Heat Release Process Research Articles

Experimental study on the influence of water immersion on spontaneous combustion of anthracite with high concentrations of sulfur-bearing minerals

The influence of water immersion on the spontaneous combustion characteristics of anthracite with high concentrations of sulfur-bearing minerals was studied using simultaneous thermogravimetry–mass spectrometry (TG-MS), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. In addition, variations in the structural parameters, mass, heat release and gas evolution processes before and after water immersion were investigated. The results showed that the coal sample contained a large amount of pyrite (FeS2). After 45 days of immersion, the pyrite content in the coal decreased, and the infrared absorption peak of Si (Al)–O at 1116 cm−1 disappeared. The TG curves did not show a mass increase. Moreover, the initial reaction temperature of immersed coal was 39 °C lower than that of raw coal, and the heat release increased by 127.3 J g−1. The gas products in the samples varied mainly in quantity but not in species. MS and FTIR analyses revealed that SO2 was the main gas produced, and the maximum SO2 gas evolution temperatures of both coal samples were similar to the peak temperatures in the differential thermogravimetry and differential scanning calorimetry (DSC) curves. Furthermore, the infrared 3D spectrogram revealed that gas generated by immersed coal was detected at a lower temperature, the peak temperature occurred earlier, and the evolved intensity was stronger.

The correlation of species concentration with heat release rate in an auto-igniting turbulent n-heptane spray flame

The quantification of the heat release process is important for engine combustion, for which species concentrations are often employed as the heat release rate indicators (HRRIs) considering the difficulty in the direct measurement of the local heat release rate (HRR). In this study, the correlation between HRR and species concentrations in auto-ignition and auto-ignition assisted flame propagation of n-heptane/air mixtures is first quantified to validate the commonly used formaldehyde-based HRRIs (i.e. [HCO] and [OH][CH2O]). Potential candidates for HRRIs are then proposed and further investigated in the auto-igniting n-heptane spray flame obtained with direct numerical simulations using a 44-species mechanism. It is found that [HCO] and [OH][CH2O], as well as the potential candidates [C2H3], [CH2], [OH][HO2] and [H][HO2], in general all have good linear correlations with the HRR in the spray flame, and [H][HO2] has the best performance. Chemical explosive mode analysis is then performed to further analyze the performance of the HRRIs in the three combustion regimes: post-flame, auto-ignition and flame propagation. It is shown that the primary combustion mode in this spray flame is auto-ignition. Regime-dependent correlation has been observed and the above HRRIs yield the best linear correlation for the region with the Damköhler number being far more than unity in this turbulent auto-igniting n-heptane flame.

Knock combustion investigation on a two-stroke spark ignition UAV engine burning RP-3 kerosene fuel

Purpose The purpose of this paper is to investigate the knock combustion characteristics, including the combustion pressure, heat release rate (HRR) and knock intensity of aviation kerosene fuel, that is, Rocket Propellant 3 (RP-3), on a port-injected two-stoke spark ignition (SI) engine. Design/methodology/approach Experimental investigation using a bench test and the statistical analysis of data to reflect the knock combustion characteristics of the two-stroke SI unmanned aerial vehicle (UAV) engine on RP-3 kerosene fuel. Findings Under the full load condition of 4,000 rpm, at the ignition timing of 25 degree of crank angle (°CA) before top dead centre (BTDC), the knock combustion is sensitive to the thinner mixture; therefore, the knock begins to occur when the excess air ratio is larger than 1.0. When the excess air ratio is set as 1.2, the knock obviously appears with the highest knock intensity. At the excess air ratio of 1.2, better engine performance is obtained at the ignition timing range of 20-30 °CA BTDC. However, the ignition timing at 30° CA BTDC significantly increases the peak combustion pressure and knock intensity with the advancing heat release process. Practical implications Gasoline has a low flash point, a high-saturated vapour pressure and relatively high volatility, and it is a potential hazard near a naked flame at room temperature, which can create significant security risks for its storage, transport and use. The authors adopt a low-volatility single RP-3 kerosene fuel for all vehicles and equipment to minimise the number of different devices using various fuels and improve the military application safety. Originality/value Most two-stroke SI UAV engines for military applications burn gasoline. A kerosene-based fuel for stable engine operation can be achieved because the knock combustion can be effectively suppressed through the combined adjustment of the fuel amount and spark timing.

