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Effect of Intake Oxygen Concentration on Particle Size Distribution Measurements from Diesel Low Temperature Combustion
Abstract:
Concepts of premixed diesel Low Temperature Combustion (LTC)
have been shown to be advantageous in greatly reducing engine-out
nitrogen oxide (NOx) and particulate matter (PM)
emissions, even below the minimum detection limit of standard
opacity-based PM mass instruments. Previous research has revealed
that significant changes to the PM size and number emissions still
occur for changes to the LTC engine operating conditions. This work
investigates the influence of reductions in intake oxygen
concentration on PM (mass, size, and number), NOx,
hydrocarbon (HC), and carbon monoxide (CO) emissions from select
LTC engine operating conditions.
Exhaust particle size distributions were measured for multiple
engine operating conditions of premixed diesel LTC within a range
of five intake oxygen concentrations from 9% to 13% (by volume) at
three intake pressures from 1.325 to 1.6 bar. For each intake
oxygen concentration and intake pressure engine operating
condition, particle size distributions were measured at the
early-LTC injection timing of minimum PM mass concentration
emissions. Reductions in inlet oxygen concentration limited the
oxygen available during the combustion process. This prolonged the
fuel and air premixing time before the start of combustion, and
decreased the temperatures during the combustion process. At the
early minimum PM injection timing (-27 and -24° aTDC, depending on
intake pressure), decreasing engine intake oxygen concentration
caused emissions of higher numbers of smaller particles. In
addition, a comparison is made between the particle size and number
emissions with the in-cylinder combustion processes and exhaust HC
emissions for reductions in intake oxygen concentration within the
premixed diesel LTC operating regime.