Patent Application
20090241541
1. Technical Field
The invention relates to exhaust system configurations for a turbocharged diesel engine and more particularly to configurations improving thermal management of the exhaust system.
2. Description of the Problem
The use of turbocharging for increasing the efficiency and boosting the peak power output of an internal combustion engine is well known. An exhaust energy recovery turbine or impeller is positioned in the exhaust stream from the engine and uses energy from the exhaust gas to drive a compressor feeding into the engine's air intake system. The compressor boosts the density and pressure of air delivered to the engine's intake manifold allowing additional fuel to be introduced to the cylinders and combusted compared to conventionally aspirated engines of like displacement. The application of turbocharging allows the use of smaller displacement, lighter weight engines in many applications, which reduces the weight of the vehicle and thereby saves fuel.
Complicating the application of turbocharging to diesel engines are thermal management issues and the need to meet government emission standards, particularly those relating to NOx and particulate emissions. Put briefly, thermal management of the exhaust system and in the engine compartment is in tension with emissions control requirements. Because turbocharging recaptures some of the energy from the exhaust stream it reduces exhaust gas temperature. In order to protect downstream exhaust system components and to capture the most energy, turbocharger exhaust turbines have traditionally directly followed the engine exhaust manifold. Although high temperatures can impose stress on turbocharger components, the immediate reduction in exhaust gas temperature has protected other downstream components from some stress. In contemporary emissions control systems however, high temperatures may be required for selected operations. Of particular interest on diesel engine equipped vehicles is the requirement of high temperatures for initiating regeneration of diesel particulate filters. The diesel particulate filter regeneration process, involving the rapid oxidation of carbon based compounds, typically adds substantial amounts of heat to the system itself once initiated.
Thermal management issues have occasionally been considered in the art. In U.S. Pat. No. 6,745,568 it was observed, among other factors, that “extreme under-hood temperatures are generated by turbochargers sometimes causing the cooling system of the vehicle to exceed its capabilities”. The '568 patent went on to observe that “extreme under-hood temperatures” could adversely affect plastic and rubber components, necessitate heat shielding around the turbocharger and impose strains on the vehicle engine cooling system. While it might have been better to say that turbochargers located in close proximity to the engine block “retain heat” in the engine compartment rather than “generate heat”, and that turbochargers impose demands on cooling systems potentially exceeding their capacities rather than that they cause cooling systems to exceed their “capabilities”, the concerns noted in the '568 patent concerning cooling systems are valid.
The '568 patent teaches displacing the turbocharger assembly from the engine compartment and placing it well downstream from the engine, where it takes the place of a vehicle's muffler. The patent termed this “remote mounting” and will be referred to here as “remote location”. By so locating the turbocharger the heat retention issues raised by the assembly are removed from the engine compartment. The '568 patent appears to be directed to aftermarket applications, in which case the efficiency gains of locating the turbocharger as close as possible to its heat source were outweighed by the concerns of imposing additional heat loads on an engine cooling system that was not necessarily designed to take on the heat load of “conventionally located” turbocharging (particularly in view of the additional load generated by combusting more fuel per piston stroke).
Remote location of the turbocharger as taught by the '568 patent also partially dealt with another load imposed on engine cooling systems by turbocharger intercoolers/charge air cooling (“CAC”) systems. The ambient air drawn and compressed by turbochargers is termed “charge air.” The compression of any gas results in an increase in its air temperature. CAC systems (sometimes referred to as “intercoolers”) are used to reduce the temperature of this air increasing its density before introduction to the engine combustion chambers. Piping for CAC systems are frequently installed on, next to, or even through the vehicle radiator, to facilitate the transfer of heat from the charge air to the vehicle cooling system. The extended length of the pipe running from the compressor to the engine in the '568 system gave the gas in the pipe some time to cool, reducing the need for a dedicated intercooler.