Thermal Characteristics of Embedded PCMs in the Pore of Activates Carbon

Objectives The use of phase change materials (PCMs) with the ability to absorb and release heat as an energy medium has been extensively studied where encapsulated material was used. Though these heat storage systems seem efficient but practical application suffers due to their high manufacturing cost, complexity in the manufacturing process, and eco-unfriendly nature. In this study, we developed an affordable, simpler and more efficient heat storage media by using activated carbon as a filling medium for PCM. The purpose of this study is to develop a method for caging a PCM by using the adsorption phenomenon where the PCM is adsorbed by the capillary phenomenon in the pores of activated carbon. The heat absorption and releasing characteristics of PCM embedded-activated carbon composite was investigated to comment on the applicability of the composite. Methods The PCM used in this experiment were caprylic acid (CH3(CH2)8COOH), Mn(NO3)2･4H2O, Mn(NO3)2･6H2O, Zn(NO3)2･6H2O, and n-hexadecane. The PCM embedded-activated carbon composites were prepared and studied by adopting a standard protocol. After adding and mixing the degassed activated carbon in a beaker containing a PCM, it was maintained in a high-pressure reactor of 10 atm to push the PCM into the pores of the activated carbon. The heat absorption/release capacity of the PCM embedded-activated carbon was examined within the range of 10℃ to 50℃. Results and Discussion The organic acid and the hydrated salt decreased the volume by decreasing the average distance between molecules as the temperature decreased. The heat absorption and release temperature of caprylic acid and n-Hexadecane was ~17℃ and ~15℃, respectively. Also, for Mn(NO3)2･4H2O and Zn(NO3)2･6H2O, the absorption and release of heat, i.e., latent heat was ~35℃ and ~25℃, respectively. In particular, the process of absorbing heat proceeds slowly while the process of heat release proceeds very rapidly. Moreover, Mn(NO3)2･4H2O and Zn(NO3)2･6H2O showed two inflection points in the heat release process. It was probably due to the supercooling phenomenon where the liquid and solid phase coexisted during the phase transition. From the evaluation of the mixed PCM, the inflection point of heat absorption and emission was given for the mixture of Mn(NO3)2･4H2O/Mn(NO3)2･6H2O and Mn(NO3)2･4H2O/Zn(NO3)2･6H2O. Similar trends were observed in repeated experiments. On the other hand, when Mn(NO3)S･6H2O and Zn(NO3)2･6H2O with higher water molecules content were mixed, reproducibility decreased in the subsequent heat absorption and release cycles. The heat absorption and emission characteristics of caprylic acid, Mn(NO3)2･6H2O and Zn(NO3)2･6H2O embedded activated carbon was found reproducible in multiple melting and freezing cycles and the overcooling phenomenon was overcome. The heat absorption and release characteristics of laminated PCM embedded activated carbon showed that the absorption of heat proceeded gradually from the bottom to the top, and the absorption of heat was significantly high at the top. On the contrary, heat dissipation was observed to proceed more at the bottom than at the top. The homogeneous mixing of various PCM embedded activated carbon composites resulted in a uniform distribution over a wide range of temperatures. Dozens of repeated experiments showed a similar pattern, which ensured that the activated carbon can be used as a stable thermal charging medium even with a PCM. Conclusions 1) Caprylic acid and n-hexadecane did not have the supercooling phenomena, but the hydrate-containing inorganic phase change material showed the supercooling phenomenon where both the liquid and solid phases coexisted. 2) The supercooling phenomena occurred during the cooling process that released the heat, especially when the hydrated water content was higher. On the other hand, when the phase change material is filled into the activated carbon pores, the supercooling phenomenon disappeared in the cooling process. It was considered that the external stimulus was formed because the phase change material expanded and contracted in a narrow space in the pore. 3) Mixing of hydrate-containing inorganic phase change materials which have different melting point resulted in the absorption and release of heat at the intrinsic melting point of raw material, even when filled in activated carbon pores. It was found that when the phase change materials having different melting points were used after being embedded in the activated carbon pores and mixed, they could be used as heat absorbers and release agents in a wider range of temperatures. Key words: Phase Change Material, Pore Embedded Technique, Heat Absorption and Release, Nanopore of Activated Carbon

