Early Ignition Research Articles

Research Progress and Challenges of Hydrogen-Ammonia Hybrid Fuel Engines

In this paper, we review the research status of hydrogen and ammonia engines, and discuss the potential of the two fuels as clean energy sources and their challenges. Hydrogen fuel has attracted attention due to its high energy density and zero-emission characteristics, but hydrogen fuel engines have problems such as increased nitrogen oxide emissions, tempering and early ignition. Ammonia fuel, as a carbon-free alternative fuel, has the advantage of being easy to store, but it is inferior to traditional fuels in combustion performance. This paper further analyzes the research progress of hydrogen/ammonia hybrid fuel engines, highlighting specific challenges such as optimizing the fuel mixture ratio, addressing safety concerns related to hydrogen's flammability and ammonia's toxicity, and overcoming technical difficulties in combustion control, points out the combustion support effect of hydrogen and the influence of ammonia on combustion rate, and discusses the advantages of hybrid fuel engines in emission control. Finally, this paper summarizes the current development trend of hydrogen/ammonia fuel engine technology and puts forward suggestions for future research directions.

Cofiring of hydrogen and pulverized coal in rotary kilns using one integrated burner

The grate-kiln process for iron-ore pellet induration utilizes pulverized coal fired burners. In a developed infrastructure for H2, it might be desirable to heat the existing rotary kilns with renewably produced H2. Technical challenges of H2 heating of grate-kilns include high emissions of NOX and maintaining sufficient heat transfer to the pellet bed. This article examined cofiring (70% coal/30% H2) in 130 kW experiments using two different integrated burner concepts. Compared to pure coal combustion, cofiring creates a more intense, smaller flame with earlier ignition and less fluctuations. The process temperature and heat transfer are enhanced in the beginning of the kiln. The co-fired flames emit 32% and 78% less NOX emissions compared to pure coal and H2 combustion, respectively. We can affect the combustion behavior and NOX emissions by the burner design. H2/coal cofiring using integrated burners is probably an attractive solution for emission minimization in rotary kilns.

Method for early ignition detection based on the sampling dispersion of dangerous parameter

The object of the study is the selective dispersion of dangerous parameters of the gas environment during material fires. The practical importance of research consists in using the difference of sample dispersions of dangerous parameters of the gas environment on the intervals of absence and presence of ignition of materials for detection of ignition. The theoretical substantiation of the method of detecting fires in premises based on sample dispersions of current measurements of an arbitrary dangerous parameter of the gas environment, corresponding to the general populations of reliable absence and presence of fire, has been carried out. The method, at a given level of significance, determines the unbiased uniformly most powerful fire detection rule. This makes it possible to determine how much differences in sample variances are significant with a given level of significance and are caused by ignition or are random factors. Laboratory experiments were conducted to verify the proposed method. It was established that the influence of ignition on the value of the difference in the sample dispersion at the corresponding intervals of monitoring the carbon monoxide concentration, smoke density, and temperature of the gaseous environment of the laboratory chamber is different and depends on the type of ignition material. At the same time, the minimum difference of the sample dispersions is characteristic for observing the smoke density for all the studied materials. However, early detection of ignition of alcohol, paper, wood, and textiles when observing the smoke density is carried out when the threshold is exceeded by 9.01, 5.31, 2.13 and 2.55 times, respectively. It is shown that the method of early detection of fires, which is based on the detection of significant differences in sample dispersions of data from the relevant general populations

Nonequilibrium Heating/Cooling Effects in a Mach Number 10 Hydrogen-Fueled Scramjet

The influence of thermal/chemical nonequilibrium on a hydrogen-fueled Ma 10 scramjet was analyzed by combining the JF-2 4 s hock tunnel test and improved delayed detached eddy simulation modeling. A remarkable change in flame stabilization mode when incorporating the two-temperature nonequilibrium model was observed. The nonequilibrium heating and cooling effects were analyzed for different sections of the scramjet. The nonequilibrium heating effect facilitates the upstream flame propagation by inducing an early ignition and thickening the inlet boundary layer. The nonequilibrium heating or cooling effect is generally weak in the nearly constant-area isolator and combustor, where the flow is mainly influenced by the chemical nonequilibrium with a variation of 10% in reaction rate. The nonequilibrium cooling effect mainly exists in the expanding nozzle, where Tv>Tt, but the energy replenishment from vibrational mode to trans-rotational mode is nearly frozen when Tt<1000 K. Under both conditions, the final mixing is nearly complete, and net thrust has been achieved. When considering the nonequilibrium effects, the final combustion efficiency increases from 87.68 to 99%, together with a 53.94% rise in peak pressure ratio and a 137.04% rise in specific impulse.

