Ignition Failure Research Articles

Chemistry and transport effects on critical flame initiation radius for alkanes and aromatic fuels

The combined effects of transport and fuel reactivity on the critical flame initiation radius for n-alkanes and aromatics are investigated experimentally and numerically using outwardly propagating spherical flames at atmospheric pressure. The effects of transport on the critical flame initiation radius are examined by comparing n-alkanes with different sizes (n-heptane vs. n-decane) but similar molecular structure and reactivity. The effect of fuel reactivity and chemistry on the flame initiation radius are investigated by comparing two alkylated benzene isomers, 1,3,5-trimethylbenzene and n-propylbenzene, which have distinctive reactivity and molecular structures but have the same molecular size and transport properties. The results showed that for n-alkanes, consistent with theoretical predictions, the effect of transport on the critical flame initiation is small for large hydrocarbon fuels. For aromatic fuels, it is found that fuel reactivity defined by fuel molecular structure has a significant impact on the critical flame initiation radius. This observation also supports the theoretical prediction. The results show that fuel with lower reactivity (1,3,5-trimethylbenzene) has a larger critical radius than that with higher reactivity (n-propylbenzene). It is also demonstrated that there is a linear correlation between the critical strain rate and the peak in-flame OH concentration. A radical index combined with transport-weighted enthalpy is proposed to correlate the critical radius of all tested alkanes and aromatic fuels. It is found that the critical radius of all fuels can be reasonably correlated to the product of the radical index and the transport-weighted enthalpy. The results reveal that, similar to flame extinction limits, the critical radius is subject to the combined effect of enthalpy transport and fuel reactivity. The present results suggest that an increase of the product of the transport weighted enthalpy and fuel reactivity may lead to lower chance of ignition failure in internal combustion engines and turbine engine relight.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВОДОРОДА НА НЕРАВНОМЕРНОСТЬ ПРОТЕКАНИЯ ПРОЦЕССА СГОРАНИЯ СЖАТОГО ПРИРОДНОГО ГАЗА В ДВИГАТЕЛЯХ ВНУТРЕННЕГО СГОРАНИЯ НА РЕЖИМАХ ХОЛОСТОГО ХОДА

Deep choke modes that include the no-load conditions are the most long lasting while operating a car in the city environment. However, the efficiency of work process at the deep choke modes remain low due to high intake depression and the large proportion of residual gases. The paper covers the evaluation of the hydrogen influence on the irregularity of compressed natural gas (CNG) combustion behavior in the engine at the no-load conditions through the assessment of change of the polytropic index as the parameter displaying the direction and the intensity of heat-exchange processes. The paper considers the feasibility to determine the quantity of residual gases and their proportion in working mixture. Carried out experimental study of the hydrogen influence on the cycles irregularity at the idle modes of the VAZ-2111 engine showed the decrease of variation of maximum pressure in the engine cylinder when increasing the proportion of hydrogen in gas fuel from 0 up to 6 %. The authors carried out the detailed study of hydrogen influence on the cycles’ irregularity for three stoichiometric ratios of the CNG mixture with the hydrogen proportion of 0, 4 and 6 %, three the most representative successive cycles displaying the irregularity of engine operation were selected for each of them. The study of the polytropic index on the selected cycles allowed determining the quantity of the residual gases and their proportion in working mixture and showed the significant influence of quality of combustion in the previous cycle on the thermodynamic processes behavior within the compression stroke and the combustion process efficiency in the next cycle. The obtained results allow evaluating the influence of hydrogen addition on the CNG combustion process and concluding that the addition of 6 % hydrogen allows better initiating the ignition process, thereby, preventing the ignition failures and decreases significantly the number of incomplete combustion cycles increasing the efficiency of working process at the idle modes.

Experimental Study of the Atmospheric Plasma Jet for Plasma-Assisted Combustion

Plasma jets were studied for usage in plasma-assisted combustion in the supersonic channel, according to the method of Takita. The electrochemical plasma torch was evaluated as a novel promising tool to initiate and support combustion. It was able to ignite the propane/butane mixture at a 200-m/s flow speed, and its thermal output was not significant in comparison with the theoretical thermal power of the combustor. The reasons for ignition failure at supersonic flow velocity are discussed.

Treatment of gait ignition failure with ropinirole.

