Patent Description:
Regulated emissions from today's heavy-duty engines demand very low levels of tailpipe emissions, and standards are expected to be further reduced in the near future. To reduce tailpipe exhaust emissions, current technologies rely on aggressive engine control strategies and exhaust after-treatment catalyst systems (catalyst systems used to treat engine exhaust are referred to herein as exhaust after-treatment systems, emissions after-treatment systems, or EAS). The EAS for a typical heavy-duty diesel or other lean-burning engine may include a diesel oxidation catalyst (DOC) to oxidize unburned fuel and carbon monoxide, a diesel particulate filter (DPF) for control of particulate matter (PM), selective catalytic reduction (SCR) systems for reduction of oxides of nitrogen (NOx), and/or an ammonia oxidation catalyst (AMOX). Performance of EAS systems, and of SCR systems in particular, is dependent upon exhaust gas temperature and other parameters.

SCR processes use catalysts to catalyze the NOx reduction and a fluid referred to as DEF (diesel emission fluid), which acts as a NOx reductant over the SCR catalyst. DEF is an aqueous solution that evaporates and decomposes to chemically release ammonia so that the ammonia is available for reaction. Efficiency of SCR operation is dependent upon temperature. For example, DEF evaporation and decomposition is dependent upon temperature, with higher temperatures (e.g., temperatures over <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> degrees Celsius) generally improving performance. Temperature levels required to ensure compliance with emissions regulations may be highly dependent upon a wide variety of variables and are in some cases determined experimentally for specific engines, trucks, and operating conditions thereof. Thus, an EAS may include a heater to increase the temperature of the exhaust, to facilitate DEF injection, evaporation, and decomposition at rates sufficient to allow efficient performance of the SCR processes.

Related technologies are known from <CIT>, <CIT>, <CIT>, and <CIT>.

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with the technology have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments.

Also, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the context clearly dictates otherwise.

The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order, but rather may only distinguish between multiple instances of an act or structure.

Terms of geometric alignment may be used herein. Any components of the embodiments that are illustrated, described, or claimed herein as being aligned, arranged in the same direction, parallel, or having other similar geometric relationships with respect to one another have such relationships in the illustrated, described, or claimed embodiments. In alternative embodiments, however, such components can have any of the other similar geometric properties described herein indicating alignment with respect to one another. Any components of the embodiments that are illustrated, described, or claimed herein as being not aligned, arranged in different directions, not parallel, perpendicular, transverse, or having other similar geometric relationships with respect to one another, have such relationships in the illustrated, described, or claimed embodiments. In alternative embodiments, however, such components can have any of the other similar geometric properties described herein indicating non-alignment with respect to one another.

Various examples of suitable dimensions of components and other numerical values may be provided herein. In the illustrated, described, and claimed embodiments, such dimensions are accurate to within standard manufacturing tolerances unless stated otherwise. Such dimensions are examples, however, and can be modified to produce variations of the components and systems described herein. In various alternative embodiments, such dimensions and any other specific numerical values provided herein can be approximations wherein the actual numerical values can vary by up to <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more percent from the stated, approximate dimensions or other numerical values.

As described herein, experiments may be performed and measurements may be taken while an engine or a vehicle including an engine are operating at "steady state. " As used herein, the term "steady state" may mean that the engine or the vehicle including the engine are operating with all operating parameters, including engine speed, power level, etc., unchanged or substantially unchanged over a period of time of at least one, at least two, at least three, at least four, at least five, at least six, or at least ten seconds.

Traditionally, heavy-duty vehicles included many components of exhaust after-treatment systems "underbody," that is, underneath the engine, cab, or another portion of the vehicle, where space is relatively freely available and these components can therefore generally be larger than would otherwise be practical. Some modern heavy-duty vehicles, however, have begun to include a "close-coupled," "up-close," or "light-off" SCR unit much closer to the engine and exhaust ports thereof (e.g., adjacent to a turbine outlet of a turbocharger) and upstream of the traditional underbody exhaust after-treatment system, which can provide certain advantages in that the temperature of the engine exhaust may be higher when it is closer to the engine, although locating an SCR unit nearer the engine limits the available space and thus its practical size. Thus, some modern heavy-duty vehicles have included both a "close-coupled" SCR unit upstream with respect to the flow of the exhaust, such as adjacent to a turbine outlet of a turbocharger, to take advantage of the higher exhaust temperatures, as well as an "underbody" SCR unit downstream with respect to the flow of the exhaust, such as under the engine or cab of the vehicle, to take advantage of the greater available space.

