JP5453737B2 - Exhaust gas purification method and exhaust gas purification device - Google Patents

Description

    The present invention relates to an exhaust gas purification method and an exhaust gas purification device for an engine.

    From the viewpoints of reducing environmental burden and reducing fuel consumption of automobiles, hybrid cars and automobiles using hydrogen as fuel are attracting attention.

    Gasoline engines that are widely used in passenger cars are generally less efficient at light loads. On the other hand, in the case of a hybrid vehicle, in a low speed range and a light load range, it is possible to drive with an electric motor instead of an engine with low efficiency, so that fuel efficiency can be improved and harmful emissions are also low. It is advantageous for reducing the environmental load.

    On the other hand, in the case of an automobile that uses only hydrogen as a fuel, unlike an automobile that uses an HC (hydrocarbon) component such as gasoline, light oil, or alcohol as fuel, it is possible to avoid exhausting HC as exhaust gas. it can. However, hydrogen fuel is disadvantageous in terms of travel distance because it generates less heat than gasoline and is disadvantageous in terms of output, and it is difficult to mount a large amount of hydrogen in an automobile.

Therefore, it has been proposed to use hydrogen and gasoline as fuel. For example, Patent Documents 1 to 3 disclose a system in which hydrogen and gasoline are switched and supplied to an engine combustion chamber. In these patent documents, when gasoline is used as fuel, the engine is usually stoichiometrically operated. Therefore, in order to purify HC, CO and NOx (nitrogen oxides) in the exhaust gas, a three-way catalyst is provided in the exhaust gas passage. It is described that it arrange | positions. Further, when hydrogen is used as fuel, NOx is discharged from the engine. However, Patent Document 3 discloses that a three-way catalyst, a NOx storage reduction catalyst, and a NOx selective reduction catalyst are used in combination.
JP 2007-51583 A JP 2007-51596 A JP 2007-269227 A

    However, when hydrogen and gasoline are used as fuel, HC is discharged without being purified even if only a three-way catalyst is used, or if a three-way catalyst is combined with a NOx storage reduction catalyst or a NOx selective reduction catalyst. Sometimes.

    That is, a canister containing an adsorbent such as activated carbon is connected to the gasoline tank in order to prevent the evaporated fuel generated in the tank from being released into the atmosphere. Since the adsorption capacity of the adsorbent is limited, it is necessary to perform a purge process in which the atmosphere is taken into the canister before the adsorption is saturated, the fuel component is released from the adsorbent, and introduced into the intake system of the engine. However, when the engine uses hydrogen as the fuel, the lean burn operation is performed and the combustion chamber temperature is low. Therefore, the evaporated fuel purged to the intake system does not completely burn in the combustion chamber, and the amount of HC discharged to the exhaust system is small. Become more. Since the exhaust gas temperature is low at that time, the three-way catalyst is also low in temperature and is normally in an inactive state. Therefore, the HC caused by the evaporated fuel in the exhaust gas is not oxidized and purified but is released into the atmosphere. Will be discharged.

    Therefore, an object of the present invention is to prevent the emission from deteriorating even if the evaporated fuel is purged when the engine is lean-burned using hydrogen as a fuel.

    In the present invention, in order to solve the above-mentioned problem, when the engine is operated by lean burn using hydrogen as a fuel, HC contained in the exhaust gas by purging the evaporated fuel is converted by an oxidation catalyst containing an HC adsorbent. It was made to oxidize.

That is, the invention according to claim 1 is an engine exhaust gas purification method in which a stoichiometric operation using fuel containing gasoline and a lean burn operation using hydrogen fuel are performed.
A canister that adsorbs the evaporated fuel generated in a fuel tank that stores the fuel containing gasoline, and a purge passage that purges the evaporated fuel adsorbed by the canister to the intake system of the engine;
During the stoichiometric operation with the fuel containing gasoline, the exhaust gas is purified by a simultaneous purification catalyst that oxidizes and purifies HC and CO in the exhaust gas and simultaneously reduces and purifies NOx in the exhaust gas,
During lean burn operation with the hydrogen fuel, HC that is not oxidized and purified by the simultaneous purification catalyst in the exhaust gas caused by the evaporated fuel purged to the intake system is oxidized and purified by the oxidation catalyst ,
The oxidation catalyst contains zeolite as an HC adsorbent carrying Pt, alumina carrying Pt, and a CeZr composite oxide as an oxygen storage / release material carrying Pt ,
The oxidation of the HC that is not oxidized and purified by the simultaneous purification catalyst in the oxidation catalyst includes the step of adsorbing the HC on the zeolite as the HC adsorbent carrying the Pt, and the adsorbed HC increasing the temperature of the oxidation catalyst. And the step of desorbing from the zeolite carrying Pt and the step of oxidizing the desorbed HC by the alumina carrying Pt, the oxygen storage / release material carrying the Pt The active oxygen released from the CeZr composite oxide as described above acts on the oxidation of the desorbed HC by the alumina supporting the Pt .

