing through the turbine; and
a turbine output coupled to an exhaust pipe;
a high pressure exhaust gas recirculation (EGR) loop having a loop input coupled to the exhaust channel upstream of the turbine and a loop output coupled to the charge aft channel downstream of the compressor and simultaneously connected to an inlet of at least one charge aft cooler;
an electrically-driven pump in the high pressure EGR loop to pump exhaust gas through the high pressure EGR loop into the charge air channel;
an electrically-controlled variable valve in the high pressure 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,
wherein the engine has no supercharger.
2. The uniflow-scavenged, two-stroke cycle, opposed-piston engine of claim 1 , in which the EGR loop further includes an EGR cooler in series with the pump.
3. A method of operating the uniflow-scavenged, two-stroke cycle, opposed-piston engine, the opposed-piston engine including:
at least one cylinder with piston-controlled exhaust and intake ports, the exhaust and intake ports being longitudinally spaced so as to be disposed near respective ends of the at least one cylinder;
two crankshafts, in which each exhaust piston couples to a first crankshaft and each intake piston couples to a second crankshaft; an exhaust channel coupled to at least one exhaust port of the engine; a charge air channel coupled to at least one intake port of the engine;
a power-assisted turbocharger with:
a compressor output coupled to the charge air channel;
a turbine coupled to the exhaust channel for being rotated by exhaust gas passing through the turbine; and
a turbine output coupled to an exhaust pipe;
a high pressure exhaust gas recirculation (EGR) loop having a loop input coupled to the exhaust channel upstream of the turbine and a loop output coupled to the charge air channel downstream of the compressor and simultaneously connected to an inlet of at least one charge air cooler;
an electrically-driven pump in the high pressure EGR loop to pump exhaust gas through the high pressure EGR loop into the charge air channel;
an electrically-controlled variable valve in the high pressure EGR loop between the loop input and the pump;
a control unit connected to provide control signals for the power-assisted turbocharger, the pump, and the valve; in which the engine has no supercharger, the method comprising:
pressurizing charge air via the compressor of the power-assisted turbocharger;
cooling the charge air being pressurized in at least one cooler;
delivering the charge air being pressurized and cooled to an intake port of each of the one or more cylinders; and
pumping engine exhaust gas in the high pressure exhaust gas recirculation (EGR) loop to an inlet of the at least one air charge cooler by controlling the electrically-driven pump in the high pressure EGR loop to reduce Nox emissions.