U.S. patent application number 09/951729 was filed with the patent office on 2002-04-04 for hydrogen-containing gas producing system and exhaust gas purifying system using same.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Akama, Hiroshi, Itou, Junji, Kaneko, Hiroaki.
Application Number | 20020038542 09/951729 |
Document ID | / |
Family ID | 18783492 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020038542 |
Kind Code |
A1 |
Akama, Hiroshi ; et
al. |
April 4, 2002 |
Hydrogen-containing gas producing system and exhaust gas purifying
system using same
Abstract
A hydrogen-containing gas producing system of an onboard type,
for producing hydrogen-containing gas to be used for purification
of exhaust gas of an internal combustion engine. The
hydrogen-containing system comprises a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas. A
carrier gas supply source is provided for supplying a carrier gas
for carrying the fuel. A device is provided for vaporizing the fuel
so as to form a vaporized fuel serving as a reaction gas. The fuel
vaporizing device is connected to the fuel supply source and the
carrier gas supply source. Additionally, a reforming section is
connected to the fuel vaporizing device, for reforming the reaction
gas so as to produce the hydrogen-containing gas.
Inventors: |
Akama, Hiroshi; (Kanagawa,
JP) ; Itou, Junji; (Yokohama, JP) ; Kaneko,
Hiroaki; (Yokohama, JP) |
Correspondence
Address: |
Richard L. Schwaab
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W.., Suite 500
Washington
DC
20007-5109
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
|
Family ID: |
18783492 |
Appl. No.: |
09/951729 |
Filed: |
September 14, 2001 |
Current U.S.
Class: |
60/283 ; 60/285;
60/286; 60/301 |
Current CPC
Class: |
F01N 3/0871 20130101;
F01N 13/009 20140601; C01B 2203/1685 20130101; F01N 2240/30
20130101; Y02T 10/12 20130101; Y02T 10/22 20130101; Y02P 20/52
20151101; C01B 2203/0261 20130101; Y02T 10/20 20130101; F01N
2610/03 20130101; C01B 3/386 20130101; F01N 2610/04 20130101; F01N
2610/08 20130101 |
Class at
Publication: |
60/283 ; 60/286;
60/285; 60/301 |
International
Class: |
F01N 003/00; F01N
003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2000 |
JP |
2000-302065 |
Claims
What is claimed is:
1. A hydrogen-containing gas producing system of an onboard type,
for producing hydrogen-containing gas to be used for purification
of exhaust gas of an internal combustion engine, said
hydrogen-containing system comprising: a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas; a
carrier gas supply source for supplying a carrier gas for carrying
the fuel; a device for vaporizing the fuel so as to form a
vaporized fuel serving as a reaction gas, -said fuel vaporizing
device being connected to said fuel supply source and said carrier
gas supply source; and a reforming section connected to said fuel
vaporizing device, for reforming the reaction gas so as to produce
the hydrogen-containing gas.
2. A hydrogen-containing gas producing system as claimed in claim
1, wherein the hydrogen-containing gas contains carbon monoxide in
an amount of not more than 100 ppm.
3. A hydrogen-containing gas producing system as claimed in claim
1, wherein said fuel supply source is adapted to supply liquid fuel
serving as the raw material of the hydrogen-containing gas, said
fuel vaporizing device is a gas mixer which is arranged to vaporize
the liquid fuel under action of the carrier gas so as to form the
vaporized fuel serving as the reaction gas.
4. A hydrogen-containing gas producing system as claimed in claim
1, wherein said reforming section includes a fuel reforming
catalyst containing rhodium.
5. A hydrogen-containing gas producing system as claimed in claim
1, further comprising a hydrogen-containing gas storing device for
storing the hydrogen-containing gas from said reforming
section.
6. A hydrogen-containing gas producing system as claimed in claim
1, wherein said fuel supply source also serves as a fuel supply
source for supplying fuel to the internal combustion engine.
7. A hydrogen-containing gas producing system as claimed in claim
3, wherein said reforming section is adapted to produce the
hydrogen-containing gas at a reaction temperature of the reaction
gas, ranging from 260 to 340.degree. C. and under a condition
represented by the following formula: an oxygen concentration in
the reaction gas.ltoreq.an average carbon number of hydrocarbons in
the liquid fuel.times.a concentration of the liquid fuel in the
reaction gas.times.1/2.
8. A hydrogen-containing gas producing system as claimed in claim
3, wherein the liquid fuel is light oil.
9. A hydrogen-containing gas producing system as claimed in claim
3, wherein the liquid fuel has hydrocarbons whose number of carbon
atoms is not smaller than 9.
10. A hydrogen-containing gas producing system as claimed in claim
1, wherein the fuel has hydrocarbons which are separated and
extracted from a liquid fuel, each of the hydrocarbons has a number
of carbon atoms, not smaller than 9.
11. An exhaust gas purifying system for an internal combustion
engine, comprising: a hydrogen-containing gas producing system of
an onboard type, for producing hydrogen-containing gas to be used
for purification of exhaust gas of an internal combustion engine,
said hydrogen-containing system including a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas, a
carrier gas supply source for supplying a carrier gas for carrying
the fuel, a device for vaporizing the fuel so as to form a
vaporized fuel as a reaction gas, said fuel vaporizing device being
connected to said fuel supply source and said carrier gas supply
source, and a reforming section connected to said fuel vaporizing
device, for reforming the reaction gas so as to produce the
hydrogen-containing gas, said reforming section being connected to
a part of an exhaust gas passageway of the internal combustion
engine so as to introduce the hydrogen-containing gas into exhaust
gas; and a NOx adsorbing and reducing catalyst disposed in the
exhaust gas passageway downstream of said part, said NOx adsorbing
and reducing catalyst being adapted to adsorb nitrogen oxides in
exhaust gas in a condition that exhaust gas is in a lean region,
and to reduce nitrogen oxides in exhaust gas in a condition that
exhaust gas is within a range including a stochiometric region and
a rich region, wherein the hydrogen-containing gas from said
reforming section of said hydrogen-containing gas is supplied into
the exhaust gas passageway at said part which is upstream of said
NOx adsorbing and reducing catalyst, at a low temperature range in
which a temperature of exhaust gas at a position immediately
upstream of said NOx adsorbing and reducing catalyst is not higher
than 250.degree. C., and in the condition that exhaust gas is
within the range including the stoichiometric region and the rich
region.