    Accordingly, when the exhaust gas containing HC is exhausted from the engine by purging the evaporated fuel to the intake system during lean burn operation, even if the simultaneous purification catalyst has not reached the activation temperature, the exhaust caused by the evaporated fuel. It is avoided that HC in the gas is adsorbed by zeolite as an HC adsorbent and discharged into the atmosphere. The HC adsorbed on the zeolite is desorbed from the zeolite as the temperature of the oxidation catalyst rises. The desorbed HC is the zeolite carrying Pt, the alumina carrying Pt, and the oxygen storage / release carrying Pt. It will be oxidized and purified by the material.

  In particular, by adopting Pt as the catalyst metal, the HC can be efficiently purified in a lean atmosphere even at a relatively low temperature. At that time, the active oxygen released from the oxygen storage / release material works effectively for the oxidation purification of the desorbed HC. That is, by adopting the CeZr composite oxide as the oxygen storage material, even in an oxygen-excess atmosphere, the oxygen in the exhaust gas is taken in and exchanged with the oxygen in the composite oxide particles due to the valence change of Ce ions. The active oxygen released by the oxygen exchange reaction effectively works for the oxidation purification of desorbed HC by the zeolite carrying Pt, the alumina carrying Pt, and the oxygen storage / release material carrying Pt. . For this reason, the amount of HC resulting from the evaporated fuel is discharged into the atmosphere without being purified.

The invention according to claim 2 is an engine exhaust gas purification device in which stoichiometric operation with fuel containing gasoline and lean burn operation with hydrogen fuel are performed,
A canister for adsorbing evaporated fuel generated in a fuel tank for storing fuel containing the gasoline;
A purge passage for purging the evaporated fuel adsorbed by the canister to the intake system of the engine;
A simultaneous purification catalyst that is disposed in the exhaust gas passage of the engine and that oxidizes and purifies HC and CO in the exhaust gas and simultaneously reduces and purifies NOx in the exhaust gas during a stoichiometric operation with fuel containing the gasoline;
Oxidation for oxidizing and purifying HC that is not oxidized and purified by the simultaneous purification catalyst in the exhaust gas caused by the evaporated fuel purged to the intake system during the lean burn operation with the hydrogen fuel disposed in the exhaust gas passage With a catalyst,
The oxidation catalyst is desorbed from zeolite as an HC adsorbent carrying Pt for adsorbing HC that is not oxidized and purified by the simultaneous purification catalyst, and from the zeolite carrying Pt as the temperature of the oxidation catalyst rises. As an oxygen storage / release material carrying Pt , alumina that carries Pt for oxidizing the released HC and releases active oxygen for oxidizing the desorbed HC by the alumina carrying Pt It contains a CeZr composite oxide.

    Therefore, during stoichiometric operation with fuel containing gasoline, HC, CO and NOx in the exhaust gas are purified by the simultaneous purification catalyst, and during lean burn operation with hydrogen fuel, in the exhaust gas due to the evaporated fuel purged to the intake system HC that is not oxidized and purified by the above simultaneous purification catalyst is oxidized by an oxidation catalyst containing zeolite as an HC adsorbent carrying Pt, alumina carrying Pt, and an oxygen storage / release material carrying Pt. And being discharged into the atmosphere without being purified is suppressed.

The invention according to claim 3 is the invention according to claim 2,
The simultaneous purification catalyst is a three-way catalyst,
The oxidation catalyst is arranged in an exhaust gas passage downstream of the exhaust gas flow from the three-way catalyst.

