Abstract:
A diesel or HHCI engine has an air intake and an exhaust for products of combustion. A pair of turbochargers receive the products of combustion in a series relationship and an exhaust aftertreatment device receive the products of combustion from the downstream turbine. A power turbine receives the output from the exhaust aftertreatment device and an EGR system of the power turbine passes a selected portion of the output to a point upstream of the upstream turbocharger compressor. A device adds fuel to the aftertreatment device to regenerate the particulate filter and the power turbine recoups the additional energy. The power turbine may be used to drive accessories or the prime output of the engine.

Description:
GOVERNMENT RIGHTS IN PATENT 
     The invention described herein was made with the proceeds from government contract no. DE-FC26-05NT42422 awarded by the Department of Energy. The U.S. government may have certain rights in this patent. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to prime mover engine systems and more specifically to such systems having aftertreatment and turbocompounding devices. 
     BACKGROUND OF THE INVENTION 
     The evermore stringent Environmental Protection Agency (EPA) limitations represented by the Tier 4 reduction of emissions has required significant development in the area of treating the exhaust from the engine to reduce oxides of nitrogen. For internal combustion engines operating on a compression ignition cycle or a homogenous charge compression ignition cycle (HCCI) there is an extra requirement of reducing particulates in the exhaust system so that these particulates are not released to the atmosphere. Such aftertreatment devices require periodic elevation of their temperatures to a point where the carbon particles trapped on the interstices of a particulate filter self combust. Such a process requires additional fuel or other energy form and reduces the efficiency of such an engine system. 
     In addition to the exhaust aftertreatment of reducing particulates, many current engines use exhaust gas recirculation (EGR) to recycle some of the products of combustion to the intake of the engine to reduce combustion temperatures by virtue of additional quantities of nitrogen. While these systems have been effective in accomplishing this purpose, they are difficult to manage throughout a complex, heavy duty operating cycle. Frequently, such systems require complex control systems whether they be high pressure EGR systems before the turbocharger or low pressure EGR systems, after the turbocharger. Approaches have been used to reduce energy losses by cooling the EGR which adds an additional level of problems to be overcome in terms of acidic condensation in the engine intake. 
     What is needed therefore is a prime mover system in which energy consumed in which the efficiency of such systems is improved and operating flexibility is achieved. 
     SUMMARY OF THE INVENTION 
     In one form, the invention includes an air breathing, fuel consuming, internal combustion engine having an air intake and an exhaust for products of combustion. At least one turbocharger having a turbine receives the products of combustion from the engine exhaust and a compressor driven by the turbocharger pressurizes air for delivery to the engine intake. An exhaust aftertreatment device receives the products of combustion from the turbine. A power turbine receives the output from the exhaust aftertreatment device. An EGR system is provided downstream of and receives the output from the power turbine for selectively passing a selected portion of the output from the power turbine to a point upstream of the turbocharger compressor. 
     In another form, the invention is a method of operating a prime mover system including the steps of operating an air breathing, fuel consuming, internal combustion engine having an air intake and an exhaust for products of combustion. At least one turbocharger has a turbine which receives the products of combustion in turn to drive a compressor to pressurize air for delivery to the engine intake. The products of combustion discharged from the turbocharger turbine are subjected to treatment. The products of combustion are then subsequently passed over a power turbine and a selected portion of the output from the power turbine is passed to a point upstream of the turbocharger compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a prime mover system embodying the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a prime mover system incorporating an internal combustion engine  10  providing a rotary output through output shaft  11 . Internal combustion engine  10  is an air breathing, fuel consuming, engine receiving intake air from an intake manifold  12  and delivering it, after combustion, to an exhaust manifold  14 . The internal combustion engine  10  may be one of a number of types of engines having a multiplicity of cylinders reciprocating within cylinder bores and connected to the output shaft  11  through a crankshaft to produce a rotary torque output. An appropriate valve mechanism is provided to provide intake air to the cylinders and pre-selected quantities of fuel, at the appropriate time in the cycle, is delivered to the engine by a fuel system, schematically indicated by reference character  13 . 
     Fuel system  13  may be a system that operates on the heat of compression within the cylinders to ignite measured and timed quantities of fuel in so that the fuel ignites by the heat of compression to produce a combustible mixture which passes to exhaust manifold  14  after it expands and does work on pistons to rotate output shaft  11 . Fuel system  13  may also be of a type that provides a homogenous charge by mixing fuel within the intake  12  so that it passes from intake manifold as a fuel/air mixture to the engine  10 . Many different configurations of homogenous charge compression HCCI engines and compression engines may be employed including systems that provide operation in one, or the other, or both configurations. The fuel system  13  is controlled by an ECM  15  through line  17 . Line  17  frequently is a series of electrical interconnections between the ECM and the fuel system. Line  17  also preferably connects to a multiplicity of sensors (not shown) that transmit to the ECM  15  various operating parameters with which to control the fuel timing and quantity. 
