Patent Application
20090282816
The present disclosure relates to a diesel engine system, and more particularly to a diesel engine system incorporating a fresh air bypass to cool down hot exhaust in a diesel particulate filter regeneration mode at low vehicle speed and idle.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A diesel particulate filter is generally required for diesel engines to meet particulate matter emission targets set by the Environmental Protection Agency for 2007 model year and beyond. The diesel particulate filter traps the particulate matter during normal operating conditions and has to be regenerated periodically at high exhaust temperatures at any operating conditions. Generally speaking, the diesel particulate filter regeneration interval is about 250 to 350 miles, depending on the duty cycles selected for the engine system. However, high exhaust temperatures of between 450 degrees Celsius and 600 degrees Celsius are encountered at the tailpipe exit during diesel particulate filter regeneration at idle, which raises a safety concern. To address the concern, an exhaust cooler or jet pump has previously been located on the tailpipe. The cooler entrains the surrounding air into the hot exhaust and lowers the exhaust temperature. In order to entrain a sufficient amount of air, the nozzle diameter of the cooler usually is smaller than the diameter of the exhaust pipe. This restricts the exhaust flow and adds additional back pressure to the exhaust system. This consequently results in increased fuel consumption and limits the maximum power that can be developed at a rated condition. Any device that is added to the tailpipe for the purposes of cooling exhaust at idle could potentially increase the back pressure at rated condition.
The system of the present disclosure provides a bypass for passing fresh air from the charger cooler outlet or inlet to the hot exhaust after the diesel particulate filter during a diesel particulate filter regeneration mode at idle and at low speed mode without adding back pressure. The fresh air will be mixed with the hot exhaust in the tailpipe and bring the exhaust temperature down at the exit.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawing described herein is for illustration purposes only and is not intended to limit the scope of the present disclosure in any way.
The FIGURE provides a schematic diagram of the engine system according to the principles of the present disclosure incorporating a fresh air bypass to cool down the hot exhaust in the diesel particulate filter regeneration mode at low vehicle speed and idle.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
With reference to the FIGURE, the engine system 10 of the present disclosure will now be described. The engine system 10 includes a diesel engine 12 including an engine block having a plurality of bores defining cylinders 14. An air intake manifold 16 is connected to the engine for providing intake air to the cylinders 14. An air intake passage 18 is connected to the air intake manifold 16 and includes an intake throttle valve 20 in communication with a turbocharger 21 and a charger air cooler 24 for providing compressed cooled air to the engine 12. Turbocharger 21 includes a compressor 22 in communication with intake air and a variable geometry (VG) turbine 32 in communication with the exhaust gas.
An air exhaust manifold 28 is provided in communication with the cylinders 14 of the engine 12 and is connected to an exhaust passage 30. The VG turbine 32 is in communication with the exhaust passage 30 and drives the compressor 22. Turbochargers with a variable geometry turbine change the output of the turbine as a function of engine load. In this way the optimum boost pressure can be maintained and optimum use can be made of the energy in the exhaust gas. Cross-sectional changes are made by resetting the turbine blades (smaller contact surface at low speeds, larger contact surface at high speeds). VG turbine turbochargers are particularly efficient at partial load and eliminate “turbo lag”. They increase engine power, increase throttle response and can also have a beneficial effect on particulate emissions. In addition, they open new perspectives regarding the control of exhaust gas recirculation. The hot exhaust from the engine cylinder spins the turbine which drives the compressor to boost the intake pressure.
An exhaust gas recirculation passage 34 is provided with an exhaust gas recirculation valve 36 that communicates exhaust gasses from the exhaust passage 30 back to the intake passage 18 as controlled by an engine controller 50. The exhaust passage 30 further includes a diesel oxidation catalyst (DOC) and NOx device 40 and a diesel particulate filter 42 for filtering particulate matter from the emissions. The diesel oxidation catalyst converts the emissions to oxide HC, CO and NO from the engine and provides heat and necessary chemical species to downstream catalyst converters. The NOx device reduces engine-out NOx emissions. A diesel after-treatment system, which is composed of DOC, NOx devices and a Diesel Particulate Filter (DPF), will control the harmful engine emissions like hydrocarbon (HC), nitrogen oxide (NOx), particulate matter (PM), carbon monoxide (CO) and so on.
The engine system 10 further includes a bypass passage 44 that can communicate from the outlet side of the charger cooler 24 to the downstream side of the diesel particulate filter 42. A bypass passage 45 can alternatively be connected to the upstream side of the charger cooler, as illustrated in dashed lines, and connected to the exhaust passage 30 at the downstream side of the diesel particulate filter 42. A bypass valve 48 is provided in the bypass passage 44 and is in communication with an engine controller 50 that controls the engine system 10 to operate in a diesel particulate filter regeneration mode based upon a selected duty cycle. The diesel particulate filter 42 will capture particulate matter entrained in the diesel exhaust on a ceramic or metallic substrate. At a certain point this particulate matter may be removed through regeneration, the process by which the temperature of the exhaust flowing through the DPF reaches a sufficient level to simply burn away the built-up particulates. In many cases, especially where there is a great amount of engine cycling or vehicle stopping and starting, temperatures may not remain high enough for a sufficient time period to remove the particulate matter. In those cases, active systems are required, most of which involve burning a small amount of diesel fuel in the exhaust stream to raise the temperature enough to burn away the particulate matter. An active DPF regeneration typically takes about 20-30 min. When the engine system 10 is in the diesel particulate filter regeneration mode, and the engine 12 is either at idle or at low speed (5 mph or less), the engine controller 50 controls the bypass valve 48 to allow fresh air from the intake passage 18 to be bypassed to the exhaust tailpipe 52 where the fresh air is mixed with the hot exhaust gases to provide a reduced exhaust temperature at the exit of the tailpipe 52. The turbocharger 21 provides compressed air at a pressure greater than the pressure of the pressure of the exhaust gas.
With the system of the present disclosure, there is no increase of back pressure that results in lower fuel economy. Furthermore, there are no moving parts in the exhaust system and there is no impact on engine performance during other driving conditions. The system also adds very little cost, including only the additional bypass passage tubing and bypass valve. The high pumping loss due to fresh charge air bypass enhances the capability of the diesel particulate filter regeneration cycle when the vehicle is at idle.
