Combustion gas purifier and internal combustion engine

Details Combustion gas purifier and internal combustion engine Combustion gas purifier and internal combustion engine

2002-11-14

2004-12-21

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S320000

Reexamination Certificate

active

06832475

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a combustion gas purification system that purifies, by an oxidation-reduction reaction, harmful components in the combustion gas from a combustion system. Furthermore, the present invention relates to an internal combustion engine that is provided in an exhaust passage thereof with an exhaust gas purification system that purifies the exhaust gas, and a heat exchanger that exchanges heat with the exhaust gas.
BACKGROUND ART
A catalytic system that purifies, by a catalytic reaction, harmful components in the exhaust gas from an internal combustion engine has a structure in which, for example, a platinum system catalyst is supported on a catalyst support, and the catalyst has an optimal temperature for the catalytic reaction. For example, when the catalyst temperature is below the activation temperature and the reactivity is poor, the catalytic system is placed on the upstream side of the exhaust passage where the exhaust gas temperature is high and is thereby heated, or a method is employed in which the catalytic system is heated by an electric heater or the combustion gas generated in a combustion system used exclusively for heating, so as to activate the catalytic reaction. Conversely, when the catalyst temperature becomes higher than its heat resistant temperature, enriching the air/fuel ratio relative to the theoretical air/fuel ratio cools the catalyst by means of the heat of vaporization of surplus fuel, thereby preventing degradation of the catalyst.
Moreover, an arrangement is known from Japanese Patent Application Laid-open No. 60-93110 in which heat exchangers are placed on both the upstream and downstream sides of a catalytic system disposed in an exhaust passage, and the catalyst is maintained at an appropriate temperature by controlling the temperature of the exhaust gas.
In order to allow the catalytic system to function most efficiently, it is of course important to use it within a temperature range that is optimal for the catalytic reaction, but if the catalyst temperature deviates from the temperature that is optimal for the catalytic reaction, it is also important that the catalyst temperature quickly recovers so that it is within the temperature range that is optimal for the catalytic reaction (ref. Table 1). With regard to the deviation from the temperature that is optimal for the catalytic reaction referred to here, there is a case in which the catalyst temperature is lower than the optimal temperature and a case in which it is higher, and for recovering the catalyst temperature so that it is within the temperature range that is optimal for the catalytic reaction, there is a case where the catalyst temperature is increased and a case where it is decreased.
TABLE 1
Examples of temperature range of catalytic reaction
Operational mode of
Generally used limit
combustion system
temperature of purification catalyst
(application)
Upper limit (° C.)
Lower limit (° C.)
Variable output
on-
800 to 900
250 to 300
rated operation
(movable devices
such as automobiles)
Constant output/rated
500 to 600
100 to 200
operation
(stationary plant
machinery)
For example, immediately after an internal combustion engine starts, the temperature of the catalytic system itself is close to ambient, and it is therefore necessary to heat the catalytic system as quickly as possible so as to increase the catalyst temperature above the activation temperature.
Among the conventional methods, the method in which the catalytic system is placed in an upstream position of the exhaust passage where the exhaust gas temperature is high places a mechanical limit on how close the catalytic system can be to the upstream end of the exhaust passage because of structural restrictions imposed by a system employing the catalytic system or by the entire system. Furthermore, the method in which the catalytic system at low temperature is heated by an electric heater or combustion gas generated by a combustion system used exclusively for heating requires a special energy source, and there is the problem that the fuel consumption of the entire system increases.
Conversely, since an excessively high catalyst temperature causes degradation of the catalyst, it is necessary to quickly cool the catalyst temperature below the heat resistant temperature. In this case, since the air/fuel ratio is enriched to cool the catalyst by means of the heat of vaporization of surplus fuel, there is the problem of an increase in the fuel consumption.
It should be noted here that in the arrangement described in Japanese Patent Application Laid-open No. 60-93110, it is inherently difficult to actively control the catalyst temperature. That is, in this method, a heat exchanger is disposed on the upstream side of the catalytic system, and there is extra thermal capacity within an exhaust passage through which the exhaust gas, which is a heat source, passes. In other words, when the temperature of the main body of an internal combustion engine is still low immediately after a cold start, the heat of the exhaust gas is consumed by increasing the temperature of the heat exchanger that is further upstream than the catalytic system, and the temperature of the exhaust gas decreases before it increases the temperature of the catalytic system.
Furthermore, when the catalyst is in an over-heated state, heat exchange is first carried out between a low temperature medium and the exhaust gas within the heat exchanger on the upstream side of the catalytic system so as to decrease the temperature of the exhaust gas, and the exhaust gas whose temperature has been decreased by the heat exchange is then supplied to the catalytic system, thereby indirectly suppressing any increase in the temperature of the catalyst. Of course, the heat exchanger on the downstream side of the catalytic system contributes almost nothing to decreasing the catalyst temperature.
As hereinbefore described, since this method indirectly controls the thermal energy that is transferred to the catalyst by controlling the temperature of the exhaust gas, which is a heat source, appropriate control of the catalyst temperature is difficult.
Furthermore, an internal combustion engine that is equipped with an exhaust gas purification system in its exhaust passage is known from Japanese Patent Application Laid-open Nos. 60-93110 and 8-68318, wherein heat exchangers are disposed in the exhaust passage on both the upstream side and the downstream side of the exhaust gas purification system in an attempt to achieve both temperature control capability for the exhaust gas purification system and waste heat recovery capability for the heat exchangers.
Although the exhaust gas purification system generates heat of reaction when removing harmful components from the exhaust gas, since in the above-mentioned conventional arrangement, the exhaust gas purification system and the heat exchangers are not in direct contact, it is difficult to utilize effectively the heat of reaction generated by the exhaust gas purification system in the heat exchangers. Although it is possible to activate the catalyst and protect it from being overheated by controlling the temperature of the exhaust gas purification system by means of the flow rate of an operating medium flowing through the heat exchanger, in the above-mentioned conventional arrangement, since the exhaust gas purification system and the heat exchangers are not in direct contact with each other, it is difficult to control the temperature of the exhaust gas purification system effectively.
DISCLOSURE OF THE INVENTION
The present invention has been carried out in view of the above-mentioned circumstances, and it is a first object of the present invention to provide an exhaust gas purification system that can actively control the catalyst temperature in the optimal temperature range without degrading the energy efficiency of the entire system.
Furthermore, it is a second object of the present invention to enable the best possible performance to be delivered by an exhaust gas purification system and

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