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Diesel Cold-Start Emission Control Research for 2015-2025 LEV III Emissions
Abstract:
The diesel engine can be an effective solution to meet future
greenhouse gas and fuel economy standards, especially for larger
segment vehicles. However, a key challenge facing the diesel is the
upcoming LEV III emissions standard which will require significant
reductions of hydrocarbon (HC) and oxides of nitrogen
(NOx) from current levels. The challenge stems from the
fact that diesel exhaust temperatures are much lower than gasoline
engines so the time required to achieve effective emissions control
with current aftertreatment devices is considerably longer.
The objective of this study was to determine the potential of a
novel diesel cold-start emissions control strategy for achieving
LEV III emissions. The strategy combines several technologies to
reduce HC and NOx emissions before the start of the
second hill of the FTP75. The technologies include: 1) intake
throttling, 2) high temperature glow plugs with model-based
temperature control, 3) multiple fuel injections, 4) high EGR idle
operation after the first hill, 5) improved diesel particulate
filter (DPF) catalyst formulation, and 6) a small close-coupled LNT
with improved an formulation. For the overall emissions control
strategy, an underfloor SCR would provide the main NOx
control starting in the second hill.
This paper describes the benefits of the engine tuning
technologies (1-4) and evaluates the strategy during transient
engine dynamometer investigations that simulate the first 162
seconds of the FTP75. Using the combined engine tuning
technologies, HC emission reduction of over 80% relative to the
baseline calibration was achieved at the tailpipe (or more
correctly, at the entrance to the underfloor NOx control
device) with the baseline aftertreatment system. This level of HC
reduction is in the range required for LEV III compliance; however,
part of the reduction was obtained by moving to higher
NOx on the HC versus NOx trade-off curve.
Additional tests with a closed-coupled LNT and DPF with improved
catalyst formulations are planned to investigate if the right
balance of engine-out HC and NOx can be obtained with
this strategy for LEV III.