Patent Application
20080087006
The following describes an apparatus for and method of diluting an exhaust gas stream in a vehicle tail pipe with ambient air, in order to reduce a temperature of the exhaust stream before releasing it to the environment.
A block diagram of an engine system 100 having an after-treatment system 102 is shown in
The exhaust pipe 103 is connected to an oxidation catalyst (OC) 105, which in turn is connected to a pipe segment 107 leading to a particulate filter (PF) 109. The PF 109 is connected to a tailpipe 111 which may also include a muffler (not shown) or other components. The after-treatment system 102 may also include a variety of sensors to monitor its operation. For example, a first temperature sensor 113 may be disposed in the pipe segment 107 upstream of the PF 109, and a second temperature sensor 114 may be disposed in the tailpipe 111 downstream of the PF 109. The after-treatment system 102 may also include one or more pressure sensor(s) 115 connected upstream and/or downstream of the PF 109 to monitor it's operation and extent of loading with particulate matter. Information from the sensors 113, 114, and 115 may be relayed to an electronic control unit (ECU) 119. The after-treatment system 102 may include additional components than the ones described herein for illustration, for example, the system 102 may include a lean NOx trap (LNT), a urea-based selective catalytic reduction (SCR) system, or a diesel fuel reformer system (DFRS), and so forth.
At times when a regeneration of the PF 109 is initiated, a temperature T1 of the exhaust gas stream 104 before the PF 109 may substantially increase to a temperature T2 after the PF 109. On a typical engine, the exhaust gas stream 104 would exit the tailpipe 111 at the temperature T2.
It is advantageous to the sociability of the vehicle to avoid higher temperature exhaust gas emissions from the tailpipe 111. For this reason, a mixer device 120 may be connected in-line with the tailpipe 111. The mixer 120 may advantageously be a venturi mixer that mixes a flow of fresh air 121, denoted by the solid headed arrows, that is pulled in from outside the tailpipe 111, with the exhaust gas stream 104, to yield a mixture 122 that may pass through a downstream portion 123 of the tailpipe 111. One portion of the mixture 122 is exhaust gas at the temperature T2, and a remaining portion of the mixture 122 is fresh air at an ambient temperature T3. A resultant temperature T4 of the mixture 122 may advantageously be lower than the temperature T2 of the exhaust gas stream 104, which is advantageous to the sociability of the vehicle.
One embodiment of an exhaust gas dilution mixer 200 is shown in
At times when a flow of exhaust gas 214, denoted by hollow-head arrows, enters the mixer 200 through an upstream portion 216 thereof, the exhaust gas flow 214 flows through the segment 202 under a pressure and velocity that depends on the diameter D. When the flow of exhaust gas 214 reaches the neck-down portion 206, it is gradually accelerated to pass through the opening 208. The higher velocity, and thus lower static pressure, of the flow of exhaust gas 214 passing through the opening 208 depends on the smaller inner diameter d. A low static pressure and high flow momentum of the accelerated flow of exhaust gas 214 exiting the opening 208 advantageously draws in a flow of ambient air 218, denoted by solid-head arrows, through the opening 212. The flow of exhaust gas 214 may mix and be diluted by the flow of ambient air 218 to yield a mixture. The mixture of flows 214 and 218 may flow out of the mixer from a downstream portion 220 thereof, at a velocity and pressure that depends on the inner diameter D′. The mixture in the downstream portion 220 is advantageously at a lower temperature than the flow in the upstream portion 216.
Another embodiment of an exhaust gas dilution mixer 400 is shown in
At times when a flow of exhaust gas 414, denoted by hollow-head arrows, enters the mixer 400 through an upstream portion 416 thereof, the exhaust gas flow 414 flows through the segment 402 under a pressure and velocity that depends on the diameter D. When the flow of exhaust gas 414 reaches the neck-down portion 406, it is gradually accelerated to pass through the opening 408. The higher velocity, and thus lower static pressure, of the flow of exhaust gas 414 passing through the opening 408 at the region 411 depends on the smaller inner diameter d. A low static pressure and high flow momentum of the accelerated flow of exhaust gas 414 passing through the region 411 advantageously draws in a flow of ambient air 418, denoted by solid-head arrows, through the plurality of openings 410. The flow of exhaust gas 414 may mix and be diluted by the flow of ambient air 418 to yield a mixture. The mixture of flows 414 and 418 may pass through the opening 408, through the neck-up portion 409, and flow out of the mixer 400 from a downstream portion 420 thereof, at a velocity and pressure that depends on the inner diameter D′. The mixture in the downstream portion 420 is advantageously at a lower temperature than the flow in the upstream portion 416.
The openings 410 may advantageously be arranged symmetrically around the region 411. The shield 413 is optional and may be used to avoid intrusion of debris, and especially water, into the mixer 400 through the openings 410. The shield 413 may be connected to one or both of the segment(s) 402 and 404 of the tailpipe with tabs (not shown) or any other suitable connection arrangement. Embodiments other than the ones shown that use a venturi effect for mixing an exhaust flow in a tailpipe with ambient air may advantageously be used to dilute the flow of exhaust gas and lower it's temperature in the tailpipe.
A flow chart for a method of reducing a temperature of an exhaust gas stream in a tailpipe of a vehicle is shown in
The tailpipe may include an inline mixer device. The flow of exhaust gas in the tailpipe may enter the mixer at step 608, be accelerated at step 610, be mixed with a flow of air from the environment to yield a mixture at step 612, and exit the mixer at step 614. The mixture may advantageously be at a lower temperature than the flow of exhaust gas. The flow of air from the environment may pass through a gap between two adjacent segments of the tailpipe, or may enter a region thereof through a plurality of openings. The mixer may advantageously use a “venturi” effect to augment mixing between the flow of exhaust gas and the flow of air.
A flow chart for a method of diluting exhaust gas generated by an internal combustion engine installed in a vehicle is shown in
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