Gait ignition failure (GIF) is a syndrome characterized by hesitation or inability to initiate gait from a static position. It may occur in a variety of conditions, including normal pressure hydrocephalus, subcortical vascular disease, parkinsonian syndromes and a variety of focal lesions. Previous information on the treatment of GIF has been primarily anecdotal, but there have been a few reports of response to dopamine agonists. We report a 63-year-old man with anoxic encephalopathy who developed GIF nine years after the initial anoxic insult. The patient’s GIF responded robustly, albeit transiently, to ropinirole. MRI was unrevealing, but a positron emission tomography scan showed hypometabolism in the deep frontal ACA/MCA watershed area; this may have disconnected the basal ganglia from the motor cortex and/or interrupted dopaminergic mesocortical transmission. Our understanding of the pathophysiology and the treatment of GIF remains limited, but there may be at least a limited therapeutic role for dopamine agonists.

MEMS 기반 고체 추력기의 마이크로 점화기를 이용한 궤도 열제어

MEMS based solid propellant thruster researched for the purpose of an academic research will be verified at space environment through CubeSat program. For this, the temperature of the MEMS thruster should be within allowable operating temperature range by proper thermal control to prevent the ignition failure caused by ignition time delay and to guarantee the structural safety of the MEMS thruster in the low temperature. In this study, we proposed an effective thermal control strategy, that is to use micro-igniter as a heater and temperature sensor for active thermal control instead of using additional heater. The effectiveness of the strategy has been verified through on-orbit thermal analysis of CubeSats with MEMS thruster.

Ignition probability of a partially premixed burner using LES

To comply with stringent pollutant emission regulation, low-emission aeronautical gas turbines rely on lean premixed combustion. Such technology raises the issue of ensuring a reliable ignition since the combustor operates closer to blow-off. Ignition is however known as a stochastic phenomenon, associated to various sources of system variability. These variabilities and their impact on the success or failure of ignition are still not fully understood. In this paper, Large Eddy Simulation (LES) of laser ignition sequences in an academic swirled turbulent partially premixed burner are performed to obtain statistical information at three selected ignition locations representative of the various ignition scenarios observed. The velocity and mixing fields are first validated against measurements to eliminate uncertainty associated with the non-reacting flow. LES is then shown to recover the ignition statistical behavior and probability for the selected ignition locations. Moreover, LES analysis allows to identify the various mechanisms that drive ignition failure or success. Statistics of flame displacement speed are used to demonstrate the effect of curvature and stretch in regions of intense turbulence and the impact of partial premixing on the ignition process.

In situ low-cost and adaptable braze tool evaluation system with vision analysis

In this study, a low-cost, flexible process monitoring system for focussed arc tungsten inert gas welder tool electrodes is presented. The system is capable of acquiring and processing geometric data that are used to define acceptance criteria. This system is used to characterise tool wear phenomena in repetitive brazing runs ensuring that the tool is operating within its process window. It was found, using this apparatus, that a build-up of zinc oxide, originating from the zinc-coated steel, on the braze tool prohibits arcing and delivery of a good quality joint. The vision system can identify build-up of this layer before failure of ignition. Measurements showed that after 990 s of continuous arcing, the zinc oxide build-up would cause system malfunction. The vision system gave a warning of zinc build-up at 577 s.

Scintillation Conditioning of Tantalum Capacitors With Manganese Dioxide Cathodes

Scintillation testing is a method that activates the self-healing mechanism in tantalum capacitors. In preliminary experiments, the deliberate activation of self-healing yielded up to 100% higher breakdown voltages in weak parts that had an increased risk of ignition failure. This improvement results in better performance under surge current conditions. This paper demonstrates that scintillation conditioning reduces surge current failures in tantalum capacitors with manganese dioxide cathodes. Tantalum capacitors with $\hbox{MnO}_{2}$ cathodes from two manufacturers are subjected to scintillation conditioning and are compared with non-conditioned populations in a surge current test. To ensure that the activation of the self-healing mechanism has no detrimental effect on the reliability of the parts, a life test is conducted. The results show that the conditioning method increases the breakdown voltage of self-healed tantalum capacitors by up to 25% under surge current conditions, which mitigates the risk of ignition failures. No detrimental effect on the life of the conditioned samples was observed.

