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

Wolk Benjamin

Tula Technology, Inc., 2460 Zanker Road, San Jose CA 95131

Northrop William

Sandia National Laboratories, 7011 East Vasco, Livermore CA 94551

Hansen Nils

Sandia National Laboratories, 7011 East Vasco, Livermore CA 94551

Moshammer Kai

PTB Physikalisch-Technische Bundesanstalt Braunschweig und Berlin, Bundesallee 100, 38116 Braunschweig, Germany

1Corresponding author.

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


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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