12. An exhaust gas purifying system as claimed in claim 11, further
comprising a three-way catalyst disposed in the exhaust gas
passageway upstream of said part to which a supply inlet for the
hydrogen-containing gas is located.
13. A hydrogen-containing gas producing system of an onboard type,
for producing hydrogen-containing gas to be used for purification
of exhaust gas of an internal combustion engine, said
hydrogen-containing system comprising: a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas; a
carrier gas supply source for supplying a carrier gas for carrying
the fuel; means for vaporizing the fuel so as to form a vaporized
fuel serving as a reaction gas, said fuel vaporizing means
receiving the fuel from said fuel supply source and the carrier gas
from said carrier gas supply source; and a reforming section
connected to said fuel vaporizing device, for reforming the
reaction gas so as to produce the hydrogen-containing gas.
14. An exhaust gas purifying system for an internal combustion
engine mounted on an automotive vehicle, comprising: a catalyst for
reducing nitrogen oxides in exhaust gas of the engine, disposed in
an exhaust gas passageway of the engine and mounted on the vehicle,
said catalyst containing at least one of platinum and palladium;
and a hydrogen-containing gas producing system for producing
hydrogen-containing gas, mounted on the vehicle, said
hydrogen-containing system including a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas, a
carrier gas supply source for supplying a carrier gas for carrying
the fuel, a device for vaporizing the fuel so as to form a
vaporized fuel as a reaction gas, said fuel vaporizing device being
connected to said fuel supply source and said carrier gas supply
source, and a reforming section connected to said fuel vaporizing
device, for reforming the reaction gas so as to produce the
hydrogen-containing gas, said reforming section being connected to
a part of the exhaust gas passageway upstream of said catalyst so
that the hydrogen-containing gas is supplied to said catalyst.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to improvements in a
hydrogen-containing gas producing system and an exhaust gas
purifying system using the hydrogen-containing gas producing
system, and more particularly to the exhaust gas purifying system
for reducing or removing nitrogen oxides (NOx) in exhaust gas
having its lean condition by using a catalyst.
[0002] Hitherto, so-called lean-burn engines operated at an
air/fuel ratio higher or leaner than a stoichiometric level have
been come into wide use from the view points of improving fuel
economy (fuel consumption) and reducing emission of carbon dioxide.
Attention has been particularly paid on diesel engines as the
lean-burn engines in view of the fact that the diesel engines are
high in combustion efficiency and good in fuel economy.
[0003] However, the lean-burn engines discharge so-called lean
exhaust gas high in oxygen content as compared with that of exhaust
gas discharged from an engine which is operated around a
stoichiometric air-fuel ratio. Therefore, drawbacks have been
encountered in the lean-burn engines, in which reduction or removal
of NOx is difficult in case of using a conventional three-way
catalyst. Additionally, the lean-burns are low in combustion
efficiency and therefore is low in exhaust gas temperature as
compared with conventional engines. There is a tendency that
exhaust gas temperature further lowers upon further improvements in
combustion of the engines. As a result, the frequency at which the
temperature of exhaust gas is 200.degree. C. or lower becomes high.
In this regard, it has been desired to effectively purify exhaust
gas in such a low exhaust gas temperature condition.
[0004] In order to solve the above problems, a variety of
countermeasures have been studied. For example, it has been
proposed to secondarily supply hydrocarbons, alcohols and the like
serving as a reducing agent to a gas inlet section of a catalyst
layer. In connection with this, for example, a method of mounting
onboard a tank for storing the reducing agent and a method of
directly using fuel for a vehicle as the reducing agent have been
proposed. However, the former method has the problems of obtaining
a place for the tank, increasing the weight of the vehicle and
supplying the reducing agent. The latter method has the problems of
unavoidably sacrificing the fuel economy or fuel consumption for an
engine, of low in NOx reducing efficiency in a low exhaust gas
temperature condition, and the like.
[0005] Additionally, a system for reducing NOx in a lean exhaust
gas at a high efficiency is disclosed in Japanese Patent No.
2600492. The system includes a NOx adsorbing or trapping agent
which functions to adsorb or trap NOx when the air/fuel ratio of
exhaust gas flowing thereinto is lean or large (as compared with a
stoichiometric value) and to release NOx by lowering an oxygen
concentration in exhaust gas flowing thereinto. In this system, a
three-way catalyst is used to release and reduce the adsorbed NOx,
so that it is required to put the air/fuel ratio of exhaust gas of
the engine around the stoichiometric value or rich (small) as
compared with the stoichiometric value, or to supply hydrocarbons
as the reducing agent to an exhaust gas passageway. This raises the
problem of sacrificing the fuel economy or fuel consumption of the
vehicle. Further, this raises the problems of mounting a tank for
storing the reducing agent and of increasing the weight of the
vehicle thereby sacrificing the fuel economy of the engine.