Surface ignition behaviors of methane–air mixture in a gas oven burner

In a gas oven burner, commonly used as a residential appliance, a surface igniter is a critical component for creating a pilot flame near the surface that can propagate safely back to the nozzle of the burner. The igniter should meet critical operating requirements: a lower surface temperature needed to ignite a methane–air mixture and a stable/safe ignition sustained. Otherwise, such failure would result in an instantaneous peak in carbon monoxide emission and a safety hazard inside a closed oven. Several theoretical correlations have been used to predict ignition temperature as well as the critical ignition/extinction limit for a stagnation flow ignition. However, there have only been a few studies on ignition modes or relevant stability analysis, and therefore a more detailed examination of the transient ignition process is required.In this study, a high-speed flame visualization technique with temperature measurement was employed to reveal a surface ignition phenomenon and subsequent flame propagation of a cold combustible methane–air mixture in a gas oven burner. The operating parameters were the temperature–time history of the igniter surface, mixture velocity, and the distance of the igniter from the nozzle. The surface ignition temperatures were analyzed for such parameters under a safe ignition mode, while several abnormal modes leading to ignition failure were also recognized.

Planar Laser-Induced Fluorescence Fuel Imaging During Gas-Turbine Relight

This experimental study investigates the influence of fuel distribution on ignition outcome during high-altitude relight of a gas turbine. Planar laser-induced fluorescence is used to image fuel inside a lean direct-injection combustor under realistic conditions. A novel apparatus is developed to permit planar laser-induced fluorescence imaging, in which large quantities of poorly atomized fuel impinges on the internal surfaces of the combustor. Results reveal high variability in atomization quality. In the absence of flame, small droplets are confined to areas of recirculating flow, whereas large droplets impact on the walls. All fuel is introduced through a pilot air-blast atomizer close to the injector centerline. However, comparatively little fuel is apparent near the igniter tip because the outside swirlers of the fuel injector create a fast-moving stream of fuel-free air that flows directly below the upper combustor wall. The droplet size and fuel concentration in the main recirculation zone do not differ radically at test conditions with markedly different fuel-to-air ratios, suggesting that turbulent straining is a more important factor than equivalence ratio in the failure of ignition when the airflow rate is high. In the presence of flame, medium-sized burning droplets are observed close to the injector centerline. Flame interference resulting from fluorescence of polycyclic aromatic hydrocarbons is apparent, but small, suggesting that kerosene planar laser-induced fluorescence is a useful tool for the analysis of all stages of altitude relight.

Thermal decomposition behaviors and burning characteristics of ammonium nitrate/polytetrahydrofuran/glycerin composite propellant

Ammonium nitrate (AN)-based propellant is plagued by several drawbacks: low burning rate, poor ignitability, and low energy. The application of an energetic binder is an effective approach to the practical use of AN-based propellants but has not been used to date because the synthesis processes are complicated and expensive. Polytetrahydrofuran (PTHF) is a raw material for rubber products and is not an energetic material. The repeating unit of PTHF has one oxygen atom, and although PTHF could not become solid with use of a curing agent alone, PTHF became rubbery with the use of glycerin as a crosslinking modifier. Thus the PTHF/glycerin mixture would be a useful binder to improve the burning characteristics of AN-based propellants, due to the oxygen atoms in the mixture. The use of PTHF/glycerin binder is theoretically effective for enhancing the performance of AN-based propellant, but the combined AN/PTHF/glycerin propellants failed to ignite; they only generated a flashing flame at the ignition event. The ignition failure of the AN/PTHF/glycerin propellant occurred because the melted binder covered the burning surface and interfered with the evolution of the AN decomposition gases and the heat flux feedback from the flame to AN. The AN/PTHF/glycerin propellant was then burned with the addition of a catalyst, and the effect of PTHF/glycerin binder on the improvement of burning characteristics was apparent. The PTHF/glycerin binder was an effective binder material for improving a performance of the AN-based composite propellant.

Flame Imaging of Gas-Turbine Relight

High-altitude relight inside a lean-direct-injection gas-turbine combustor is investigated experimentally by highspeed imaging. Realistic operating conditions are simulated in a ground-based test facility, with two conditions being studied: one inside and one outside the combustor ignition loop. The motion of hot gases during the early stages of relight is recorded using a high-speed camera. An algorithm is developed to track the flame movement and breakup, revealing important characteristics of the flame development process, including stabilization timescales, spatial trajectories, and typical velocities of hot gas motion. Although the observed patterns of ignition failure are in broad agreement with results from laboratory-scale studies, other aspects of relight behavior are not reproduced in laboratory experiments employing simplified flow geometries and operating conditions. For example, when the spark discharge occurs, the air velocity below the igniter in a real combustor is much less strongly correlated to ignition outcome than laboratory studies would suggest. Nevertheless, later flame development and stabilization are largely controlled by the cold flowfield, implying that the location of the igniter may, in the first instance, be selected based on the combustor cold flow. Copyright © 2010.

