Emission reduction in a diesel engine by selective use of high-and low-pressure EGR loops
View Patent ↗A compression ignition engine ( 10 ) has an EGR system operable to provide a first EGR loop ( 46, 52, 54 ) when the engine is lightly loaded and a second EGR loop ( 46, 52, 56 ) when the engine is more heavily loaded. When the first EGR loop is selected, exhaust gas is recirculated from a location upstream of a turbine ( 20 ) of a turbocharger ( 18 ) to a location downstream of the turbocharger compressor ( 22 ). When the second EGR loop is selected, exhaust gas is recirculated from a location downstream of the turbine to a location upstream of the compressor.
1. A turbocharged compression ignition engine comprising:
engine cylinders within which combustion occurs to run the engine;
an intake system through which charge air is introduced into the cylinders;
an exhaust system through which products of combustion from the engine cylinders are exhausted;
a turbocharger having a turbine in the exhaust system and a compressor in the intake system;
a fueling system for fueling the cylinders;
an exhaust gas recirculation system for conveying exhaust gas from the exhaust system to the intake system and comprising
a direction control valve having an outlet, a first inlet communicated to the exhaust system upstream of the turbine, a second inlet communicated to the exhaust system downstream of the turbine, and an element that selectively communicates the inlets to the outlet to provide exhaust gas from a selected inlet to the outlet,
a cooler through which exhaust gas passes after leaving the direction control valve outlet,
a first EGR valve and a second EGR valve each having a respective inlet to which exhaust gas that has passed through the cooler is delivered,
the first EGR valve being operable, when the direction control valve is selecting the first inlet, to control flow of recirculated exhaust gas to a location in the intake system downstream of the compressor while the second EGR valve is closed, and
the second EGR valve being operable, when the direction control valve is selecting the second inlet, to control flow of recirculated exhaust gas to a location in the intake system upstream of the compressor while the first EGR valve is closed.
2. An engine as set forth in claim 1 wherein the intake system comprises an intercooler downstream of the compressor, and the first EGR valve delivers the throughflow to the intake system downstream of the intercooler.
3. An engine as set forth in claim 1 wherein the exhaust system comprises an exhaust gas treatment device downstream of the turbine and the second inlet of the direction control valve is communicated to the exhaust system downstream of the exhaust gas treatment device.
4. An engine as set forth in claim 3 wherein the exhaust gas treatment device comprises a diesel particulate filter.
5. An engine as set forth in claim 1 further including an engine control system for controlling the engine, including controlling the direction control valve and the first and second EGR valves.
6. An engine as set forth in claim 5 wherein the engine control system also controls fueling of the engine by the fueling system to cause the engine to operate, at least at times, by an alternative diesel combustion process.
7. An engine as set forth in claim 5 wherein the engine control system causes one of the EGR valves to be closed when operating the direction control valve to direct exhaust gas flow to the other EGR valve.
8. An engine as set forth in claim 7 wherein the engine control system causes the other EGR valve to be closed when operating the direction control valve to direct exhaust gas flow to the one EGR valve.
9. An engine as set forth in claim 5 wherein the engine control system comprises a processor for processing data values indicative of engine load and controlling the direction control valve and the first and second EGR valves in accordance with a result of the processing of those data values.
10. An engine as set forth in claim 9 wherein the engine control system causes the direction control valve to allow exhaust gas flow to the first EGR valve, causes the second EGR valve to be closed, and sets the extent to which the first EGR valve is allowed to open when the processing result discloses the engine operating at relatively lower load.
11. An engine as set forth in claim 9 wherein the engine control system causes the direction control valve to allow exhaust gas flow to the second EGR valve, causes the first EGR valve to be closed, and sets the extent to which the second EGR valve is allowed to open when the processing result discloses the engine operating at relatively higher load.