Furthermore, even this system has been desired to be improved in
NOx adsorption or trap performance of the NOx adsorbing agent and
in NOx reducing performance of the three-way catalyst in a low
exhaust gas temperature condition of 200.degree. C. or lower.
SUMMARY OF THE INVENTION
[0006] It is, therefore, an object of the present invention to
provide an improved hydrogen-containing gas producing system and an
improved exhaust gas purifying system using the hydrogen-containing
gas producing system, which can overcome drawbacks encountered in
conventional exhaust gas purifying systems.
[0007] Another object of the present invention is to provide
improved hydrogen-containing gas producing system and exhaust gas
purifying system using the hydrogen-containing gas producing
system, which can remove or reduce NOx at a high efficiency in a
low exhaust gas temperature-condition of 200.degree. C. or lower,
preventing the fuel economy or fuel consumption of a vehicle from
degrading owing to mounting a tank for storing a NOx reducing agent
and the like on a vehicle.
[0008] An aspect of the present invention resides in a
hydrogen-containing gas producing system of an onboard type, for
producing hydrogen-containing gas to be used for purification of
exhaust gas of an internal combustion engine. The
hydrogen-containing system comprises a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas. A
carrier gas supply source is provided for supplying a carrier gas
for carrying the fuel. A device is provided for vaporizing the fuel
so as to form a vaporized fuel serving as a reaction gas. The fuel
vaporizing device is connected to the fuel supply source and the
carrier gas supply source. Additionally, a reforming section is
connected to the fuel vaporizing device, for reforming the reaction
gas so as to produce the hydrogen-containing gas.
[0009] Another aspect of the present invention resides in an
exhaust gas purifying system for an internal combustion engine. The
exhaust gas purifying system comprises a hydrogen-containing gas
producing system of an onboard type, for producing
hydrogen-containing gas to be used for purification of exhaust gas
of an internal combustion engine, the hydrogen-containing system
including a fuel supply source for supplying fuel as a raw material
of the hydrogen-containing gas, a carrier gas supply source for
supplying a carrier gas for carrying the fuel, a device for
vaporizing the fuel so as to form a vaporized fuel as a reaction
gas, the fuel vaporizing device being connected to the fuel supply
source and the carrier gas supply source, and a reforming section
connected to the fuel vaporizing device, for reforming the reaction
gas so as to produce the hydrogen-containing gas. The reforming
section is connected to a part of an exhaust gas passageway of the
internal combustion engine so as to introduce the
hydrogen-containing gas into exhaust gas. Additionally, a NOx
adsorbing and reducing catalyst is disposed in the exhaust gas
passageway downstream of the part. The NOx adsorbing and reducing
catalyst is adapted to adsorb nitrogen oxides in exhaust gas in a
condition that exhaust gas is in a lean region, and to reduce
nitrogen oxides in exhaust gas in a condition that exhaust gas is
within a range including a stochiometric region and a rich region.
In the above exhaust gas purifying system, the hydrogen-containing
gas from the reforming section of the hydrogen-containing gas is
supplied into the exhaust gas passageway at the part which is
upstream of the NOx adsorbing and reducing catalyst, at a low
temperature range in which a temperature of exhaust gas at a
position immediately upstream of the NOx adsorbing and reducing
catalyst is not higher than 250.degree. C., and in the condition
that exhaust gas is within the range including the stoichiometric
region and the rich region.
[0010] A further aspect of the present invention resides in a
hydrogen-containing gas producing system of an onboard type, for
producing hydrogen-containing gas to be used for purification of
exhaust gas of an internal combustion engine. The
hydrogen-containing system comprises a fuel supply source for
supplying fuel as a raw material of the hydrogen-containing gas. A
carrier gas supply source is provided for supplying a carrier gas
for carrying the fuel. A fuel vaporizing means is provided for
vaporizing the fuel so as to form a vaporized fuel serving as a
reaction gas, the fuel vaporizing means receiving the fuel from the
fuel supply source and the carrier gas from the carrier gas supply
source. Additionally, a reforming section is connected to the fuel
vaporizing device, for reforming the reaction gas so as to produce
the hydrogen-containing gas.
[0011] A still further aspect of the present invention resides in
an exhaust gas purifying system for an internal combustion engine
mounted on an automotive vehicle. The exhaust gas purifying system
comprises a catalyst for reducing nitrogen oxides in exhaust gas of
the engine, disposed in an exhaust gas passageway of the engine and
mounted on the vehicle, the catalyst containing at least one of
platinum and palladium. Additionally, a hydrogen-containing gas
producing system is provided for producing hydrogen-containing gas,
mounted on the vehicle. The hydrogen-containing system includes a
fuel supply source for supplying fuel as a raw material of the
hydrogen-containing gas, a carrier gas supply source for supplying
a carrier gas for carrying the fuel, a device for vaporizing the
fuel so as to form a vaporized fuel as a reaction gas, the fuel
vaporizing device being connected to the fuel supply source and the
carrier gas supply source, and a reforming section connected to the
fuel vaporizing device, for reforming the reaction gas so as to
produce the hydrogen-containing gas. The reforming section is
connected to a part of the exhaust gas passageway upstream of the
catalyst so that the hydrogen-containing gas is supplied to the
catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic illustration of an embodiment of an
exhaust gas purifying system including a hydrogen-containing gas
producing system, according to the present invention, incorporated
in an exhaust system of an automotive internal combustion
engine;
[0013] FIG. 2A is a graph showing difference in hydrogen yield in
tests for producing a hydrogen-containing gas, depending on the
kinds of catalysts used in the hydrogen-containing gas producing
system of FIG. 1;
[0014] FIG. 2B is a graph showing difference in H.sub.2/CO ratio in
the hydrogen-containing gas in the tests for producing the
hydrogen-containing gas, depending on the kinds of the catalysts
used in the hydrogen-containing gas producing system of FIG. 1;
[0015] FIG. 3A is a graph showing difference in hydrogen yield in
the tests for producing a hydrogen-containing gas, depending on the
kinds of fuels or raw materials (different in the number of carbon
atoms) used in the hydrogen-containing gas producing system of FIG.
