In an effort to reduce harmful pollutants emitted by medium and heavy duty diesel engines, stringent emission regulations have been imposed by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). Effective aftertreatment thermal management is critical for controlling tail pipe outlevels of NOx and soot, while improved fuel efficiency is also necessary to meet greenhouse gas emissions standards and customer expectations. Engine manufacturers have developed and implemented several engine and non-engine based techniques for emission reduction, a few examples being: exhaust gas recirculation (EGR), use of delayed in-cylinder injections, exhaust throttling, electric heaters and hydrocarbon dosers. This work elaborates the use of variable valve actuation strategies for improved aftertreatment system (ATS) thermal management of a modern medium-duty diesel engine while presenting opportunities for simplification of engine air handling architecture.<div><br></div><div>Experimental results at curb idle demonstrate that exhaust valve profile modulation enables effective ATS warm-up without requiring exhaust manifold pressure
(EMP) control. Early exhaust valve opening with internal exhaust gas recirculation
(EEVO+iEGR) resulted in 8% lower fuel consumption and reduction in engine out
emissions. Late exhaust valve opening with internal EGR in the absence of EMP
control was able to reach exhaust temperature of 287<sup>◦</sup>C, without a penalty in fuel
consumption or emissions compared to conventional thermal management. LEVO combined with EMP control could reach turbine outlet temperature of nearly 460<sup>◦</sup>C
at curb idle.<br></div><div><br></div><div>LEVO was studied at higher speeds and loads to assess thermal management
benefits of LEVO in the absence of EMP control, with an observation that LEVO
can maintain desirable thermal management performance up to certain speed/load
conditions, and reduction in exhaust flow rate is observed at higher loads due to the
inability of LEVO to compensate for loss of boost associated with absence of EMP
control.<br></div><div><br></div><div>Cylinder deactivation (CDA) combined with additional valvetrain flexibility results in low emission, fuel-efficient solutions to maintain temperatures of a warmed-up
ATS. Late intake valve closing, internal EGR and early exhaust valve opening were
studied with both three cylinder and two cylinder operation. Some of these strategies showed additional benefits such as ability to use earlier injections, elimination
of external EGR and operation in the absence of exhaust manifold pressure control. Three cylinder operation with LIVC and iEGR is capable of reaching exhaust
temperatures in excess of 230<sup>◦</sup>C with atleast 9% lower fuel consumption than three
cylinder operation without VVA. Three cylinder operation with early exhaust valve
opening resulted in exhaust temperature of nearly 340<sup>◦</sup>C, suitable for extended idling
operation. Two cylinder operation with and without the use of valve train flexibility
also resulted in turbine outlet temperature relevant for extended idling (and low load
operation), while reducing fuel consumption by 40% compared to the conventional
thermal management strategy.<br></div><div><br></div><div>A study comparing the relative merits of internal EGR via reinduction and negative valve overlap (NVO) is presented in order to assess trade-offs between fuel efficient
stay-warm operation and engine out emissions. This study develops an understanding
of the optimal valve profiles for achieving reinduction/NVO and presents VVA strategies that are not cylinder deactivation based for fuel efficient stay-warm operation.
Internal EGR via reinduction is demonstrated to be a more fuel efficient strategy for ATS stay-warm. An analysis of in-cylinder content shows that NOx emissions are
more strongly affected by in-cylinder O2 content than by method of internal EGR.<br></div>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/11527854 |
| Date | 06 January 2020 |
| Creators | Mrunal C Joshi (8231772) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Opportunities_to_Improve_Aftertreatment_Thermal_Management_and_Simplify_the_Air_Handling_Architectures_of_Highly_Efficient_Diesel_Engines_Incorporating_Valvetrain_Flexibility/11527854 |
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