The numerical simulation and experimental study of heat release in a heat storage system with various diameters of aluminum tubes

Phase change materials (PCMs) can be used to store solar energy. The heat released from PCMs is directly influenced by the efficiency of thermal energy storage and the scope of application. In this study, paraffin was used as the PCM, and was encapsulated in an aluminum tube. The temperature of the inner PCM was measured, and the heat release process of the PCM was simulated. The results indicate that the melt temperature of the PCM ranged from 45 °C to 60 °C, and the latent heat was 177 J/g. The heat release processes of the PCM in different aluminum tubes included three stages: 1) the stage during which no phase change occurred at temperatures above the melt temperature and at a rapidly decreasing temperature; 2) the stage during which phase change occurred at very slowly decreasing temperatures; 3) the stage during which no phase change occurred at temperatures lower than the melt temperature. The temperature of the PCM decreased when the radius of the aluminum tube increased. The temperature results obtained via simulation were similar to the actual temperature data. The total energy released from the PCM increased linearly with the time required to complete the energy release process of the PCM in aluminum tubes with different diameters, as well as with the increase in the aluminum tube diameter. The diameter of the PCM exerted no significant influence on the energy release rate. The relationship between the tube diameter and the time required to complete heat release, and the relationship between the amount of heat released, the diameter of the aluminum tube, and the release time, were established. These equations could predict actual values and provide theoretical guidance for heat release in heat storage systems. They could also be used as a guide in practical production.

Mixing and heat release characteristics in the combustor of solid-fuel rocket scramjet based on DES

Based on the previous experimental results, in order to improve the understanding of the mixing and heat release process of the internal flow field in the solid-fuel scramjet combustor, and to provide theoretical reference for the layout of the combustor configuration in the next step, the numerical simulation method of DES combined with the gas mixing degree, mixing layer thickness and mixing fraction was used to analyze quantitatively the microscopic structures and the mixing combustion enhancement mechanism in the combustor at different lobe sweep angles based on the influence of the change of lobe sweep angle on engine performance, and then the influence law was explained from the microscopic point of view. Results demonstrate that 1) based on the engine configuration in this paper, in the design process of staggered support plate structure, the lobe sweep angle should be based on the width and the straight section length of the support plate. And the engine performance improves with the decrease of the lobe sweep angle. 2) The growth of the reaction mixture layer is in four typical stages: the initial growth zone, the rapid growth zone, the saturated growth zone and the full development zone. 3) The downstream part of combustor is in the full development zone of the reaction mixing layer. The full development zone as the main area determining the heat release performance of the engine, the mixing degree increases with the decrease of the lobe sweep angle in the behind part of the combustor. Therefore, the pressure in the downstream flow passage of the combustor and the space of combustor occupied by the high pressure area increase with the decrease of the lobe sweep angle.

Numerical research on effect of hydrogen blending fractions on idling performance of an n-butanol ignition engine with hydrogen direct injection

In this paper, a numerical research on an n-butanol ignition engine with hydrogen direct injection was carried out, aiming to observe the effect of hydrogen blending fractions on idling performance. A three-dimensional dynamic mesh model coupled with a detailed chemical kinetic mechanism of n-butanol oxidation were established to investigate the engine combustion process in CFD software CONVERGE. And the numerical model was validated through experiments. The performance of pressure and temperature inside cylinder, HC and CO emissions and formaldehyde and acetaldehyde emissions with four hydrogen fractions were simulated and analyzed. The simulation results showed that in comparison with pure n-butanol, the peak cylinder pressure increased 18.62%, 22.86% and 25.41% at φH2 = 5%, φH2 = 10% and φH2 = 15%, respectively. Meanwhile, the process of heat release can be accelerated and concentrated by hydrogen blending. The HC and CO emissions decreased gradually with the increase of hydrogen fraction. The largest magnitude of reduced HC and CO emissions was at φH2 = 5% as 31.31% and 19.05%, respectively. In terms of unregulated emissions, the acetaldehyde emissions remained a higher level than formaldehyde emissions for all hydrogen fractions at idle condition, and both decreased with the increase of hydrogen fraction. The distribution of formaldehyde and acetaldehyde concentration were closely related to the temperature field inside cylinder. The improvement of acetaldehyde emissions affected by adding hydrogen was more significant than that of formaldehyde emissions. Through hydrogen direct injection, a local hydrogen-enriched area near the spark plug can be formed, which contributed to better combustion performance of n-butanol engine at idle condition.

