Ignition Of Fuels Research Articles

Construction of a Chemical Kinetic Model of Five-Component Gasoline Surrogates under Lean Conditions.

The requirements for improving the efficiency of internal combustion engines and reducing emissions have promoted the development of new combustion technologies under extreme operating conditions (e.g., lean combustion), and the ignition and combustion characteristics of fuels are increasingly becoming important. A chemical kinetic reduced mechanism consisting of 115 species and 414 elementary reactions is developed for the prediction of ignition and combustion behaviors of gasoline surrogate fuels composed of five components, namely, isooctane, n-heptane, toluene, diisobutylene, and cyclohexane (CHX). The CHX sub-mechanism is obtained by simplifying the JetSurF2.0 mechanism using direct relationship graph error propagating, rate of production analysis, and temperature sensitivity analysis and CHX is mainly consumed through ring-opening reactions, continuous dehydrogenation, and oxygenation reactions. In addition, kinetic parameter corrections were made for key reactions R14 and R391 based on the accuracy of the ignition delay time and laminar flame velocity predictions. Under a wide range of conditions, the mechanism’s ignition delay time, laminar flame speed, and the experimental and calculated results of multi-component gasoline surrogate fuel and real gasoline are compared. The proposed mechanism can accurately reproduce the combustion and oxidation of each component of the gasoline-surrogate fuel mixture and real gasoline.

Forest Fuel Drying, Pyrolysis and Ignition Processes during Forest Fire: A Review

Forest ecosystems perform several functions that are necessary for maintaining the integrity of the planet’s ecosystem. Forest fires are thus a significant danger to all living things. Forest fire fighting is a foreground task for modern society. Forest fire prediction is one of the most effective ways to solve this urgent issue. Modern prediction systems need to be developed in order to increase the quality of prediction; therefore, it is necessary to generalize knowledge about the processes occurring during a fire. This article discusses the key features of the processes prior to forest fuel ignition (drying and pyrolysis) and the ignition itself, as well as approaches to their experimental and mathematical modeling.

Phases and Time-Scales of Ignition and Burning of Live Fuels

Wildland fires impact ecosystems and communities worldwide. Many wildfires burn in living or a mixture of living and senescent vegetation. Therefore, it is necessary to understand the burning behavior of living fuels, in contrast to just dead or dried fuels, to more effectively support fire management decisions. In this study, the ignition and burning behaviors of needles placed in convective heat flux were evaluated. The species included longleaf pine (Pinus palustris), Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja plicata), ponderosa pine (Pinus ponderosa), western larch (Larix occidentalis), pacific yew (Taxus brevifolia), white spruce (Picea glauca), and sagebrush (Artemisia tridentate). The ignition and burning behaviors were related to live fuel moisture content (LFMC), pilot flame temperatures, and convective heat fluxes. The different phases of ignition and burning were captured using high-speed imaging. In general, four burning phases can be observed: droplet ejection and burning, a transition phase, flaming combustion, and smoldering combustion. Ejection and subsequent burning of droplets can occur prior to sustained flaming ignition only in live fuels. For some species (e.g., longleaf pine, ponderosa pine, white spruce) droplet ejection and burning can reduce ignition times relative to dried fuel with lower LFMC. In general, the transition phase tends to take longer than the flaming and droplet phases (when these occur). During the transition phase, the fuels are heated and pyrolysis occurs. Time-scales to ignition and the different phases of ignition and burning vary more among live fuels than dead and dried fuels. This conclusion indicates that other parameters, such as chemical composition and structural morphology of the fuel, can significantly influence the burning of live fuels.

Experimental study on the ignition characteristics of leaking RP-3 aviation kerosene on a horizontal hot wall

The accidental ignition of liquid fuels is an industrial safety concern due to the storage and transport of pressurized flammable liquids near components at elevated temperatures. In this work, the ignition process of leaked RP-3 aviation kerosene on the surface of the high temperature heat meter was studied experimentally and the critical temperature of the 50% ignition probability was obtained by the statistical method. The ignition process of fuel on horizontal hot wall was analysed by using the ignition video shot by high-speed camera, and the fuel steam plume model of the minimum hot surface ignition temperature for spilled fuel was established, which provided a theoretical basis for quantitative research on the ignition characteristics of leaking fuel on the hot surface. It shows that the temperature field and spatial concentration distribution produced by oil evaporation are time-varying and helpful for engine room fire protection. This study complements the related content of the fuel ignition mechanism on hot wall, at the same time, and provides fundamental understanding of the physical phenomena involved in the thermal ignition of impinging sprays in different regimes toward the goal of improved industrial safety.