Experimental study on the factors influencing performance and emissions of hydrogen internal combustion engines

Hydrogen internal combustion engines (H2-ICEs) have advantages such as clean combustion and zero carbon emissions, and have become one of the important technical routes for decarbonization in the internal combustion engine industry. In this paper, several key factors affecting the performance and emissions of hydrogen internal combustion engines, such as ignition timing, excess air coefficient, and hydrogen injection timing, were systematically studied on a spark ignition multi-point injection (MPI) hydrogen internal combustion engine bench. The experimental results indicate that the ignition timing controls the combustion phase of hydrogen. Moderate early ignition can improve the brake thermal efficiency (BTE) while having little impact on the NOX emissions. Excess air coefficient(λ) can significantly affect the performance and emissions of H2-ICE. Along with the increase of the λ, the NOX emissions first increases and then continues to decline. When the λ reaching 2.1 or above, near zero emissions of NOX can be achieved. The advance of hydrogen injection timing will slightly increase the peak of cylinder pressure and instantaneous heat release rate. However, overall, the impact of hydrogen injection timing on BTE and NOX emissions is not significant on MPI H2-ICE.

The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames

Abstract The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ=0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3, and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flowrate at the moment of ignition and the high reactivity of hydrogen, which shifts the flammability limit toward lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a nonmonotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m s–1 and fixed laminar burning velocity Sl0=0.25 m s–1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.

A Numerical Study on the Ignition and Flame Propagation for Locally Stratified Methanol/n-Heptane Dual-Fuel Mixtures

ABSTRACT Flame propagation under thermal and compositional stratifications is relevant to a wide range of applications in combustion devices. In this work, numerical studies are conducted to investigate the multi-stage ignition process and flame propagation in the stratified methanol/n-heptane-air dual-fuel mixture under engine-like conditions. Firstly, the effects of the initial gas temperature of the oxidizer (TOX) and fuel stream on the ignition process and combustion modes are investigated. The results show that TOX affects the early-stage ignition, and a fuel-rich stabilization mode is observed at low temperatures. For example, at 800 K, both cool and hot flames are initiated at the regions close to the most reactive mixture fraction, . A transition from the fuel-lean to fuel-rich and then back to the fuel-lean regions in the mixture fraction space is observed at higher temperatures. Then, hot flames propagate into the methanol/air premixture, forming quasi-steady hot-flame fronts in the fuel-rich regions at TOX = 800 and 900 K owing to the lack of oxygen and low adiabatic flame temperatures. At 1000 K, another flame front propagates into the n-heptane/air mixtures owing to enhanced reaction rate at higher local temperatures. By increasing TOX, a balance owing to the gas expansion is observed at 1020 K, and a spontaneous ignition mode appears at temperatures above 1050 K owing to the high reactivity and early ignition of the methanol/air premixture. Secondly, the effect of compositional stratification on the ignition and flame structures is investigated. Compared with the double flame structure under thermal and compositional stratification conditions, only a single flame structure is observed for those cases with uniform temperatures. A high temperature in the fuel stream region accelerates the decomposition of n-heptane, resulting in the complete consumption of oxygen.

Ethanol stratified ultra-lean combustion with hydrogen enrichment in a constant volume vessel

An experimental study was conducted to determine the effects of ignition timings, injection pressures, and hydrogen enrichment on ethanol stratified ultra-lean combustion. The combustion chamber was a constant volume vessel with an injection and ignition system. The ignition and combustion characteristics of ethanol spray with different ignition timings (0–50 ms after start of injection), injection pressures (5, 15, and 25 MPa), and hydrogen premixed equivalence ratios (0.05, 0.1, and 0.2) under ambient temperature 353 K and 1 atm. The direct injection of ethanol and hydrogen enrichment results in an increase in the stable ignition limit to an extremely lean condition: a global equivalence ratio of 0.15 (67% ethanol/33% H2). Furthermore, the probability of ignition first increased then decreased with the delay in ignition timings; rose with an increase in the injection pressure and hydrogen ratio. However, the delay in ignition timings and high injection pressures resulting in extremely lean zone in the constant volume vessel, which led to incomplete combustion. The addition of hydrogen not only stabilized ignition process but also improved the combustion characteristics. Stable ignition and combustion were achieved at early ignition timing (2–3 ms), moderate injection pressure (15 MPa), and a minimum global equivalence ratio of 0.2 (50% ethanol/ 50% H2).