Industrial accidents triggered by lightning

Natural disasters can cause major accidents in chemical facilities where they can lead to the release of hazardous materials which in turn can result in fires, explosions or toxic dispersion. Lightning strikes are the most frequent cause of major accidents triggered by natural events. In order to contribute towards the development of a quantitative approach for assessing lightning risk at industrial facilities, lightning-triggered accident case histories were retrieved from the major industrial accident databases and analysed to extract information on types of vulnerable equipment, failure dynamics and damage states, as well as on the final consequences of the event. The most vulnerable category of equipment is storage tanks. Lightning damage is incurred by immediate ignition, electrical and electronic systems failure or structural damage with subsequent release. Toxic releases and tank fires tend to be the most common scenarios associated with lightning strikes. Oil, diesel and gasoline are the substances most frequently released during lightning-triggered Natech accidents.

Large eddy simulation of forced ignition of an annular bluff-body burner

The optimization of the ignition process is a crucial issue in the design of many combustion systems. Large eddy simulation (LES) of a conical shaped bluff-body turbulent nonpremixed burner has been performed to study the impact of spark location on ignition success. This burner was experimentally investigated by Ahmed et al. [Combust. Flame 151 (2007) 366–385]. The present work focuses on the case without swirl, for which detailed measurements are available. First, cold-flow measurements of velocities and mixture fractions are compared with their LES counterparts, to assess the prediction capabilities of simulations in terms of flow and turbulent mixing. Time histories of velocities and mixture fractions are recorded at selected spots, to probe the resolved probability density function (pdf) of flow variables, in an attempt to reproduce, from the knowledge of LES-resolved instantaneous flow conditions, the experimentally observed reasons for success or failure of spark ignition. A flammability map is also constructed from the resolved mixture fraction pdf and compared with its experimental counterpart. LES of forced ignition is then performed using flamelet fully detailed tabulated chemistry combined with presumed pdfs. Various scenarios of flame kernel development are analyzed and correlated with typical flow conditions observed in this burner. The correlations between, velocities and mixture fraction values at the sparking time and the success or failure of ignition, are then further discussed and analyzed.

Primary gait ignition disorder: report of three cases

Gait ignition failure (GIF) classifications all had major limitations. Few years ago, a new and simpler classification was proposed by Liston. The aim of this paper is to discuss three GIF patients with respect to this new classification. All three patients presented with hesitation to start walking and turning and their neurological examination revealed start and turn hesitation without any other abnormality. We classified our patients according to Liston's classification as ignition apraxia, which enabled us to approach the patients in a practical way. This classification helps to understand the underlying pathologies and combines clinical characteristics and pathophysiology. We reported our experience with pergolide in the treatment of patients suffering from primary GIF and underline the fact that more research is needed on the treatment of this condition.

Probable Trimethoprim/Sulfamethoxazole–Induced Higher-Level Gait Disorder and Nocturnal Delirium in an Elderly Man

To report a case of probable trimethoprim/sulfamethoxazole (TMP/SMX)-induced higher-level gait disorder (HLGD) and nocturnal delirium in an elderly patient on high-dose oral therapy. An 82-year-old man with a recent history of depression became comatose following an overdose of escitalopram and oxazepam. He was admitted, ventilated for 7 days in the intensive care unit, and treated with piperacillin/tazobactam and cefepime for aspiration pneumonia. Following discharge to a medical ward, respiratory symptoms persisted and imaging confirmed pulmonary abscesses. Stenotrophomonas maltophilia was isolated from sputum and, on day 15, TMP/SMX 800 mg/160 mg 1 tablet every 12 hours was initiated. On day 35, the dose was increased to 800 mg/160 mg 2 tablets every 12 hours. By day 37, the patient was unsteady when attempting to stand. From day 40, he was noted to have features of HLGD with gait ignition failure, poor balance, and frequent falls. His other medications at this time were thiamine 100 mg daily, multivitamin 1 tablet daily, omeprazole 20 mg every 12 hours, and modified-release venlafaxine 150 mg daily. Investigation did not reveal any cause for his acute gait disturbance. TMP/SMX was stopped on day 48 and, by day 51, the patient's gait had returned to normal. Neuropsychiatric adverse reactions with TMP/SMX have been infrequently reported. The Naranjo probability scale indicated that TMP/SMX was the probable cause of HLGD in this patient. At time of writing, this was the first reported case of HLGD associated with TMP/SMX. Clinicians should consider this adverse reaction as a potential cause of HLGD, especially in the elderly and those with malnutrition and hepatic or renal dysfunction.