<FIG> illustrates a diagram of an exhaust after-treatment system <NUM> that has a first, upstream end <NUM> and a second, downstream end <NUM> opposite to the first, upstream end <NUM>. The exhaust after-treatment system <NUM> is a component of a vehicle, such as a large, heavy-duty, diesel truck, and in use carries exhaust from the diesel engine of the truck to a tailpipe of the truck. For example, the first, upstream end <NUM> of the exhaust after-treatment system <NUM> may be coupled directly to an exhaust port or an outlet port of the diesel engine, such as a turbine outlet of a turbocharger thereof, and the second, downstream end <NUM> may be coupled directly to an inlet port of a tailpipe or muffler of the truck. Thus, when the engine is running and generating exhaust, the exhaust travels along the length of the exhaust after-treatment system <NUM> from the first, upstream end <NUM> thereof to the second, downstream end <NUM> thereof.

As illustrated in <FIG>, the exhaust after-treatment system <NUM> includes, at its first, upstream end <NUM>, or proximate or adjacent thereto, a first temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the engine and enters the exhaust after-treatment system <NUM>, before heat begins to be lost through the exhaust after-treatment system <NUM> to the environment. The exhaust after-treatment system <NUM> also includes, at its first, upstream end <NUM>, or proximate or adjacent thereto, or just downstream of the first temperature sensor <NUM>, a first NOx sensor <NUM>, to measure the content of NOx gases in the exhaust gas flow as it leaves the engine and enters the exhaust after-treatment system <NUM>. The exhaust after-treatment system <NUM> also includes, at its first, upstream end <NUM>, or proximate or adjacent thereto, or just downstream of the first NOx sensor <NUM>, a first DEF injector <NUM>, to inject DEF into the exhaust gas flow as it leaves the engine and enters the exhaust after-treatment system <NUM>.

The exhaust after-treatment system <NUM> may also include, proximate or adjacent its first, upstream end <NUM>, or just downstream of the first DEF injector <NUM>, a first heater <NUM>, which may be an electrically-powered resistive heater or heating element, a burner, or any other suitable heater, to inject heat energy into the exhaust gas flow and the injected DEF as they flow through the exhaust after-treatment system <NUM>. The exhaust after-treatment system <NUM> also includes, just downstream of the first heater <NUM>, a second temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the first heater <NUM> and just before or just as it enters a first, close-coupled SCR system <NUM>, or at the inlet to the close-coupled SCR system <NUM>. The exhaust after-treatment system <NUM> also includes, just downstream of the first heater <NUM> and the second temperature sensor <NUM>, the first, close-coupled SCR system <NUM>, which is configured to reduce oxides of nitrogen (NOx) in the exhaust gas flow.

The exhaust after-treatment system <NUM> also includes, just downstream of the first SCR system <NUM>, a third temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the first SCR system <NUM>. In some implementations, the second temperature sensor <NUM> and the third temperature sensor <NUM> may be collectively referred to as an SCR bed temperature sensor. For example, a temperature of a catalytic bed of the first, close-coupled SCR system <NUM> may be measured, calculated, estimated, or otherwise determined based on the measurements provided by the second temperature sensor <NUM> and the third temperature sensor <NUM>, such as by averaging the temperature measurements provided by the second temperature sensor <NUM> and the third temperature sensor <NUM>.

The exhaust after-treatment system <NUM> also includes, just downstream of the first SCR system <NUM> and/or the third temperature sensor <NUM>, a second NOx sensor <NUM>, to measure the content of NOx gases in the exhaust gas flow as it leaves the first SCR system <NUM>. In practice, the first NOx sensor <NUM> and the second NOx sensor <NUM> can be used together to monitor, assess, or measure the performance of the first SCR system <NUM>. Together, the first temperature sensor <NUM>, the first NOx sensor <NUM>, the first DEF injector <NUM>, the first heater <NUM>, the second temperature sensor <NUM>, the first, close-coupled SCR system <NUM>, the third temperature sensor <NUM>, and the second NOx sensor <NUM> can be referred to as a close-coupled portion of the exhaust after-treatment system <NUM>, as they can be collectively located at or adjacent to the engine of the vehicle.

The exhaust after-treatment system <NUM> also includes, downstream of the first SCR system <NUM>, the third temperature sensor <NUM>, and the second NOx sensor <NUM>, a DOC component <NUM>, to oxidize unburned fuel and carbon monoxide in the exhaust gas flow. The exhaust after-treatment system <NUM> also includes, downstream of the DOC component <NUM>, a DPF <NUM>, to reduce or otherwise control particulate matter in the exhaust gas flow. The exhaust after-treatment system <NUM> also includes, downstream of the DPF <NUM>, a fourth temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the DPF <NUM>. The exhaust after-treatment system <NUM> also includes, downstream of the DPF <NUM>, or just downstream of the fourth temperature sensor <NUM>, a second DEF injector <NUM>, to inject DEF into the exhaust gas flow as it leaves the DPF <NUM>.