1;
[0016] FIG. 3B is a graph showing difference in H.sub.2/CO ratio in
the hydrogen-containing gas in the tests for producing the
hydrogen-containing gas, depending on the kinds of the fuels or raw
materials (different in the number of carbon atoms) used in the
hydrogen-containing gas producing system of FIG. 1; and
[0017] FIG. 4 is a graph showing the NOx removal rate of a NOx
adsorbing and reducing catalyst upon supply of the
hydrogen-containing gas from the hydrogen-containing gas producing
system of FIG. 1 in terms of the CO concentration in a laboratory
model gas flowing through the catalyst, in tests for evaluation of
the hydrogen-containing gas on NOx reduction characteristics for
the catalyst.
DETAILED DESCRIPTION OF THE INVENTION
[0018] According to the present invention, a hydrogen-containing
gas producing system of an onboard type is for producing
hydrogen-containing gas to be used for purification of exhaust gas
of an internal combustion engine. The hydrogen-containing system
comprises a fuel supply source for supplying fuel as a raw material
of the hydrogen-containing gas. A carrier gas supply source is
provided for supplying a carrier gas for carrying the fuel. A
device is provided for vaporizing the fuel so as to form a
vaporized fuel serving as a reaction gas. The fuel vaporizing
device is connected to the fuel supply source and the carrier gas
supply source. Additionally, a reforming section is connected to
the fuel vaporizing device, for reforming the reaction gas so as to
produce the hydrogen-containing gas. The hydrogen-containing gas
producing system is mounted on a vehicle such as an automotive
vehicle.
[0019] The hydrogen-containing gas producing system is used as a
part of an exhaust gas purifying system for an internal combustion
engine. The exhaust gas purifying comprises a NOx adsorbing and
reducing catalyst is disposed in the exhaust gas passageway
downstream of the part. The NOx adsorbing and reducing catalyst is
adapted to adsorb nitrogen oxides in exhaust gas in a condition
that exhaust gas is in a lean region, and to reduce nitrogen oxides
in exhaust gas in a condition that exhaust gas is within a range
including a stochiometric region and a rich region. The reforming
section of the hydrogen-containing gas producing system is
connected to the exhaust gas passageway upstream of said NOx
adsorbing and reducing catalyst. In the above exhaust gas purifying
system, the hydrogen-containing gas from the reforming section of
the hydrogen-containing gas is supplied into the exhaust gas
passageway at the part which is upstream of the NOx adsorbing and
reducing catalyst, at a low temperature range in which a
temperature of exhaust gas at a position immediately upstream of
the NOx adsorbing and reducing catalyst is not higher than
250.degree. C., and in the condition that exhaust gas is within the
range including the stoichiometric region and the rich region.
[0020] The principle of the present invention is founded on the
present inventors' findings that NOx in exhaust gas can be very
effectively reduced when a noble metal-based catalyst containing Pt
and/or Pd (palladium) is used as an exhaust gas purifying catalyst,
and hydrogen (H.sub.2) is supplied as a NOx reducing agent to the
noble metal-based catalyst, even under a low exhaust temperature
condition in which the temperature of exhaust gas immediately
upstream of the noble metal-based catalyst is around 250.degree. C.
This is assumed to be based on the fact that the reactivity of
H.sub.2 with NOx is considerably high.
[0021] In this connection, there are phenomena that CO impedes the
reduction reaction of NOx in a relatively low temperature condition
of not higher than 250.degree. C. Additionally, when an air/fuel
(A/F) ratio is made small or rich (in fuel) to, for example, about
11, a CO concentration in exhaust gas is remarkably increased to
several % (by volume). Under a circumstance having such a high CO
concentration and a low exhaust gas temperature condition of not
higher than 250.degree. C., a sufficient reducing ability for NOx
cannot be obtained even if H.sub.2 high in reactivity with NOx is
used as the reducing agent.
[0022] In the exhaust gas purifying system using the
hydrogen-containing gas, according to the present invention, the
NOx reduction impeding phenomena of CO can be avoided while H.sub.2
having the high NOx reducing ability even in the low exhaust gas
temperature condition can be used without raising the CO
concentration by positively making the air/fuel ratio small. This
synergistic effect depends on the present inventors' knowledge can
realize a high NOx reducing characteristics suppressing degradation
of fuel consumption (or fuel economy). In other words, according to
the present invention, NOx can be reduced or removed at -a high
efficiency even under a low exhaust gas temperature condition while
making it unnecessary to conduct a control for positively making
the air/fuel ratio small so that a sufficient NOx reduction effect
can be obtained even at the air/fuel ratio of about 13.
Additionally, it is very important that the hydrogen-containing gas
which is low in CO content or concentration (% by volume or ppm)
can be produced in an onboard manner, i.e., in a
hydrogen-containing gas producing system mounted on the vehicle
(automotive vehicle).
[0023] The hydrogen-containing gas producing system according to
the present invention depends also on the following inventors'
findings: The hydrogen-containing gas can be produced suitably in
the onboard manner upon the fact that the hydrogen-containing gas
producing system includes a reforming section using a Rh-based fuel
reforming catalyst, a reaction temperature and an oxygen
concentration in a reaction gas to be supplied to the reforming
catalyst are regulated respectively within certain ranges.
