External Ignition Research Articles

Combustion Test for the Smallest Reciprocating Piston Internal Combustion Engine with HCCI on the Millimeter Scale

Micro reciprocating piston internal combustion engines are potentially desirable for high-energy density micro power sources. However, complex subsystem functions hinder the downsizing of reciprocating piston internal combustion engines. The homogeneous charge compression-ignition (HCCI) combustion mode requires no external ignition system; it contributes to structural simplification of the reciprocating piston internal combustion engines under a micro space constraint but has not been adequately verified at the millimeter scale. The study used a millimeter-scale HCCI reciprocating piston internal combustion engine fueled by a mixture of kerosene, ether, castor oil, and isopropyl nitrate for combustion investigation. The test engine with a displacement of 0.547 cc is the smallest reciprocating piston internal combustion engine known to have undergone in-cylinder combustion diagnosis. It is observed that the HCCI combustion mode at the millimeter scale can realize stable combustion with excellent cooperation for the thermodynamic cycle under appropriate structural and operating conditions, which is essentially not inferior to those in conventional-sized reciprocating piston internal combustion engines. This finding helps the next step of scaling down reciprocating piston internal combustion engines.

Influence of high-reactivity energetic materials on microstructure and performance on iron-based cladding layer under low laser power

Abstract Under low laser power conditions, the cladding layer is constrained by inadequate energy density, resulting in incomplete melting of certain powder particles and the occurrence of defects such as cracks and pores within the layer. This paper utilizes a QT500 substrate and synergistically integrates high-reactivity energetic materials (H-REMs) with metal powder. By external laser energy ignition, the localized combustion of the H-REMs (Al + Fe2O3) is induced, thereby providing additional heat input during the laser cladding process. Through in-depth analysis of extensive experimental data, the influence of H-REMson microstructure and performance of alloy cladding layerhas beenrevealed. The research results demonstrate that the inclusion of H-REMs leads to a 450 K increase in the maximum temperature of the molten pool. By incorporating high-reactivity energetic materials, the energy density utilization of the composite material increased from 0.2663 to 0.7375. The combustion wave generated by H-REMs induces mixing in the molten pool, resulting in cladding layer grain refinement and an average hardness increase of 80 HV1. The friction coefficient decreases from 0.71024 (prior to the addition of H-REMs) to 0.35809, representing a reduction of approximately 49 %.

Experimental study on nonlinear development process of oil-filled equipment fire under external fire source

Abstract The transformer is the key oil-filled equipment in the power system, and its fire behavior seriously affects the safe operation of the power grid. In this paper, in order to analyze the fire development process and combustion behavior of oil-filled equipment, a mesoscale model of transformer equipment was constructed, and fire simulation experiments of transformer equipment under the action of external ignition sources were conducted. The flame temperature, flame height, heat release rate, oil temperature, and pressure were measured. The experimental results show that the oil-filled equipment fire presents the characteristics of nonlinear development. The fire can be divided into three stages: ignition stage, stable growth stage, and combustion mutation stage. The transformer oil near the wall is pyrolyzed by the external heat source, and the combustible gas and transformer oil form a gas-liquid two-phase flow, which is the main reason for the nonlinear development of oil-filled equipment fire. The experimental results are of great significance for the safe operation and fire control of power system oil-filled equipment.

“One for two” strategy to construct an organic-inorganic polymer colloid for flame-retardant modification of flax fabric and rigid polyurethane foam

Polymeric materials such as fabric and foam have high flammability which limits their application in the field of fire protection. To this end, an organic-inorganic polymer colloid constructed from carboxymethyl chitosan and ammonium polyphosphate was used to improve the flame retardancy of flax fabric (FF) and rigid polyurethane foam (RPUF) based on a “one for two” strategy. The modification processes of FF and RPUF relied on pad-dry-cure method and UV-curing technology, respectively, and the modified FF and RPUF were severally designated as CMC/APP-FF and RFR-RPUF. Flame retardancy studies showed that CMC/APP-FF and RFR-RPUF exhibited limiting oxygen index values as high as 39.4 % and 42.6 %, respectively, and both achieved self-extinguishing behavior when external ignition source was removed. Thermogravimetric analysis and cone calorimetry test confirmed that CMC/APP-FF and RFR-RPUF had good charring ability and demonstrated reduced peak heat release rate values of 90.1 % and 10.8 %, respectively, distinct from before they were modified. In addition, condensed phase analysis showed that after burning, CMC/APP-FF became an integration char structure, whereas RFR-RPUF turned into a sandwiched char structure. In summary, the “one for two” strategy reported in this work provides a new insight into the economical fabrication of flame-retardant polymeric materials.