Model Predictive Control of Combustion Phasing in Compression Ignition Engines by Coordinating Fuel Injection Timing and Ignition Assist

Internal combustion engines may use ignition assisting heating elements such as glow plugs to facilitate combustion control in automotive or aircraft powertrains that operate with synthetic fuels of varying ignition behavior or at extreme inlet conditions. This work presents a model predictive controller (MPC) that regulates combustion phasing in compression ignition engines on a cycle-to-cycle basis by coordinating fuel start of injection (SOI) with power supplied to a glow plug acting as an ignition assist (IA) device, while enforcing IA actuator range and rate constraints. Simulations were conducted using a nonlinear virtual engine informed by data from a commercial engine operating at a condition that induced high combustion variability. A rate-based MPC formulation leveraging state estimate feedback and integral setpoint tracking was developed. Simulation results show the MPC scheme ensures steady-state tracking of combustion phasing within 70 engine cycles, conserves IA usage whenever possible to reduce thermo-mechanical stress on the actuator, and maintains closed-loop combustion variability at only 4% higher than the open-loop system variability. Furthermore, the controller maintains reference tracking even if combustion sensitivity to the actuators deviates by more than 20% from the controller's internal model, without the need for retuning control parameters.

Effects of the stability of 2-methyl furan and 2, 5 dimethyl furan on the autoignition and combustion characteristics of a gasoline-like fuel

Renewable liquid fuels have potential to greatly reduce the carbon footprint of the transportation sector while leveraging existing powertrain technologies and infrastructure. Prior studies identified a mixture of 2-methyl furan and 2, 5 dimethyl furan as one of the most promising components for formulating renewable gasoline fuel blends. Within the Co-Optima initiative, this furan mixture was used in the formulation of a custom renewable gasoline-like fuel, termed CB#2, that contains 40% of the furans in volume. Although CB#2 has demonstrated better performance than regular E10 gasoline for advanced compression ignition and boosted spark ignition engines, several concerns arose regarding stability of furans. Stability can be improved by adding antioxidant additives, but the effect of furans’ stability and the antioxidants on the ignition and combustion characteristics of gasoline fuels is unknown.In the present work, the effects of the stability of 2-methyl furan and 2, 5 dimethyl furan and the addition of butylhydroxytoluene on the autoignition and combustion characteristics of CB#2 were studied. Experimental measurements were performed using unstabilized CB#2 and CB#2 stabilized using butylhydroxytoluene (added in a concentration of 250 ppm to the furan species). From the test result, both fuel batches showed the same octane rating. Moreover, homogeneous charge compression ignition engine experiments at naturally aspirated and lean conditions showed that the two batches have the same autoignition reactivity and combustion characteristics. Therefore, fuel performance was not affected by the stability of the furans and the addition of butylhydroxytoluene at the concentration explored in this paper.

A simplified analytical model for radiation dominated ignition of solid fuels exposed to multiple non-steady heat fluxes

Heat fluxes from fires are strongly time-dependent. Historically, the thermal ignition theory in its classical form has neglected this time dependency until recent years, where theories have been developed to include time-varying incident heat fluxes. This article proposes a simplified general model formulation for the heating of solid fuels exposed to four different heat flux behaviors, considering the penetration of radiation into the medium. The incident heat flux cases developed where: Constant, Linear, Exponential and Polynomial, which represent different situations related to structural and wildland fires. The analytical models consider a spatially averaged medium temperature and exact and approximate solutions are presented, based on the critical ignition temperature criterion, which are valid for solids of any optical thickness. The results were validated by comparison with various models presented in the literature, where the model granted in this work was capable to adjust to all of them, especially when high heat fluxes are involved. Therefore, the proposed model acquires a significant engineering utility since it provides a single model to be used as a general and versatile tool to predict the ignition delay time in a manageable way for solid fuels exposed to different fire conditions.