In some embodiments, the exhaust after-treatment system <NUM> may also include, just downstream of the fourth temperature sensor <NUM> and the second DEF injector <NUM>, a mixer <NUM> and a second heater, which may be an electrically-powered resistive heater or heating element, a burner, or any other suitable heater, to inject heat energy into the exhaust gas flow and the injected DEF as they flow through the exhaust after-treatment system <NUM>. The exhaust after-treatment system <NUM> also includes, just downstream of the mixer <NUM> and the second heater, a fifth temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the second heater and just before or just as it enters a second, underbody SCR system <NUM>, or at the inlet to the underbody SCR system <NUM>. The exhaust after-treatment system <NUM> also includes, just downstream of the mixer <NUM>, the second heater, and the fifth temperature sensor <NUM>, the second, underbody SCR system <NUM>, which is configured to reduce oxides of nitrogen (NOx) in the exhaust gas flow.

The exhaust after-treatment system <NUM> also includes, just downstream of the second SCR system <NUM>, a sixth temperature sensor <NUM>, which may be a thermocouple, to measure the temperature of the exhaust gas flow as it leaves the second SCR system <NUM>. In some implementations, the fifth temperature sensor <NUM> and the sixth temperature sensor <NUM> may be collectively referred to as an SCR bed temperature sensor. For example, a temperature of a catalytic bed of the second, underbody SCR system <NUM> may be measured, calculated, estimated, or otherwise determined based on the measurements provided by the fifth temperature sensor <NUM> and the sixth temperature sensor <NUM>, such as by averaging the temperature measurements provided by the fifth temperature sensor <NUM> and the sixth temperature sensor <NUM>.

In some alternative embodiments, the exhaust after-treatment system <NUM> may not include the second heater and may include only a single heater, i.e., the first heater <NUM>, to reduce overall costs. Similarly, in some embodiments, the exhaust after-treatment system <NUM> may not include all of the temperature sensors described herein, such as the third temperature sensor <NUM>, fourth temperature sensor <NUM>, fifth temperature sensor <NUM>, and/or sixth temperature sensor <NUM>, such as to further reduce overall costs. In such implementations, such temperature sensors may be replaced by virtual temperature sensors, which may measure, calculate, estimate, simulate, or otherwise determine a temperature at the same location, such as based on equations, data, simulations, and/or models of the behavior of temperatures at such locations under the operating conditions of the systems described herein.

The exhaust after-treatment system <NUM> also includes, just downstream of the second SCR system <NUM> and/or the sixth temperature sensor <NUM>, and at its second, downstream end <NUM>, or proximate or adjacent thereto, a third NOx sensor <NUM>, to measure the content of NOx gases in the exhaust gas flow as it leaves the second SCR system <NUM>. In practice, the second NOx sensor <NUM> and the third NOx sensor <NUM> can be used together to monitor, assess, or measure the performance of the second SCR system <NUM>. Together, the DOC component <NUM>, the DPF <NUM>, the second DEF injector <NUM>, the fourth temperature sensor <NUM>, the mixer <NUM>, the second heater, the fifth temperature sensor <NUM>, the second SCR system <NUM>, the sixth temperature sensor <NUM>, and the third NOx sensor <NUM> can be referred to as an underbody portion of the exhaust after-treatment system <NUM>, as they can be collectively located underneath the engine, cab, or another portion of the vehicle.

As noted previously, performance of exhaust after-treatment systems, and of SCR systems in particular, is dependent upon exhaust gas temperature. More specifically, DEF evaporation and decomposition is dependent upon temperature, with higher temperatures generally improving performance. Thus, operation of a heater to increase the temperature of the exhaust gas flow can be critical to maintaining compliance with emissions regulations. Nevertheless, operation of a heater to increase the temperature of the exhaust gas flow naturally incurs a fuel penalty and thus a reduction of overall system fuel efficiency. Thus, it is critical to ensure accurate and precise performance of such heaters, to ensure compliance with emissions standards without unduly reducing overall fuel efficiency.

There are additional trade-offs involved in relying on the close-coupled SCR system <NUM> and/or the underbody SCR system <NUM> to reduce NOx levels in the exhaust gas flow. For example, as noted previously, use of the close coupled SCR system <NUM> may be advantageous because the exhaust gas flow is ordinarily already naturally at a higher temperature than it is at the underbody SCR system <NUM> (ignoring operation of the first heater <NUM> and/or the second heater), particularly under cold-start conditions and/or low load operation. Nevertheless, as also noted previously, the underbody SCR system <NUM> may be larger than the close-coupled SCR system <NUM>.