    Therefore, even if the HC in the exhaust gas caused by the evaporated fuel passes through the three-way catalyst without being oxidized and purified, it is adsorbed by the zeolite as the HC adsorbent of the oxidation catalyst, and the catalyst metal Pt. It will be oxidized and purified. In addition, the three-way catalyst is upstream of the oxidation catalyst and easily heated by the heat of the exhaust gas. Therefore, the three-way catalyst is advantageous for exhaust gas purification during the stoichiometric operation, particularly when the engine is cold. Is downstream of the three-way catalyst, and the heat effect of the exhaust gas is reduced, which is advantageous for preventing thermal degradation, particularly for preventing the thermal degradation of zeolite as an HC adsorbent.

The invention according to claim 4 is the invention according to claim 2 or claim 3,
The engine is mounted on a hybrid vehicle that can be driven by an electric motor, and is used for driving a generator for the electric motor.

    Therefore, when the engine of the hybrid vehicle is lean burned with hydrogen fuel, HC contained in the exhaust gas by purging the evaporated fuel to the intake system, which is not oxidized and purified by the simultaneous purification catalyst, becomes HC adsorbent. It is suppressed from being adsorbed and / or oxidized by an oxidation catalyst and discharged into the atmosphere without being purified.

As described above, according to the present invention, when the engine is lean burned with hydrogen fuel, the HC in the exhaust gas caused by the evaporated fuel purged by the intake system is absorbed by the HC adsorbing Pt. The adsorbed HC is desorbed from the zeolite carrying Pt as the temperature of the oxidation catalyst rises, and the desorbed HC is oxidized by the alumina carrying Pt. The active oxygen released from the CeZr composite oxide as the oxygen storage / release material carrying Pt acts on the oxidation of the desorbed HC by the alumina carrying Pt , so that HC, CO and NOx are simultaneously purified. Even if the catalyst to be activated is inactive, HC is prevented from being discharged into the atmosphere without being purified.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

<Schematic configuration of hybrid vehicle>
FIG. 1 is a schematic configuration diagram of a hybrid vehicle according to an embodiment of the present invention. This vehicle is provided with an engine 1 and a motor 2 as a power source, but the engine 1 is a so-called series hybrid vehicle that uses only the power generation, and all the power for moving the vehicle depends on the motor 2. The engine 1 is a dual fuel engine configured to use gasoline as a fuel by switching between gasoline and hydrogen and further mixing gasoline and hydrogen.

    The hybrid vehicle includes a gasoline fuel tank 3 that supplies gasoline to the engine 1, a hydrogen fuel tank 4 that supplies hydrogen to the engine 1, a generator (generator) 6 driven by the output shaft 5 of the engine 1, and a motor drive. A battery (high voltage battery) 7 for storing electric power is provided.

    The battery 7 is connected to the motor 2 and the generator 6 via the DC-AC converter 11 and the AC-DC converter 12, respectively, so that the generated power from the generator 6 and the regenerative power from the motor 2 are supplied. Charged. The battery 7 supplies power to the motor 2 and the generator 6. The output shaft of the motor 2 is connected to the drive wheel 13 via a differential gear 14.

    AC power generated by the generator 6 is converted into DC power by the AC-DC converter 12, further converted into AC power by the DC-AC converter 11, and supplied to the motor 2. The DC power of the battery 7 is converted into AC power having a predetermined frequency by the DC-AC converter 11 and supplied to the motor 2. AC power generated by the generator 6 is converted into DC power by the AC-DC converter 12 and supplied to the battery 7.

    A canister 15 that adsorbs evaporated fuel (gasoline) generated in the tank is connected to the gasoline fuel tank 3 via an evaporated fuel passage 16. The canister 15 has an air intake at the bottom and is made of a breathable member filled with activated carbon or the like. The canister 15 is connected to an intake passage on the downstream side of the throttle valve of the engine 1 via a purge passage 17, and a purge control valve 18 is disposed in the middle of the purge passage 17. The purge control valve 18 is electromagnetically controlled in its opening / closing operation. By opening the valve, the evaporated fuel adsorbed by the canister 15 is supplied (purged) together with air to the intake passage.

    In this case, the amount of evaporated fuel adsorbed by the canister 15 is estimated based on the temperature of the gasoline fuel tank 3, the time during which purging is not performed, and the purge control valve 18 is turned on when the estimated amount exceeds a predetermined value. The valve is opened for a predetermined time. The purge control valve 18 may be periodically opened for a predetermined time without estimating the evaporated fuel adsorption amount.