Research on the Control Mode of Homogeneous Charge Compression Ignition Combustion Working Process and Its Technical Prospect

The homogeneous charge compression ignition (HCCI) engine is considered an advanced technique, a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. HCCI engines have higher thermal efficiency and lower emissions than Spark Ignition (SI) and Compression Ignition (CI) engines. The emissions of NOx can be neglected compared to the CI engine. In addition, a wide variety of fuels, combinations of fuels and alternative fuels can be used in this type of internal combustion engine. Moreover, when investigating the heat release rate of a HCCI engine for both single- and two-stage ignition fuels, the results show that for both fuel types, the cycle changes in the ignition and combustion phases increase with the delay of the combustion phase. Also, the cycle change of iso-octane (the single-stage ignition fuel) is higher than that of PRF80 (the two-stage ignition fuel). This paper will first introduce the control mode of the HCCI engine and then review its current status from the perspective of combustion, emissions, and consumption. After presenting the current status, the authors present suggestions about the prospect of further development with respect to the timing of ignition, the expansion of the engine operating range, and the choice of fuel mixture in this new mode of technology.

Critical Conditions for the Ignition of a Gel Fuel under Different Heating Schemes

A model was developed to research the critical conditions and time characteristics of the ignition of gel fuels in the course of conductive, convective, radiant and mixed heat transfer. MATLAB was used for numerical modeling. Original MATLAB code was established pursuant to the developed mathematical model. For gel fuel ignition at initial temperatures corresponding to cryogenic storage conditions with different heating schemes, a numerical analysis of interconnected processes of heat and mass transfer in the chemical reaction conditions and exothermic and endothermic phase transitions was conducted. The model was tested by comparing the theoretical results with the experimental data. Dependencies were established between the key process characteristic (i.e., the ignition delay time) and the ambient temperature when the following parameters were varied: emissivity, heat emission coefficient, activation energy and pre-exponential factor of the fuel vapor oxidation reaction. The critical values of the main parameters of the energy source were determined. For these values, gel fuel ignition conditions were consistently realized for each heating scheme. The critical heat fluxes necessary and sufficient for the ignition of typical gel fuels were determined.

An optical investigation of dual fuel and RCCI pilot ignition in a medium speed engine

Driven by the Paris agreement and tightening IMO regulations, the marine sector is focusing on lowering engine emissions and moving to low-carbon fossil or renewable fuel such as methane. The dual-fuel concept allows the usage of methane as main energy-source in diesel engines. A small pilot diesel injection acts as an ignition source for the premixed methane. It was investigated how NOx formation, mainly taking place during combustion of the pilot fuel, could be minimized.To better understand the process of ignition of a pilot injection in dual-fuel engines, optical research has been performed on a medium speed dual fuel marine engine. A unique Bowditch 200 mm single cylinder setup enabled high speed recordings of natural luminescence. Both Reactivity Controlled Compression Ignition (RCCI) and Conventional Dual Fuel (CDF) combustion was investigated. The RCCI combustion was created by an early pilot injection, allowing a long mixing time. The CDF cases had a late injection timing.In RCCI operation the higher degree of premixing was recognized by combustion luminescence starting further away from the injector, at a varying location. The diluted pilot combustion generated a limited brightness. The heat release profile was Gaussian/bell-shaped, without the typical diesel premixed peak. In CDF operation the recorded images show that combustion follows the shape of the diesel injector jet. The heat release profile was showing a strong initial peak, resembling the premixed peak known from conventional diesel combustion. This heat release peak in CDF combustion, correlated to NOx emissions, is absent in RCCI mode.

Differences of Fuel and Capacitor Discharge Ignition in Energy Output of Motorcycle

The combustion engine is one of the internal combustion engines or often referred to as an internal combustion engine, namely a machine that converts energy thermal energy into mechanical energy. The energy itself can be obtained from the combustion process. One of the simple motorized vehicle transportation tools that are widely used by society today is the motorcycle. The ability of a motorcycle is influenced by several factors, including the quality of the fuel and the ignition system. The use of poor quality fuel can result in a decrease in motorcycle engine performance. Therefore, the selection of the right fuel refers to the compression ratio of each motorcycle. The higher the compression ratio of a motorcycle, the better the quality of fuel it must use.

