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research-article

Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies

[+] Author and Article Information
Ekoto Isaac

Sandia National Laboratories, 7011 East Vasco, Livermore CA 94551
iekoto@sandia.gov

Wolk Benjamin

Tula Technology, Inc., 2460 Zanker Road, San Jose CA 95131
wolkb@tulatech.com

Northrop William

Sandia National Laboratories, 7011 East Vasco, Livermore CA 94551
wnorthro@umn.edu

Hansen Nils

Sandia National Laboratories, 7011 East Vasco, Livermore CA 94551
nhansen@sandia.gov

Moshammer Kai

PTB Physikalisch-Technische Bundesanstalt Braunschweig und Berlin, Bundesallee 100, 38116 Braunschweig, Germany
kai.moshammer@ptb.de

1Corresponding author.

ASME doi:10.1115/1.4037207 History: Received February 22, 2017; Revised May 08, 2017

Abstract

In-cylinder reforming of injected fuel during a negative valve overlap (NVO) recompression period can be used to optimize main-cycle combustion phasing for low-load Low-Temperature Gasoline Combustion. The objective of this work is to examine the effects of reformate composition on main-cycle engine performance. An alternate-fire sequence was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest, with performance metrics measured for these custom cycles. NVO reformate was also separately collected using a dump valve apparatus and characterized by both gas chromatography and photoionization mass spectroscopy. To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline. For the gasoline, it was found that an advance of the NVO start-of-injection (SOI) led to a corresponding advance in main-period combustion phasing as the combination of longer residence times and lower amounts of liquid spray piston impingement led to a greater degree of fuel decomposition. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. Main-period combustion phasing was also found to advance as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.

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