Additionally, the hydrogen-containing gas which hardly contains CO
can be obtained by using as the fuel (hydrocarbons) or raw material
whose carbon number (the number of carbon atoms in a hydrocarbon)
is not smaller than 9 (C.sub.9).
[0024] Thus, the present invention is basically different from
conventional techniques in a point of realizing production and
supply of the hydrogen-containing gas which takes account of
impeding a NOx reduction reaction by CO. Additionally, the
hydrogen-containing gas having a relatively low CO concentration
can be obtained at a low temperature without inviting a
weight-increase of the vehicle and a degradation of fuel economy,
or the like problem encountered in the conventional techniques in
which a tank for storing hydrocarbons and alcohols as a NOx
reducing agent is mounted on the vehicle or fuel (for engine) is
used as the reducing agent. Hence, the present invention can
provide less disadvantages against cost and fuel economy of the
vehicle.
[0025] Hereinafter, the hydrogen-containing gas producing system
will be discussed.
[0026] The hydrogen-containing gas producing system produces
hydrogen-containing gas having a gas composition suitable for
purification of exhaust gas of the engine in the onboard manner or
on the vehicle. The hydrogen-containing gas is supplied to an
exhaust gas purifying catalyst thereby reducing or removing NOx in
exhaust gas at a high efficiency even in a low exhaust gas
temperature condition in which the temperature of exhaust gas at a
position immediately upstream of the exhaust gas purifying catalyst
is not higher than 250.degree. C.
[0027] The hydrogen-containing gas producing system includes a fuel
supply source for supplying fuel as a raw material of the
hydrogen-containing gas; a carrier gas supply source for supplying
a carrier gas for carrying the fuel; a fuel vaporizing means or
device for vaporizing the fuel so as to form a vaporized fuel as a
reaction gas, the fuel vaporizing device being connected to the
fuel supply source and the carrier gas supply source; and a
reforming section connected to the fuel vaporizing device, for
reforming the reaction gas so as to produce the hydrogen-containing
gas.
[0028] An example of the fuel vaporizing means is a device or
process in which the carrier gas from the carrier gas supply source
is blown to a liquid fuel from the fuel supply source in a gas
mixer so as to atomize the liquid fuel thereby obtaining vaporized
fuel. However, the fuel vaporizing means is not limited
particularly to this example. A gas discharged from the gas mixer
contains the vaporized fuel and the carrier gas which are in a
mixed state, and is sent as a reaction gas to the reforming
section. When the gas from the gas mixture is passed through the
reforming section, a reforming reaction occurs to produce the
hydrogen-containing gas.
[0029] The carrier gas is not limited to a particular gas as far as
it is suitable for producing the hydrogen-containing gas, so that
the carrier gas may be air. It is practical that the carrier gas is
a part of exhaust gas discharged from the internal combustion
engine mounted on the vehicle, the part of the exhaust gas being
introduced into the gas mixer so as to be used as the carrier gas.
The carrier gas functions not only to atomize the liquid fuel but
also to carry the vaporized fuel to the reforming section.
[0030] The fuel supply source may be a fuel tank containing fuel
used to producing the hydrogen-containing gas; however, it is
preferable in the present invention that a fuel tank for fuel to be
supplied to the internal combustion engine is commonly used also as
the fuel tank for the fuel to be used for production of the
hydrogen-containing gas, from the viewpoint of suppressing fuel
consumption and the like of the engine under size-reduction and
weight-lightening of the hydrogen-containing gas producing
system.
[0031] The reforming section for reforming the above-mentioned
reaction gas from the gas mixer includes the fuel reforming
catalyst containing rhodium (Rh). Preferably, the fuel reforming
catalyst contains Rh carried on alumina. By using this fuel
reforming catalyst containing Rh carried on alumina, the
hydrogen-containing gas containing a low CO concentration can be
produced in the onboard manner by controlling a reaction
temperature (at which the reforming reaction occurs) of the
reaction gas at 260 to 340.degree. C. and by controlling an oxygen
concentration (% by volume or ppm) in the reaction gas, at a value
represented by the following formula (1):
An oxygen concentration in the reaction gas.ltoreq.an average
carbon number of hydrocarbons in the liquid fuel.times.a
concentration (% by volume or ppm) of the liquid fuel in the
reaction gas.times.1/2 (1)
[0032] The above formula (1) may be converted as follows, in case
that the concentration of the liquid fuel is calculated as that of
a hydrocarbon having one carbon atom: An oxygen concentration in
the reaction gas<a concentration of the liquid fuel (calculated
as a hydrocarbon having one carbon atom) in the reaction
gas.times.1/2. In this connection, for example, in case that the
concentration of C.sub.8H.sub.18 is 100 ppm, the concentration
calculated as a hydrocarbon having one carbon atom is 800 ppm.
[0033] Although controlling the reaction temperature may be made
under heating by a heater, it is practical to controlling the
reaction temperature under heating by using heat of exhaust gas
discharged from the internal combustion engine.
[0034] The hydrogen-containing gas producing system may be provided
with a hydrogen-containing gas storing means or device for storing
the hydrogen-containing gas produced by the hydrogen-containing gas
producing system. It will be understood that the
hydrogen-containing gas stored in the hydrogen-containing gas
storing means can be supplied to the exhaust gas purifying catalyst
at a suitable timing. A practical example of the
hydrogen-containing gas storing means is a tank; however, the
hydrogen-containing gas storing means is not limited to the tank as
far as it is suitable for storing and supplying the
hydrogen-containing gas.