Influence of Forest Combustible Material on the Characteristics and Conditions of Ignition of Bio-coal Water Fuels

ABSTRACT The results of the experimental studies of the particles ignition of bio-coal water fuels have been presented. The experiments have been carried out on the setup providing an error level of not more than 6.1% of the main recorded characteristics. The effect of the temperature of the oxidizing agent and the characteristic size of the fuel drops on the duration of the induction period of the fuel compositions has been studied. It has been established that the introduction of the additives from forest combustible materials of three typical tree species leads to an acceleration of the ignition process of substantially flooded particles of bio-coal water fuels. According to the results of a detailed analysis of the frames of the videogram, it has been shown that the duration of the intensive chemical reaction of the gaseous pyrolysis products with a high-temperature oxidizer is not more than 0.02% of the entire induction period. Colloquium. One of the possible promising directions for the development of the coal technologies in the energy sector and for reducing the negative anthropogenic impact of the thermal power plants that burn coal is the use of the composite fuels (coal- water (CWF), organ coal- water, etc.) based on coal. But a number of the technological problems significantly complicate the use of such fuels in the energy sector. This is evidenced by a significant increase (over the past 10 years) in the number of the publications devoted to the problems of carbonic fuels. The ignition process of CWF is quite long (ignition delay time (tign) up to 20 seconds). The use of fuel with such a large induction period in a real practice is practically impossible. One of the possible options for reducing the tign value of the liquid composite fuels is the introduction of biomass into their composition. This is a new composite bio-coal water fuel (Bio-CWF). At present, there are practically no publications devoted to the experimental and theoretical studies of the ignition of Bio -CWF particles under conditions corresponding to the furnaces of the typical boiler units of the thermal power plants. The duration of the characteristic stages of ignition of Bio-CWF particles (made on the basis of coal, water and various types of biomass) is an important characteristic necessary for carrying out the experimental design works on the development of new innovative boiler units burning bio-coal water fuel.

Catching Fire: Are Operating Room Fires a Concern in Orthopedics?

Operating room (OR) fires are considered "never events," but approximately 650 events occur annually in the United States. Our aim was to detail fires occurring during orthopedic procedures via a questionnaire because of the limited information present on this topic. A 25-question survey on witnessing surgical fires, hospital policies on surgical fires, and surgeons' perspective on OR fires was sent to 617 orthopedic surgeons in 18 institutions whose residency program is a member of the Collaborative Orthopaedic Educational Research Group. The response rate was 28%, with 172 surgeons having completed the survey. Twelve of the 172 orthopedic surgeons surveyed reported witnessing at least 1 surgical fire in an OR setting. Electrocautery was the leading ignition source, causing fires in 7 events. A saw, laser, and light source were reported to have caused 1 fire each. Regarding fuel source for the fires, bone cement was a common culprit (n = 4), followed by gauze (n = 3). Oxygen delivery to patients was via a closed system in most cases (n = 9). No patient harm was reported in any of these cases.Just under half of the respondents (47.7%) reported not receiving any formal OR fire prevention or response training. The most common answer for frequency of concern about a surgical fire was "never" (42.4%). Fires pose a risk in surgery, even in an orthopedics setting. Room oxygen can supply enough oxidizing power for a fire to occur, especially with the ubiquitous nature of ignition sources and fuels in the OR. Prevention is key with these events. Operating room personnel education must be sought, and surgeons should be mindful of the fire components in the OR.

An experimental investigation into the fuel oil-free start-up of a coal-fired boiler by the main solid fossil fuel with additives of brown coal, biomass and charcoal for ignition enhancement

The research is focused on the ignition of solid fuels in a heated air flow. The experimental conditions correspond closely to solid fuel combustion in coal-fired boiler furnaces. Charcoal, wood, brown and bituminous coals were used as independent solid fuels and as fuel mixture components. The particle sizes of these fuels were less than 40 μm, 40–140 μm, 140–250 μm, 250–375 μm and 375–800 μm. They were ignited under the conditions of radiant-convective heating as they were moving in a heated air flow with a temperature of 500–800 °C and at a velocity of 5 m/s. The ignition delay time was the main investigated characteristic, recorded by a high-speed video camera. The induction period of bituminous coal shortens by 25–35% when 25–50% brown coal or wood in an air-dry state is added. The lowest ignition delay times were established for the fuel mixtures of bituminous coal with dry charcoal. The experimental curves of the ignition delay times of fuels and their mixtures versus the heated air temperature were presented as approximation equations. Based on the conducted research findings, a muffle burner design with a vortex structure of the fuel-air flow was proposed for the fuel oil-free start-up of coal-fired boilers.