    In the exhaust gas passage of the engine 1, a three-way catalyst 22 is disposed as a simultaneous purification catalyst that purifies HC and CO in the exhaust gas by oxidation and simultaneously purifies NOx in the exhaust gas by reduction. An oxidation catalyst 23 is disposed on the downstream side of 22. The three-way catalyst 22 is provided with a catalyst temperature sensor 24 for detecting the temperature thereof. Further, in the exhaust gas passage, an oxygen sensor 25 for detecting the oxygen concentration of the exhaust gas flowing into the three-way catalyst 22 and the three-way catalyst are provided. An oxygen sensor 26 for detecting the oxygen concentration of the exhaust gas that has passed through 22 is disposed. Specific configurations of the three-way catalyst 22 and the oxidation catalyst 23 will be described later.

<Engine and control system configuration>
As shown in FIG. 2, the engine 1 of the present example includes a pair of rotor housings 31 and 32, two rotors 33 and 34 that are supported by an output shaft (eccentric shaft) 5 and rotate along the inner peripheral surface thereof. Is a two-rotor rotary piston engine. In FIG. 2, the pair of rotor housings 31 and 32 are schematically shown as being developed left and right.

    An intake passage 35 of the engine 1 is provided with a throttle valve 36 driven by an actuator 37 in a common passage portion on the upstream side. Two independent passage portions branched downstream of the intake passage 35 are provided with gasoline fuel injection valves 38 and 39 for performing port injection, and hydrogen for injecting fuel into the combustion chambers in the rotor housings 31 and 32. Fuel injection valves 40 and 41 are installed. In addition, two spark plugs 42 to 45 are installed in each of the rotor housings 31 and 32. The throttle valve actuator 37, the fuel injection valves 38 to 41, the spark plugs 42 to 45, the DC-AC converter 11 and the AC-DC converter 12 are controlled by a control means (PCM (powertrain control module)) 46 using a computer. Be controlled.

    The control means 46 includes a battery current / voltage sensor 47, a fuel sensor 48 for detecting the remaining amount of gasoline in the gasoline fuel tank 3, a pressure sensor 49 for detecting the remaining amount of hydrogen in the hydrogen fuel tank 4, and a vehicle. The detection signals of the fuel changeover switch 50, the vehicle speed sensor 51, the accelerator opening sensor 52, the catalyst temperature sensor 24, and the like provided on the instrument panel are input. The battery current / voltage sensor 47 is attached to the battery 7 and is used to determine the electric power that enters the battery 7 and the electric power that leaves the battery 7 from the current and voltage, and detects the storage amount of the battery 7. belongs to. Note that the temperature of the three-way catalyst 22 is not directly detected by the sensor 24 but may be estimated from the exhaust temperature or the operation history of the engine 1.

    Hereinafter, the control will be specifically described. Regarding the operation of the engine 1, when the output torque required for the motor 2 (hereinafter referred to as “requested torque”) is greater than or equal to a predetermined value based on the detection signals of the vehicle speed sensor 51 and the accelerator opening sensor 52. Further, based on the detection signal of the battery current / voltage sensor 47, it is determined that the operation of the engine 1 is necessary when the storage amount of the battery 7 is equal to or less than a predetermined value. The required engine torque is calculated based on the required torque of the motor 2 and the amount of electricity stored in the battery 7, and the engine 1 is operated.

    The fuel switching between gasoline and hydrogen used in the engine 1 is performed by the temperature (catalyst activity) of the three-way catalyst 22 detected by the catalyst temperature sensor 24 and the gasoline remaining amount in the gasoline fuel tank 3 detected by the fuel sensor 48. This is executed based on the remaining amount of hydrogen in the hydrogen fuel tank 4 detected by the pressure sensor 49 and the type of fuel selected by the driver using the fuel changeover switch 50. That is, when the engine is started, hydrogen is automatically used to improve the exhaust emission performance until the three-way catalyst 22 is activated. After the activation of the three-way catalyst 22, gasoline is used when the driver selects gasoline, and hydrogen is used when hydrogen is selected. However, when the fuel has run out of hydrogen, gasoline is used, including when the engine is started, and when the fuel has run out of gasoline, hydrogen is used.

    The target air-fuel ratio (target excess air ratio λ) of the engine 1 is different between when gasoline is used and when hydrogen is used. When gasoline is used, λ = 1 is set (stoichiometric operation). It is set to near λ = 2.0, which is the closest to the optimum fuel efficiency at zero (lean burn operation). By performing lean burn operation of the engine 1 when using hydrogen, an increase in combustion temperature is suppressed and NOx emission is suppressed. However, even when hydrogen is used, when the required torque for the engine 1 is large (when the battery 7 is charged or when the vehicle electrical load is large), the lean burn operation is performed by appropriately reducing the lean degree of the target air-fuel ratio. The air-fuel ratio of the engine 1 is feedback controlled based on the detection signal from the oxygen sensor 25.