Gamma background calculation for the HEXRI diagnostic at the National Ignition Facility

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is nearing completion and the commencement of experiment campaigns leading to ignition. Different parameters of an implosion, such as the neutron yield and images of the target, will be inferred from the measurement of emitted neutrons, gammas, and x-rays using different diagnostics. The High-Energy X-Ray Imager (HEXRI) is one of these diagnostics and will be used on cryogenic Deuterium-Tritium implosions at NIF to provide data on the size and shape of the imploding inertial confinement fusion (ICF) capsules. These data are fundamental for understanding the reasons for ignition failure. Following an implosion, the background from neutrons and photons can be very large and can affect the quality of HEXRI images in terms of lowering the signal-to-background ratio below the threshold of 1. In this work we present Monte Carlo simulations of the n-gamma background from the components present inside the target chamber, i.e. the cryogenic target positioner, the Laser Plasma Interaction collimators, the neutron and HEXRI pinholes, and the hohlraum. We found that the ratio of the self-emission x-ray signal to n-gamma background signal stays well above 1 in all cases, allowing a good HEXRI image quality.

Study on the Thermodynamics and Kinetics in the Combustion Reaction between Titanium and Boron Powders

Combustion synthesis of titanium diboride(TiB2) from titanium(Ti) and boron(B) powders was studied by theoretical calculation and experimental analysis. In high temperature range or in low temperature range, the calculated activation energies are 140KJ/mol or 355KJ/mol respectively, which is described by a change from dissolution-precipitation controlled process to diffusion-controlled process. With the increase of particle size of the raw materials, combustion temperature and propagating rate will both reduce. The propagating rate decreases with the addition of diluents. Further increase of diluents may result in a stop of the combustion wave halfway or even a failure of ignition.

Pure akinesia with gait freezing: A third clinical phenotype of progressive supranuclear palsy

The clinical syndrome of pure akinesia has most often been associated with progressive supranuclear palsy (PSP) and is characterized by difficulty initiating gait and "freezing" during walking, writing and speaking. Similar syndromes have been described under the rubrics of primary progressive freezing gait and primary gait ignition failure. We investigated the specificity of the clinical syndrome of pure akinesia with gait freezing (PAGF) for PSP-tau pathology. Among 749 patients archived at the QSBB, only 7 fulfilled proposed diagnostic criteria of: gradual onset of freezing of gait or speech; absent limb rigidity and tremor; no sustained response to levodopa; and no dementia or ophthalmoplegia in the first 5 years of disease. In these cases detailed pathological examination was performed. PSP was the pathological diagnosis in six patients, and Parkinson's disease (PD) in the seventh. As defined, this syndrome had a positive predictive value of 86% for PSP-tau pathology. In the cases with PSP there were no additional features of coexistent vascular or PD and the median PSP-tau score was 3, reflecting relative mild tau load. The clinical syndrome of PAGF appears to have a high specificity for PSP-tau pathology. This relatively uncommon presentation of PSP-tau pathology has less severe tau accumulation than in the more common, "classic" PSP clinical phenotype: Richardson's disease.

Recovery Process of Gait Disturbance after Ventriculo-Peritoneal Shunt in Patients with Idiopathic Normal Pressure Hydrocephalus

To clarify the characteristics of the recovery process of gait disturbances after ventriculo-peritoneal shunt (VP shunt) surgery in patients with idiopathic normal pressure hydrocephalus (iNPH), we investigated three areas in two severely disabled patients: longitudinal changes of the severity of postural instability of motor aspects of the Unified Parkinson's disease Rating Scale (UPDRS); time taken in the "timed up and go (TUG)" test; and the prevalence of freezing episodes and the severity of bradykinesia. We also compared the computed tomography findings before and after VP shunt. Gait disturbances in the early stage after VP shunt fall under the frontal gait disorder of Nutt's classification or the mixed gait apraxia of Liston's classification. Disequilibrium clearly improved gradually after VP shunt, however, gait ignition failure and hypokinesia showed no significant improvement in our study. In the early stage after VP shunt, complementing disequilibrium using high-heeled shoes was highly effective at improving the time taken in TUG. The improvements in radiographic findings were reported after VP shunt.