Furthermore, relative weighting of the burden of NOx reduction between the close-coupled SCR system <NUM> and the underbody SCR system <NUM> results in different levels of various tailpipe emissions. NOx (oxides of nitrogen) in the exhaust gas flow include both NO (nitric oxide) and NO<NUM> (nitrogen dioxide), but diesel engine exhaust typically includes NOx predominantly in the form of NO rather than NO<NUM>. As the exhaust gas flow passes across the DOC <NUM>, however, NO is oxidized to NO<NUM>, and as such, the underbody SCR system <NUM> has higher levels of NO<NUM> than the close-coupled SCR system <NUM>. As such, the close-coupled SCR system <NUM> is more heavily governed by the standard SCR reaction and other NO-based reactions than the underbody SCR system <NUM>. Under cold conditions (e.g., SCR bed temperatures under <NUM> degrees Celsius), dosing of DEF in the presence of NO<NUM> can form nitrates, which subsequently form N<NUM>O, which is a greenhouse gas. Under conditions when the underbody SCR system <NUM> is cold, therefore, it can be preferable to leverage the close-coupled SCR system <NUM>. The control strategy therefore heavily weights operation of the close-coupled SCR system <NUM> relative to operation of the underbody SCR system <NUM> under cold-start and low-load operation conditions.

Additionally, the DPF <NUM> includes a catalyst that traps soot (e.g., black carbon) from the exhaust gas flow. The DPF <NUM> has a maximum capacity that, once reached, requires active regeneration of the DPF <NUM> to oxidize the soot to CO<NUM>. Active regeneration is achieved by raising the temperature of the exhaust to greater than <NUM> degrees Celsius, and therefore increases both fuel consumption and CO<NUM> emissions. Under warm conditions (e.g., exhaust temperature greater than <NUM> degrees Celsius), the soot in the DPF <NUM> can undergo passive regeneration using NO<NUM> generated by the DOC <NUM>. It is desirable to maximize passive regeneration (soot oxidation) in the DPF <NUM> to reduce, minimize, avoid, or optimize reliance on active regeneration. Therefore, under warm conditions, the dual SCR control strategy shifts the burden of NOX reduction toward the underbody SCR system <NUM>, to increase, maximize, or optimize the amount of NO<NUM> delivered to the DPF <NUM>.

Finally, overall SCR conversion efficiency can suffer under high exhaust flow conditions such as at high load operation and hard acceleration conditions of the diesel engine. To improve overall system NOx reduction efficiency under such conditions, or decrease the degree to which such efficiency suffers, the close-coupled SCR <NUM> and the underbody SCR <NUM> may both be used at or near their respective maximum capacities, under which conditions the close-coupled SCR system <NUM> may be considered additional volume to the underbody SCR system <NUM>. That is, under some conditions, irrespective of the temperature operating regime, the close-coupled SCR system <NUM> is leveraged to reduce the effective NOx flow into the underbody SCR system <NUM>, to reduce high exhaust flow emissions.

Thus, at some times during operation of a diesel engine, only the close-coupled SCR system <NUM> may be used to reduce NOx levels to comply with tailpipe emissions regulations, while at other times during operation of a diesel engine, only the underbody SCR system <NUM> may be used to reduce NOx levels to comply with tailpipe emissions regulations, while at yet other times, the burden of reducing NOx levels to comply with tailpipe emissions regulations may be shared by the two SCR systems <NUM>, <NUM>, such as by any suitable ratio.

For example, the close coupled SCR system <NUM> may reduce NOx levels by <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% (or any other intermediate percentage) of the amount required to comply with tailpipe emissions regulations, while the underbody SCR system <NUM> may reduce NOx levels by a complementary amount (e.g., <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>%, respectively) of the amount required to comply with tailpipe emissions regulations. Thus, it has been found that it is also valuable to balance the NOx reduction burden between the two SCR systems <NUM> and <NUM> to further improve efficiency of operation, to ensure compliance with emissions standards without unduly reducing overall fuel efficiency, and to increase, maximize, or optimize NOx reduction per unit DEF utilized.

First, an initial lookup table or database is built or populated under ideal or idealized conditions in accordance with standardized laboratory experiments. Such experiments may operate a heavy-duty diesel engine at steady state under a variety of operating conditions to determine properties of the exhaust gas flow generated by the engine at steady state under such conditions. For example, for each set of given operating conditions, the experiments may measure a mass flow rate (ṁexh) of the exhaust gas flow generated by the engine, which may be specified in units such as kg/s, determine a resulting molar specific heat at constant pressure (Cp) of the exhaust gas flow generated by the engine (which may be unique to each individual engine but may be expected to be constant over the range of operation of any given engine), and measure a resulting exhaust temperature (T<NUM>) of the exhaust gas flow generated by the engine immediately adjacent to an exhaust port or outlet port of the engine itself, such as a turbine outlet of a turbocharger thereof, which may be measured by the first temperature sensor <NUM> and may be specified in units such as K or degrees Celsius.

