Spectroscopic and chemical-kinetic analysis of the phases of HCCI autoignition and combustion for single- and two-stage ignition fuels

Hwang, Wontae; Dec, John E.; Sjöberg, Magnus

doi:10.1016/j.combustflame.2008.03.019

Cited by 156 publications

(81 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…• A lack of reactivity in the LLNL chemical kinetic model, especially under HCCI engine operating conditions has been encountered by previous researchers [30,47]. The detailed chemical kinetic model has been validated against fundamental experiments in shock tubes and rapid compressions machines, so modifying the kinetic rate constants to match the HCCI engine data is not a suitable approach to resolving the discrepancy.…”

Section: Resultsmentioning

confidence: 99%

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

Singh¹,

Waqas²,

Johansson³

et al. 2017

SAE Technical Paper Series

View full text Add to dashboard Cite

The blending of ethanol with primary reference fuel (PRF) mixtures comprising n-heptane and iso-octane is known to exhibit a non-linear octane response; however, the underlying chemistry and intermolecular interactions are poorly understood. Well-designed experiments and numerical simulations are required to understand these blending effects and the chemical kinetic phenomenon responsible for them. To this end, HCCI engine experiments were previously performed at four different conditions of intake temperature and engine speed for various PRF/ethanol mixtures. Transfer functions were developed in the HCCI engine to relate PRF mixture composition to autoignition tendency at various compression ratios. The HCCI blending octane number (BON) was determined for mixtures of 2-20 vol % ethanol with PRF70. In the present work, the experimental conditions were considered to perform zerodimensional HCCI engine simulations with detailed chemical kinetics for ethanol/PRF blends. The simulations used the actual engine geometry and estimated intake valve closure conditions to replicate the experimentally measured start of combustion (SOC) for various PRF mixtures. The simulated HCCI heat release profiles were shown to reproduce the experimentally observed trends, specifically on the effectiveness of ethanol as a low temperature chemistry inhibitor at various concentrations. Detailed analysis of simulated heat release profiles and the evolution of important radical intermediates (e.g., OH and HO 2 ) were used to show the effect of ethanol blending on controlling reactivity. A strong coupling between the low temperature oxidation reactions of ethanol and those of n-heptane and iso-octane is shown to be responsible for the observed blending effects of ethanol/PRF mixtures.

show abstract

Section: Resultsmentioning

confidence: 99%

Simulating HCCI Blending Octane Number of Primary Reference Fuel with Ethanol

Singh¹,

Waqas²,

Johansson³

et al. 2017

SAE Technical Paper Series

View full text Add to dashboard Cite

show abstract

“…Furthermore, a combination of a 500-nm shortwave-pass (SWP) filter and a BG39 colored-glass filter reject long-wavelength (green through IR) soot luminosity (if present). The recorded luminosity is likely chemiluminescence from CH 2 O ⁄ , HCO ⁄ , CH ⁄ , and CO 2 ⁄ , broadband emission from the CO continuum [16,17], and well after ignition, possibly some soot luminosity that is not entirely rejected by the BG39 filter. The HSC images are acquired with a resolution of 512 Â 512 pixels and the exposure time for each frame is 125 ls.…”

Section: Optical Diagnosticsmentioning

confidence: 99%

Evaluating temperature and fuel stratification for heat-release rate control in a reactivity-controlled compression-ignition engine using optical diagnostics and chemical kinetics modeling

Kokjohn

Musculus

Reitz

2015

Combustion and Flame

159

View full text Add to dashboard Cite

a b s t r a c tThe combustion process in a dual-fuel, reactivity-controlled compression-ignition (RCCI) engine is investigated using a combination of optical diagnostics and chemical kinetics modeling to explain the role of equivalence ratio, temperature, and fuel reactivity stratification for heat-release rate control. An optically accessible engine is operated in the RCCI combustion mode using gasoline primary reference fuels (PRF). A well-mixed charge of iso-octane (PRF = 100) is created by injecting fuel into the engine cylinder during the intake stroke using a gasoline-type direct injector. Later in the cycle, n-heptane (PRF = 0) is delivered through a centrally mounted diesel-type common-rail injector. This injection strategy generates stratification in equivalence ratio, fuel blend, and temperature. The first part of this study uses a high-speed camera to image the injection events and record high-temperature combustion chemiluminescence. The chemiluminescence imaging showed that, at the operating condition studied in the present work, mixtures in the squish region ignite first, and the reaction zone proceeds inward toward the center of the combustion chamber. The second part of this study investigates the charge preparation of the RCCI strategy using planar laser-induced fluorescence (PLIF) of a fuel tracer under non-reacting conditions to quantify fuel concentration distributions prior to ignition. The fuel-tracer PLIF data show that the combustion event proceeds down gradients in the n-heptane distribution. The third part of the study uses chemical kinetics modeling over a range of mixtures spanning the distributions observed from the fuel-tracer fluorescence imaging to isolate the roles of temperature, equivalence ratio, and PRF number stratification. The simulations predict that PRF number stratification is the dominant factor controlling the ignition location and growth rate of the reaction zone. Equivalence ratio has a smaller, but still significant, influence. Temperature stratification had a negligible influence due to the NTC behavior of the PRF mixtures.

show abstract

“…1°ca later, the spectra features change completely. Hwang et al, for iso-octane and PRF80 at temperature of 950 K, observed that the ITHR spectrum is predominantly in the blue-ligth emission with a peak at 450 nm, although it extends from 350 nm to about 650 nm [32]. Overlapped to the main broad peak are many small peaks that occur at regular intervals from 340 to 550 nm.…”

Section: Diesel Injectormentioning

confidence: 97%

“…Differences in the spectra band structure and underlying 'continuum' are due to the temperatures of the various flames [34]. Moreover, Hwang et al [32] analyzing the spectra of PRF80, a two -stage ignition fuel, suggested that chemiluminescence consisted of strong formaldehyde bands that were possibly overlapped to an emission from the CO continuum. However, the chemical-kinetic analysis showed that the CO + O -> CO 2 + hm reaction responsible for the CO-continuum emission was not active during the ITHR phase indicating that only formaldehyde contributed to the chemiluminescence.…”

Section: Diesel Injectormentioning

confidence: 98%