Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Committee Chair

Gregory M. Shaver

Committee Member 1

Peter H. Meckl

Committee Member 2

John H. Lumkes

Committee Member 3

Oleg Wasynczuk

Abstract

Fuel consumption in heavy-duty vehicles is expected to double by the year 2050 [1]. The majority of heavy duty vehicles incorporate diesel engines which emit air pollutants including particulate matter (PM), unburnt hydrocarbons (uHC) and oxides of nitrogen (NOx). Increasing demand for heavy duty transportation coupled with strict emission regulations by the Environmental Protection Agency (EPA) and California Air Regulations Board (CARB) to improve air quality drive innovation of advanced engines and auxiliary systems. Complex exhaust aftertreatment (AFT) systems are required to meet stringent tailpipe-out emission regulations. The effectiveness of AFT systems, affected by emission conversion efficiency, is limited when turbine outlet temperatures (TOTs) are low (usually used to reduce the fuel consumption by 5 to 30% depending on the engine load, increase the rate of warm-up of AFT, maintain higher AFT temperatures, and achieve active diesel particulate filter regeneration without requiring HC dosing of the diesel oxidation catalyst. At cruise operating condition (1200 rpm/300 ft-lbs), Late IVC (LIVC) strategy does not show any fuel economy penalty when compared to conventional operation of the valves, but shows a TOT increase of about 150-200◦C, thereby enabling warmer AFT temperatures. This dissertation also introduces several novel engine breathing modes, viz. fired/non-fired reverse breathing and intake/exhaust re-breathing. Reverse breathing is a novel method where exhaust gases are recirculated, as needed, from exhaust manifold to intake manifold via one or more cylinders. Re-breathing is an innovative method, where the gas exchange takes place only in either the intake or exhaust manifold for a certain number of cylinders. These strategies provide in-cylinder oxygen dilution and reduction in airflow leading to lower pumping work at low-load engine operation. Approximately 40% of typical heavy-duty vehicle operation occurs at loaded curb idle, during which the conventional diesel engines are unable to maintain sufficient AFT component temperatures while retaining fuel economy. Fuel economy and thermal management at loaded curb condition can be improved via reverse breathing due to reduced airflow. Several strategies for implementation of reverse breathing are described in detail and compared to CDA and internal EGR operation. Experimental data demonstrates 26% fuel consumption savings, when compared to conventional stay-warm operation; 60◦C improvement in TOT, and 28% reduction in exhaust flow compared to conventional best fuel consumption operation at the curb idle condition (800RPM, 1.3 bar BMEP). Similarly, intake rebreathing in three of the six cylinders yields 50◦C improvement in TOT and 20% reduction in exhaust flow while maintaining NOx levels without using EGR. The incorporation of non-fired reverse breathing, in order to efficiently maintain desired AFT temperatures during curb idle conditions, is experimentally demonstrated to result in fuel savings of 2% over the HDFTP drive-cycle relative to conventional operation.

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