Abstract:
A method and systems for supplying oxygen-enriched feedgas to a reformer. The reformer is placed on an exhaust bypass line, which has a valve upstream the reformer, for opening and closing the flow of exhaust gas into the bypass line. The bypass line receives atmospheric air at a venturi, and this air is mixed with the exhaust gas to supply feedgas to the reformer. The output of the reformer is directed via the bypass line to a point on a main exhaust line upstream an emissions control device, such as a NAC.

Description:
RELATED PATENT APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/548,354, filed Feb. 27, 2004 and entitled “Oxygen-Enriched Feedgas for Reformer in NOx Adsorber Emissions System”. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     This invention relates to reducing exhaust emissions from internal combustion engines, and more particularly to providing oxygen-enriched feedgas for an exhaust gas reformer used upstream of an emissions control device, such as a lean NO x  catalyst.  
       BACKGROUND OF THE INVENTION  
       [0003]     Internal combustion engines are a major contributor to harmful emissions. Internal combustion engines dominate land transportation propulsion—cars, trucks, off-highway vehicles, railroad, marine, motorcycles—as well as provide mechanical and electrical power for a wide range of large and small applications. The two dominant types of internal combustion engines are spark-ignition and diesel. The amount and composition of the emissions exhausted from these engines depend on the details of the processes that occur within the engine during operation, the characteristics of the fuel used, and the type of emissions control system used.  
         [0004]     For diesel engines, the main pollutants of concern are nitrogen oxides (NOx) and particulate matter (PM). The latter is composed of black smoke (soot), sulfates generated by the sulfur in fuel, and organic components of unburned fuel and lubricating oil.  
         [0005]     In-cylinder design changes have had some success in reducing emissions, but have fallen short of allowing diesel engines to meet today&#39;s emissions limits. Post-combustion treatment systems often include catalysts and particulate filters for reducing NOx and PM respectively. Technology advances in the catalyst field have made it possible for integrated systems of engine and exhaust treatment to achieve extremely low emissions. Yet, more emission reduction efficiencies are sought from existing systems and new catalytic reduction solutions are needed to achieve even lower emissions.  
         [0006]     Indications are that diesel oxidation catalyst performance improves with increased engine speed, airflow, and hence oxygen content. For particulate filters, both oxygen content and exhaust gas temperature their regeneration.  
         [0007]     On the other hand, for regeneration of modern NO x  reduction catalysts such as the lean NO x  trap (NO x  adsorber catalyst), reduced oxygen content in the exhaust is desirable. Normally in diesel exhaust, attempts are made to reduce oxygen to regenerate the system from its stored nitrogen compounds. Attempts to reduce exhaust oxygen content are usually combined with increasing exhaust hydrocarbon to obtain the rich mixture needed for the NO x  regeneration process.  
         [0008]     It is customary in diesel NO x  adsorber technology to place a diesel oxidation catalyst upstream from the lean NO x  trap. Its purpose is to condition the exhaust hydrocarbon or reform it to obtain the ideal reductant for the lean NO x  trap regeneration.  
         [0009]     Having established the need for controlling the composition of the reductant, some companies have announced plans for using onboard fuel reformers to accomplish their needs. Onboard fuel reformers involve some kind of catalyst that is provided with a supply of fuel and a supply of air. Providing a continuous but controllable supply of fuel has not been a significant obstacle. However, providing a suitable supply of air to the reformer has been challenging.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:  
         [0011]      FIG. 1  illustrates a first embodiment of the invention; and  
         [0012]      FIG. 2  illustrates a second embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     The following description is directed to an engine-based means and method, used in conjunction with a diesel emissions control system, for supplying an exhaust reformer with a source of air. The air enriches the feedgas to the reformer, which generates a reformate. In the example of this description, the enriched feedgas is used by the reformer to provide a reductant during regeneration of a NO x  adsorbtion catalyst (NAC).  
         [0014]      FIG. 1  illustrates a method and system for supplying air to a reformer  101  in accordance with the invention. Reformer  101  is part of an emissions control system  100 , which also has at least one emissions control device  102  that has cause to use feedgas from reformer  101 . In the example of this description, the emissions control device  102  is a NAC (NO x  adsorber catalyst) sometimes also referred to as an LNT (lean NO x  trap).  
         [0015]     Engine  103  is a diesel engine, and in the example of this description, is a dual bank engine. It is equipped with an air-charging device  104 , such as a turbocharger. In the example of this description, turbocharger  104  is a VNT (variable nozzle turbocharger).  
         [0016]     The method is particularly useful for supplying oxygen-enriched feedgas to reformer  101  under low flow and/or low load engine operating conditions. Under such conditions, fresh air from a boosted source (such as turbocharger  104 ) is low or unavailable.  
