Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
1999-09-13
2001-04-17
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C060S274000
Reexamination Certificate
active
06216676
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Application Nos. HEI 10-285585 filed on Oct. 7, 1998 and HEI 10-288321 filed on Oct. 9, 1998 including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an internal combustion engine system having a combustion chamber into which inert gas is introduced so as to cause combustion.
2. Description of Related Art
Conventionally, in an internal combustion engine, for example, in a diesel engine, in order to restrict the generation of NOx, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter, referred to as EGR) passage so as to recirculate exhaust gas, that is, EGR gas into the engine intake passage via the EGR passage. In this case, the EGR gas has a relatively high specific heat and is able to absorb a large amount of heat. Hence, as the amount of EGR gas is increased, that is, as the EGR rate (the amount of EGR gas/(the amount of EGR gas+the amount of intake air)) is increased, the combustion temperature in a combustion chamber decreases. If the combustion temperature decreases, the generation amount of NOx is reduced. Thus, the larger the EGR rate becomes, the smaller the generation amount of NOx becomes.
As described hitherto, it has been conventionally known that the generation amount of NOx is reduced by increasing the EGR rate. However, in the process of increasing the EGR rate, when the EGR rate exceeds a certain threshold value, the generation amount of soot, namely smoke, starts increasing abruptly. In this respect, it has been conventionally considered that if the EGR rate is increased beyond this certain threshold value, the amount of smoke increases endlessly. In other words, the EGR rate at which the amount of smoke starts increasing abruptly has been considered to be a maximum allowable value of the EGR rate.
Accordingly, the EGR rate conventionally has been set below the maximum allowable value. Although the maximum allowable value of the EGR rate differs greatly depending on a type of the engine or fuel, it is approximately 30% to 50%. Therefore, in the diesel engine, the EGR rate is at most set to 30% to 50%.
As described above, it has been conventionally considered that the EGR rate has a maximum allowable value. Thus, the EGR rate is set so as to reduce a generation amount of NOx and smoke to the maximum possible extent, by ensuring that the EGR rate does not exceed the maximum allowable value. However, even if the EGR rate has been thus determined, the generation amount of NOx and smoke cannot be reduced limitlessly. In fact, the generation of a considerable amount of NOx and smoke is inevitable.
SUMMARY OF THE INVENTION
In the course of studies of combustion in diesel engines, the following fact has been discovered. That is, as described above, if the EGR rate is made larger than the maximum allowable value, the generation amount of smoke increases abruptly. However, the generation amount of smoke has a peak. If the EGR rate is further increased after the generation amount of smoke has reached its peak, the generation amount of smoke then starts decreasing abruptly. If the EGR rate is set to 70% or more during an idling operation, or if the EGR rate is set to about 55% or more in the case where EGR gas is cooled intensively, NOx is hardly generated and the generation amount of smoke becomes almost zero. Namely, soot is hardly generated.
Thereafter, based on this discovery, further studies have been conducted on the reason why soot is hardly generated. As a result, a novel unprecedented combustion system capable of reducing soot and NOx simultaneously has been constructed. This novel combustion system will be explained later in detail. In summary, this combustion system is based on the idea that the growth of hydrocarbon is stopped before it develops into soot.
In other words, it has been determined by repeated experiments and studies that if the temperature of fuel and ambient gas in the combustion chamber during combustion is equal to or lower than a certain temperature, the growth of hydrocarbon is stopped before it becomes soot, and that if the temperature of fuel and ambient gas becomes higher than the aforementioned certain temperature, the hydrocarbon rapidly develops into soot. In this case, the temperature of fuel and ambient gas is greatly affected by the endothermic effect of the gas surrounding fuel at the time of fuel combustion. If the endothermic value of the gas surrounding the fuel is adjusted in accordance with an exothermic value during the fuel combustion, the temperature of fuel and ambient gas can be controlled.
Accordingly, if the temperature of fuel and ambient gas in the combustion chamber during combustion is set equal to or lower than a temperature at which the growth of hydrocarbon is stopped halfway, soot is no longer generated. The temperature of fuel and ambient gas in the combustion chamber during combustion can be set equal to or lower than a temperature at which the growth of hydrocarbon is stopped halfway, by adjusting an endothermic value of the gas surrounding the fuel. On the other hand, the hydrocarbon that has stopped growing before becoming soot can be removed easily by means of an after-treatment that uses an oxidation catalyst or the like. This is the basic concept of the novel combustion system.
An engine can be controlled such that it switches between a first combustion mode, which corresponds to the new combustion mode, and a second combustion mode, which corresponds to a conventional combustion mode, based on engine performance requirements. However, each time the combustion mode is switched, a large amount of smoke is briefly generated. Accordingly, it is desirable to avoid switching between the first and second combustion modes too often.
One object of the present invention is to provide an internal combustion engine system which achieves suitable combustion, that is, prevents generation of soot (smoke) and NOx, simultaneously, and reduces an undesirable situation where a generation amount of soot is increased in accordance with the transition between a first combustion mode and a second combustion mode. The first combustion mode is a mode in which the amount of inert gas supplied to the combustion chamber is more than the amount that causes the peak amount of soot to be generated. The second combustion mode is the conventional combustion mode.
In order to achieve the above and other objects, in accordance with one aspect of the present invention, there is provided an internal combustion engine system in which a generation amount of soot increases to a peak when increasing an amount of an inert gas supplied to a combustion chamber, the system including a controller that controls the combustion mode in which the engine is to operate. The controller switches between a first combustion mode where an amount of the inert gas supplied to the combustion chamber is larger than an amount of the inert gas that causes the generation amount of soot to become a peak amount (and thus soot is hardly generated), and a second combustion mode where an amount of the inert gas supplied to the combustion chamber is smaller than the amount of the inert gas that causes the generation amount of soot to become the peak amount. The controller also can determine the frequency of switching between the first combustion mode and the second combustion mode. Furthermore, the controller controls the execution of the first combustion mode and the second combustion mode so that the frequency of switching between the first combustion mode and the second combustion mode is inhibited from becoming too high (i.e., more than a predetermined amount), for example, when it is determined that the frequency is high.
Accordingly, it is possible to reduce soot and NOx discharged from the combustion chamber simultaneously, and an undesirable situation where the generation amount of soot is increased in a
Gotoh Masato
Ito Takekazu
Murata Hiroki
Sasaki Shizuo
Yoshizaki Kouji
Castro Arnold
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Wolfe Willis R.
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