The effect of ignition diesel injection conditions on the combustion process of natural gas engine

As transportation is a major contributor to carbon emissions, the significance of researching dual-fuel engines lies in their potential to substantially reduce such emissions. Based on the experimental engine of diesel micro-ignition and air intake channel injection natural gas engine, the effects of pilot diesel quality, diesel injection timing and excess air coefficient on combustion process were studied. The test was performed on a single-cylinder engine modified with the WP12 natural gas engine at 1000 rpm under medium load condition. The results revealed that there is a critical pilot energy proportion that affects the combustion stability and that increasing the pilot diesel mass below the critical value improves the combustion stability. The critical diesel energy share increases as the diesel injection moment is delayed and the λ is increased. From the combustion process analysis early ignition diesel injection time is beneficial to improve the thermal efficiency, reduce THC and CO emissions, but sometimes worsen the NOx emissions. Reasonably improving the quality of pilot diesel can accelerate the combustion process and improve thermal efficiency by up to 47.7%.

Accelerating Chemical Kinetics Calculations With Physics Informed Neural Networks

Abstract Detailed chemical kinetics calculations can be very computationally expensive, and so various approaches have been used to speed up combustion calculations. Deep neural networks (DNNs) are one promising approach that has seen significant development recently. Standard DNNs, however, do not necessarily follow physical constraints such as conservation of mass. Physics Informed Neural Networks (PINNs) are a class of neural networks that have physical laws embedded within the training process to create networks that follow those physical laws. A new PINN-based DNN approach to chemical kinetics modeling has been developed to make sure mass fraction predictions adhere to the conservation of atomic species. The approach also utilizes a mixture-of-experts (MOE) architecture where the data is distributed on multiple subnetworks followed by a softmax selective layer. The MOE architecture allows the different subnetworks to specialize in different thermochemical regimes, such as early stage ignition reactions or post-flame equilibrium chemistry, then the softmax layer smoothly transitions between the subnetwork predictions. This modeling approach was applied to the prediction of methane-air combustion using the GRI-Mech 3.0 as the reference mechanism. The training database was composed of data from 0D ignition delay simulations under initial conditions of 0.2–50 bar pressure, 500–2000 K temperature, an equivalence ratio between 0 and 2, and an N2-dilution percentage of up to 50%. A wide variety of network sizes and architectures of between 3 and 20 subnetworks and 6,600 to 77,000 neurons were tested. The resulting networks were able to predict 0D combustion simulations with similar accuracy and atomic mass conservation as standard kinetics solvers while having a 10-50× speedup in online evaluation time using CPUs, and on average over 200× when using a GPU.

New insights into the pre-ignition behavior of methane behind reflected shock waves

Pre-ignition is an undesired combustion event known to restrict kinetic modeling validation. Previous methane oxidation studies reported premature ignition as part of ignition delay time measurements in shock tubes. In this context, the effect on the pre-ignition propensity and auto-ignition behavior of stoichiometric methane mixtures at different dilution levels of hbox {N}_2, Ar, He, and hbox {CO}_2 was studied at 10 bar and 25 bar and temperatures between 1080 K and 1350 K. In addition to conventional sidewall pressure and endwall light emission measurements, a high-speed imaging setup was utilized to visualize the ignition process. Relevant physicochemical parameters to describe and predict the pre-ignition phenomenon were used. The results suggest that dilution levels up to 80% of bath gas are not successful in mitigating early ignition occurrence and its effects at moderate pressures. Replacing hbox {N}_2 by He was found to suppress early ignition at 10 bar, attributed to an enhanced dissipation of temperature inhomogeneities in the test gas section. The present findings demonstrate that hbox {CO}_2 has potential for pre-ignition heat release mitigation, while Ar was confirmed to promote premature ignition. To the best of our knowledge, we present the first detailed study on pre-ignition mitigation for methane mixtures in shock tubes, where further insights into its ignition non-idealities are given.