External and internal ignition of a hydrogen-air gas mixture induced by a recombiner

External and internal ignition of a hydrogen-air gas mixture induced by a recombiner

Disaster evaluation of hydrogen explosion leakage from industrial-scale non-metallic pipeline

This work is aimed at evaluating the disaster consequence of leaked hydrogen explosion from the industrial-scale non-metallic pipeline. The flame evolution and explosion overpressure are experimentally obtained. A standard k-ε turbulence model and a beta flame model is established to analyze the explosion overpressure generation. The results indicated that whether there is an external ignition source or not, the hydrogen explosion still occurs when the high-pressure hydrogen leaks from non-metal pipelines. The formation of three overpressure peaks could be attributed to the non-metallic pipeline rupture, leaked hydrogen explosion and sand soil spread. The explosion overpressure peaks continue to decrease with increasing monitoring point distance. The moving speed of explosion overpressure is between 349.34 m/s and 436.21 m/s. The leaked hydrogen concentration outside non-metallic pipeline could reach up to about 10% and the explosion overpressure generation is dependent on the concentration distribution.

Flame morphology and laminar flame assessments affected by flames interaction using multi-ignition sources of NH3/H2-air flames

A detailed assessment of flame–flame interaction and laminar flame evolution using multi-ignition sources is experimentally studied. To understand the flame interaction, the centrally ignited flame is measured and calculated for comparison with multi-ignition sources hydrogen–ammonia/flame. The location of the external ignition source, the delay time, the hydrogen blending, and the mixture equivalence ratio at an initial pressure of 0.1 MPa affect the propagation and morphology of the flame. It can be observed that the advancement of the pressure wave of the external flame causes deformation to the central flame front; This deformation occurs even before the interaction of the flames. The deformation can be decomposed into horizontal deformation, which decelerates the flame front as a result of the drag or accelerates due to the thrust of the flow field on the flame front. At the same time, vertical deformation is influenced by drag and thrust-lift forces. Therefore, the equivalent flame decelerates with time. This effect gives a nonsymmetric shape for expanding flame, and the shape changes from spherical to ellipsoidal, then a triaxial quasi-ellipsoid flame (scalene). The equivalent flame speed and laminar burning velocity are maximized near stoichiometry for all delay times and locations of the ignition source. As the delay time of the stoichiometric hydrogen ammonia/air increases, the equivalent laminar flame speed and laminar burning velocity monotonously decrease, as well as the time and location of the interaction. The equivalent flame speed and laminar burning velocity for ignition sources 1 and 2 decreases with delay time, and this becomes evident on the rich side. While employing a third ignition source increases with delay time since the drag force get eliminated from the horizontal axis. Furthermore, the hydrogen blending effect enhances and highlights these tendencies.

0D bio-based carbon dots and 2D MXene hybridization toward fabricating flame-retardant, conductive and sensing cellulose fabrics

With the rapid development of the smart era, there is an urgent need to replace traditional cellulosic textiles with flame retardant multifunctional cellulosic textiles. Herein, two novel multifunctional textiles (MXene@CDG-C/L and MXene@CDM-C/L) were obtained by constructing coatings consisting of MXene and bio-based carbon dot mixtures (CDG and CDM) on cellulose fabrics using a one-pot impregnation method. MXene@CDG-C/L and MXene@CDM-C/L exhibited desirable flame retardancy, electrical conductivity and sensing properties due to the synergistic effect of MXene and carbon dot mixtures. In the vertical burning test, MXene@CDG-C/L and MXene@CDM-C/L showed self-extinguishing when the external ignition source was removed, with limiting oxygen index values increasing from 18.1 % of untreated fabric to 34.4 % and 36.0 %, respectively. Meanwhile, the conductivities of MXene@CDG-C/L and MXene@CDM-C/L were as high as 31.8 S m−1 and 21.4 S m−1, respectively. Notably, benefiting from the inherent flexibility of cellulose fabrics, MXene@CDG-C/L and MXene@CDM-C/L were able to monitor human movement in a stable and continuous manner. In addition, MXene@CDG-C/L and MXene@CDM-C/L retained good integration properties including flame retardancy, electrical conductivity and sensing property after 20 washing cycles. In conclusion, the strategy reported in this work provided a new idea for the development of environment-friendly and economical multifunctional smart textiles.