12. A turbocharged compression ignition engine comprising:
engine cylinders within which combustion occurs to run the engine;
an intake system through which charge air is introduced into the cylinders;
an exhaust system through which products of combustion from the engine cylinders are exhausted;
a turbocharger having a turbine in the exhaust system and a compressor in the intake system;
an exhaust gas recirculation system for conveying exhaust gas from the exhaust system to the intake system to aid in limiting in-cylinder combustion temperature comprising a first EGR loop comprising a first EGR valve and a second EGR loop comprising a second EGR valve for selectively recirculating exhaust gas and a direction control valve for controlling flow through the EGR loops;
and an engine control system for selectively operating the direction control valve to select one of the EGR loops to convey exhaust gas from the exhaust system to the intake system to the exclusion of the other of the EGR loops, wherein selection of the first EGR loop causes exhaust gas to be recirculated from a location upstream of the turbine through the first EGR valve and the direction control valve to a location downstream of the compressor and selection of the second EGR loop causes exhaust gas to be recirculated from a location downstream of the turbine through the second EGR valve and the direction control valve to a location upstream of the compressor.
13. A method of controlling exhaust emission during operation of a turbocharged compression ignition engine having engine cylinders within which combustion occurs to run the engine, an intake system through which charge air is introduced into the cylinders, an exhaust system through which products of combustion from the engine cylinders are exhausted, a turbocharger having a turbine in the exhaust system and a compressor in the intake system, a fueling system for fueling the cylinders, and an exhaust gas recirculation system for conveying exhaust gas from the exhaust system to the intake system to aid in limiting in-cylinder combustion temperature, the method comprising,
selectively operating a direction control valve for selecting between a first EGR loop containing a first EGR valve and a second EGR loop containing a second EGR valve to recirculate exhaust gas, wherein selection of the first EGR loop causes exhaust gas to be recirculated from a location upstream of the turbine through the direction control valve and first EGR valve to a location downstream of the compressor and selection of the second EGR loop causes exhaust gas to be recirculated from a location downstream of the turbine through the direction control valve and the second EGR valve to a location upstream of the compressor.
14. A method as set forth in claim 13 wherein the exhaust system comprises an exhaust gas treatment device downstream of the turbine, and when the second EGR loop is selected, exhaust gas is recirculated from a location downstream of the exhaust gas treatment device.
15. A method as set forth in claim 13 wherein the exhaust system comprises a diesel particulate filter downstream of the turbine, and when the second EGR loop is selected, exhaust gas is recirculated from a location downstream of the diesel particulate filter.
16. A method as set forth in claim 13 wherein the intake system comprises an intercooler downstream of the compressor, and when the first EGR loop is selected, exhaust gas is recirculated to a location in the intake system downstream of the intercooler.
17. A method as set forth in claim 13 including controlling the fueling system to cause the engine to operate, at least at times, by an alternative diesel combustion process.
18. A method as set forth in claim 13 wherein the step of selectively operating a direction control valve for selecting between a first EGR loop containing a first EGR valve and a second EGR loop containing a second EGR valve includes controlling recirculation of exhaust gas by controlling the first EGR valve when the direction control valve is in a first operating condition and controlling recirculation of exhaust gas by controlling the second EGR valve when the direction control valve is in the a second operating condition.
19. A method as set forth in claim 18 comprising operating the second EGR valve closed when the direction control valve is in the first operating condition and operating the first EGR valve closed when the direction control valve is in the second operating condition.
20. A method as set forth in claim 12 wherein the step of selectively operating a direction control valve for selecting between a first EGR loop containing a first EGR valve and a second EGR loop containing a second EGR valve comprises processing data values indicative of engine load and operating the direction control valve to select one of the EGR loops according to a result of the processing.
21. A method as set forth in claim 20 wherein the step of operating the direction control valve to select one of the EGR loops according to a result of the processing comprises operating the direction control valve to select the first EGR loop when a result of the processing discloses relatively lower engine load and operating the direction control valve to select the second EGR loop when a result of the processing discloses relatively higher engine load.