A Study on Combustion Characteristics of Insensitive Triple-Base Propellant

Research on combustion characteristics can provide basic information and theoretical support for the design of insensitive propellant. This work aims to investigate the combustion characteristics of insensitive triple-base propellant. All propellants were prepared based on same triple-base propellant, but they were desensitized with the same desensitizer in different ways. The high-speed camera, spontaneous luminescence, NO, NH chemiluminescence, and OH-planar laser induction fluorescence (PLIF) methods were employed to capture the combustion flame and derive the distributions of important intermediates. Results show that ignition delay times of insensitive propellants are obviously longer. This indicated that the application of the desensitizer has a partly hindering effect on the early ignition stage. The combustion time of insensitive propellants is mostly similar, which means that the desensitizer has little influence on the intensity of actual combustion. The change in flame height and area of insensitive propellants over time indicated that the combustion progressivity of some insensitive propellants was more prominent, which means that the desensitizer concentration and desensitizing methods all affect the performance of insensitive propellant. The signal intensities of NO and NH show a negative correlation, indicating that a competitive relationship probably exists between the formation of NO and NH radicals during the reaction process. The high concentration of OH mainly locates outside NO, suggesting that there may be a transformation between NO and OH. The maximum signal intensity of NO and NH of different insensitive propellants confirmed that both the concentration of desensitizers and the desensitizing methods exhibit important effect on the reaction process.

Flame regimes in DI diesel combustion: LES study for light- and heavy-duty injectors

Experimental and numerical studies contributed significantly to the overall understanding of diesel spray combustion phenomena over recent decades. In particular, the conceptual model proposed by Dec (1997) [1] and its extensions, describing the mechanisms behind spray formation, vaporization, mixing, ignition, as well as pollutant formation and consumption, have provided new insights for DI diesel engine applications. However, the literature still lacks detailed studies on the local flame regimes of diesel spray combustion. This study presents a comprehensive flame regime analysis of two benchmark cases of the Engine Combustion Network, Spray A and Spray D, which represent light- and heavy-duty applications. To this end, the established gradient-free regime identification (GFRI) approach is extended to cover diesel spray flames and applied to numerical LES data, based on tabulated chemistry, using the unsteady flamelet progress variable (UFPV) approach. The applicability of the tabulated chemistry approach for flame regime identification is validated based on DNS data. For both light- and heavy-duty diesel injectors, a different ignition behavior and temporal evolution of the flame regime distribution is observed. In both configurations the main ignition is dominated by multi-regime combustion, which governs the flame stabilization, and non-premixed combustion, most prominent when approaching steady-state. However, the spatial separation of flame regimes, especially multi-regime and the low-temperature regime, significantly differs when comparing the two spray flames. Based on this qualitative analysis, the impact of the single flame regimes on the overall heat release is analyzed. This is followed by a conditional flame structure analysis, with respect to the mixture fraction and flame regime, for representative times, e.g., early and main ignition as well as quasi steady-state combustion. Finally, the outcome of the local flame regime analysis is consolidated, and an extended conceptual model is proposed, including a detailed understanding of the predominant flame regimes.

Effects of blending energetic iron nanoparticles in B20 fuel on lower CO and UHC emissions of the diesel engine in cold start condition

Biodiesel blended fuels as alternative fossil fuels have a higher viscosity than diesel fuel which increases emissions in cold climates and cold-start conditions. The present study investigates the effect of iron nanoparticles additive to B20 fuel on lower CO and UHC emissions of the diesel engine in low temperatures and cold start conditions. A dilute homogeneous mixture (500 ppm) was prepared from iron nanoparticles in palm oil biodiesel B20 blended fuel (nanofuel). Then a 406 cc, single-cylinder, air-cooled, 4-stroke, direct injection diesel engine was fueled with prepared nano fuel, and CO, UHC, and NOx pollutant emissions were investigated. The results indicated that iron nanoparticles decrease the viscosity of blend fuel by as much as 14%. Furthermore, the fuel droplets’ heat absorption during the compression process and early ignition of energetic iron nanoparticles increases the temperature and enhances the evaporation and mixing rate of fuel droplets. So, the ignition delay time and the burning time of the fuel droplets reduce, and the complete combustion condition strengthens. The reduction of fuel consumption and maximum CO and UHC emissions during the cold cold-start at T = 0 °C, were 10%, 42% and 54%, respectively. Also, in the case of nanofuel, an increase in cold start temperature from 0 °C to 10 °C decreases the maximum CO and UHC emissions up to 31% and 23.7% respectively while increasing the NOx emission from 79 to 90 ppm.

