Premixed ignition behavior of alternative diesel fuel-relevant compounds in a motored engine experiment

A motored engine study using premixed charges of fuel and air at a wide range of diesel-relevant equivalence ratios was performed to investigate autoignition differences among surrogates for conventional diesel fuel, gas-to-liquid (GTL) diesel fuel, and biodiesel, as well as, n-heptane. Experiments...

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Bibliographic Details
Published in:Combustion and flame 2007-04, Vol.149 (1), p.112-128
Main Authors: Szybist, James P., Boehman, André L., Haworth, Daniel C., Koga, Hibiki
Format: Article
Language:English
Subjects:
02 PETROLEUM
09 BIOMASS FUELS
ADVANCED PROPULSION SYSTEMS
AIR
ALDEHYDES
ALKANES
Applied sciences
AUTOIGNITION
Biodiesel
BIOFUELS
CARBON DIOXIDE
CARBON MONOXIDE
COMBUSTION
Combustion. Flame
COMPRESSION RATIO
CONDENSATES
DECANOIC ACID
DECARBOXYLATION
Diesel
DIESEL ENGINES
DIESEL FUELS
Energy
Energy. Thermal use of fuels
ESTERS
Exact sciences and technology
Exhaust
EXHAUST GASES
Fischer–Tropsch
Fuels
HEPTANE
HTHR
Ignition
KETONES
LTHR
ORGANIC ACIDS
TEMPERATURE RANGE 0400-1000 K
Theoretical studies. Data and constants. Metering
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Summary:A motored engine study using premixed charges of fuel and air at a wide range of diesel-relevant equivalence ratios was performed to investigate autoignition differences among surrogates for conventional diesel fuel, gas-to-liquid (GTL) diesel fuel, and biodiesel, as well as, n-heptane. Experiments were performed by delivering a premixed charge of vaporized fuel and air and increasing the compression ratio in a stepwise manner to increase the extent of reaction while monitoring the exhaust composition via Fourier transform infrared (FTIR) spectrometry and collecting condensable exhaust gas for subsequent gas chromatography/mass spectrometry (GC/MS) analysis. Each fuel demonstrated a two-stage ignition process, with a low-temperature heat release (LTHR) event followed by the main combustion, or high-temperature heat release (HTHR). Among the three diesel-relevant fuels, the magnitude of LTHR was highest for GTL diesel, followed by methyl decanoate, and conventional diesel fuel last. FTIR analysis of the exhaust for n-heptane, the conventional diesel surrogate, and the GTL diesel surrogate revealed that LTHR produces high concentrations of aldehydes and CO while producing only negligible amounts of CO 2. Methyl decanoate differed from the other two-stage ignition fuels only in that there were significant amounts of CO 2 produced during LTHR; this was the result of decarboxylation of the ester group, not the result of oxidation. GC/MS analysis of LTHR exhaust condensate for n-heptane revealed high concentrations of 2,5-heptanedione, a di-ketone that can be closely tied to species in existing autoignition models for n-heptane. GC/MS analysis of the LTHR condensate for conventional diesel fuel and GTL diesel fuel revealed a series of high molecular weight aldehydes and ketones, which were expected, as well as a series of organic acids, which are not commonly reported as products of combustion. The GC/MS analysis of the methyl decanoate exhaust condensate revealed that the aliphatic chain acts similarly to n-paraffins during LTHR, while the ester group remains intact. Thus, although the FTIR data revealed that decarboxylation occurs at significant levels for methyl decanoate, it was concluded that this occurs after the aliphatic chain has been largely consumed by other LTHR reactions.
ISSN:0010-2180
1556-2921
DOI:10.1016/j.combustflame.2006.12.011