Study on the Effect of Coupled Internal and External EGR on Homogeneous Charge Compression Ignition under High Pressure Rise Rate

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency.

Analysis of Thermal Runaway in Pouch-Type Lithium-Ion Batteries Using Particle Image Velocimetry

Despite widespread recognition of the serious risk of battery thermal runaway (BTR) in lithium-ion batteries, the process and associated external ignition mechanism remain poorly understood. In this study, BTR was measured using thermodynamics and visualization techniques in 10 lithium-ion batteries under thermal abuse conditions. The venting speed was measured by particle image velocimetry and boundary detection. The external ignition mechanism was characterized in terms of flame area. The average BTR onset temperature across the 10 test batteries was 215.6°C. The average maximum temperature was 831.1°C, and the variation between experiments was high compared with the BTR onset temperature due to swelling, repairing, and venting. BTR occurred in four stages (ejection of vent gas with flame, extinction of flame, random and simultaneous ignition, and flame propagation and flame jet formation). The initial average venting speed was approximately 123.8 m/s. The structural and venting speeds of vent gas were similar after a stable flame jet formed. The speed of the core of the gas jet peaked at 20 to 40 m/s. The venting speed decreased as the distance from the jet core increased.

Characterization of fire behaviors associated with a thermal runaway in large-scale commercial LiNi0.8Co0.1Mn0.1O2/graphite cells under external ignition

The fire behaviors of large-format commercial batteries at varying states of charge (SOCs) under an external ignition source were experimentally studied. The thermal runaway of the battery mainly starts in the temperature interval of 470.1–526.5 K. The trigger time and temperature of the thermal runaway present a relatively stronger decreasing tendency with an increase in SOC. This implies that the thermal stability of the battery decreases with SOC. The maximum flame temperature is found in the temperature range of 1062.5–1492.0 K, which depends on the combustion efficiency and flame shape. Two peaks of the observed heat release rate (HRR) show that the battery undergoes two intense burning processes at a low SOC. There is no monotonically increasing relationship between total heat release (THR) and SOC. However, the remaining mass of the battery decreases as SOC increases. This indicates that the materials eject fiercely so that some of them are extremely fast to be ignited, resulting in insufficient combustion, particularly for a battery at a high SOC. The gas emission and physicochemical analysis of residue can support this point. The fire hazards involving thermal risk and gas toxicity are also evaluated and discussed.

Experimental investigation on effect of misfire and postfire on backfire in a hydrogen fuelled automotive spark ignition engine

This study investigates the effect of misfire and postfire on backfire in a hydrogen-fuelled automotive spark ignition engine. Backfire is a preignition phenomenon and the flame propagates toward the engine's intake manifold during the suction stroke. Postfire is a post-ignition phenomenon occurring in the exhaust manifold during the exhaust stroke and the flame propagates towards the exhaust manifold or backflow to the combustion chamber or combined both. Misfire occurs when cranking the engine (starting), fouled spark plug, and unoptimized spark timing. Several misfire cycles lead to an increase in the accumulation of unburnt hydrogen-air charge inside the cylinder and 13% hydrogen leaves the exhaust manifold resulting in postfire occurrence in a subsequent cycle. The postfire in the current cycle acting as an external ignition source for the preignition of the accumulated hydrogen-air charge results in backfire in the immediate next cycle. The misfire, postfire and backfire stall the engine operation due to a drop in indicated mean effective pressure. The experimental data indicates the backfire limiting equivalence ratio (BLER) should decrease with an increase in the engine speed as the equivalence ratio varies from 0.91 at 2000 rpm to 0.4 at 4900 rpm. As too advancement of spark timing increases the probability of misfire leading to postfire and backfire, the engine must be operated at backfire limiting spark timing to avoid misfire, postfire, and backfire occurrence. An important point emerged from this study that misfire without postfire does not lead to backfire occurrence. Physical mechanisms and mitigative measures for misfire, postfire and backfire are discussed in detail.