[0035] The liquid fuel to be used for production of the
hydrogen-containing gas is preferably light oil or diesel fuel. It
is to be noted that the CO concentration of the hydrogen-containing
gas to be produced can be suppressed to a low level by using light
oil as the liquid fuel to be used for production of the
hydrogen-containing gas. Additionally, the CO concentration in the
hydrogen-containing gas can be suppressed to a low level also by
using fuel whose hydrocarbons have the carbon number of not smaller
than 9. In this regard, it is also effective to prepare
hydrocarbons as the raw material for the hydrogen-containing gas by
separating and extracting the hydrocarbons having the carbon number
of not smaller than 9, from the liquid fuel.
[0036] The hydrogen-containing gas contains much hydrogen (H.sub.2)
and is useful as the NOx reducing agent. The hydrogen-containing
gas also contains, for example, carbon dioxide (CO.sub.2), and
unreacted HC (hydrocarbons) remaining after production of CO and
the hydrogen-containing gas, in which it is preferable that the CO
content or concentration in the hydrogen-containing gas is low. The
CO content is preferably not higher than 100 ppm. When the
hydrogen-containing gas is produced under conditions including the
above-mentioned catalyst having Rh carried on alumina, reaction
temperature and oxygen concentration, the hydrogen-containing gas
having the CO content of not higher than 100 ppm can be
obtained.
[0037] Next, the exhaust gas purifying system using the
hydrogen-containing gas, according to the present invention will be
discussed.
[0038] The exhaust gas purifying system includes the
hydrogen-containing gas producing system and a NOx adsorbing
(trapping) and reducing catalyst disposed in an exhaust gas
passageway of the internal combustion engine. The NOx adsorbing and
reducing catalyst functions to adsorb (trap) NOx when exhaust gas
is in a lean region and to reduce NOx when exhaust gas is in a
stoichiometric region or in a rich region. In the lean region,
exhaust gas has an air/fuel ratio larger or leaner (in fuel) than a
stoichiometric level, and therefore corresponds to so-called lean
exhaust gas. In the stoichiometric region, exhaust gas has an
air/fuel ratio around the stoichiometric level. In the rich region,
exhaust gas has an air/fuel ratio smaller or richer (in fuel) than
the stoichiometric level, and therefore corresponds to so-called
rich exhaust gas. The NOx adsorbing and reducing catalyst is a
noble metal-based catalyst including a carrier formed of refractory
inorganic compound such as alumina, carrying or containing noble
metal(s) such as Pt and/or Pd. It is preferable for increasing the
amount of NOx to be adsorbed in the NOx adsorbing and reducing
catalyst in the lean region of exhaust gas, that the NOx adsorbing
and reducing catalyst contains alkali metal(s), alkaline-earth
metal(s) and/or rare earth element(s) such as barium (Ba), cesium
(Cs), magnesium (Mg), potassium (K), sodium (Na), lanthanum (La),
cerium (Ce) and/or the like.
[0039] The hydrogen-containing gas produced by the
hydrogen-containing gas producing system is supplied to the exhaust
gas passageway upstream of the NOx adsorbing and reducing catalyst
so as to be used for exhaust gas purification or reduction of NOx.
Supply of the hydrogen-containing gas is regulated in relation to
an oxygen concentration in exhaust gas discharged from the internal
combustion engine. More specifically, the hydrogen-containing gas
is supplied to the NOx adsorbing and reducing catalyst when exhaust
gas is in the stoichiometric region or the rich region and the
temperature of exhaust gas at the position immediately upstream of
the NOx adsorbing and reducing catalyst is not higher than
250.degree. C. At this time, H.sub.2 is supplied in a concentration
(% by volume) of preferably not less than 1%, more preferably not
less than 1.5% in exhaust gas flowing through the exhaust gas
passageway immediately upstream of the NOx adsorbing and reducing
catalyst. In order to supply the hydrogen-containing gas under the
above-mentioned conditions, it is preferable, for example, to once
store the produced hydrogen-containing gas in the tank for
hydrogen-containing gas, and then to supply the stored
hydrogen-containing gas under pressure into exhaust gas in relation
to the oxygen concentration in exhaust gas. The oxygen
concentration in exhaust gas can be detected by an oxygen (O.sub.2)
sensor or the like, disposed at a suitable position in the exhaust
gas passageway which position is upstream of a hydrogen-containing
gas supply inlet at which the hydrogen-containing gas is supplied
into exhaust gas flowing through the exhaust gas passageway.
[0040] The exhaust gas purifying system according to the present
invention may be provided with a three-way catalyst, in which the
three-way catalyst, the hydrogen-containing gas supply inlet and
the NOx adsorbing and reducing catalyst are arranged or disposed in
the exhaust gas passageway in the order mentioned in a direction of
flow of exhaust gas. With this arrangement, first, gas components
such as NOx, HC, CO and the like are removed, and then NOx
remaining not-reduced by the upstream-side three-way catalyst is
reduced at a high efficiency by the downstream-side NOx adsorbing
and reducing catalyst. This is effective particularly in the low
exhaust gas temperature condition where NOx cannot be sufficiently
reduced by the three-way catalyst.
[0041] According to the above exhaust gas purifying system, NOx can
be reduced or removed at a very high efficiency even in a condition
where exhaust gas temperature is low. This can realize a clean
exhaust gas in internal combustion engines such as diesel engines,
thus making it possible to offer automotive vehicles which are
excellent in environmental protection and in fuel economy (fuel
consumption), taking warming-up phenomena of the earth into
consideration.
EXAMPLES
[0042] The present invention will be more readily understood with
reference to the following Examples in comparison with Comparative
Examples; however, these Examples are intended to illustrate the
invention and are not to be construed to limit the scope of the
invention.
[0043] An embodiment of the exhaust gas purifying system including
the hydrogen-containing gas producing system, according to the
present invention will be discussed hereinafter with reference to
FIG. 1.