Such experiments may also operate the diesel engine in combination with the exhaust after-treatment system <NUM> at steady state under a variety of operating conditions to determine how the operation of the exhaust after-treatment system <NUM> affects properties of the exhaust gas flow as it travels through the exhaust after-treatment system <NUM> at steady state under such conditions. For example, for each set of given operating conditions, the experiments may use the temperature sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> to measure the temperature of the exhaust gas flow at the locations of the temperature sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively. The resulting measured temperatures can be stored in the lookup table or database.

As another example, for each set of given operating conditions, the experiments may use the first NOx sensor <NUM> to measure NOx levels at the location of the first NOx sensor <NUM>, may use the second NOx sensor <NUM> to measure NOx levels at the location of the second NOx sensor <NUM>, and may use such measurements to calculate a percentage reduction in NOx levels between the first and second NOx sensors <NUM>, <NUM>, which may be taken as a percentage efficiency of the close coupled SCR system <NUM>. Thus, as noted elsewhere herein, the first NOx sensor <NUM> and the second NOx sensor <NUM> can be used together to monitor, assess, or measure the performance of the first SCR system <NUM> at steady state under the various experimental conditions. Similarly, for each set of given operating conditions, the experiments may use the second NOx sensor <NUM> to measure NOx levels at the location of the second NOx sensor <NUM>, may use the third NOx sensor <NUM> to measure NOx levels at the location of the third NOx sensor <NUM>, and may use such measurements to calculate a percentage reduction in NOx levels between the second and third NOx sensors <NUM>, <NUM>, which may be taken as a percentage efficiency of the underbody SCR system <NUM>. Thus, as noted elsewhere herein, the second NOx sensor <NUM> and the third NOx sensor <NUM> can be used together to monitor, assess, or measure the performance of the second SCR system <NUM> at steady state under the various experimental conditions. The resulting measured NOx levels and calculated percentage efficiencies of the SCR systems can be stored in the lookup table or database. In some implementations, the resulting measured NOx levels and calculated percentage efficiencies of the SCR systems can be stored in the lookup table or database as a function of or otherwise correlated with or related to the measured temperatures.

As another example, for each set of given operating conditions, the experiments may monitor the rate at which the first and second DEF injectors <NUM>, <NUM> inject DEF into the exhaust gas flow, and may use such information in combination with the measurements provided by the first, second, and third NOx sensors <NUM>, <NUM>, and <NUM>, to calculate ammonia-to-NOx ratios (ANR) at the close-coupled SCR system <NUM> and at the underbody SCR system <NUM>. The injection rates and calculated ANRs can be stored in the lookup table or database.

As another example, for each set of given operating conditions, the experiments may monitor the rate at which N<NUM>O is generated and emitted, as well as the state of the DPF <NUM>, the level of passive regeneration thereof that occurs, and the degree to which active regeneration thereof is or would be required. Such information can be stored in the lookup table or database.

Based on such measurements, calculations, and data stored in the lookup table or database, ideal, optimal, efficient, or most efficient relative divisions of the labor or burden of reducing NOx levels to comply with tailpipe emissions regulations between the first, close-coupled SCR <NUM> and the second, underbody SCR <NUM> may be determined. For example, it may be determined that it is efficient to allocate the NOx reduction burden between the close-coupled SCR <NUM> and the underbody SCR <NUM> based on the temperature of the catalytic bed of the underbody SCR <NUM>, such as based on the temperatures of the exhaust gas flow measured by the fifth temperature sensor <NUM> and/or the sixth temperature sensor <NUM> (e.g., an average thereof).

For example, it may be determined that it is more efficient to allocate a larger portion of the NOx reduction burden, or even all of the NOx reduction burden, to the close-coupled SCR <NUM> when the temperatures at the underbody SCR <NUM> are relatively cold (indicating, for example, that the diesel engine and/or the exhaust after-treatment system <NUM> are cold or just starting up), and to allocate a larger portion of the NOx reduction burden, or even all of the NOx reduction burden, to the underbody SCR <NUM> when such temperatures are relatively hot (indicating, for example, that the diesel engine and/or the exhaust after-treatment system <NUM> are hot or operating at or near steady-state).

In some embodiments, dividing the labor of reducing NOx levels to comply with tailpipe emissions regulations includes controlling a rate at which the first DEF injector <NUM> injects DEF into the exhaust gas flow upstream of the close-coupled SCR system <NUM> (e.g., as a function of the NOx levels measured by the first NOx sensor <NUM>) to control an ANR within the close-coupled SCR system <NUM> and/or to prevent ammonia slip from the close-coupled SCR system <NUM>, thereby controlling operation and SCR reduction efficiency of the close-coupled SCR system <NUM>, and operating the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations.

