The influence of charge stratification on the spectral signature of partially premixed combustion in a light-duty optical engine

Najafabadi, Mohammad Izadi; Egelmeers, Luc; Somers, Lmt Bart; Deen, NG Niels; Johansson, Bengt; Dam, Nico

doi:10.1007/s00340-017-6688-9

Cited by 12 publications

(10 citation statements)

References 29 publications

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“…After this time, as shown in Figure 10, strong luminous flames were observed first systematically in the intake valves region and then in random locations near the walls. As observed in previous works [13,39,51,60], these flames were due to the diffusive combustion of stratified fuel in the injector region and on the piston surfaces. In terms of spectroscopic evidence (Figure 18b), these flames featured a continuous signal that increased with a wavelength similar to the blackbody curve described by Planck's radiation law [61].…”

Section: Hcoh + Hν → H + Hco Hcoh + Hν → H + Hcosupporting

confidence: 75%

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

et al. 2017

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Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NO x ) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, reduced tendency to abnormal combustion, and reduction of pumping and heat losses. During homogenous charge operation with lean mixtures, flame development is prolonged and incomplete combustion can even occur, causing a decrease in stability and engine efficiency. On the other hand, charge stratification results in fuel impingement on the combustion chamber walls and high particle emissions. Therefore, lean operation requires a fundamentally new understanding of in-cylinder processes for developing the next generation of direct-injection (DI) SI engines. In this paper, combustion was investigated in an optically accessible DISI single cylinder research engine fueled with gasoline. Stoichiometric and lean operations were studied in detail through a combined thermodynamic and optical approach. The engine was operated at a fixed rotational speed (1000 rpm), with a wide open throttle, and at the start of the injection during the intake stroke. The excess air ratio was raised from 1 to values close to the flammability limit, and spark timing was adopted according to the maximum brake torque setting for each case. Cycle resolved digital imaging and spectroscopy were applied; the optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. Flame front propagation speed, flame morphology parameters, and centroid motion were evaluated through image processing. Chemical kinetics were characterized based on spectroscopy data. Lean burn operation demonstrated increased flame distortion and center movement from the location of the spark plug compared to the stoichiometric case; engine stability decreased as the lean flammability limit was approached.

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Section: Hcoh + Hν → H + Hco Hcoh + Hν → H + Hcosupporting

confidence: 75%

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

et al. 2017

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“…The RCEM was operated with a compression ratio of 20 n-Dodecane was used as a non-fluorescing diesel-surrogate pilot fuel. Injection parameters were kept constant: 600bar pressure, 580s hydraulic duration, total injected mass 1.18mg.…”

Section: Experimental Conditionsmentioning

confidence: 99%

Effect of methane on pilot-fuel auto-ignition in dual-fuel engines

Srna

Bolla²,

Wright³

et al. 2019

Proceedings of the Combustion Institute

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The ignition behavior of n-dodecane micro-pilot spray in a lean-premixed methane/air charge was investigated in an optically accessible Rapid Compression-Expansion Machine at dual-fuel engine-like pressure/temperature conditions. The pilot fuel was admitted using a coaxial single-hole 100µm injector mounted on the cylinder periphery. Optical diagnostics include combined high-speed CH 2 O-PLIF (10kHz) and Schlieren (80kHz) imaging for detection of the firststage ignition, and simultaneous high-speed OH* chemiluminescence (40kHz) imaging for high-temperature ignition. The aim of this study is to enhance the fundamental understanding of the interaction of methane with the auto-ignition process of short pilot-fuel injections. Addition of methane into the air charge considerably prolongs ignition delay of the pilot spray with an increasing effect at lower temperatures and with higher methane/air equivalence ratios. The temporal separation of the first CH 2 O detection and high-temperature ignition was found almost constant regardless of methane content. This was interpreted as methane mostly deferring the cool-flame reactivity. In order to understand the underlying mechanisms of this interaction, experimental investigations were complemented with 1D-flamelet simulations using detailed chemistry, confirming the chemical influence of methane deferring the reactivity in the pilot-fuel lean mixtures. This shifts the onset of first-stage reactivity towards the fuel-richer conditions. Consequently, the onset of the turbulent cool-flame is delayed, leading to an overall increased high-temperature ignition delay. Overall, the study reveals a complex interplay between entrainment, low-T and high-T chemistry and micro-mixing for dual-fuel autoignition processes for which the governing processes were identified.

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“…The use of OH* chemiluminescence at 310 nm is a traditional and well-established approach for defining the lift-off length, giving the best detectability and image quality of the most upstream flame location [29]. However, the fact that soot incandescence contributes to the downstream region is sometimes overlooked [29,30,31]. Comparisons between experimental and numerical OH* fields can potentially benefit from estimation or illustration of the effect of soot incandescence in the downstream region of the spray.…”

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confidence: 99%

Heavy-Duty Diesel Engine Spray Combustion Processes: Experiments and Numerical Simulations

Maes¹,

Dam²,

Somers³

et al. 2018

SAE Technical Paper Series

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A contemporary approach for improving and developing the understanding of heavy-duty Diesel engine combustion processes is to use a concerted effort between experiments at well-characterized boundary conditions and detailed, high-fidelity models. In this paper, combustion processes of n-dodecane fuel sprays under heavy-duty Diesel engine conditions are investigated using this approach. Reacting fuel sprays are studied in a constant-volume pre-burn vessel at an ambient temperature of 900 K with three reference cases having specific combinations of injection pressure, ambient density and ambient oxygen concentration (80, 150 & 160 MPa-22.8 & 40 kg/m 3-15 & 20.5% O 2). In addition to a free jet, two different walls were placed inside the combustion vessel to study flame-wall interaction. Experimentally, low-and high-temperature reaction product distributions are imaged simultaneously using single-shot planar laser-induced fluorescence (PLIF) of formaldehyde and high-speed line-ofsight imaging of the chemically-excited hydroxyl radical (OH*). Interference of soot incandescence in experimental OH* recordings is assessed to improve interpretation of the results. Interference by poly-cyclic aromatic hydrocarbon (PAH) LIF and soot radiation is mostly evaded by evaluating flame structures shortly after ignition for one of the studied cases, but presumably included in others. Simulations were performed using a recently developed computational fluid dynamics (CFD) methodology with detailed chemistry and turbulence-chemistry interaction. Apart from the capability to model flame structures and combustion indicators based on optical diagnostics, heat-release rate trends are predicted accurately at varying boundary conditions. Significant variation in the distribution of low-temperature combustion products under heavy-duty operating conditions are explained using both CFD simulations and a one-dimensional jet model. Fuel pump Resato P16-400-2 Fuel injector Bosch CRI2 solenoid (0.205 mm) Injector driver EFS IPoD 8532 Fuel pressure sensor Kistler 4067E3000 Vessel pressure sensor Kistler 6041 AU20 Burst disk rupture pressure 35 MPa Vessel volume 1260 cc Mixing fan motor Maxon motor (custom) Inlet and exhaust valves Sitec 710.3124-D

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The influence of charge stratification on the spectral signature of partially premixed combustion in a light-duty optical engine

Cited by 12 publications

References 29 publications

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

Effect of methane on pilot-fuel auto-ignition in dual-fuel engines

Heavy-Duty Diesel Engine Spray Combustion Processes: Experiments and Numerical Simulations

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