[0044] The exhaust gas purifying system was incorporated with an
exhaust system (not identified) of engine 1 which is of the
cylinder direct injection type wherein fuel is directly injected
into each engine cylinder, and has four engine cylinders and a
displacement of 2.5 liters. Engine 1 was equipped with a common
rail type fuel injection system (not shown). Throttle valve 3 was
disposed in intake pipe or intake air passageway 2 of the engine so
as to control an amount of air to be supplied to the engine
cylinders. The engine cylinders of the engine were in communication
with a catalytic converter 5A including three-way catalyst 5,
through exhaust gas passageway 4. Catalytic converter 5A was in
communication with another catalytic converter 6A including NOx
adsorbing and reducing catalyst 6, through exhaust gas passageway
4. The NOx adsorbing and reducing catalyst is honeycomb-type and
monolithic, and has a volume of 1.7 liters.
[0045] The hydrogen-containing gas producing system included fuel
tank 7 for storing fuel as a raw material for production of the
hydrogen-containing gas. The fuel in the fuel tank is fed through
pipe 8 to gas mixer 9. A part of exhaust gas (as the carrier gas)
of the engine and/or air are blown to the fuel within the gas
mixer, so that the fuel is vaporized. In the gas mixer, the
vaporized fuel is in a state of being mixed with the part of
exhaust gas and/or air thereby forming a reaction gas. This
reaction gas was introduced into catalytic reactor 10 which had
been heated at 260 to 340.degree. C. The catalytic reactor included
a reforming catalyst 10a by which a reforming reaction of the fuel.
In the catalytic reactor, hydrogen was produced to form the
hydrogen-containing gas. The hydrogen-containing gas was stored in
reserve tank 11. The stored hydrogen-containing gas was to be
injected through hydrogen-containing gas ejection nozzle 12 in
accordance with a variation or change of the air/fuel ratio of
exhaust gas flowing through exhaust gas passageway 4, so that the
hydrogen-containing gas was supplied into the exhaust gas
passageway upstream of the NOx adsorbing and reducing catalyst and
downstream of the three-way catalyst. The air/fuel ratio of exhaust
gas was controlled by regulating the throttle valve, the common
rail type fuel injection system and/or a so-called post fuel
injection (accomplishing combustion control in the engine
cylinders) under a feedback control using oxygen (O.sub.2) sensor
13 disposed in the exhaust gas passageway. The post fuel injection
means an auxiliary fuel injection made subsequent to a main fuel
injection in each engine cylinder.
[0046] The reforming catalyst of catalytic reactor 10 includes a
honeycomb type substrate having about 400 cells per square inch and
having a volume of 150 cc. The substrate had been coated with
Rh/alumina catalyst component in an amount of 120 g per one liter
of the substrate. The Rh/alumina catalyst component had been
prepared by causing alumina to carry about 2% by weight of Rh. The
walls (defining each cell) had been covered with a coat layer of
the Rh/alumina catalytic component, so that each cell serves as a
gas passage through which exhaust gas flows.
[0047] In order to maintain the temperature within catalytic
reactor 10 at 260 to 340.degree. C., it is practical to use heat of
exhaust gas of the engine though heating by a heater may be
proposed. To heat the catalytic reactor by using heat of exhaust
gas, catalytic reactor 10 may be connected to exhaust gas
passageway or pipe 4 to constitute a heat exchanger.
<Tests for Producing Hydrogen-containing Gas>
Example 1
[0048] Tests for producing the hydrogen-containing gas was
conducted by operating the hydrogen-containing gas producing system
including the catalytic reactor 10, under a condition simulating
that of a so-called micro-reactor (the catalytic reactor) which is
small-sized and suitable for an onboard use, thereby producing the
hydrogen-containing gas which was discharged from the catalytic
reactor. The tests included four tests which were the same with
each other with the exception that the four tests respectively used
undecane (C.sub.11), decane (C.sub.10), nonane (C.sub.9) and octane
(C.sub.8) as the fuel (hydrocarbons) contained in the fuel tank 7.
The reaction temperature of a catalytic layer of the reforming
catalyst of the catalytic reactor 10 was set within a range of 200
to 500.degree. C.
[0049] In these tests, the reforming catalyst of the catalytic
reactor 10 had been prepared by coating the honeycomb type
substrate with a coat layer of a Rh/alumina catalyst component
which had been prepared by causing .gamma.-alumina having a
specific surface area of about 230 m.sup.2/g to carry about 2% by
weight of Rh.
[0050] In each test, the yield of H.sub.2 in the
hydrogen-containing gas was continuously measured upon variation of
the reaction temperature, and a H.sub.2/CO ratio (volume or ppm) in
the hydrogen-containing gas was continuously measured upon
variation of the reaction temperature. The results of these
measurements are shown in FIGS. 3A and 3B in which the four tests
using undecane, decane, nonane and octane are indicated
respectively by "undecane", "decane", "nonane" and "octane". The
results of the measurements in the test using decane are shown as
"Rh-based" also in FIGS. 2A and 2B.
Comparative Example 1
[0051] The procedure in Example 1 was repeated with the exception
that a coat layer of a Ru/alumina catalyst component prepared
similarly to that of Example 1 was used in place of the coat layer
of the Rh/alumina catalyst component, and that only one test using
decane (C.sub.10) as the fuel was conducted in place of the four
tests of Example 1. In this test, the yield of H.sub.2 in the
hydrogen-containing gas was continuously measured upon variation of
the reaction temperature, and a H.sub.2/CO ratio (volume) was
continuously measured upon variation of the reaction temperature.
The results of these measurements are shown as "Ru-based" in FIGS.