Catalyzed combustion of a nanofluid fuel droplet containing polydopamine-coated metastable intermixed composite n-Al/CuO

The ignition and combustion characteristics of kerosene fuels containing polydopamine (PDA)-coated metastable intermixed composite (MIC) nano-aluminum (n-Al)/nano-copper oxide (CuO) are experimentally investigated, with a focus on the mass content of CuO in n-Al@PDA@CuO MICs. The total heat release of n-Al@PDA@CuO (2%) is found to be higher than that of the other n-Al@PDA@CuO samples. During the combustion of n-Al@PDA@CuO (2% and 5%)/kerosene droplets, a yellow flame appears around the agglomerate, which eventually evolves into a yellow light sphere with a diameter of around 5 mm after the kerosene flame extinguishes. Examination of the normalized droplet diameter curves and the morphology of combustion residues shows that the n-Al@PDA@CuO (2%)/kerosene droplet has the best all-around combustion characteristics. A mechanism is proposed for the enhancement of kerosene combustion by n-Al@PDA@CuO. Supporting data from thermogravimetry and differential scanning calorimetry (TG-DSC) measurements are presented. The findings and data in this study are expected to advance the development of new kerosene-based nanofluid fuels that meet the high energy demands of liquid propulsion systems.

Promoted stable combustion of alcohol-based fuel accompanied by inhibition of Leidenfrost effect in a wide temperature range

Combustion of bio-alcohols helps alleviate energy crisis and environmental pollution. However, the Leidenfrost effect (LE) of alcohols triggered by the adiabatic vapor layer greatly reduces the heat transfer efficiency, which makes alcohols exhibit a long ignition delay time (IDT) at low temperatures, hindering energy efficiency and clean combustion. Here, we first develop a scalable strategy to inhibit LE via self-propagating oxidation heat release and concomitant in-situ active radical generation. Reliable ignition and stable combustion of alcohol-based fuels are achieved in a wide temperature range by using a reactive organometallic compound methoxydiethylborane (MDEB). The theoretically released heat of MDEB self-oxidation is two orders of magnitude greater than the evaporation latent heat of ethanol or n-decane by thermodynamic calculation. Experiments show that the flammable temperature limits of MDEB/ethanol and MDEB/ethanol/n-decane are extended to 225 and 125 °C, which dropped by 370 and 465 °C, respectively. Moreover, the IDT of MDEB/ethanol/n-decane hybrid fuel significantly decreases to 27 ms. The 100% ignition achievement and disappearance of negative temperature behavior highlight the reliable start-up in the Liedenfrost region. This work thus provides a promising tool for promoting the ignition reliability and combustion stability of alcohols for ICEs at low temperatures, as well as pollutant control.

Thermodynamic and Chemical Analysis of Water-Coal Fuel Ignition and Combustion in Adiabatic Combustion Chamber

The article presents results of improvement of physicochemical model of coal-water fuel ignition and combustion processes, taking into account ash content and release of volatile substances of solid phase. In this case, model of ignition and combustion of two systems of atomized coal-water fuel: drops and pure coal particles is taken as a basis. As a result of the analysis, the influence of ash content of coal-water fuel on output of combustible gases and content of water vapor in furnace atmosphere was established. Based on comparison of the diffusion coefficients of gases and the calculated values of equilibrium constants of reaction in combustion zone, conclusion has been of the leading role of water vapor oxidation of carbon in vortex adiabatic furnace. Performed numerical calculations have shown that combustion process of the above inhomogeneous systems (droplets and particles) in an adiabatic furnace within a short time becomes identical. Concentrations of volatile substances, oxygen (O2) and carbon dioxide (CO2) in various sections of the furnace have been established

Rapid prediction of fuel research octane number and octane sensitivity using the AFIDA constant-volume combustion chamber

