Effect of Intake Oxygen Concentration on Particle Size Distribution Measurements from Diesel Low Temperature Combustion 2011-01-1355

Concepts of premixed diesel Low Temperature Combustion (LTC) have been shown to be advantageous in greatly reducing engine-out nitrogen oxide (NO_x) 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), NO_x, 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.