     The products of combustion in exhaust manifold  14  pass through exhaust line  16  to a turbocharger  18  incorporating a turbine  19 . Products of combustion pass over turbine  19  and may be delivered directly to an exhaust aftertreatment device, or in the case illustrated, through an exhaust line  20  to the turbine  23  of a second turbocharger  22  to further extract energy in the exhaust products of combustion of engine  10 . Turbine  23  is connected to a line  24  that passes the products of combustion to an exhaust aftertreatment device  26 . 
     Exhaust aftertreatment device  26  frequently includes a particulate filter having filtration media capable of withstanding high temperature with which to collect carbon particles arising from the combustion cycle in the engine  10 . Exhaust aftertreatment  26  may also include a catalyst to convert the oxides of nitrogen into less harmful and deleterious forms. In order to prevent clogging of the particulate filter within exhaust aftertreatment device  26 , it is necessary to burn off such carbon particles, usually by raising the temperature to above approximately 600 degrees centigrade. Some forms of accomplishing this may be electrical in nature in which a suitable source of electricity is passed to heaters into the upstream of exhaust aftertreatment  26  to raise its temperature. Alternatively, the mode of increasing the exhaust system temperature may be a device  25  receiving an appropriate supply of fuel from a source (not shown) and injecting it in the exhaust upstream of exhaust aftertreatment device  26  to increase the temperature to above approximately 600 degrees centigrade. As herein illustrated, a line  27  connects the device  25  to the ECM  15  which provides a common and integrated control of the functions of the system. The output from the exhaust aftertreatment device  26  passes through line  31  to the power turbine  29  of a turbo compound device  28 . 
     Turbo compound device  28  may have a load  33  which may be any form of accessory load or a device coupling the power turbine  29  to the rotary output shaft  11  by dashed line  35 . This connection may be mechanical, hydraulic or electrical. The connection may also be to various accessory components of engine  10  such as coolant circulation, hydraulic accessory drives and other elements in the system. The products of combustion from power turbine  29  pass from line  30  to ambient A having the maximum energy taken out of the gas energy in the form of pressure and temperature taken out by turbines  19  and  23  and power turbine  29 . 
     The gasses from line  30  are selectively connected to intake line  34  by an EGR system  32 . Line  34  receives air that has been filtered from the ambient for use by the engine  10 . The EGR device may take many forms but in typical form it is may be a variable valve assembly for selectively passing a controlled portion of the gasses from line  30  to line  34 . The EGR device  32  is typically controlled by a line  37  extending to the ECM  15  for implementing the common integrated control of the device. The EGR valve may be actuated to recirculate gasses by a sensor  39  exposed to line  34  and providing a signal to ECM  15  by a line  41 . The parameters sensed by sensor  39  may be humidity, temperature or a combination of both as later described. Line  34  extends to the intake of a compressor  36  driven by turbine  23  to pressurize air for delivery through a line  38  which in turn extends to the inlet of a compressor  48  driven by turbine  19 . The discharge from compressor  48  extends via line  42  to an aftercooler or intercooler  44  where the pressurized air is cooled to increase its density and thus provide a greater charge density within engine  10 . A line  46  connects the output of intercooler  44  to the intake of engine  12 . 
     In operation, engine  10  receives appropriate fuel quantities from fuel injection system  13  as controlled by the ECM  15  to produce a combustible mixture which is ignited according to the particular cycle used within the cylinders of engine  10  and discharged to exhaust manifold  14 . From there, it passes over turbine  19  and preferably additional turbine  23  thereby providing staged pressurization of air by compressors  36  and  48 . The output of turbine  23  is connected to the exhaust aftertreatment device  26  and from there to power turbine  29  where energy is recouped by the device  33  to be utilized by the engine  10 , either in accessory drives or contributing to the primary power output in shaft  11 . This configuration extracts the maximum energy out of the engine exhaust stream to provide highest efficiency. Because the pressure, as well as the temperature, has been substantially reduced by the extraction of energy, the exhaust gases  32  have already been cooled for a point where they have a minimal adverse effect on the density of the charge passing to intake  12  of the engine  10 . 
     The sensor  39  is integrated with the ECM  15  so that EGR does not occur under conditions where there is excessive condensation so as to avoid chemical reaction with the gases to produce acidic constituents. Temperature may also be used to provide this function or a combination of the two may be employed. 
     The particulates collected in the exhaust aftertreatment device  26  are, as illustrated, burned off by the injection of hydrocarbons by the device  25 . This in turn raises the temperature of the exhaust aftertreatment device  26  to burn off the carbon particles and, in addition, increases the energy level of the gases discharged into line  31 . Because the exhaust from line  31  passes over power turbine  29 , the energy that is otherwise lost to ambient A through line  30  is connected to device  33  for utilization by engine  10 . In addition to recouping energy otherwise lost during the regeneration cycle, the system may be programmed so that the ECM  15  selectively increases the energy level of the gases in line  31  to produce additional power in power turbine  29  to drive the device  33 , for example an auger system in agricultural processing equipment. 
     The above system provides extremely low emissions thus satisfying stricter requirements like Tier 4. While doing this however, it maximizes the efficiency and energy recovery of the overall system. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.