Current research octane number (RON) and motor octane number (MON) gasoline performance characterization techniques use dated, complex engine testing methodology and limit researchers’ ability to easily characterize small volumes of experimental fuels. A novel methodology is presented that correlates measured ignition delay (ID) time to RON in an Advanced Fuel Ignition Delay Analyzer (AFIDA) constant-volume combustion chamber device at a single pressure/temperature condition, with an r2 of 0.99 and standard error (SE) of 1.0. The correlation of the slope of the ID time between two additional temperature points to octane sensitivity (S) produces an r2 of 0.97 and SE of 0.69; however, fuels with S > 12 are indistinguishable. These results are based on methodology calibration using 31 primary and toluene reference fuels containing 0%─40% ethanol with RON values ranging from 85 to 113. Validation of these methods using a 102-sample fuel matrix spanning an array of base fuels and additive chemistry designed to test the robust applicability of the method, along with pump gasoline and high-octane surrogate blend samples, demonstrates an r2 of 0.94 and SE of 1.3 for the RON correlation over all samples, whereas the equivalent S correlation produces an r2 of 0.78 and SE of 1.2 by excluding two additives, 3-pentanone and diisobutylene, which displayed poor S correlation results. This novel AFIDA analysis method can be performed in 1 h and with 40 mL of fuel, offering significant improvements in time and volume requirements over traditional techniques.

Experimental research into the ignition and combustion characteristics of slurry fuels based on dry and wet coal processing waste

The paper presents the results of comparing the integral characteristics of ignition and combustion of coal and composite fuels, prepared from coal processing waste in a dry and wet state, in a model combustion chamber. We calculated the relative fuel performance coefficients, taking into account the established ignition delay times, fuel burnout duration, concentrations of gaseous anthropogenic emissions, as well as temperature changes (reduction at the initial stage and growth during rapid combustion) in the model combustion chamber. It was shown that the ignition delay times of coal processing waste in a dry state are 30–70% lower than in the initial wet state. However, burning wet coal processing waste provides the lowest concentrations of NOx and SO2 (5–44% lower than in a dry state and 35–70% lower than they are for coal). Considering the main environmental, economic and energy performance indicators, optimal conditions were established for the combustion of abundant coal processing waste as part of water-containing slurry fuels. It was established that the relative performance coefficient of slurry fuels ranges from 2.05 to 58.87 when varying the moisture content and component composition. This coefficient is maximum for wet filter cake without oil. This allowed us to conclude that wet coal processing waste is highly promising.

Rapid ignition of “green” bipropellants enlisting hypergolic copper (II) promoter-in-fuel

Ionic liquid-with-promoter fuels and H2O2 oxidizer require optimization and further exploration of inexpensive initiators that can be understood at the molecular level; it is advantageous when exacting structural characterization comparisons can also be made. For the first time, hypergolic energetic copper(II) complexes viz. [CuII(1-H-imidazole)4(BH3CN)][BH3CN] (Cu-P1) and [CuII(1-methyl imidazole)4(BH3CN)2] (Cu-P2) were developed as new ‘promoters’ for “green” space vehicle propulsion. Cu-P1 and Cu-P2 exhibited ignition delay times (IDTs) of 3.75 and 8.5 ms, respectively, with 95% H2O2. The superior solubility of Cu-P1 in ionic and non-ionic fuels helped to promote the hypergolic ignition of green liquid fuels. The ionic liquid, 1-ethyl-3-methyl imidazolium cyanoborohydride ([EMIM][BH3CN]), non-ionic tetraglyme, and mixtures thereof (1:1, wt/wt%) were employed. A 13 wt% of Cu-P1 in [EMIM][BH3CN] improved the IDT from >1000 ms to 9.50 ms with 95% H2O2 and from >5000 ms to 21.25 ms with 70% H2O2. Hence, the development of a suitable energetic promoter, soluble in ionic liquid, gained significant attention for “green” bipropellant development. Interestingly, tetraglyme is non-hypergolic with H2O2; a 13 wt% Cu-P1 induced the hypergolic ignition with an IDT of 9.0 ms (95% H2O2). Moreover, the fuel mixture of [EMIM][BH3CN] and tetraglyme (1:1, wt/wt%) with 13 wt% Cu-P1 also revealed the shortest IDT of 7.75 ms (95% H2O2) and 16.5 ms (70% H2O2). The superior ignition performance, reasonable viscosity and density, long-term stability of promoter in the fuel, and comparable theoretical performance of hypergolic propellants are advantages of our approach.