    The control means 46 controls the DC-AC converter 11 and the AC-DC converter 12, and controls power transfer and conversion among the battery 7, the generator 13, and the motor 17. In this case, the motor 2 is driven by the electric power supplied from the battery 7 at the time of low torque operation where the required torque is low, such as during constant speed operation of the vehicle, or when the vehicle is started, and is driven by the engine 1 at the time of medium torque operation. It is driven by electric power supplied from the generator 6, and is driven by electric power supplied from both the generator 6 and the battery 7 during high torque operation with a high required torque such as during rapid acceleration. When the amount of power stored in the battery 7 is small, the engine 1 causes the generator 6 to generate electric power larger than that required for the motor 2, and extra power is supplied to the battery 7 for charging.

<Configuration of three-way catalyst / oxidation catalyst>
As shown in FIG. 3, the three-way catalyst 22 has a two-layer coat structure using Pd and Rh as catalyst metals, and the two catalyst layers 61 and 62 are formed on the cell wall 63 of the honeycomb carrier. . The lower catalyst layer 61 on the cell wall side contains oxygen storage / release material particles and alumina particles each carrying Pd, and the upper catalyst layer 62 contains oxygen storage / release material particles and alumina particles each carrying Pd. This will be specifically described below.

The lower catalyst layer 61 includes a Pd / CeZrYLaAl composite oxide in which Pd is supported on CeZrYLaAl composite oxide particles having oxygen storage / release ability, and a Pd / La-containing alumina in which Pd is supported on activated alumina particles containing La. Are mixed together with ZrO ₂ binder (zirconyl nitrate) as a catalyst component. The upper catalyst layer 62 has an Rh / CeZrNd composite oxide in which Rh is supported on CeZrNd composite oxide particles having oxygen storage / release ability, and a support material in which ZrO ₂ is supported on the surface of activated alumina particles. The supported Rh / ZrO ₂ -supported alumina is mixed with the ZrO ₂ binder as a catalyst component. The lower catalyst layer 61 does not contain Rh, and the upper catalyst layer 62 does not contain Pd.

    An example of the composition and loading amount of each component of the three-way catalyst 22 (the loading amount per 1 L of the carrier; hereinafter the same) will be described.

Regarding the Pd / CeZrYLaAl composite oxide of the lower catalyst layer 61, the composition of the CeZrYLaAl composite oxide particles is CeO ₂ : ZrO ₂ : La ₂ O ₃ : Y ₂ O ₃ : Al ₂ O ₃ = 11.7: 7. 7: 1.0: 0.4: 79.2 (mass%) and the loadings may be Pd = 2 g / L and CeZrYLaAl composite oxide particles = 30 g / L. Regarding the Pd / La-containing alumina, the La-containing alumina particles contain 4% by mass of La ₂ O ₃ , and the supported amounts may be Pd = 5 g / L and La-containing alumina particles = 60 g / L. The ZrO ₂ binder loading of the lower catalyst layer 61 may be 10 g / L.

Regarding the Rh / CeZrNd composite oxide of the upper catalyst layer 62, the composition of the CeZrNd composite oxide particles is ZrO ₂ : CeO ₂ : Nd ₂ O ₃ = 67: 23: 10 (mass%), and the supported amount is Rh. = 2 g / L, CeZrNd composite oxide particles = 70 g / L. Regarding the Rh / ZrO ₂ -supported alumina, the supported amounts may be Rh = 1 g / L, ZrO ₂ = 2.3 g / L, and alumina particles = 27 g / L. The amount of ZrO ₂ binder supported by the upper catalyst layer 62 may be 15 g / L.

The honeycomb carrier of the three-way catalyst 22 may be made of cordierite having a cell wall thickness of 4.5 mil (114.3 × 10 ⁻³ mm) and 400 cells per square inch (645.16 mm ² ), for example. The diameter may be 105.7 mm and the length may be 118 mm.

