Exhaust gas recirculation methods and apparatus for reducing NOx emissions from internal combustion engines
View Patent ↗A method of operating an internal combustion engine employs exhaust gas recirculation (EGR) in combination with directly injected gaseous fuels that are burned within the engine in a stratified combustion mode. An engine that employs EGR includes an injector adapted to provide a high pressure quantity of fuel into a combustion chamber within a given pressure range, at a given angle and through a nozzle hole size to help provide for EGR tolerance and, consequently, reduce emissions.
1. A method of operating a gaseous-fuelled internal combustion engine, said method comprising:
during a cycle of said engine:
(a) directing an intake charge from an intake line into a combustion chamber of said internal combustion engine,
(b) compressing said intake charge within said combustion chamber,
(c) injecting a directly injected gaseous fuel into said compressed intake charge within said combustion chamber at a pressure above 12 MPa,
(d) igniting said directly injected gaseous fuel,
(e) burning said directly injected gaseous fuel,
(f) directing exhaust gas produced during burning of said directly injected gaseous fuel from said combustion chamber into an exhaust line,
wherein a quantity of said exhaust gas from said exhaust line is directed through an EGR line to said intake line and, during a subsequent cycle of said engine, a subsequent intake charge comprises said quantity of said exhaust gas; and
wherein said quantity of said exhaust gas is dependent on at least one of: (1) a target NOx concentration resulting from burning said directly injected gaseous fuel, and (2) said pressure.
2. The method of claim 1 wherein said pressure is dependent on said quantity of said exhaust gas.
3. The method of claim 1 further comprising injecting said directly injected gaseous fuel for a predetermined duration, said predetermined duration dependent on said quantity of said exhaust gas.
4. The method of claim 1 further comprising injecting said directly injected gaseous fuel for a predetermined timing, said predetermined timing dependent on said quantity of said exhaust gas.
5. The method of claim 1 further comprising commencing injection of said gaseous fuel at between −20 and 5 degrees ATDC.
6. The method of claim 1 wherein said directly injected gaseous fuel is injected at a pressure below 30 MPa.
7. The method of claim 1 wherein said directly injected gaseous fuel burns in a stratified combustion mode.
8. The method of claim 7 further comprising promoting diffusion combustion of said directly injected gaseous fuel.
9. The method of claim 7 wherein said intake charge within said intake line is substantially free of a gaseous fuel.
10. The method of claim 7 wherein said intake charge is substantially free of a gaseous fuel prior to introduction of said directly injected gaseous fuel.
11. The method of claim 1 further comprising cooling said quantity of said exhaust gas prior to directing said quantity of said exhaust gas from said intake line into said combustion chamber.
12. The method of claim 1 further comprising compressing said quantity of said exhaust gas prior to directing said quantity of said exhaust gas from said intake line into said combustion chamber.
13. The method of claim 1 further comprising directing a remaining quantity of said exhaust gas through a turbine of a turbo-charger after said quantity of said exhaust gas is directed into said EGR line.
14. The method of claim 1 further comprising directing said exhaust gas through a turbine of a turbo-charger before said quantity of said exhaust gas is directed into said EGR line.
15. A method of operating a gaseous-fuelled internal combustion engine, said method comprising:
during a cycle of said engine:
(a) directing an intake charge from an intake line into a combustion chamber of said internal combustion engine,
(b) compressing said intake charge within said combustion chamber,
(c) injecting a directly injected gaseous fuel into said compressed intake charge within said combustion chamber at a pressure above 12 MPa,
(d) igniting said directly injected gaseous fuel,
(e) burning said directly injected gaseous fuel,
(f) directing exhaust gas produced during burning of said directly injected gaseous fuel from said combustion chamber into an exhaust line,
(g) determining an emissions concentration within said exhaust gas directed from said combustion chamber, said emissions concentration being the concentration of one of:
(1) carbon monoxide,
(2) hydrocarbons,
(3) combined carbon monoxide and hydrocarbons,
(4) combined carbon monoxide and particulates,
(5) combined hydrocarbons and particulates, or
(6) combined carbon monoxide, hydrocarbons and particulates,
(h) determining an EGR rate set point at which said emissions concentration exceeds a maximum emissions concentration,
(i) adjusting said quantity of said exhaust gas to provide an EGR level below said set point when said emissions concentration exceeds said maximum emissions concentration,
wherein a quantity of said exhaust gas from said exhaust line is directed through an EGR line to said intake line and, during a subsequent cycle of said engine, a subsequent intake charge comprises said quantity of said exhaust gas.
16. A method of operating an internal combustion engine, said method comprising:
during a cycle of said engine:
(a) directing an intake charge from an intake line into a combustion chamber of said internal combustion engine,
(b) compressing said intake charge,
(c) introducing a fuel into said intake charge within said combustion chamber,
(d) igniting said fuel,
(e) burning said fuel,
(f) directing exhaust gas generated by combustion of said fuel from said combustion chamber into an exhaust line;
(g) determining an emissions concentration within said exhaust gas, said emissions concentration being the concentration of one of:
(1) carbon monoxide,
(2) hydrocarbons,
(3) combined carbon monoxide and hydrocarbons,
(4) combined carbon monoxide and particulates,
(5) combined hydrocarbons and particulates, or
(6) combined carbon monoxide, hydrocarbons and particulates,
(h) determining an EGR level set point at which said emissions concentration equals or exceeds a maximum emissions concentration,
(i) determining a predetermined quantity of said exhaust gas to direct through an EGR line, said quantity of said exhaust gas providing an EGR level below said set point,
(j) directing a quantity of said exhaust gas based on said predetermined quantity of said exhaust gas to an EGR line to said intake line, wherein during a subsequent cycle of said engine, a subsequent intake charge comprises said quantity of said exhaust gas.
17. The method of claim 16 wherein said emissions concentration is determined from a look up table based on a set of engine operating parameters.
18. The method of claim 16 wherein said emissions concentration is determined by a mathematical model based on a set of engine operating parameters.
19. The method of claim 16 wherein said emissions concentration is determined by reference to bench tests.
20. The method of claim 16 wherein said emissions concentration is measured directly.
21. The method of claim 16 further comprising injecting said fuel directly into said combustion chamber.
22. The method of claim 21 further comprising injecting said fuel for a predetermined pressure, said predetermined pressure dependent on said quantity of said exhaust gas.
23. The method of claim 21 further comprising injecting said fuel for a predetermined duration, said predetermined duration dependent on said quantity of said exhaust gas.
24. The method of claim 21 further comprising injecting said directly injected gaseous fuel for a predetermined timing, said predetermined timing dependent on said quantity of said exhaust gas.
25. The method of claim 21 further comprising injecting said fuel into said combustion chamber when a piston disposed in a cylinder within said internal combustion engine is at or near top dead center.
26. The method of claim 21 wherein said fuel is a gaseous fuel.
27. The method of claim 16 wherein said fuel bums in a stratified combustion mode.
28. The method of claim 21 wherein said fuel burns in a stratified combustion mode.
29. The method of claim 21 wherein said fuel comprises natural gas.
30. The method of claim 16 wherein said fuel is a gaseous fuel.
31. The method of claim 30 wherein said fuel bums in a stratified combustion mode.
32. The method of claim 30 wherein said fuel comprises natural gas.
33. The method of claim 31 wherein said fuel comprises natural gas.
34. The method of claim 16 wherein said fuel comprises natural gas.