Thermodynamics of hydrothermal carbonization: Assessment of the heat release profile and process enthalpy change

A reliable and reproducible procedure for the determination of the heat release rate profile and for the enthalpy change of the hydrothermal carbonization (HTC) process is applied using High Pressure Differential Scanning Calorimetry (HP-DSC). Cellulose, wood, and digestate are used as feedstocks. The temperature program is run once to let the process complete in the first run, whereas in the second the thermal effect of products is assessed. A provisional heat release profile is obtained subtracting the two curves, with a very high reproducibility (standard deviations between 1.8 and 8.0%). To consider the heat capacity difference between reactants and products, a baseline is computed and subtracted from the heat release profile. The integral of this curve gives the enthalpy change associated to HTC, which was −0.88, −0.64, and −0.25 MJ/kg for cellulose, wood and digestate respectively. This methodology can be adopted for the development of accurate thermal-based HTC kinetics.

Investigation of heat release in metals under uniaxial stress state as a parameter of fatigue damage in metal bridges

The purpose of the issue is to study the process of heat release in metals under a symmetric loading cycle under conditions of uniaxial stress in order to assess the development of fatigue damage in the elements of metal superstructures of railroad and highway bridges. The author considered bending and axial loads of specimens with and without artificial concentrators. During the experiments, the samples were covered with matte paint, which ensured an emission coefficient of 0.95. For simultaneous fixation of thermal radiation on the upper and lower surfaces of the slots, mirrors were used. To eliminate interference from thermal radiation from surrounding objects, a fabric screen was installed between these objects and samples. As a result of experimental work, the author found that in all samples, regardless of their configuration and loading conditions, fatigue failure (the appearance of visible cracks) was preceded by a sharp increase in surface temperature at the same stress level, which the author called critical. The author during the study revealed that the magnitude of the critical stresses for the tested samples under uniaxial stress state and symmetric loading cycle does not depend on the number of concentrators, their sizes and location, but depends on the self-heating temperature and the type of deformation. Thus, the critical stress can be considered a characteristic of the material. The author also noted that at stresses greater than critical, an almost linear dependence of the temperature change on the total value of the stress increment is observed. Summarizing the noted properties of critical stresses, it can be argued that such stresses can be used to assess the development of fatigue damage when assessing the technical condition of a structure during bridge inspections. The work was performed as part of a dissertation research with the support of a grant from Russian Railways for the development of scientific and pedagogical schools.

Polyethylene glycol infused acid-etched halloysite nanotubes for melt-spun polyamide-based composite phase change fibers

The unique tubular structure and morphology of inorganic nanotubes makes them very useful supporting materials for thermal energy storage. Lending these properties in the form of composites together with traditional organic phase change materials (PCMs) can solve the existing energy storage and thermal stability problems in PCMs. Here, the acid-etching halloysite nanotubes (A-HNTs) are prepared and employed as inorganic supporting materials to encapsulate polyethylene glycol (PEG). The N2 physisorption results indicated that the specific surface area and pore volume of A-HNTs increased from 45.4m2/g, 0.243cm3/g to 253.4 m2/g and 0.621 cm3/g before and after acid etching leading to an effective PEG load increase from 50 mass% to 70 mass% of composite PCMs. This increasing encapsulation capacity of PEG had a beneficial effect on the phase change performances and the latent heat of the prepared PEG/A-HNTs composite PCMs which reached 112 J/g (as compared to 70.64 J/g of PEG/HNTs). The temperature- regulating time of heat storage and release process were >500 s and 491 s respectively. Further, the DSC thermograms with 100 thermal cycles and TGA results demonstrated that the PEG/A-HNTs composites had an excellent thermal reliability and stability for preparing phase-change fibers by high-temperature melt spinning. The thermal enthalpy, thermal regulating time and relative temperature difference of resultant PA6/PEG/A-HNTs reached 13.57 J/g, 206 s and 3.2 °C, respectively.

