NOx decreasing apparatus for an internal combustion engine

• US 5,412,946 A
• Filed: 10/15/1992
• Issued: 05/09/1995
• Est. Priority Date: 10/16/1991
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Yokota, Koji, Nakanishi, Kiyoshi, Muraki, Hideaki, Oshima, Yujiro
• Primary Examiner(s): Lazarus, Ira S.
• Assistant Examiner(s): HEYMAN, LEONARD
• Application Number:
  US07/961,230
• Time in Patent Office: 936 Days
• Field of Search: 60/286, 60/287, 60/295, 60/301, 60/303, 60/317, 60/320, 60/276, 423/213.2, 423/213.5, 423/239.2, 423/248
• US Class Current: 60/286
• CPC Class Codes: B01D 2251/202 Hydrogen
• CPC Class Codes: B01D 2251/208 Hydrocarbons
• CPC Class Codes: B01D 2251/21 Organic compounds not provided for in groups B01D2251/206 or B01D2251/208
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 2255/20746 Cobalt
• CPC Class Codes: B01D 2255/20753 Nickel
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/20784 Chromium
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 53/8696 Controlling the catalytic process
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: B01F 25/3131 with additional mixing means other than injector mixers, e.g. screens, baffles or rotating elements
• CPC Class Codes: B01F 25/31331 Perforated, multi-opening, with a plurality of holes
• CPC Class Codes: B01F 25/433 Mixing tubes wherein the shape of the tube influences the mixing, e.g. mixing tubes with varying cross-section or provided with inwardly extending profiles
• CPC Class Codes: B01F 25/4337 Mixers with a diverging-converging cross-section
• CPC Class Codes: F01N 2240/30 a fuel reformer
• CPC Class Codes: F01N 2610/04 : the substance being hydrogen
• CPC Class Codes: F01N 3/206 : Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence
• CPC Class Codes: F02B 1/04 : with fuel-air mixture admission into cylinder
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies

Abstract

A lean NOx reduction catalyst capable of reducing NOx through reaction of H₂ with NOx at low temperatures below 350° C. is installed in a downstream portion of an exhaust pipe of an internal combustion engine in or near a muffler. Such an NOx reduction catalyst comprises, for example, Pt/zeolite catalyst. An H₂ generator is installed so as to supply the H₂ to an inlet side of the NOx reduction catalyst. The H₂ generator may include a reforming catalyst for reforming methanol, LPG, or natural gas to generate H₂. The generated H₂ flows to the NOx reduction catalyst where it reacts with NOx to purify the exhaust gas.

Claims

1. An NO_x decreasing apparatus for an internal combustion engine comprising:

an internal combustion engine capable of fuel combustion at lean air-fuel ratios, the engine having an exhaust conduit, an upstream end of which is connected to the engine, and an exhaust muffler installed in the exhaust conduit;

an NO_x reduction catalyst installed at a downstream, low temperature location in the exhaust conduit, the NO_x reduction catalyst being a zeolite catalyst capable of causing H₂ to selectively react NO_x at temperatures lower than 300°

C. under a predetermined engine running condition, wherein the predetermined engine running condition includes an excess oxygen condition, to thereby decompose the NO_x into N₂ and H₂ O;

an H₂ generator for generating H₂, the H₂ generator including an inner core constructed of a tube inserted in the exhaust conduit, an electro-magnetic valve for injecting one of methanol and hydrocarbons into one end of the tube, and a reforming catalyst housed in the inner core; and

means for supplying the generated H₂ to an inlet side of the NO_x reduction catalyst, wherein the means for supplying the generated H₂ comprises a mixer for mixing H₂ with exhaust gas from the engine, wherein the mixer is located in the exhaust conduit at an inlet side of the NO_x reduction catalyst.

2. An apparatus according to claim 1, wherein the NOx reduction catalyst is a Pt/zeolite catalyst including zeolite and Pt carried on the zeolite and having a peak NOx conversion through reaction of NOx with H₂ at 100°

-150°

C.

3. An apparatus according to claim 1, wherein the H₂ generator includes a reforming catalyst for reforming methanol to generate H₂.

4. An apparatus according to claim 3, wherein the reforming catalyst includes at least one kind of catalyst metal selected from the group composed of noble metal including Pt and Pd and transition metal including Cu, Cr, and Ni, said methanol being evaporated by heat from exhaust gas and reformed at the reforming catalyst at about 300°

C. to generate H₂.

5. An apparatus according to claim 3, wherein the reforming catalyst comprises a Cu--Ni--Cr/alumina catalyst, said methanol being evaporated by heat from exhaust gas, mixed with air, and reformed at the reforming catalyst at 400°

-500°

C. to generate H₂.

6. An apparatus according to claim 3, wherein the reforming catalyst includes either one of Cu-Mn and Cu-Zn, said methanol being added with at least one of water vapor, air, and methanol water, and reformed at the reforming catalyst at about 250°

C. to generate H₂.

7. An apparatus according to claim 1, wherein the H₂ generator includes a reforming catalyst for reforming hydrocarbons selected from the group consisting of LPG and natural gas to generate H₂.