The proprietor of the '568 patent maintains a website for marketing of aftermarket turbocharging products (www.ststur.com) The products sold appear oriented to spark ignition engines and are installed on vehicles downstream from exhaust system pollution control systems. While the '568 patent is represented as applicable to spark ignition and diesel cycle engines, no specific teachings appear relating to incorporating such a system into a diesel vehicle. Remote mounting or location of a turbocharger on a contemporary diesel equipped must take into account the operating requirements of diesel engine emission control systems, particularly the requirement of delivering heat to a diesel particulate filter (DPF) for periodic regeneration of the filter.
The regeneration of diesel particulate filters involves the oxidation of carbon compounds retained in the filter from the engine exhaust. In many conventional turbocharger installations on diesel vehicles, the turbocharger is located in the engine compartment and adjacent to the exhaust manifold, with an exhaust pipe connecting an outlet from the exhaust turbine to a diesel particulate filter. The pipes connecting the turbocharger outlet to the DPF have been insulated to retain heat to help initiate carbon oxidation in the DPF for regeneration. It has been recognized that there is some inherent inefficiency in this arrangement since the turbocharger removes heat from the exhaust system which would be useful in initiating DPF regeneration. In addition, DPF regeneration, once initiated, heats the exhaust. This has required the addition of diffusers to the exhaust system to draw ambient air into the stream to reduce its temperature before it is vented to the atmosphere.
Another feature of emissions control on diesel engines is partial exhaust gas recirculation. Exhaust gas for recirculation to the engine air induction or intake system on a turbocharged vehicle can be sampled before or after the exhaust turbine. On some vehicles the exhaust gas for recirculation has been drawn from ahead of the turbocharger to avoid the need to boost the pressure of the gas for insertion to the pressurized induction system. Such gas is unfiltered and contributes to clogging or “gumming up” of contemporary EGR systems. Still another feature is a one way valve (akin to an automotive positive crankcase ventilation or PCV valve) is connected to dump blow by into the exhaust system after the turbocharger exhaust impeller but ahead of the DPF. In considering the present invention it may also be taken into consideration that diesel engines can be deliberately operated in an inefficient manner to supply oxygen (and fuel) in the exhaust stream to support DPF regeneration.
According to the invention there is provided an air induction and exhaust system for a turbocharged internal combustion engine, particularly a diesel engine. An air induction subsystem utilized compressed charge air, with an induction compressor being part of a turbocharger system. The turbocharger system provides an exhaust turbine and the induction compressor which are jointly located at a point displaced from an engine compartment of a vehicle. The exhaust subsystem provides a diesel particulate filter which is located in the exhaust system in close proximity to an engine exhaust manifold and upstream from the exhaust turbine. With the diesel particulate filter so located exhaust heat helps initiate carbon oxidation in the filter, and heat generated by oxidation in the filter contributes to turbocharger operation. Exhaust gas recirculation is provided from the exhaust subsystem to the air induction subsystem from between the filter and the exhaust turbine to the pressurized portion of the air induction subsystem. A positive crankcase ventilation type valve is connected to discharge into the exhaust system ahead of the diesel particulate filter so that the diesel particulate filter clears oil from the engine blow by. This arrangement reduces exhaust turbine “coking”. Charge air cooling is partially provided along the length of conduit connecting the compressor to the remainder of the air induction subsystem.
Additional effects, features and advantages will be apparent in the written description that follows.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
Referring now to the figures and in particular to
Extending toward the back of vehicle chassis 10 from the high pressure exhaust stage 16 is a low pressure exhaust system 19 which includes an exhaust pipe 20, a particulate trap 22, an SCR catalytic converter or NOx adsorber 24 and a muffler 26. Typically exhaust systems have included either the particulate trap 22 or the muffler 26, but not both. An exhaust gas recirculating (EGR) line 21 is connected via sampling line 18 to exhaust pipe 20 at a point downstream from NOx adsorber 24 and between the adsorber and muffler 26 (if present). The point of connection has been relatively displaced from the engine compartment 15 to allow for cooling of the exhaust gas in the exhaust pipe 20 and EGR recirculating line 21 before reintroduction to the air intake system 14. Exhaust gas is drawn into EGR sampling line 18 by an electrically driven compressor pump 28 located in return line 21. Compressor 28 is likewise located at a point relatively removed from engine compartment 15. EGR return line 21 extends between compressor 28 and air intake system 14 and is made relatively long to allow cooling of the compressed exhaust gas before introduction to the air intake system. Preferably, EGR return line 21 delivers exhaust gas to an engine intake manifold following the compressor stage of the air intake system 14 although exhaust gas can be returned to other points in the intake system, such as upstream from the compressor/supercharger.