2A and 2B.
Comparative Example 2
[0052] The procedure in Example 1 were repeated with the exception
that a coat layer of a Pt/alumina catalyst component prepared
similarly to that of Example 1 was used in place of the coat layer
of the Rh/alumina catalyst component, and that only one test using
decane (C.sub.10) as the fuel was conducted in place of the four
tests of Example 1. In this test, the yield of H.sub.2 in the
hydrogen-containing gas was continuously measured upon variation of
the reaction temperature, and a H.sub.2/CO ratio (volume) was
continuously measured upon variation of the reaction temperature.
The results of these measurements are shown as "Pt-based" in FIGS.
2A and 2B.
Comparative Example 3
[0053] The procedure in Example 1 were repeated with the exception
that a coat layer of a Ni/alumina catalyst component prepared
similarly to that of Example 1 was used in place of the coat layer
of the Rh/alumina catalyst component, and that only one test using
decane (C.sub.10) as the fuel was conducted in place of the four
tests of Example 1. In this test, the yield of H.sub.2 in the
hydrogen-containing gas was continuously measured upon variation of
the reaction temperature, and a H.sub.2/CO ratio (volume) was
continuously measured upon variation of the reaction temperature.
The results of these measurements are shown as "Ni-based" in FIGS.
2A and 2B.
[0054] The test results in FIGS. 2A to 3B depict the followings: In
case that nonane, decane or undecane is used as the fuel (raw
material), the amount of CO (by-product) produced is peculiarly
very small within a reaction temperature range of from 260 to
340.degree. C., thereby proving that the preferable conditions for
production of the hydrogen-containing gas are very effective.
Additionally, in case that octane is used as the fuel (raw
material), it is recognized that a considerable amount of CO
(by-product) produced is produced within the above reaction
temperature range. In contrast, in case of nonane, decane or
undecane is used as the fuel (raw material), it is apparent that
the amount of CO (by-product) produced is sharply reduced, in which
the CO concentration becomes not higher than 100 ppm.
[0055] <Tests for Evaluation of Hydrogen-containing Gas on NOx
Reduction Characteristics for NOx Adsorbing and Reducing
Catalyst>
[0056] A NOx adsorbing and reducing catalyst as shown in FIG. 1 was
prepared to contain Pt/Rh-based catalyst component and carry Ba
component upon impregnation of Ba. The NOx adsorbing and reducing
catalyst was subjected to six tests. In each test, two laboratory
model gases (lean gas and rich gas) simulating actual lean exhaust
gas and rich exhaust gas from an automotive internal combustion
engine were flown alternately through the NOx adsorbing and
reducing catalyst, in which the lean gas was flown for 40 seconds
whereas the rich gas was flown for 2 seconds; and the temperature
of the lean or rich gas immediately upstream of the NOx adsorbing
and reducing catalyst was set at 180.degree. C. In this test, the
hydrogen-containing gas obtained in Example 1 was introduced into
the model gas upstream of the NOx adsorbing and reducing catalyst.
In the six tests, the CO concentration in the rich gas were
respectively 0, 0.5, 1.0, 1.5, 2.0 and 2.5% by volume. The
compositions of the lean gas and the rich gas were as follows:
[0057] The lean gas:
[0058] HC (C.sub.3H.sub.6)=1500 ppm
[0059] NO=200 ppm
[0060] CO=1000 ppm
[0061] H.sub.2O=10 vol %
[0062] O.sub.2=5 vol %
[0063] N.sub.2=balance
[0064] The rich gas:
[0065] HC (C.sub.3H.sub.6)=3500 ppm
[0066] NO=200 ppm
[0067] CO=0.5, 1.0, 1.5, 2.0 and 2.5 vol %
[0068] H.sub.2=1.0 vol %
[0069] O.sub.2=1000 ppm
[0070] H.sub.2O=10 vol %
[0071] N.sub.2=balance
[0072] During each test, a NOx removal rate was determined in the
following manner: The concentration (volume or ppm) A of NOx in the
model gas upstream of the NOx adsorbing and reducing catalyst was
measured while the concentration B of NOx in the model gas
downstream of the NOx adsorbing and reducing catalyst was measured.
The NOx removal rate (% by volume) was calculated by [(1-the
concentration B/the concentration A).times.100]. The results of the
tests are shown in FIG. 4.
[0073] The results of FIG. 4 depicts that, in case using hydrogen
(or the hydrogen-containing gas) as a reducing agent for NOx, an
extremely high NOx removal rate was obtained even in a low gas
temperature condition of 180.degree. C. under a condition where the
concentration of co-existing CO is low, thus proving the
effectiveness of the hydrogen-containing gas to exhaust gas
purification.
[0074] As appreciated from the above, according to the present
invention, the hydrogen-containing gas containing much hydrogen and
low in CO content is used as the reducing agent for NOx contained
in exhaust gas. This hydrogen-containing gas is produced in the
onboard manner by the hydrogen-containing gas producing system
which is incorporated in the exhaust gas purifying system.
Accordingly, NOx can be removed or reduced at a high efficiency
even in a low exhaust gas temperature condition of 200.degree. C.
or lower, without degrading the fuel economy by avoiding mounting
onboard a tank or the like for storing the NOx reducing agent.
[0075] The entire contents of Japanese Patent Application
P2000-302065 (filed Oct. 2, 2000) are incorporated herein by
reference.
[0076] Although the invention has been described above by reference
to certain embodiments and examples of the invention, the invention
is not limited to the embodiments and examples described above.
Modifications and variations of the embodiments and examples
described above will occur to those skilled in the art, in light of
the above teachings. The scope of the invention is defined with
reference to the following claims.
* * * * *