Characteristics optimization of composite phase-change wall during intermittent heating process

The indoor thermal environment under an intermittent heating condition can be maintained by rationally utilizing the heat storage and release processes of the composite phase-change wall (composite-PCW), leading to heating time and energy consumption reductions. In order to optimize its heat storage and release processes, the influences of different parameters on the dynamic thermal processes of composite-PCW were studied, including the position and thickness of phase-change material (PCM), phase transition temperature, phase-change latent heat, and PCM thermal conductivity, according to two typical intermittent conditions summarized by experimental data. With large heat storage efficiency η and small heat loss rate ε, the optimized composite-PCW that was adaptive for intermittent heating was the composite-PCW with 10 mm PCM integrated to the wall inside. Its phase-transition temperature was 19–20 °C (66.2–68 °F), the phase-change latent heat was 220 kJ/kg (95.58 btu/lb), and the thermal conductivity was 0.4 W/(m·K) (0.23 btu/(ft·h·°F)) at liquid states and 0.8 W/(m·K) (0.46 btu/(ft·h·°F)) at solid states.

Numerical simulation of heat release performance of filling body under condition of heat extracted by fluid flowing in buried tube

It is the basic requirement of the synergetic exploitation of deep mineral resources and geothermal resources to arrange the heat transfer tube in filling body. The heat release performance of filling body directly impacts on the exploiting efficiency of geothermal energy. Based on heat transfer theory, a three-dimensional unsteady heat transfer model of filling body is established by using FLUENT simulation software. Taking the horizontal U-shaped buried pipe as research object, the variation of temperature field in filling body around buried pipe is analyzed during the heat release process of filling body; the initial temperature of filling body, the diameter of buried pipe, the inlet temperature and inlet velocity of heat transfer fluid influencing of coupling heat transfer, which exists between heat transfer fluid and surrounding filling body within a certain axial distance of buried tube, and influencing of temperature difference between inlet and outlet of heat transfer fluid and on heat transfer performance of filling body are also discussed. It not only lays a theoretical foundation for the synergetic exploitation of mineral resources and geothermal energy in deep mines, but also provides a reference basis for the arrangement of buried pipes in filling body as well as the selection of working conditions for heat transfer fluid.

An experimental and theoretical study of the solidification process of phase change materials in a horizontal annular enclosure

The main purpose of this paper is to examine experimentally and theoretically the process of heat accumulation and heat release for PCM (phase change materials) in an annular space.The theoretical part of this work provides a solution of the problem of liquid solidification in an annular space under the influence of free convection. Here a simplified quasi-steady-state model for solidification has been applied. The new simplified model describes the solidification phenomenon with an imposed boundary condition on the solidification interface by applying a heat transfer coefficient. From the developed model, the influence of various dimensionless parameters on the phase change problem can be seen clearly.Measurements and observation of the thickness of the solidified layer were performed in a newly built apparatus. In addition, this paper is also concerned with the role of the contact layer in the solidification process. Results are showing the thickness of the solidification layer depending on time and the distribution of the local heat transfer coefficient on the surface of the solidification front. The obtained experimental and numerical results show good agreement.The examined solidification process makes it possible to use the results obtained for the design of new heat accumulators. The presented method to analyse heat accumulation is important for power engineering. It opens up the possibility to reduce the size of heat accumulators, thus, possible leading to a reduction in their production costs.

