The Influence of Diesel End-of-Injection Rate Shape on Combustion Recession

Koci, Chad; Martin, Glen C.; Bazyn, Tim; Morrison, Wayne M.; Svensson, Kenth; Gehrke, Christopher

doi:10.4271/2015-01-0795

Cited by 19 publications

(10 citation statements)

References 28 publications

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“…After the end of injection, the luminous combustion is seen to split into two parts, one short tail traveling upstream ("combustion recession") and a second tail, corresponding to burn out of the jet, traveling downstream. The progression of the luminous zone towards the injector is similar to the observations and analyses of previous studies, and can be interpreted as an ignition event [20,25,40,41].…”

Section: Oh* Chemiluminescencesupporting

confidence: 86%

Characterization of Spray A flame structure for parametric variations in ECN constant-volume vessels using chemiluminescence and laser-induced fluorescence

Maes

Meijer

Dam

et al. 2016

Combustion and Flame

113

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The transient and quasi-steady flame structure of reacting fuel sprays produced by single-hole injectors has been studied using chemiluminescence imaging and Planar Laser-Induced Fluorescence (PLIF) in various constant-volume facilities at different research institutes participating in the Engine Combustion Network (ECN). The evolution of the high-temperature flame has been followed based on chemiluminescence imaging of the excited-state hydroxyl radical (OH *), and PLIF of ground-state OH. Regions associated with low-temperature chemical reactions are visualized using formaldehyde (CH 2 O) PLIF with 355-nm excitation. We compare the results obtained by different research institutes under nominally identical experimental conditions and fuel injectors. In spite of design differences among the various experimental facilities, the results are consistent. This lends confidence to studies of transient behavior and parameter variations performed by individual research groups. We present results of the transient flame structures at Spray A reference conditions, and include parametric variations around this baseline, involving ambient temperature, oxygen concentration and injection pressure. Key results are the observed influence of an entrainment wave on the transient flame behavior, model-substantiated explanations for the high-intensity OH * lobes at the lift-off length and differences with OH PLIF, and a general analogy of the flame structures with a spray cone along which the flame tends to locate for the applied parametric variations.

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Section: Oh* Chemiluminescencesupporting

confidence: 86%

Characterization of Spray A flame structure for parametric variations in ECN constant-volume vessels using chemiluminescence and laser-induced fluorescence

Maes

Meijer

Dam

et al. 2016

Combustion and Flame

113

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“…From this perspective, it can be seen that the RANS simulations well replicate the extents of combustion recession reactions seen in the experiments, and if multiple experimental realizations were available, the ensemble average of those realizations would appear more similar to the RANS simulations, with a more uniform distribution of OH* upstream of the LOL as combustion recession progresses. This general combustion recession sequence, including ignition of isolated pockets upstream of the LOL, followed by expansion and merging of the initial reaction regions, has also been observed in experiments of Knox et al 5 and Koci et al 9 for low ambient temperatures and low oxygen concentrations.…”

Section: Simulation Of Combustion Recessionsupporting

confidence: 66%

“…Recent experimental studies have shown that under negative ignition-dwell conditions, second-stage ignition may or may not occur in near-nozzle mixtures after EOI, depending jointly on the in-cylinder thermodynamic conditions and the magnitude and speed of the EOI entrainment wave. 5–11 When second-stage ignition occurs in mixtures upstream of the lifted diesel flame after EOI, this phenomenon has been termed “combustion recession.” Combustion recession can appear as either separated pockets of high-temperature reaction zones between the injector nozzle and the lifted diffusion flame position, or lift-off length (LOL), or as a rapid sequence of ignition reactions that travel back toward the injector nozzle. In contrast to “flash back,” 1 a term adopted in the gas turbine community for conditions where flames propagate back toward the fuel nozzle because of a mismatch in the local flame speed and fuel jet velocity, autoignition appears to drive combustion recession in diesel sprays.…”

Section: Introductionmentioning

confidence: 99%

“…8 Thermodynamic conditions that promote higher reactivity, including high ambient temperature conditions, high oxygen concentration, and higher fuel reactivity, are observed to promote combustion recession in diesel sprays. 5,9 The injector nozzle diameter, injection pressure, and duration of EOI also affect the propensity and behavior of combustion recession. 5 Understanding and controlling combustion recession via injection rate shaping may offer a meaningful way to control engine emissions.…”