As one specific example, it may be determined that when the temperature of the catalytic bed of the underbody SCR system <NUM> is <NUM> degrees Celsius or lower, it is most efficient from a systemic perspective to operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a minimum rate sufficient to ensure that the ANR in the first, close-coupled SCR is equal to or <NUM>% of the ANR required to reduce NOx levels in the exhaust gas flow just downstream of the close-coupled SCR system <NUM> (e.g., as measured by the second NOx sensor <NUM>) to levels in compliance with emissions regulations, that is, such that the first, close coupled SCR system <NUM> handles the full NOx reduction burden, and to not begin operating the second DEF injector <NUM>, the second heater, and the underbody SCR system <NUM>. It may further be determined that when the temperature of the catalytic bed of the underbody SCR system <NUM> is <NUM> degrees Celsius, it is most efficient from a systemic perspective to operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a minimum rate sufficient to ensure that the ANR in the first, close-coupled SCR is <NUM>% of the ANR required to reduce NOx levels in the exhaust gas flow just downstream of the close-coupled SCR system <NUM> (e.g., as measured by the second NOx sensor <NUM>) to levels in compliance with emissions regulations, and to operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations.

It may further be determined that when the temperature of the catalytic bed of the underbody SCR system <NUM> is <NUM> degrees Celsius, it is most efficient from a systemic perspective to operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a minimum rate sufficient to ensure that the ANR in the first, close-coupled SCR is <NUM>% of the ANR required to reduce NOx levels in the exhaust gas flow just downstream of the close-coupled SCR system <NUM> (e.g., as measured by the second NOx sensor <NUM>) to levels in compliance with emissions regulations, and to operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations. It may further be determined that when the temperature of the catalytic bed of the underbody SCR system <NUM> is <NUM> degrees Celsius, it is most efficient from a systemic perspective to operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a minimum rate sufficient to ensure that the ANR in the first, close-coupled SCR is <NUM>% of the ANR required to reduce NOx levels in the exhaust gas flow just downstream of the close-coupled SCR system <NUM> (e.g., as measured by the second NOx sensor <NUM>) to levels in compliance with emissions regulations, and to operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations.

It may further be determined that when the temperature of the catalytic bed of the underbody SCR system <NUM> reaches an upper threshold or boundary, it is most efficient from a systemic perspective to cease operating the first DEF injector <NUM>, the first heater <NUM>, and the close-coupled SCR system <NUM>, and to operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to handle the full NOx reduction burden and reduce NOx levels to ensure compliance with emissions regulations. At temperatures between those identified herein, or at temperatures between any other set of temperatures so studied or investigated in such experiments, any interpolation functions, such as a linear interpolation function, may be used to determine appropriate DEF injection rates. For example, it may further be determined by linear interpolation that when the temperature of the catalytic bed of the underbody SCR system <NUM> is <NUM> degrees Celsius, it is most efficient from a systemic perspective to operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a minimum rate sufficient to ensure that the ANR in the first, close-coupled SCR is <NUM>% of the ANR required to reduce NOx levels in the exhaust gas flow just downstream of the close-coupled SCR system <NUM> (e.g., as measured by the second NOx sensor <NUM>) to levels in compliance with emissions regulations, and to operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations. Such information can be stored in the lookup table or database.

Second, during operation of a vehicle, such as a motor vehicle such as a heavy-duty diesel truck, the exhaust after-treatment system <NUM>, including the first, close-coupled SCR system <NUM> and the second, underbody SCR system <NUM>, may be operated to ensure compliance with emissions regulations while minimizing an incurred fuel penalty resulting from operation of the components of the exhaust after-treatment system <NUM>, including the first heater <NUM> and/or the second heater, as described elsewhere herein. In particular, as the truck and its engine and its engine control unit ("ECU") are operating, the engine control unit of the truck may continuously monitor how the operation of the exhaust after-treatment system <NUM> affects properties of the exhaust gas flow as it travels through the exhaust after-treatment system <NUM>. For example, the ECU may continuously measure or monitor temperatures of the exhaust gas flow at the locations of the temperature sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, as well as temperatures of the catalytic beds of the first and second catalytic reduction systems <NUM>, <NUM>.

As another example, the ECU may use the first NOx sensor <NUM> to measure NOx levels at the location of the first NOx sensor <NUM>, may use the second NOx sensor <NUM> to measure NOx levels at the location of the second NOx sensor <NUM>, and may use such measurements to calculate a percentage reduction in NOx levels between the first and second NOx sensors <NUM>, <NUM>, which may be taken as a percentage efficiency of the close-coupled SCR system <NUM>. Similarly, the ECU may use the second NOx sensor <NUM> to measure NOx levels at the location of the second NOx sensor <NUM>, may use the third NOx sensor <NUM> to measure NOx levels at the location of the third NOx sensor <NUM>, and may use such measurements to calculate a percentage reduction in NOx levels between the second and third NOx sensors <NUM>, <NUM>, which may be taken as a percentage efficiency of the underbody SCR system <NUM>.