Experimental Study on Heat Storage and Release Processes of Composite Phase Change Wall under Short Intermittent Heating Conditions

During intermittent heating, the short intermittent conditions are common in meeting rooms of office buildings and school classrooms. The thermal process of building envelope has coupling effects on the indoor thermal environment in the frequent start-stop of heating equipment. This paper integrated phase change materials (PCMs) with building envelope to improve its thermal performance. Measurements were carried out to study the dynamic thermal process of composite phase change wall (composite-PCW) in case 1 (heating 1h + suspension 1h) and case 2 (hating 2h + suspension 2h). Results showed that: 1) the indoor air temperature fluctuations were around 14°C and 18°C respectively for case 1 and case 2 when the indoor thermal processes reached relatively stable. 2) The heat storage of composite-PCW could maintain the inner surface temperature relatively constant, so that the inner surface temperature fluctuations were only 5°C and 6°C respectively for case 1 and case 2. 3) The heat storage utilization rates of the last cycles were 5.08% and 14.86% for case 1 and case 2. Thus, the heat transferred into the wall during the heating period was stored inside the wall to improve the indoor thermal environment by rational use to maintain the inner surface temperature during the cooling-down period.

Exergy analysis of novel dual-pressure evaporation organic Rankine cycle using zeotropic mixtures

Organic Rankine cycle is a power system for the widely use of medium- to low-grade (<200 °C) thermal energy. Adopting the dual-pressure evaporation cycle and zeotropic mixtures are important approaches to increase the efficiency of organic Rankine cycle system. The combination of two approaches presents considerable potential to integrate their advantages and further increase the system efficiency significantly. However, for the dual-pressure evaporation organic Rankine cycle using zeotropic mixtures, the studies on the exergy performance are blank up to now. The obtained efficiency increments by combination, reached exergy efficiency, and characteristics of irreversible loss distribution remain unclear. This study carried out a comprehensive exergy analysis on the dual-pressure evaporation organic Rankine cycle using isobutane/isopentane mixtures. The exergy efficiency and irreversible loss distribution were analyzed. The superiority of combining dual-pressure evaporation cycle and zeotropic mixtures was evaluated. Results show that the largest exergy efficiency of dual-pressure evaporation cycle using isobutane/isopentane mixtures is 43.1%–61.7% for heat sources of 100–200 °C, and the largest exergy efficiency initially increases and then decreases with increasing heat source temperature. The largest irreversible loss occurs in the heat absorption, expansion, and heat release processes for heat sources of 100–160 °C, 170–180 °C and 190–200 °C, respectively. The exergy efficiency of dual-pressure evaporation cycle using isobutane/isopentane mixtures is the largest for heat sources below approximately 180 °C, and the maximum relative increments are 11.6% and 25.6% compared with the dual-pressure evaporation cycle using isobutane and single-pressure evaporation cycle using isobutane/isopentane mixtures, respectively.

Heat storage and release behavior in a thin vessel heat storage unit using salt hydrate latent heat storage material

Recently, there has been considerable interest in heat storage materials. Among them, sodium acetate trihydrate (melting point: 58 °C; latent heat: 264 kg/kg) is a suitable latent heat storage material for recovering and using exhaust heat in a temperature range lower than 100 °C, which is discharged in homes and factories. The purpose of this study was to investigate the heat storage and release behavior of sodium acetate trihydrate in a thin-vessel heat storage unit (160 mm × 130 mm × 4.8 mm) made of glass and polycarbonate. The sodium acetate trihydrate in the unit was heated or cooled by flowing water in water channels (width: 1 mm) disposed on both sides of the heat storage unit. From the experimental results, performance deterioration was evident in the heat storage and release process of sodium acetate trihydrate due to phase separation during heat storage and supercooling during heat release. Therefore, a thickener and a nucleating agent were added to sodium acetate trihydrate to suppress phase separation and supercooling effects. The results revealed that the thickener and nucleating agent were unevenly distributed in the case of repeated heat storage and release. The heat transfer numerical simulation adopting the lumped capacitance model was confirmed to be useful for investigating the melting behavior of sodium acetate trihydrate.