Referring now to
The basic flow of air through the induction and exhaust systems is modified to some extent by pollution control measures including provisions for partial exhaust gas recirculation and the handling of crankcase blow by. Since the exhaust gas is returned to a pressurized induction chamber it has been considered desirable in some applications to sample pressurized exhaust gas from the exhaust manifold as represented by EGR option A 223. Such gas is dirty and hot compromising the effectiveness of charge air cooling (since the gas is highly corrosive it is inserted after the intercooler to protect the intercooler from corrosion). An alternative has been to recirculate exhaust gas after filtering by the DPF 222 as represented by EGR option B 221. This is termed Clean Gas Insertion (CGI) but has required a compression pump in the return line to provide the pressure to overcome the pressure in the induction system. The returned gas is sufficiently clean for the charge air cooling system 244. Finally, crankcase blow-by is discharged by valve 242 to the exhaust system downstream from the exhaust turbine 216, avoiding fouling of the turbine, but upstream from filter 222 so that the blow by is treated.
Referring now to
The major elements of the exhaust system are otherwise substantially unchanged. Extending toward the back of vehicle chassis 10 from the turbocharger are an SCR catalytic converter or NOx adsorber 24 and, possibly, a muffler 26 connected serially by exhaust pipe 20. CGI is provided at pressure by providing an exhaust gas recirculation conduit 123 from just downstream of the DPF 32, but ahead of turbocharger 116 back to the induction system 314.
Referring now to
Typically regeneration of diesel particulate filters is initiated by a vehicle control system, which may adjust engine operation to supply fuel in the form of unburned or partially burned hydrocarbons to support ignition and rapid oxidation in the filter of carbon based deposits. Oxidation of course requires ample air and a valve 449 in the charge line from the induction compressor 419 to the CAC system 244 can be operated by the control system to admit air from compressor 419 into the filter 32.
The basic flow of air through the induction and exhaust systems is modified to some extent by pollution control measures including provisions for partial exhaust gas recirculation and the handling of crankcase blow by. Since the exhaust gas which recirculated is to be returned to a pressurized induction chamber the recirculated exhaust gas is drawn at a relatively high pressure ahead of exhaust turbine 417. At this stage the exhaust gas has been filtered by the DPF 32 and thus Clean Gas Insertion (CGI) is obtained. While such gas may be at sufficient pressure to allow intercooling, the recirculation link shown returns the exhaust gas to the induction system post after CAC system 244 where induction subsystem pressure is lower. Crankcase blow by is discharged to the exhaust system upstream of the diesel particulate filer 32, and from the exhaust turbine 417, avoiding fouling of the turbine because the gas has been filtered.
The arrangement of particulate filter and exhaust turbine of the present invention reduces the amount of exhaust reheat required to support initiation of oxidation in a diesel particulate filter. The invention further provides CGI without the need for an exhaust gas recirculation line compressor. At the price of some turbocharger efficiency, less heat is retained in the engine compartment of a vehicle. In addition, placing the turbocharger after the particulate filter allows use of the turbocharger for the efficient reduction of post filter exhaust gas temperature. Remote mounting of the turbocharger reduces the engine compartment heat sink requirements for charge air cooling, possibly allowing a reduction in radiator size. No exhaust system diffuser is required for cooling exhaust gas during filter regeneration to meet outlet temperature limitations. The engine does not have to be run in a high NOx state to supply the filter with oxygen to support regeneration. If desired for further heat retention reduction in the engine compartment, the diesel particulate filter may also be displaced from the engine compartment and placed physically further downstream in the exhaust subsystem, as long as it remains ahead of the turbocharger.
While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.