As another example, the ECU may monitor the rate at which the first and second DEF injectors <NUM>, <NUM> inject DEF into the exhaust gas flow, and may use such information in combination with the measurements provided by the first, second, and third NOx sensors <NUM>, <NUM>, and <NUM>, to calculate ammonia-to-NOx ratios (ANR) at the close-coupled SCR system <NUM> and at the underbody SCR system <NUM>.

Based on such measurements and calculations, in combination with the data stored in the lookup table or database, the engine control unit of the truck may continuously assess or determine a desired, optimal, or most efficient division of the labor of reducing NOx levels to comply with tailpipe emissions regulations between the first, close-coupled SCR <NUM> and the second, underbody SCR <NUM>. For example, the engine control unit may continuously use the bed temperature of the underbody SCR system <NUM> in combination with the data stored in the lookup table or database to determine a desired or optimal rate at which to inject DEF into the exhaust gas flow upstream of the close-coupled SCR system <NUM>. Such a determination may rely on interpolation between data points stored in the lookup table or database.

The engine control unit may then operate the first DEF injector <NUM> to inject DEF into the exhaust gas flow at that rate. The engine control unit may then operate the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations. The engine control unit may furthermore continually control and/or adjust or update operation of the first DEF injector <NUM> to inject DEF into the exhaust gas flow at a rate that varies over time, such as over at least <NUM> seconds, <NUM> seconds, one minute, two minutes, or four minutes, and as a function of an average of the temperature measurements provided by the fifth temperature sensor <NUM> and the sixth temperature sensor <NUM>, such as across a range in such an average temperature of at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> degrees Celsius. As such operation of the first DEF injector <NUM> varies, the engine control unit may also continually control and/or adjust or update operation of the second DEF injector <NUM>, the second heater, and the second, underbody SCR system <NUM> to further reduce NOx levels to ensure compliance with emissions regulations.

The systems and techniques described herein can facilitate continuous and simultaneous dosing of DEF onto the catalytic beds of two independent SCR systems, namely, the close-coupled SCR system <NUM> and the underbody SCR system <NUM>, such as by using two independent DEF injectors, each located upstream of a respective one of the SCR systems, namely, the first DEF injector <NUM> and the second DEF injector <NUM>, to increase overall systemic efficiency while maintaining compliance with NOx emissions regulations. The systems and techniques described herein can be used to reduce NOx tailpipe emissions to ultra-low levels, which may be referred to as "ultra-low NOx" or "ULN" levels. Further, the systems and techniques described herein can be leveraged to reduce especially high NOx emissions, such as on hard acceleration transients, to within regulated levels. The systems and techniques described herein may include or use a minimal number of sensors, that is, the systems and techniques described herein may include or use exactly or no more than a specified number of sensors necessary for performance as described herein. The systems and techniques described herein allow efficient operation of the close-coupled SCR system <NUM> and/or the underbody SCR system <NUM> without ammonia slip, or with minimal ammonia slip, from the SCR systems <NUM>, <NUM>.

<FIG> illustrates results of experimental testing of a heavy-duty vehicle including a diesel engine and the exhaust after-treatment system <NUM>. In particular, <FIG> illustrates two charts, one on top of the other. In the bottom of the two charts, the horizontal X-axis represents time and the vertical Y-axis represents the instantaneous NOx levels, in units of parts per million, measured by the first, second, and third NOx sensors <NUM>, <NUM>, and <NUM>. In the top of the two charts, the horizontal X-axis represents time on the same scale and interval as in the bottom of the two charts, and the vertical Y-axis represents the cumulative NOx measured by the first NOx sensor <NUM> (see the line indicated by reference numeral <NUM>), the second NOx sensor <NUM> (see the line indicated by reference numeral <NUM>), and the third NOx sensor <NUM> (see the line indicated by reference numeral <NUM>).

As illustrated in <FIG>, the difference between the NOx levels measured by the first and second NOx sensors <NUM>, <NUM>, and the resulting difference between the cumulative NOx measured by the first and second NOx sensors <NUM>, <NUM>, rise early in the testing, reflecting the fact that it is generally more efficient to reduce NOx levels near start-up or at cold temperatures at the close-coupled SCR <NUM> than at the underbody SCR <NUM>. As also illustrated in <FIG>, the difference between the NOx levels measured by the second and third NOx sensors <NUM>, <NUM>, and the resulting difference between the cumulative NOx measured by the second and third NOx sensors <NUM>, <NUM> rise later in the testing, reflecting the fact that it is generally advantageous to reduce NOx levels near steady-state operation or at hot temperatures at the underbody SCR <NUM> than at the close-coupled SCR <NUM>.