Numerical simulation on the shock wave focusing detonation process in the semicircle reflector

Shock wave focusing is considered a new type of initiation method that does not require external ignition devices. For this method, understanding the shock wave/flame interaction accurately is one of the critical issues for revealing the ignition and triggering mechanisms during shock wave focusing processes. In this study, numerical simulations were carried out to investigate the detailed flow field evolution of the focusing process with kerosene as fuel. Two detonation initiation modes were found during the shock wave focusing processes, which were the direct initiation mode and the reflected shock wave collision initiation mode, respectively. At the detonation wave propagation stage, the primary detonation wave decouples and fails to propagate out of the cavity. The multiple initiation phenomenon occurs in the cavity, and it dominated detonation waves to propagate outside of the cavity to accomplish one thermal cycle. There is no positive correlation between jet temperature and detonation wave propagation velocity. When the jet temperature is low, the detonation wave velocity dominated by the multiple initiation mode is the fastest. The analysis of the shock wave focusing process under different jet velocities showed that when the jet velocity was lower than 2 Ma, the decoupling of the primary detonation wave failed to induce multiple detonation waves. Driven by the vortex in the semicircular cavity, the flame is almost stationary, which means the failure of the detonation wave propagation process.

Numerical and experimental studies on minimum ignition energies in primary reference fuel/air mixtures

Understanding flame initiation is of great interests to combustion research. For induced ignition, a minimum ignition energy (MIE) must be provided by an external ignition source for the formation of a flame kernel. In this paper, the minimum ignition energy in lean primary reference fuel (PRF) /air mixtures is investigated by simulations and experiments. The simulations feature a detailed treatment of chemical kinetics and molecular transport to solve the conservation equations for a flame evolving from an ignition source. In the experiments, a cruciform burner is used for the ignition of the fuel/air mixture. After applying the heat source, three qualitatively different types of evolution are observed: ignition failure, flame kernel formation with subsequent flame extinction, and flame propagation. We define two kinds of MIEs: one for flame initiation, and one for flame propagation. The dependence of MIE for flame propagation on the research octane number (RON) in both experiments and simulations exhibits an upturn at a certain RON: Below this RON, the MIE for flame propagation increases weakly, and above this RON, the MIE for flame propagation increases rapidly with increasing RON. The existence of the upturn can be explained by different reaction pathways of the n-heptane and iso-octane flame. At smaller RON, the massive production of C2H5 during the oxidation of n-heptane helps to sustain the critical early phase of flame with strong diffusion. The results in this study highlight the importance of the interaction between chemical reactions and transport for understanding behaviours of practical ignition processes.

Electric Vehicle Fire Risk Assessment Based on WBS-RBS and Fuzzy BN Coupling

(1) Background: In recent years, electric vehicle fire accidents have occurred frequently. Studying the risk factors leading to electric vehicle fire can take corresponding safety measures to reduce the occurrence of electric vehicle fire accidents. (2) Methods: The Work Breakdown Structure (WBS) was constructed to decompose the electric vehicle system, the Risk Breakdown Structure (RBS) was constructed to decompose the risk of electric vehicle fire accidents, a WBS-RBS coupling matrix was built to identify the risk factors that lead to electric vehicle fire accidents in the electric vehicle system, and the fuzzy Bayesian network was used to evaluate the risk of electric vehicle fire accidents. (3) Results: In this study, the electric vehicle was divided into four systems, and 15 risk factors leading to electric vehicle fire were found. The first risk factor was external collision ignition, followed by battery failure, artificial modification, battery-pack flooding, and charging equipment failure, and safety measures were proposed; (4) Conclusions: The results show that the WBS-RBS and fuzzy BN coupling research method can identify the risk factors leading to an electric vehicle fire, and the risk factors were ranked, providing a reference for the safety protection of electric vehicles.

Experimental investigation of a micelle encapsulator F-500 on suppressing lithium ion phosphate batteries fire and rapid cooling

Thermal runaway (TR) in lithium-ion batteries (LIBs) and LIB fires have attracted a considerable amount of attention. In this study, the micelle encapsulator F-500 was experimentally investigated to understand its extinguishing effect and cooling capacity for lithium iron phosphate (LFP) cells in modules. The gases produced from the batteries were collected and analysed. The extinguishing effectiveness and cooling capacity of a 3% F-500 solution and pure water mist (WM) were compared and discussed. Furthermore, the concentration of H2 was evaluated during the tests. The experimental results showed that H2 is the major gas released during thermal runaway. The combustion of LFP batteries requires external ignition and fire-intensified TR propagation in the LFP battery module. The cooling capacity of the 3% F-500 solution was appropriately three times that of WM according to temperature reduction calculations. The peak concentration for H2 was 14 ppm when the micelle encapsulator was employed, while the peak concentration was 217 ppm when WM was applied. The control mechanisms were qualitatively discussed by comparing the connection between thermal runaway and fire progress. The cooling effect was identified as the most significant factor not only for rapidly extinguishing LIB flames but also for preventing TR propagation. These results are expected to provide guidelines for fighting LIB fires and for cooling LIB systems.