Determination of risk of spontaneous waste ignition and leachate quality for open municipal solid waste dumpsite

The waste receiving capacity of most municipal solid waste (MSW) landfill sites in India is exhausted, resulting in the formation of larger waste heaps. In the majority of Indian cities, these old waste heaps are prone to frequent smoldering and ignition resulting into fires. In this study, the potential risk of spontaneous ignition of landfilled waste at landfill surface was analyzed based on the physico-chemical characteristics of waste, carbon monoxide (CO) levels, landfill surface temperature (LST). The leachate pollution index was also determined to analyze the leachate quality for three different seasons (monsoon, pre-monsoon and post-monsoon). The regression analysis was carried out to understand the thermal properties (smoldering temperature, smoldering time, ignition temperature etc.) of MSW. The results showed that old waste has a higher tendency to undergo ignition compared to fresh waste. It has also been observed that the lower MC of old waste samples in the range of 3.4% and 18.2% is the most likely cause of early smoldering (106.6–109.5 °C) and ignition (198.6–208.4 °C) of old waste. In pre-monsoon season, CO concentrations for sub-surface (10–30 cm depth) smoldering events (SSE) were observed to be between ∼ 150 to 200 ppm. This CO level substantially dropped to 10 ± 1 ppm in the post-monsoon season. The estimation of the leachate pollution index (LPI) showed an index score of 27.35, 30.47 and 10.71 for pre-monsoon, monsoon and post-monsoon seasons, respectively. The determination of CO levels, increased LST and physico-chemical properties of landfilled waste will greatly assist in the abatement of environmental pollution arising from landfill fires.

The Effect of Ignition Timing on the Emission and Combustion Characteristics for a Hydrogen-Fuelled ORP Engine at Lean-Burn Conditions

The application of hydrogen fuel in ORP engines makes the engine power density much higher than that of a reciprocating engine. This paper investigated the impacts of combustion characteristics, energy loss, and NOx emissions of a hydrogen-fuelled ORP engine by ignition timing over various equivalence ratios using a simulation approach based on FLUENT code without considering experiments. The simulations were conducted under the equivalence ratio of 0.5~0.9 and ignition timing of −20.8~8.3° CA before top dead centre (TDC). The engine was operated under 1000 RPM and wide-open throttle condition which was around the maximum engine torque. The results indicated that significant early ignition of the ORP engine restrained the flame development in combustion chambers due to the special relative positions of ignition systems to combustion chambers. In-cylinder pressure evolutions were insensitive to early ignition. The start of combustion was the earliest over the ignition timing of −17.3° CA for individual equivalence ratios; the correlations of the combustion durations and equivalence ratios were dependent on the ignition timing. Combustion durations were less sensitive to equivalence ratios in the ignition timing range of −14.2~−11.1° CA before TDC. The minimum and maximum heat release rates were 15 J·(°CA)−1 and 22 J·(°CA)−1 over the equivalence ratios of 0.5 and 0.9, respectively. Indicated thermal efficiency was higher than 41% for early ignition scenarios, and it was significantly affected by late ignition. Energy loss by cylinder walls and exhaust was in the range of 10~16% and 42~58% of the total fuel energy, respectively. The impacts of equivalence ratios on NOx emission factors were affected by ignition timing.

Experimental study on the ignition process of a pulsed capacitively coupled RF discharge: Effects of gas pressure and voltage amplitude

The effects of gas pressure and voltage amplitude on the ignition process of a pulse capacitively coupled RF argon discharge are experimentally investigated. The electron density is measured by a hairpin probe, the spatiotemporal distribution of the electron impact excitation dynamics is determined by phase resolved optical emission spectroscopy, and the electrical parameters are obtained by analyzing the measured current and voltage waveforms. In this work, the pulse plasma is ignited with few initial electrons, so the ignition process behaves like gas breakdown. Based on the measured RF breakdown curve, the gas pressures and voltage amplitudes are selected, and then different characteristics of ignition processes are compared and discussed in detail. Particularly, the spatiotemporal pattern of the electron impact excitation rate obtained within the selected pressure range, as well as other results, aid the intuitive understanding of a typical “V-shaped” RF breakdown curve. At lower pressures, the excitation pattern exhibit shorter and tilted regions, ending at electrodes during the early ignition stage, implying a substantial electron energy loss, while at relatively high pressures, the excitation pattern becomes wider and less tilted, and the proportion of electron energy consumed by excitation processes increases. In addition, by increasing the voltage amplitude, the ignition is advanced and becomes more significant, manifesting a faster increase in discharge current and a stronger overshoot of RF power deposition. Meanwhile, at high voltage amplitude, the excitation pattern exhibits complex spatiotemporal distribution due to enhanced local electric field when the plasma emission intensity overshoots.