8. An apparatus according to claim 7, wherein the reforming catalyst includes at least one metal selected from the group composed of Ni, Co, and Rh, said hydrocarbons being added with at least one of water vapor, air, and water, and reformed at the reforming catalyst at 300°

-800°

to generate H₂.

9. An apparatus according to claim 1, wherein the engine is a hydrogen engine, and the H₂ generator comprises an H₂ fuel tank for the engine.

10. An apparatus according to claim 1, further comprising:

an NOx sensor for detecting an NOx concentration of exhaust gas to generate an output;

an intake air sensor for detecting a volume flow of intake air to generate an output; and

a controller for determining an amount of NOx included in exhaust gas from the engine based on the outputs of the NOx sensor and the intake air sensor, and determining an amount of H₂ required to reduce the determined amount of NOx.

11. An apparatus according to claim 1, further comprising:

engine operating condition detecting sensors for detecting engine operating conditions and generating output, the engine operating condition detecting sensors including an engine speed sensor and an engine load sensor;

a controller for determining an amount of NOx included in exhaust gas from the engine based on the outputs from the engine operating condition detecting sensors, and determining an amount of H₂ required to reduce the determined amount of NOx.

12. An apparatus according to claim 1, further comprising an oxidizing device located in the exhaust conduit upstream of the NO_x reduction catalyst for oxidizing hydrocarbons and CO included in exhaust from the engine, and wherein the engine has an exhaust manifold having an outlet and the muffler has an upstream end through which exhaust enters the muffler and a downstream end through which exhaust gas exits the muffler, the H₂ generator being disposed at the exhaust conduit upstream of the muffler, wherein the NO_x reduction catalyst is located downstream of an inlet end of the muffler.

13. An apparatus according to claim 1, further comprising an oxidizing device for oxidizing HC and CO included in exhaust gas from the engine, and wherein the NOx reduction catalyst is a Pt type catalyst which comprises platinum deposited on a carrier selected from the group consisting of zeolite, silica, and alumina.

14. An apparatus according to claim 13, wherein the Pt type catalyst of the NOx reduction catalyst is housed in the muffler to constitute a single assembly of the NOx reduction catalyst and the muffler.

15. An apparatus according to claim 1, wherein the tube includes a coiled portion and wherein the valve injects methanol into the tube, and wherein the reforming catalyst includes Pd.

16. An apparatus according to claim 1, wherein the NOx reduction catalyst comprises a pellet type catalyst.

17. An apparatus according to claim 1, wherein the NOx reduction catalyst comprises a monolithic type catalyst, and wherein the mixer comprises an injection nozzle connected to the H₂ generator and having a plurality of radially directed holes for injecting H₂ therethrough.

18. An apparatus according to claim 17, has an outside diameter equal to or greater than 20% of an inside diameter of the exhaust conduit, the exhaust conduit being enlarged in diameter at a portion in which the injection nozzle is disposed, the injection nozzle being spaced apart from the NOx reduction catalyst by a distance at least twice the inside diameter of the exhaust conduit and no more than ten times the inside diameter of the exhaust conduit.

19. An apparatus according to claim 1, wherein the NOx reduction catalyst comprises a monolithic type catalyst, and wherein the mixer comprises an injection nozzle having a first diameter, and a cylinder coaxial with and downstream of the injection nozzle, the cylinder having a second diameter greater than the first diameter and having a plurality of injection apertures formed in a wall of the cylinder.

20. An apparatus according to claim 19, wherein a ratio of the second diameter to the first diameter is in the range of 1.7 to 3.

21. An apparatus according to claim 20, wherein the ratio of the second diameter to the first diameter is substantially 2.

22. An apparatus according to claim 14, further comprising a mixing plate disposed in the muffler and upstream of the NOx reduction catalyst, the mixing plate comprising a plate having apertures of different sizes.

23. An apparatus according to claim 14, wherein the means for supplying the generated H₂ comprises a mixing pipe disposed in the muffler and connected to the exhaust conduit, the mixing pipe having apertures formed in a wall of the mixing pipe, the H₂ generator injecting the generated H₂ into the mixing pipe.

24. An apparatus according to claim 13, wherein the oxidizing device is any one of an afterburner, a reactor, a three-way catalyst, and an oxidation catalyst.

25. An apparatus according to claim 1, wherein the NO_x reduction catalyst is located downstream of an inlet end of the exhaust muffler.

26. An apparatus according to claim 25, wherein the NO_x reduction catalyst is located within the muffler.

27. An apparatus according to claim 25, wherein the NO_x reduction catalyst is located downstream of the muffler, near an outlet end of the muffler.