장애물이 있는 챔버 내부의 정전기 방전 에너지에 의한 가스 폭발시 초기화염과 화염전파 특성에 대한 PIV 계측

A visualization study using the schlieren method is adopted in an optically-accessible, cylindrical constant volume combustion chamber to identify the mechanism of ignition energy and ignition system interaction in spark ignited, lean gasoline-air mixture. In order to research the effects of ignition system on flame propagation, two kinds of ignition system are designed, and several kinds of spark plugs are tested and evaluated. To control the discharge energy, the dwell time is varied. The initial flame development is quantified in terms of 2-D images which provides information about the projected flame area and development velocity as a function of ignition system and discharge energy. The results show that high ignition energy and extended spark plug gap can shorten the combustion duration in lean mixtures. The material, diameter and configuration of electrodes the flame development by changing the transfer efficiency from electrical energy to chemical energy and discharge energy. However these factors do not affect of flame development as much a ignition energy or extended gap does.

Experimental study of minimum ignition energy of lean H2-N2O mixtures

Validation of a new formula for predicting the lower flammability limit of hybrid mixtures

Experimental study on vented gas explosion in a cylindrical vessel with a vent duct

Effect of CO2 dilution on forced ignition and development of CH4/air ignition kernels

Study on the inhibition influence on gas explosions by metal foam based on its density and coal dust

On the ignition and flame development in a spray-guided direct-injection spark-ignition engine

The influence of water sprays on gas explosions. Part 1: water-spray-generated turbulence

Previous works employed pressure-based heat release analysis, spark-discharge current/voltage measurements, and cycle-resolved combustion imaging to identify four periods of stratified-charge spark-assisted compression ignition: spark discharge, early kernel growth (EKG), flame propagation, and compression ignition. While it was found that variability in the EKG, and not the spark discharge, influenced combustion phasing, the influence of the spark discharge on the EKG could not be assessed because the imaging system was incapable of recording both the spark discharge and the flame development from the same cycle. This limitation has been overcome here by recording images of both the spark discharge and combustion chemiluminescence during each engine cycle. Additionally, the spark discharge plasmas were recorded from two nearly-orthogonal views to assure that out-of-plane excursions were measured; such are not available from a single view. The results in this study demonstrate that the spark discharge event was not deterministic of the EKG. Circumstantial evidence is given to suggest that the fuel/air distribution and velocity at the spark plug dominate the EKG period variability, though this could not be confirmed definitively.

Flexible materials deform during flame propagation, altering their blockage ratio and the force exerted on the fluid due to various influencing factors. This affects gas explosion characteristics, changes the flame structure, and reduces explosion overpressure and flame speed. To determine the impact of flexible protective devices on the protection mechanism against gas explosions, this experiment used flexible obstacles (polyurethane sponge) as the protective apparatus. Employing a self-built explosion experiment platform, the research investigated methane explosion flame evolution, flame propagation speed, and explosion overpressure under various sizes of pre-positioned flexible obstacles. The study focused on observing the morphological evolution of methane explosion flames, the speed of flame spread, and the explosion overpressure in scenarios with pre-positioned obstacles of different sizes. The results showed that inserting flexible obstacles effectively reduced explosion overpressure and flame front propagation speed. Based on the working conditions set up in this experiment, the maximum rate of decrease in explosion overpressure exceeds 50% and the maximum rate of decrease in flame front velocity is around 20%. With pre-positioned flexible obstacles, as the blockage ratio of the flexible obstacle increased, the severity of deflagration also increased, with both explosion overpressure and flame front speed rising with the blockage ratio. Explosion overpressure and flame front speed also increased with the thickness of the flexible obstacle; simultaneously, the flame front position advanced with the thickness of the flexible obstacle. When constructing close-range protection devices, the height of the protection device should be lower than the protected object (H < h), and the thickness of the protection device should not be too thick.

Experimental study on the effect of explosion suppression in low-concentration gas transportation

Environmental regulations imposed stringent requirements, including the adoption of biofuels and the reduction of fuel consumption. As these measures are integrated, reliable engine operation, particularly for in-flight re-ignition and high-altitude ground ignition, must be ensured. Flame development and propagation in annular combustion chambers strongly depend on kernel characteristics generated by the igniter used and their interaction with a surrounding environment that is typically challenging to ignite. Therefore, a more detailed understanding of ignition kernel properties under adverse conditions is essential. The primary objective of the present study is to characterize ignition kernel properties using a real helicopter igniter, focusing on the characteristic times at the onset of the ignition phase during spark generation, a stage for which fine-scale data are currently lacking. Such information is crucial for accurately initializing numerical simulations dedicated to predicting ignition success or failure in the engine. To this end, several diagnostic techniques have been employed, including microcalorimetry, schlieren visualization, and filtered plasma chemiluminescence. The results indicate a decrease in energy transfer efficiency and an increase in final ignition kernel volume as initial pressure decreases. An existing simple model has been evaluated for its ability to predict the experimentally obtained results.