Thermal Characteristics of ISO 13785-2 Alternative Ignition Sources

In this study, the types of ignition sources suggested by the international standard ISO 13785-2 by external wall fire evaluation methods were examined. The suitability of these sources was reviewed through a large-scale test to determine the agreement between main and alternative fire sources. ISO 13785-2 implements external ignition of the flame by a propane burner, which is a standard ignition source, and uses liquid fuel or a wood crib as an alternative ignition source of the propane burner. The thermal characteristics of wood crib among alternative ignition sources were analyzed, and the maximum heat release rate of wood crib is approximately 5.11 MW which is calculated with formula. In the case of a full-scale experiment two repeated experiments were performed to ensure data reliability, and Test 1 was approximately 2.9 MW and Test 2 was approximately 3 MW. The standard temperature of the calibration range is defined as the average temperature of the top three thermocouples (T1~T3) above 800 ℃, and the measurement results showed that Test 1 was 472.4 ℃ and Test 2 was 514.9 ℃. Comparison of the value calculated using the formula derived in previous studies with that of the experimental results, it was concluded that there was a difference between the main and alternative ignition sources in the range of intersections suggested in the international standard.

Plasma Flows From Linear High-Voltage Nanosecond Vacuum Discharges on the Surface of Polymer Materials at 2–6 kA

Particle flow from vacuum flashover on surface of PTFE, PMMA, and PE initiated by 60-kV nanosecond pulses in self-breakdown mode is studied in this work in the range of discharge currents of 2–6 kA. The feature of this work is changing the discharge current at the constant working voltage (~60 kV). The discharge current is varied by changing a ballast resistor. The time lag between voltage application and current rise is ~12 ns for all the values of the discharge current. This lag corresponds to the stage of conductive channel formation (high-voltage stage) and depends only on working voltage of the generator. In contrast to the low-voltage experiments (~1–5 kV) with external ignition, in our case, plasma flow characteristics depend only on intrinsic properties of the breakdown. The novelty of the proposed approach is that all the measurements are carried out at high repetition rate of pulse application (30–100 Hz). We obtained the dependence of particle flow thrust, mass loss, and share of ion component on the value of the discharge current. The results show that there is a share of the ion beam, intensity of which does not depend on the discharge current. Presumably, these ions are generated at the high-voltage stage of the flashover process. The thrust is directly proportional to the charge passed through the discharge channel. It indicates that the key factor in raise of particle flow intensity is the widening of the discharge channel at higher currents. Some of the results are of practical interest for the development of high-voltage pulsed plasma thrusters.

Hypergolic Ignition of 1,3-Cyclodienes by Fuming Nitric Acid toward the Fast and Spontaneous Formation of Carbon Nanosheets at Ambient Conditions

A hypergolic system is a combination of organic fuel and oxidizer that ignites spontaneously upon contact without any external ignition source. Although their main usage pertains to rocket bipropellants, it is only recently that hypergolics have been established from our group as a revolutionary preparative method for the synthesis of different types of carbon nanostructures depending on the organic fuel-oxidizer pair. In an effort to further enrich this concept, the present work describes new hypergolic pairs based on 1,3-cyclohexadiene and 1,3-cyclooctadiene as the organic fuels and fuming nitric acid as the strong oxidizer. Both carbon-rich compounds (ca. 90% C) share a similar chemical structure with unsaturated cyclopentadiene that is also known to react hypergolically with fuming nitric acid. The particular pairs ignite spontaneously upon contact of the reagents at ambient conditions to produce carbon nanosheets in suitable yields and useful energy in the process. The nanosheets appear amorphous with an average thickness of ca. 2 nm and containing O and N heteroatoms in the carbon matrix. Worth noting, the carbon yield reaches the value of 25% for 1,3-cyclooctadiene, i.e., the highest reported so far from our group in this context. As far as the production of useful energy is concerned, the hot flame produced from ignition can be used for the direct thermal decomposition of ammonium dichromate into Cr2O3 (pigment and catalyst) or the expansion of expandable graphite into foam (absorbent and insulator), thus demonstrating a mini flame-pyrolysis burner at the spot.

Carbon Nanostructures Derived through Hypergolic Reaction of Conductive Polymers with Fuming Nitric Acid at Ambient Conditions.

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.