Section: Introductionmentioning

confidence: 99%

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Computational analysis of end-of-injection transients and combustion recession

Jarrahbashi

Kim

Knox

et al. 2017

International Journal of Engine Research

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Mixing and combustion of engine combustion network Spray A after end of injection are modeled using highly resolved multidimensional numerical simulations to explore the physics underlying recent experimental observations of combustion recession. Reacting spray simulations are performed using a traditional Lagrangian–Eulerian coupled formulation for two-phase mixture transport with a Reynolds-averaged Navier–Stokes approach using the open-source computational fluid dynamics code OpenFOAM. Chemical kinetics models for n-dodecane by Cai et al. and Yao et al. are deployed to evaluate the impact of mechanism formulation and low-temperature chemistry on predictions of combustion recession behavior. Simulations with the Cai mechanism show that under standard Spray A conditions, the end-of-injection transient induces second-stage ignition in distinct regions near the nozzle that are initially spatially separated from the lifted diffusion flame, but then rapidly merge with flame. By contrast, the Yao mechanism fails to predict sufficient low-temperature chemistry in mixtures upstream of the diffusion flame during the end-of-injection transient and does not predict combustion recession for the same conditions. The effects of the shape and duration of the end-of-injection transient on the entrainment wave near the nozzle, the likelihood of combustion recession, and the spatiotemporal development of mixing and chemistry in near-nozzle mixtures are also investigated. With a more rapid ramp-down injection profile (ramp-down duration < 400 µs), a weaker combustion recession occurs earlier in time after the start of ramp-down. For extremely fast ramp-down (ramp-down duration = 0), the entrainment flux varies rapidly near the nozzle and over-leaning of the mixture completely suppresses combustion recession. For a slower ramp-down profile with respect to the standard Spray A condition, complete combustion recession back toward the nozzle is observed and combustion recession occurred later in time. Simulations qualitatively agreed with the past experimental and modeling observations of combustion recession with different end-of-injection transients.

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“…The extent to which second-stage ignition is able to recess toward the injector is different for the three injection timings. Similar combustion recession processes have been seen in other studies [25,28,[36][37][38] .…”

Section: Single-injection Experimental Resultssupporting

confidence: 73%

Effect of post injections on mixture preparation and unburned hydrocarbon emissions in a heavy-duty diesel engine

O’Connor

Musculus

Pickett

2016

Combustion and Flame

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a b s t r a c tThis work explores the mechanisms by which a post injection can reduce unburned hydrocarbon (UHC) emissions in heavy-duty diesel engines operating at low-temperature combustion conditions. Post injections, small, close-coupled injections of fuel after the main injection, have been shown to reduce UHC in the authors' previous work. In this work, we analyze optical data from laser-induced fluorescence of both CH 2 O and OH and use chemical reactor modeling to better understand the mechanism by which post injections reduce UHC emissions. The results indicate that post-injection efficacy, or the extent to which a post injection reduces UHC emissions, is a strong function of the cylinder pressure variation during the post injection. However, the data and analysis indicate that the pressure and temperature rise from the post injection combustion cannot solely explain the UHC reduction measured by both engine-out and optical diagnostics. The fluid-mechanic, thermal, and chemical interaction of the post injection with the main-injection mixture is a key part of UHC reduction; the starting action of the post jet and the subsequent entrainment of surrounding gases are likely both important processes in reducing UHC with a post injection.

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The Influence of Diesel End-of-Injection Rate Shape on Combustion Recession

Cited by 19 publications

References 28 publications

Characterization of Spray A flame structure for parametric variations in ECN constant-volume vessels using chemiluminescence and laser-induced fluorescence

Characterization of Spray A flame structure for parametric variations in ECN constant-volume vessels using chemiluminescence and laser-induced fluorescence

Computational analysis of end-of-injection transients and combustion recession

Effect of post injections on mixture preparation and unburned hydrocarbon emissions in a heavy-duty diesel engine

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