         [0017]     As illustrated, NAC  102  is mounted along the engine exhaust pipe. NAC  102  is essentially a storage device for NO x  contained in the exhaust gas. It has two principal elements: a NO x  adsorbent and a three-way conversion catalyst. NAC  102  has three primary functions: conversion of NO to NO 2 , adsorption of NO 2 , and release and reduction of NO 2  during regeneration of the NAC  102 .  
         [0018]     As stated in the Background, regeneration of NAC  102  is performed under rich exhaust gas conditions. Under such conditions, the stored NO x  is released from the adsorbent and simultaneously reduced to N 2  (and/or N 2 O or NH 3 ) over precious metal sites.  
         [0019]     Reformer  101  is placed on an exhaust bypass  105 . As explained below, the purpose of reformer  101  is to supply reductant for regeneration of the NAC  102 . Reformer  101  typically has a catalyst, and is provided with a supply of fuel and a supply of air. A supply line (not shown) may be used to supply fuel or any other liquid or gas consumed by the reformer.  
         [0020]     In the example of this description, where engine  103  is a dual-bank engine, exhaust bypass  105  is routed off one side of the exhaust manifold, prior to turbocharger  104 . For an in-line engine, the bypass would be installed upstream of the turbocharger. Bypass  105  joins the main exhaust pipe upstream the NAC  102   
         [0021]     Exhaust bypass  105  is normally closed, using valve  107 . When flow through reformer  101  is desired, and exhaust flow conditions are low, valve  107  blocking the exhaust bypass  105  is opened.  
         [0022]     At the same time, the turbocharger  104  is operated to as to obstruct exhaust flow from the turbocharger. For example, the turbine vanes may be closed. Essentially, while exhaust gas is flowing through bypass  105 , turbocharger  104  is used to put backpressure on the exhaust flow. If the turbocharger  104  does not sufficiently obstruct exhaust flow, an optional exhaust valve  106  may be closed to increase the flow through the exhaust bypass  105 .  
         [0023]     Flow through exhaust bypass  105  may be metered by using a metering valve for valve  107 . An example of a suitable valve is an EGR (exhaust gas recirculation) metering valve. A venturi  108  is placed downstream valve  107 .  
         [0024]     A fresh air line  109  is plumbed to the center of venturi  108 , which pulls air in. During low flow conditions, the air into venturi  108  is not necessarily charged; charged air is not required for operation of the invention. However, in various embodiments of the invention, charged air may be available and used.  
         [0025]     In the example of  FIG. 1 , fresh air line  109  is routed through the compressor side of turbocharger  104 . This permits fresh air line  109  to receive charged air from turbocharger  104  if available and desired. As explained below in connection with  FIG. 2 , in other embodiments, fresh air line  109  may be routed directly from atmosphere.  
         [0026]     The fresh air entering exhaust bypass  105  at venturi  108  provides oxygen-enrichment of the exhaust, which already has a high oxygen content at low load and idle. Under these conditions, the exhaust prior to enrichment already typically has more than 15% oxygen.  
         [0027]     The oxygen-enriched gas mixture is then supplied to reformer  101 . An example of a suitable reformer  101 , is a fuel-based reformer, which burns diesel fuel, and makes the exhaust gas fuel-rich, to be used for regeneration of NAC  102 .  
         [0028]     Optionally, a small diesel particulate filter  110  can be placed at the entrance to exhaust bypass  105 , to clean the exhaust gas. The filter  110  may be placed anywhere upstream reformer  101 .  
         [0029]     Various sensors, such as mass airflow (MAF) sensor  111  and/or an oxygen sensor  112  can be used to determine an oxygen mass flow rate. This measurement is especially useful for closed-loop control of fuel to the reformer  101 . A metering valve  113  may be used to control the amount of oxygen received at venturi  108 .  
         [0030]     A controller  120  can be used to receive measurements from various sensors, such as sensors  111  and  112 . Controller  120  would deliver control signals to various valves, such as valves  107 ,  106 , and  113 . Controller  120  would be programmed to perform the method described above, and wherein the emissions control device  102  is a NAC, would be programmed to provide oxygen-enriched feedgas via the bypass line  105  during regeneration of NAC.  
         [0031]      FIG. 2  illustrates a second embodiment of the invention, in which fresh air line  209  is routed directly to atmosphere, rather than being routed through the compressor side of turbocharger  204 . The embodiment of  FIG. 2  operates in the same manner as the embodiment of  FIG. 1 , being particularly designed for use during low-flow/low-load conditions. It is conceivable that engine  203  may lack a turbocharger or other air-charging device, in which case the above-described method is operable independently of such devices.