Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2003-02-26
2004-06-29
Denion, Thomas (Department: 3747)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C123S496000, C239S088000
Reexamination Certificate
active
06755022
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to internal combustion engines, and in particular, to turbo-charged internal combustion engines with fuel injection rate shaping and internal exhaust gas recirculation.
DESCRIPTION OF THE RELATED ART
Emission control standards for internal combustion engines have tended to become more stringent over time. The sorts of emissions to be controlled tend to fall into at least four broad categories: unburned hydrocarbons, carbon monoxide, particulates, and oxides of nitrogen (NOx). Unburned hydrocarbons and carbon monoxide tend to be produced by inefficient or incomplete combustion. Efficient, complete combustion, on the other hand, tends to produce oxides of nitrogen.
Efficient, complete combustion tends to be characterized by high combustion chamber temperatures. The heat associated with high combustion chamber temperatures acts as a catalyst, promoting the binding of oxygen in the air charge to the otherwise inert nitrogen and producing oxides of nitrogen. An engine that is running efficiently, therefore, may produce oxides of nitrogen. Controlling the amounts of emissions produced by an internal combustion engine, then, becomes an issue of balancing combustion efficiency against raising combustion temperatures high enough to produce oxides of nitrogen.
Since the ingredients of oxides of nitrogen come from the intake air, one possibility to reduce the amounts of oxides of nitrogen may be to limit the air available for combustion. Compression-ignition engines, unlike spark-ignition engines, are often run with an excess of air over the stoichiometric ratio, so there is lots of nitrogen available for oxidation. This is because the production of particulates, such as ash, tends to rise as the air/fuel (A/F) mixture approaches stoichiometric. This is evidenced by the observation that diesel trucks often emit puffs of smoke under heavy acceleration. Since compression-ignition engines need to run with an excess of air to avoid emitting particulates, reducing the production of oxides of nitrogen by reducing the amount of air available for combustion is not a practical solution.
Another way to control the production of oxides of nitrogen is to reduce peak combustion chamber temperatures. Since production of oxides of nitrogen tends to depend on high combustion chamber temperatures as a catalyst, reducing the peak temperature ameliorates one of the conditions necessary for the production of oxides of nitrogen. Reducing the peak combustion chamber temperature may thus reduce the amount of oxygen that binds with nitrogen, with a consequent reduction in the quantity of oxides of nitrogen produced.
One means of lowering the high combustion chamber temperatures produced by an efficient combustion event is to cool the combustion chamber during combustion. The combustion chamber may be cooled by, e.g. reintroducing some of the products of previous combustion events back into the combustion chamber, a process known as exhaust gas recirculation (EGR). Since the products of efficient combustion are primarily water and carbon dioxide, neither of which is very flammable, this has the effect of extinguishing the combustion somewhat. The peak temperatures reached in the combustion chamber will consequently be lower, which retards the production of oxides of nitrogen. Clearly, the amount and timing of the introduction of products of combustion must be controlled accurately to avoid impairing the performance of the engine.
Lowering combustion chamber temperatures may have the collateral benefit of reducing exhaust manifold temperatures, as well as stack temperatures. Reducing stack temperatures reduces the temperature in exhaust after-treatment equipment such as oxidation catalysts, with a consequent reduction in the formation of, e.g. sulfates. Reducing stack temperatures may also reduce the production of particulates.
One way to reintroduce some of the products of previous combustion events into the combustion chamber is with external EGR. In external EGR, a tube or plenum conducts some post-combustion gases from the combustion chamber, usually through an exhaust manifold, to a valve. When the valve is opened, the post-combustion gases are readmitted to the combustion chamber, often passing through the intake manifold first. If the post-combustion gases pass through the intake manifold they will mix with fresh make-up air coming in through the air cleaner and be distributed relatively evenly to each of the combustion chambers when its respective intake valve opens.
External EGR, however, relies on high engine heat rejection to work, since the post-combustion gases must travel a relatively long way. Also, the valves and other hardware associated with external EGR increase the cost and complexity of the engine. Furthermore, the addition of external EGR and its associated hardware to an existing engine may require the chassis, front clip, or sheet metal to be re-arranged to allow the engine to fit. Furthermore, if the external EGR is plumbed through the intake manifold, it may be difficult to control the amount of exhaust gas that is re-admitted to each individual combustion chamber. This may pose a problem if, e.g. some combustion chambers run hotter than other combustion chambers, such as those that are nearer the water jacket exit.
A combustion chamber near the exit to the water jacket will be transferring heat to warmer coolant, other things being equal, than a combustion chamber near, e.g. the entrance to the water jacket, since the coolant has already been past the other combustion chambers when it reaches the exit. There will thus be a smaller temperature differential between the combustion chamber and the coolant. Thus the metal around, e.g. the combustion chamber will be maintained at a higher temperature, other things being equal. It would be desirable if the amount of exhaust gas that is readmitted to a combustion chamber could be controlled on an individual basis, commensurate with the temperatures prevailing in that combustion chamber.
The EGR valve, along with the associated actuator and control hardware, is also a point of potential failure, jeopardizing the durability of the engine. It would be desirable if the EGR valve, and its associated actuator and control hardware, could be eliminated. It would further be desirable if the amount and timing of post-combustion gases that re-enter the combustion chamber could be controlled by varying the pressure in the exhaust manifold relative to the pressure in the combustion chamber, rather than with an external valve. Finally, allowing post-combustion gases to re-enter the combustion chamber directly from the exhaust manifold may reduce the transfer time of the post-combustion gases back into the combustion chamber, improving the responsiveness of the EGR system and allowing their application to be optimized or, at least, reduced.
Many truck engines are supercharged. Some superchargers are belt-, chain- or gear-driven, while others, so-called turbo-chargers, rely on a turbine to convert the kinetic energy in exhaust gases to rotational momentum in a compressor. There are those who define superchargers and turbo-chargers as separate entities. For the purposes of this application, however, a turbo-charger will be defined as a turbine-driven supercharger.
Turbo-machinery, such as superchargers, have components that rotate. These components possess inertia. These components gain momentum with respect to this inertia when they are turned, by, e.g. a belt or a turbine. Building rotational momentum requires time, which manifests itself as lag. The lag is generally proportional to the inertia of the turbine rotor and compressor. Thus the inertia of the turbine rotor and the compressor rotor contribute to lag. There are advantages to be found with using smaller compressors and turbine trim, such as better transient engine response, which in turn helps to control emissions, such as, for example, particulates. It would be desirable to be able to reduce the sizes of the turbine and the compressor rotors, thus reduci
Kim Charlie Chang-Won
Suder Timothy Andrew
Trevitz Steven Stuart
Zsoldos Jeffrey Scott
Mack Trucks, Inc.
Rothwell, Figg Ernst & Manbeck, PC
Trieu Thai-Ba
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