Development and validation of a new n-dodecane-n-butanol-PAH reduced mechanism under diesel engine-relevant conditions

Abstract

In this work, a new n-dodecane-n-butanol-polycyclic aromatic hydrocarbon (PAH) reduced mechanism that consists of 105 species and 584 reactions was developed to model the combustion and soot characteristics of diesel, n-butanol and its blends. The current mechanism was formulated by merging a n-dodecane and PAH reduced mechanism to a n-butanol reduced mechanism that was developed through the direct relation graph with error propagation (DRGEP), isomer lumping and reaction pathway analysis (RPA) methods. Good predictions were obtained when the mechanism was validated against the ignition delay (ID) times, species concentrations in jet-stirred reactor (JSR) and premixed flame and laminar flame speed. Moreover, the non-reacting liquid and vapour penetration lengths of Bu0, Bu20 and Bu40 (0 vol%, 20 vol% and 40 vol% n-butanol blended in n-dodecane) at ambient temperatures of 800 K, 850 K and 900 K were well predicted with a maximum deviation of 4%. The ID and flame lift-off length (FLOL) deviated with a maximum value of 20% and 12%, respectively. As compared to the measurements, the peak soot volume fraction (SVF) of Bu0 fuel at ambient temperatures of 850 K and 900 K were reasonably predicted with maximum deviations of 1.0 ppm and 0.3 ppm, respectively. At higher n-butanol blending ratios and at lower ambient temperatures, soot was reduced significantly due to lower equivalence ratio, lower flame temperature and the high oxygen content which suppressed the formation of soot precursor species.