Diesel engines are extensively used in heavy-duty transportation, power generation, and marine vehicles due to their superior thermal efficiency and extended high-load operability compared to spark ignition (SI) engines. However, combustion in diesel engines is generally characterized by locally rich fuel-air mixtures and high combustion temperatures, causing significant amounts of soot and NOx emissions from these engines. Utilizing carbon-free alternative fuels and enhancing fuel efficiency represent promising strategies to mitigate greenhouse gas (GHG) and other emissions in the heavy-duty transportation sector. In this context, ammonia (NH3), as a hydrogen carrier, has received significant attention as a viable substitute for hydrocarbon fuels, due to its carbon-free composition, relatively high energy density, and well-established infrastructure. Many previous studies have considered combustion and emission characteristics of ammonia-hydrocarbon fuel blends in engines and simplified flames. However, detailed investigations on the effect of ammonia on the performance of hydrocarbon fuels under engine conditions are lacking. In the present study, we perform large-eddy simulations (LES) of the ignition and flame processes in a constant volume combustion reactor, where n–heptane is injected in an ammonia/air ambient mixture in a diesel-like environment. A detailed and validated reaction mechanism containing 302 species and 1981 reactions is employed. The ECN Spray H experimental data is used to validate the spray model under non-reacting and reacting conditions. Dual-fuel combustion is simulated using the well-stirred reactor (WSR) approach. Results are presented for two spray cases: (1) Single fuel (SF) with n-heptane injected into a mixture of air and combustion products; (2) Dual-fuel (DF) with the injection of n-heptane in a mixture of air, ammonia, and combustion products. It is observed that the presence of ammonia has a significant effect on the ignition and flame development processes. With ammonia addition, both the first and second stage ignition delay times increase, but the effect of ammonia on the second stage ignition is significantly more prominent. In addition, the ignition kernel size and growth rate decrease noticeably. For SF spray, the main ignition is characterized by multiple ignition kernels near spray tip, whereas for DF spray, a single relatively small ignition kernel forms and grows slowly in the downstream direction. The flame development and the final quasi-steady flame structure are also modified due to ammonia. The outcome of this research would enable better understanding of ammonia-diesel dual-fuel spray flame behavior and guide development of associated engine combustion strategies.

Fires and explosions are serious hazards in the process industries. Mitigation methods, such as suppression and venting, can be expensive. Ideally, the best option would be to avoid fire or explosion, which may be accomplished by either removing the explosible fuel/oxidant mixture, or the ignition source.One of the most overlooked and preventable ignition sources is electrostatic discharge (ESD). To evaluate the potential for ignition of a fuel/oxidant mixture, one must determine its minimum ESD ignition energy. Once the initiation thresholds have been identified, one can evaluate the likelihood of electrostatic charging and storage, which could result in an electrostatic discharge.Identifying this threshold level can be problematic. An ASTM standard has been developed but, for this test standard to be effective, it must reflect the true hazard potentials observed in industry. Some important questions that need to be addressed to increase the utility of any minimum ignition energy standard are: (1) discharge geometry, (2) duration of the discharge and (3) calculation of the energy of the discharge. This paper will discuss the importance of these factors when evaluating the least amount of energy required to initiate an explosion.

The ignition of gaseous premixtures in the cube with regular vortexes describing by time–independent ABC–flow field was investigated numerically in the frame of three–dimensional thermal–diffusion model. The effects of Lewis number, vortex size and the velocity amplitude on ignition energy have been studied. It was found that in the case of fixed velocity amplitude of the ABC–flow, there is a critical eddies size corresponding to the maximal ignition energy. Numerical results show that in large–scale eddies flow, the ignition energy is almost constant until the velocity amplitude exceeds some critical value, then the abrupt linear increase of ignition energy is observed. It is shown that ignition energy is changing very slowly in the range of Lewis numbers from 0.3 to 1.2, and rapidly increases for Lewis numbers large of 1.2. Obtained results coincide with experimental data available in literature and with previous theoretical results obtained for the spherical flame initiation in the quiescent mixtures.