Effects of primary air velocity on co-combustion characteristics of bituminous coal and semicoke under reducing-to-oxidizing environment

This study evaluated the effect of primary air velocity (PAV) on the ignition characteristics of bituminous coal and semicoke mixture (1:1, wt%) in a reducing-to-oxidizing environment (R-O) in a 300-kW pilot-scale furnace that characterized the ignition behaviors of pulverized coal (PC) furnaces. The early ignition characteristics of the primary combustion zone (PCZ), including ignition distance, ignition mode, flame stability and kinetic parameters, were studied. The results showed that the difference in ignition delays obtained from the flame temperature and O2 profiles indicated that convection heating was more important than radiant heating for fuel ignition. The transformation of the ignition mode from non-homogeneous to homogeneous with the increase in PAV was confirmed by the changes of flame temperature, residues, and flue gas composition. Flame stability was optimized by the earlier appearance of the continuous flame boundary and was the best at a PAV of 18 m/s. A simplified first-order kinetic model based on the CO2 evolution profile was established to calculate the reaction rate of the blended fuel during ignition, and the experimental char burnout ratio was consistent with the predicted result. For the potential application of co-firing bituminous coal with a large proportion of semicoke, the recommended PAV may be no more than 22 m/s.

MDIR Monthly Ignition Risk Maps, an Integrated Open-Source Strategy for Wildfire Prevention

Countries unaccustomed to wildfires are currently experiencing wildfire as a new climate-change reality. Understanding how fire ignition and propagation are correlated with temperature, orography, humidity, wind, and the mixture and age of individual plants must be considered when designing prevention strategies. While wildfire prevention focuses on fire ignition avoidance, firefighting success depends on early ignition detection, meaning that, in either case, ignition plays a major role. The current case study considered three Portuguese municipalities that annually observe frequent fire ignitions (Tomar, Ourém, and Ferreira do Zêzere) as the testing ground for the Modernized Dynamic Ignition Risk (MDIR) strategy, thus evaluating the efficiency of MDIR and the efficacy of the variables used. This methodology uses geographic information systems technology sustained by open-source satellite imagery, along with the Habitat Risk Assessment model from the InVEST software package, as drivers for the MDIR application. The MDIR approach grants frequent update capabilities and fully open-sourced high ignition risk area identification, producing monthly ignition risk maps. The advantage of using this method is the ease of adaptation to any current monitoring strategy, awarding further efficiency and efficacy in reducing ignitions. The approach delivered adequate results in estimating ignitions for the three Portuguese municipalities, achieving, for several months, prediction accuracy percentages of over 70%. For the studied area, MDIR clearly identifies areas of high ignition risk and delivers an average of 62% success in predicting ignitions, thus showing potential for analyzing the impact of policy implementation and monitoring through the strategy design.

Effect of NO 2 on ignition characteristics of methanol and chemical kinetics analysis

Based on the shock tube experiments, the influence of NO2 on the ignition characteristics of methanol fuel was systematically studied. The ignition delay time of the CH3OH/NO2/O2/Ar mixture with equivalence ratios of 0.5, 1, and 1.5 was measured at the reflected shock temperatures of 1100 ~ 1650 K and the reflected shock pressure of 0.20 MPa. The methanol–NO2 mechanism was newly constructed based on previously developed mechanisms for methanol and NO2 reaction pathways. The new combined reduced mechanism could well predict the ignition delay time of the CH3OH/NO2/O2/Ar mixture. Based on the newly constructed methanol–NO2 mechanism, the reaction path, sensitivity, and important elementary reactions of the stoichiometric mixture were analyzed, and the reasons why NO2 promoted the ignition of methanol fuel were found out: the increase of OH radicals generation and rapid accumulation in the early ignition stage enhanced the activity of the reaction system, interfered the ignition process of CH3OH/NO2/O2/Ar mixture in advance, and promoted the ignition of methanol fuel.