<FIG> illustrates results of experimental testing of a heavy-duty vehicle including a diesel engine and the exhaust after-treatment system <NUM>. In particular, <FIG> illustrates two charts, one on top of the other. In the bottom of the two charts, the horizontal X-axis represents time and the vertical Y-axis represents the instantaneous rates of DEF dosing, in units of grams per hour, by the first DEF injector <NUM> and the second DEF injector <NUM>. In the top of the two charts, the horizontal X-axis represents time on the same scale and interval as in the bottom of the two charts, and the vertical Y-axis represents the cumulative ammonia-to-NOx ratio resulting (e.g., from ammonia released by the DEF injected by the respective DEF injectors) in the close-coupled SCR system <NUM> (see the line indicated by reference numeral <NUM>) and in the underbody SCR system <NUM> (see the line indicated by reference numeral <NUM>).

As illustrated in <FIG>, the DEF dosing by the first DEF injector <NUM> and the cumulative ammonia-to-NOx ratio resulting in the close-coupled SCR system rise quickly early in the testing, reflecting the fact that it is generally more efficient to reduce NOx levels near start-up or at cold temperatures at the close-coupled SCR <NUM> than at the underbody SCR <NUM>. As also illustrated in <FIG>, the DEF dosing by the first DEF injector <NUM> and the cumulative ammonia-to-NOx ratio resulting in the close-coupled SCR system <NUM> fall, and the DEF dosing by the second DEF injector <NUM> and the cumulative ammonia-to-NOx ratio resulting in the underbody SCR system <NUM> rise quickly, later in the testing, reflecting the fact that it is generally advantageous to reduce NOx levels near steady-state operation or at hot temperatures at the underbody SCR <NUM> than at the close-coupled SCR <NUM>.

<FIG> illustrates a flow chart <NUM> of a summarized version of a method in accordance with the present disclosure. As illustrated in <FIG>, the method includes, at <NUM>, operating a diesel engine, thereby generating an exhaust gas flow. The method further includes, at <NUM>, monitoring a temperature of the exhaust gas flow at an underbody selective catalytic reduction system, and at <NUM>, controlling a DEF injector upstream of a close-coupled selective catalytic reduction system to inject DEF into the exhaust gas flow at a rate that varies as a function of the monitored temperature across a range of at least <NUM> degrees Celsius in the monitored temperature.

Claim 1:
A method, comprising:
operating a diesel engine of a heavy-duty truck such that the diesel engine generates an exhaust gas flow that enters an exhaust after-treatment system (<NUM>) of the heavy-duty truck, the exhaust after-treatment system including a close-coupled selective catalytic reduction system (<NUM>), and an underbody selective catalytic reduction system (<NUM>) downstream of the close-coupled selective catalytic reduction system with respect to the exhaust gas flow;
monitoring a temperature of the exhaust gas flow at the underbody selective catalytic reduction system;
controlling a DEF injector (<NUM>) upstream of the close-coupled selective catalytic reduction system to inject DEF into the exhaust gas flow at a rate that varies as a function of the monitored temperature across a range of at least <NUM> degrees Celsius in the monitored temperature; and
controlling a DEF injector (<NUM>) downstream of the close-coupled selective catalytic reduction system and upstream of the underbody selective catalytic reduction system to inject DEF into the exhaust gas flow at a rate that varies as a function of the monitored temperature,
wherein the DEF injector (<NUM>) initially injects DEF into the exhaust gas flow at a rate sufficient for the close-coupled selective catalytic reduction system to reduce NOx levels to comply with emissions regulations,
wherein, after the DEF injector (<NUM>) injects DEF into the exhaust gas flow at the rate sufficient for the close-coupled selective catalytic reduction system to reduce NOx levels to comply with emissions regulations, the DEF injector injects DEF into the exhaust gas flow at a lower rate sufficient for the close-coupled selective catalytic reduction system to reduce NOx levels halfway to compliance with emissions regulations, and
wherein, while the DEF injector (<NUM>) upstream of the close-coupled selective catalytic reduction system injects DEF into the exhaust gas flow at the rate sufficient for the close-coupled selective catalytic reduction system to reduce NOx levels halfway to compliance with emissions regulations, controlling a DEF injector (<NUM>) downstream of the close-coupled selective catalytic reduction system and upstream of the underbody selective catalytic reduction system to inject DEF into the exhaust gas flow at a rate sufficient for the underbody selective catalytic reduction system to reduce NOx levels to comply with emissions regulations.