Patent Application
20250198317
Vehicle emissions aftertreatment devices are essential devices to enable compliance with current and future emissions regulations in internal combustion engine (ICE) powered vehicles. While there are several regulated emissions species, nitrogen oxides (NOX), often represent the most challenging criteria to meet.
Modern aftertreatment devices are highly effective but require a minimum amount of thermal energy to operate. Typically, the source of this thermal energy is the exhaust gas itself. However, in cold ambient conditions and during cold starts, the aftertreatment devices may warm up slowly, resulting in high tailpipe emissions during the warmup period.
One approach to shorten this warmup time is to add thermal energy to the exhaust gas flow. Researchers have investigated various methods to increase exhaust gas energy by spraying fuel into the exhaust and/or using electric heaters to heat the exhaust gases. While these methods do significantly shorten warmup time, they are only active when the engine is running.
The following description is directed to a heating system and method to enable warmup of exhaust aftertreatment device(s) of an internal combustion engine. The system and method heat warm air in a recirculation path around the aftertreatment device, enabling an efficient use of added thermal energy. High emissions associated with cold starts are mitigated. The system and method can be used in various modes-before the engine is running, during start-up, and during normal engine operation.
The system and method are well-suited to hybrid electrified vehicles but can also be used in conventional (non-electrified) internal combustion engine vehicles or even in stationary or non-road engine applications. The invention is especially beneficial for electrified vehicles due to the availability of stored electrical energy and the intermittent operation of the internal combustion engine.
The exhaust is emitted through an exhaust manifold 102 and often to a turbine 105, which drives a compressor 104 used to charge the engine's intake air. In other embodiments, the engine may be naturally aspirated with the exhaust exiting through tailpipe 206 without a turbine. Engine 100 is assumed to have other parts and controls associated with internal combustion engine.
Exhaust from the engine is routed to an exhaust line 300. Aftertreatment device 201 is installed on the exhaust line 300 to treat the exhaust before it flows into the atmosphere via a tailpipe portion 206 of the exhaust line 300. In the example of this description, there is but one aftertreatment device but the same concepts apply if there is more than one.
System 200 has an air-heating loop 210 which is in fluid communication with exhaust line 300 at a point upstream the aftertreatment device 201 and again at a point downstream the aftertreatment device 201. As explained below, loop 210 allows warmed air to recirculate through the aftertreatment device 201 in the same direction as the exhaust flow, that is, from the exhaust inlet of the aftertreatment device 201 to its outlet. Two valves (three-way valves) are installed on the exhaust line 300; a first valve 204 is upstream of the aftertreatment device 201 and a second valve 205 is downstream of the aftertreatment device 201.
A compressor 202 is installed on air-heating loop 210 to create a flow of air when desired, as explained below. Compressor 202 may be implemented with various air compressors or blowers, collectively referred to herein as “compressors”. Compressor 202 may use one or more different energy sources, but most likely would be an electrically powered centrifugal compressor or root-style blower driven by a motor (not shown) on-board the vehicle.
As explained below, compressor 202 is operable to circulate air or an air/exhaust mix within warm-air loop 210, into the exhaust line upstream the aftertreatment device, through the aftertreatment device(s), and back into the recirculation loop. Compressor 202 has a fresh air inlet 202a, which allows compressor 202 to receive either fresh air as well as flow from loop 210.
System 200 further has a heater 203 to heat this fresh air and/or exhaust gas flow. Heater 203 may be electrically powered or powered via another energy source. In the example of
In the embodiment of
Additional valving to isolate and/or direct the airflow toward specific aftertreatment components may be used but is not specifically required.
A control unit 220 controls system 200 to achieve the various modes of operation of system 200 described below. It receives data representing engine operation conditions as appropriate for determining which mode is to be in use (engine off, on, or warmup), and delivers control signals to compressor 202, heater 203, and valves 204 and 205. In other embodiments, control unit 220 may receive input representing exhaust gas and aftertreatment device conditions, such as their temperature, content, or condition such as needed for regeneration. Control unit 220 may be stand-alone or part of a larger more comprehensive control system.
In engine-off warmup mode, using valves 204 and 205 as described in the preceding paragraph, engine 100 does not run because there is no path for engine exhaust gas. Although the system may be implemented without valves, this will result in leakage and reduce system efficiency.
Although compressor 202 need not have active flow control, in other embodiments, compressor 202 may be equipped so that its flow rate can be controlled. This feature could be used to optimize the balance between fresh air and exhaust during the engine-on warmup mode.
The engine-on warmup mode is most beneficial during low load engine operation when exhaust flow rate and temperatures are low. This is particularly true of lean-burn engines.
A feature of the above-described warmup modes is the recirculation aspect of the warm-air loop 210. In the engine-off warmup mode, valves 204 and 205 isolate warm air flow through the aftertreatment device(s) 201. In engine-on warmup mode, compressor 202 increases exhaust mass flow by supplementing the natural engine exhaust flow with fresh air drawn from inlet 202a. This blended air is heated and introduced upstream the aftertreatment device at valve 204.
For warmup (engine off or on), it is also possible to operate compressor 202 and heater 203 in an open configuration, in which valves 204 and 205 are open (or there are no valves). In other words, there is no recirculation provided by loop 210. However, this open configuration results in high energy loss because the heated air or air/exhaust is only passed through the aftertreatment device(s) once. A significant amount of the thermal energy provided by heater 203 exits the aftertreatment system via tailpipe 206.
A key benefit of using recirculation loop 210 is that heat energy is used efficiently. The heater 203 need not continually heat ambient temperature air. Because the heated air is recirculated, the required heating energy is significantly lower than in an open configuration (without recirculation around loop 210).
Another feature of the invention is the location of heater 203. In the embodiment of
To evaluate the effectiveness of system 200, both engine testing and computer modeling were conducted. Engine testing was conducted using a four cylinder, 2.8 L, light duty diesel engine. Exhaust aftertreatment devices 201 were a close coupled combination diesel oxidation catalyst (DOC) and diesel particulate filter (DPF), followed by two selective catalytic reduction (SCR) catalysts. For this work, an electric heater 203 was installed downstream of the DOC/DPF but upstream of the SCRs. Air under ambient conditions was compressed with a root-style blower 202 and input to the exhaust system just upstream of the heater 203. The engine was operated over the FTP-75 driving schedule, simulating hybrid vehicle operation. Testing was conducted without energizing the heater and with energizing the heater.
In addition to providing heat during engine warmup, system 200 can be used for thermal management of aftertreatment devices, such as any type of catalyst. For example, system 200 could be activated either as an isolated recirculation loop or as supplemental exhaust heating to enable catalyst regeneration or to allow an aftertreatment device to reach peak catalytic activity. As stated above, control unit 220 can be implemented to receive aftertreatment conditions and to control system 200 accordingly.