    The oxidation catalyst 23 contains an HC adsorbent and a catalyst metal Pt, and is formed by forming a catalyst layer 65 on the cell wall 64 of the honeycomb carrier as shown in FIG. That is, in the catalyst layer 65, Pt / zeolite in which Pt is supported on zeolite (in this embodiment, β zeolite is used) as an HC adsorbent, and Pt / in which Pt is supported on alumina particles. Alumina and a Pt / CeZr composite oxide in which Pt is supported on a CeZr composite oxide as an oxygen storage / release material are mixed together with an alumina binder.

Regarding the supported amount of Pt / zeolite, β zeolite = 30 g / L to 150 g / L (for example, 60 g / L), Pt = 0.5 g / L to 20 g / L (for example, 1 g / L), Pt / Regarding the supported amount of alumina, alumina particles = 30 g / L or more and 150 g / L or less (for example, 60 g / L), Pt = 0.5 g / L or more and 20 g / L or less (for example, 2 g / L), Pt / CeZr composite Regarding the oxide loading, CeZr composite oxide particles = 30 g / L to 150 g / L (for example, 60 g / L), Pt = 0.5 g / L to 20 g / L (for example, 2 g / L), Alumina binder = 10 g / L to 40 g / L (for example, 25 g / L). The composition of the CeZr composite oxide particles may be, for example, CeO ₂ : ZrO ₂ = 70: 30 (mass%). Although β zeolite acts as a catalyst for decomposing NOx, Pt can be supported on this β zeolite to further promote the decomposition of NOx.

In addition, the catalyst layer 65 may contain Pd of 20 g / L or less and Rh of 20 g / L or less. As the binder, a ZrO ₂ binder or a CeO ₂ binder can be used alone or mixed with an alumina binder.

The honeycomb carrier of the oxidation catalyst 23 may be made of, for example, cordierite having a cell wall thickness of 6.5 mil (165.1 × 10 ⁻³ mm) and 400 cells per square inch (645.16 mm ² ), The diameter may be 105.7 mm and the length may be 118 mm.

    Therefore, the engine 1 is stoichiometrically operated when gasoline is used as fuel, and HC, CO, and NOx in the exhaust gas at that time are purified by the three-way catalyst 22. In this case, the three-way catalyst 22 is upstream of the oxidation catalyst 23 and is easily heated by the heat of the exhaust gas, which is advantageous for purifying the exhaust gas during stoichiometric operation, particularly when the engine is cold. On the other hand, the oxidation catalyst 23 is on the downstream side of the three-way catalyst 22, and the thermal influence of the exhaust gas is reduced. Further, since Pd and Rh are arranged in different catalyst layers, both the catalyst metals are prevented from being alloyed, which is advantageous for preventing deterioration of the catalyst.

    Next, the engine 1 is lean burned when hydrogen is used as fuel, and the combustion chamber temperature is low. For this reason, when the evaporated fuel is purged from the canister 15 to the intake passage 35, the evaporated fuel is not completely burned in the combustion chamber, and the amount of HC discharged to the exhaust gas passage increases. At that time, since the exhaust gas temperature is low, the three-way catalyst 22 is also low in temperature and is normally in an inactive state. Therefore, the three-way catalyst 22 does not oxidize and purify HC in the exhaust gas due to the evaporated fuel.

    However, in the case of the present invention, the oxidation catalyst 23 is arranged on the downstream side of the three-way catalyst 22 and the oxidation catalyst 23 contains β zeolite as the HC adsorbent. The HC caused by the evaporated fuel is adsorbed by the β zeolite and is prevented from being discharged into the atmosphere. The HC adsorbed on the β zeolite is desorbed from the β zeolite as the temperature of the oxidation catalyst 23 rises, but the desorbed HC is oxidized and purified by Pt / alumina. In particular, by adopting Pt as the catalyst metal, the HC can be efficiently purified in a lean atmosphere even at a relatively low temperature.

    Further, at that time, the CeZr composite oxide particles cause oxygen exchange reaction in which oxygen in the exhaust gas is taken in and exchanged with oxygen in the composite oxide particles due to a change in the valence of Ce ions even in an oxygen-excess atmosphere. The active oxygen released thereby works effectively for the oxidation purification of the desorbed HC by Pt / alumina. For this reason, the amount of HC resulting from the evaporated fuel is discharged into the atmosphere without being purified.

    In addition, since the β zeolite that works as the HC adsorbent also works to purify NOx in the exhaust gas, in the lean burn operation with hydrogen fuel, for example, the air-fuel ratio is controlled so as to increase the engine output and the combustion chamber temperature is high. Thus, even if the amount of NOx generated increases slightly, the deterioration of emissions can be avoided.