Experimental research on thermal characteristics of PCM thermal energy storage units

To explore thermal management integration in electric vehicles (EVs), a phase change materials (PCMs) thermal energy storage unit using flat tubes and corrugated fins is designed. The investigation focuses on the thermal characteristics of the PCM unit, such as the temperature variation, heat capacity, and heat transfer time, etc. Meanwhile, the heat storage and release process will be influenced by different inlet temperature, liquid flow rate, melting point of the PCM, and the combination order of the units. Under the same inlet temperature and flow rate condition, the PCM unit with higher melting point enters the latent heat storage stage slowly and enters the phase change melting release stage quickly. Furthermore, the heat storage and release rates increase with increasing liquid flow rates, but the effects are diminishing in the middle and later periods. The multiple PCM units with different melting temperatures are cascaded to help recycle low-grade heat energy with different temperature classes and exhibit well heat storage and release rates.

Multi-point micro-flame ignited hybrid lean-burn combustion of gasoline with direct injection dimethyl ether

Lean-burn combustion is effective in reducing fuel consumption of gasoline engines because of the higher specific heat ratio of the fuel lean mixture and reduced heat loss from lower combustion temperature. However, its application to real engines is hampered by the unstable ignition, high cyclic variability, and partial-burn due to slower combustion, as well as the restricted maximum lean-burn air/fuel ratio limit and the insufficiently low nitrogen oxides emission. Multi-point micro-flame-ignited hybrid combustion has been proposed and applied to extend the lean burn limit of premixed gasoline and air mixture. To achieve micro-flame-ignited combustion in premixed lean gasoline mixture formed by port fuel injection, a small amount of dimethyl ether is injected directly into the cylinder of a four-stroke gasoline engine to control and accelerate the ignition and combustion process so that the engine could be operated with the overall excess air coefficient (Lambda) of 1.9. The results show that heat release processes can be grouped into three forms, that is, ramp type, double-peak type, and trapezoid type. Regardless of single or split injections, direct injection timing of dimethyl ether dominates the features of heat release. The ramp type occurs at early injection timing while the double-peak type takes place at late injection timing. Trapezoid type appears between the above two types. Dimethyl ether injection timing controls the ignition timing and has less effect on combustion duration. Single injection of dimethyl ether leads to much earlier ignition timing and slightly longer combustion duration, forming higher nitrogen oxides emissions than the split injections. Ultra-low nitrogen oxides emissions and higher thermal efficiency are achieved in the ramp type combustion compared to the other two types of combustion in both injection approaches.

Simulation Analysis of Thermal Storage Process of Phase Change Energy Storage Materials

In order to solve the difficult problem of phase change heat transfer, a numerical model is used to establish a mathematical model for the phase change material. Numerical simulation of heat storage and release process of phase change heat exchanger based on fluent software. The simple experiment is carried out to verify that the phase change energy storage heat exchanger has better heat transfer characteristics than the ordinary heat exchanger, and provides a theoretical basis for the application of phase change energy storage materials to practical engineering.

Impact of Assimilating Himawari‐8‐Derived Layered Precipitable Water With Varying Cumulus and Microphysics Parameterization Schemes on the Simulation of Typhoon Hato

AbstractUnderstanding moisture information ahead of tropical cyclone (TC) convection is very important for predicting TC track, intensity, and precipitation. The advanced Himawari imager onboard the Japanese Himawari‐8/‐9 satellite can provide high spatial and temporal resolution moisture information. Three‐layered precipitable water (LPW) with its three water vapor absorption infrared bands can be assimilated to generate better understanding and prediction of TC evolution. The impacts of LPW assimilation in the Weather Research and Forecasting model with nine combinations of physical parameterization schemes, including three cumulus parameterization (CP) and three microphysics parameterization (MP) schemes on TC prediction, have been comprehensively analyzed using Typhoon Hato as a case study. The results indicate that LPW assimilation reduces the average track error and speed up TC movement by better adjustment of the atmospheric circulation fields via changing the vertical structure of moisture and thermal profile. The track forecasts retain sensitivity to CP schemes after LPW assimilation. Also, LPW assimilation improves TC intensity prediction because the latent heat release process is accurately adjusted. It has been revealed that LPW assimilation can weaken the intensity sensitivity to MP schemes more than to CP schemes. Skill scores were used to evaluate precipitation forecasts after Hato's landfall. The results indicate that heavy precipitation forecasts are more sensitive to the choice of MP schemes. After LPW assimilation, the equitable threat scores among different results become similar and all forecast skills are increased. In addition, group statistic results with different initial time show the same conclusions.