Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-08-19
2001-06-05
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S284000, C060S276000, C060S278000, C060S286000, C060S285000, C123S295000
Reexamination Certificate
active
06240721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an internal combustion engine introducing inert gas into a combustion chamber to cause combustion.
2. Description of the Related Art
Recently, in an internal combustion engine, for example, a diesel engine, to restrict generation of nitrogen oxides NOx, the diesel engine is structured such that an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation passage (hereinafter, refer to an EGR) for recirculating an exhaust gas, that is, an EGR gas, into the engine intake passage via the EGR passage. In this case, since the EGR gas has a relatively high specific heat and can absorb a large amount of heat, a combustion temperature within the combustion chamber is lowered as an amount of the EGR gas is increased, that is, a rate of the EGR (EGR gas amount/(EGR gas amount+intake air amount)) is increased. When the combustion temperature is lowered, a generated amount of nitrogen oxides NOx is lowered. Therefore, the more the EGR rate is increased, the lower the generated amount of nitrogen oxides NOx becomes.
As mentioned above, it has been conventionally known that the generated amount of nitrogen oxides NOx is lowered when the EGR rate is increased. However, in the case where the EGR rate is increased, a generated amount of soot, that is, smoke, suddenly starts increasing when the EGR rate exceeds a certain limit. With respect to this point, it has been conventionally considered that the smoke is unlimitedly increased when the EGR rate is increased beyond a certain limit. That is, it has been considered that the EGR rate at which the smoke suddenly starts increasing is the maximum allowable limit of the EGR rate. Accordingly, the EGR rate is defined within a range which does not exceed the maximum allowable limit. The maximum allowable limit of the EGR rate is significantly different in relation to the type of engine and fuel, however, is within a range between approximately 30% and 50%. Therefore, in the diesel engine, the EGR rate is restricted to the range between 30% and 50% at the maximum.
As mentioned above, since it has been conventionally considered that the maximum allowable limit exists with respect to the EGR rate, the EGR rate has been defined within a range which does not exceed the maximum allowable limit. Therefore, the generated amount of nitrogen oxides NOx becomes as small as possible. However, even when the EGR rate is defined as discussed above, a reduction in the generated amount of nitrogen oxides NOx has a limit such that in actuality a significant amount of nitrogen oxides NOx is still generated.
SUMMARY OF THE INVENTION
In the process of researching combustion in the diesel engine in consideration of the problems mentioned above, it has been found that, when making the EGR rate greater than the maximum allowable limit, the amount of generated smoke is suddenly increased, as discussed above. However, the generated amount of smoke has a peak, and when the EGR rate is further increased beyond the peak, the amount of generated smoke suddenly starts reducing at this point. This indicates that, when setting the EGR rate to a value equal to or more than 70% during an idling operation or strongly cooling the EGR gas, nitrogen oxides NOx are hardly generated and the amount of smoke generated becomes substantially zero. In other words, soot is hardly generated when the EGR rate is set to a value equal to or more than 55%. Thereafter, on the basis of this information, the reason why substantially no soot has been generated was considered.
It is ascertained, as a result of multiple experiments and research, that the growth of the hydrocarbon stops in the middle of the step before becoming soot when a temperature of the fuel and the surrounding gas during combustion within the combustion chamber is equal to or less than a predetermined temperature, and that the hydrocarbon becomes soot at a stroke when the temperature of the fuel and the surrounding gas reach the predetermined temperature. In this case, the temperature of the fuel and the surrounding gas is greatly influenced by an endothermic effect of the gas surrounding the fuel when the fuel is being burned, thereby making it possible to control the temperature of the fuel and the surrounding gas by adjusting the heat absorption amount of the gas surrounding the fuel in correspondence to the generated amount of smoke during combustion of the fuel.
Accordingly, when restricting the temperature of the fuel and the surrounding gas during combustion within the combustion chamber to the level equal to or less than the temperature at which the growth of the hydrocarbon stops soot is not generated. Thus, it is possible to restrict the temperature of the fuel and the surrounding gas during combustion within the combustion chamber to the level equal to or less than the temperature at which the growth of the hydrocarbon stops by adjusting the heat absorption amount of the gas surrounding the fuel. On the contrary, the hydrocarbon that stops growing before becoming soot can easily be cleaned by an after treatment using an oxidation catalyst or the like.
The combustion system, as mentioned above, cleans a hydrocarbon, or the like, which stops growing before becoming soot using the oxidation catalyst or the like. That is, when the oxidation catalyst or the like is not activated, combustion cannot be performed. However, since the temperature of the exhaust gas becomes low during an engine idling operation, the temperature of the catalyst is lowered if the engine is left in the idling operation state for an extended period of time. Then, the temperature of the catalyst becomes lower than the activation temperature at which the hydrocarbon or the like can be oxidized, and as a result, a large amount of hydrocarbon or the like is discharged into the ambient air.
In order to solve the above-mentioned problem, an object of this invention is to provide an internal combustion chamber which can adjust the temperature of a catalyst such that the temperature of the catalyst is within a desired range.
In order to achieve this object, in accordance with an aspect of this invention, there is provided an internal combustion engine wherein a generated amount of soot is gradually increased to a peak when increasing an amount of an inert gas supplied within a combustion chamber. The internal combustion engine includes an inert gas amount controller that controls an amount of the inert gas so that an amount of the inert gas supplied to the combustion chamber is more than an amount of the inert gas when the generated amount of soot reaches the peak. A catalyst is provided in an exhaust passage of an engine to perform oxidation. A detector detects a temperature of the catalyst and a catalyst temperature adjusting device adjusts the temperature of the catalyst within a predetermined temperature range.
Accordingly, it is possible to adjust the temperature of the catalyst such that the temperature of the catalyst is within a desired range.
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patent: 5967113 (2000-07-01), Kaneko et al.
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Gotoh Masato
Ito Takekazu
Murata Hiroki
Sasaki Shizuo
Yoshizaki Kouji
Denion Thomas
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Trieu Thai-Ba
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