    In the above embodiment, the engine 1 switches between gasoline and hydrogen. However, the present invention is not limited to this, and an operation mode in which gasoline and hydrogen are mixed and used can also be adopted. .

    Moreover, although the engine of the said embodiment is a rotary piston engine, this invention is not limited to this, A reciprocating engine may be sufficient.

    Further, although the above embodiment relates to a series hybrid vehicle, the present invention can be applied to a parallel hybrid vehicle, a series parallel hybrid vehicle, and a vehicle driven only by an engine without using a motor. .

It is a block diagram of the hybrid vehicle which concerns on this invention. It is a block diagram of the engine and control system of the vehicle. It is a block diagram of the three way catalyst and oxidation catalyst which concern on this invention.

1 Engine 2 Motor 3 Gasoline fuel tank 4 Hydrogen fuel tank 6 Generator (generator)
15 canister 16 evaporative fuel passage 17 purge passage 18 purge control valve 22 three-way catalyst 23 oxidation catalyst

Claims (4)

An exhaust gas purification method for an engine in which stoichiometric operation with fuel including gasoline and lean burn operation with hydrogen fuel are performed,
A canister that adsorbs the evaporated fuel generated in a fuel tank that stores the fuel containing gasoline, and a purge passage that purges the evaporated fuel adsorbed by the canister to the intake system of the engine;
During the stoichiometric operation with the fuel containing gasoline, the exhaust gas is purified by a simultaneous purification catalyst that oxidizes and purifies HC and CO in the exhaust gas and simultaneously reduces and purifies NOx in the exhaust gas,
During lean burn operation with the hydrogen fuel, HC that is not oxidized and purified by the simultaneous purification catalyst in the exhaust gas caused by the evaporated fuel purged to the intake system is oxidized and purified by the oxidation catalyst ,
The oxidation catalyst contains zeolite as an HC adsorbent carrying Pt, alumina carrying Pt, and a CeZr composite oxide as an oxygen storage / release material carrying Pt ,
The oxidation of the HC that is not oxidized and purified by the simultaneous purification catalyst in the oxidation catalyst includes the step of adsorbing the HC on the zeolite as the HC adsorbent carrying the Pt, and the adsorbed HC increasing the temperature of the oxidation catalyst. And the step of desorbing from the zeolite carrying Pt and the step of oxidizing the desorbed HC by the alumina carrying Pt, the oxygen storage / release material carrying the Pt The active oxygen released from the CeZr composite oxide as described above acts on the oxidation of the desorbed HC by the alumina on which the Pt is supported . An exhaust gas purifying device for an engine in which stoichiometric operation with fuel including gasoline and lean burn operation with hydrogen fuel are performed,
A canister for adsorbing evaporated fuel generated in a fuel tank for storing fuel containing the gasoline;
A purge passage for purging the evaporated fuel adsorbed by the canister to the intake system of the engine;
A simultaneous purification catalyst that is disposed in the exhaust gas passage of the engine and that oxidizes and purifies HC and CO in the exhaust gas and simultaneously reduces and purifies NOx in the exhaust gas during a stoichiometric operation with fuel containing the gasoline;
Oxidation for oxidizing and purifying HC that is not oxidized and purified by the simultaneous purification catalyst in the exhaust gas caused by the evaporated fuel purged to the intake system during the lean burn operation with the hydrogen fuel disposed in the exhaust gas passage With a catalyst,
The oxidation catalyst is desorbed from zeolite as an HC adsorbent carrying Pt for adsorbing HC that is not oxidized and purified by the simultaneous purification catalyst, and from the zeolite carrying Pt as the temperature of the oxidation catalyst rises. As an oxygen storage / release material carrying Pt , alumina that carries Pt for oxidizing the released HC and releases active oxygen for oxidizing the desorbed HC by the alumina carrying Pt An exhaust gas purifying apparatus for an engine, comprising a CeZr composite oxide. In claim 2,
The simultaneous purification catalyst is a three-way catalyst,
An exhaust gas purification apparatus for an engine, wherein the oxidation catalyst is disposed in an exhaust gas passage downstream of the exhaust gas flow from the three-way catalyst. In claim 2 or claim 3,
The engine is mounted on a hybrid vehicle that can be driven by an electric motor, and is used for driving a generator for the electric motor.

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