High Latent Heat Of Vaporization Research Articles

Understanding the role of methanol as a blended fuel on combustion behavior for rotary engine operations

Methanol, being one of the most promising carbon-neutral fuels, has the potential to enhance the fuel mixture homogeneity of gasoline rotary engines, thereby improving engine performance. This study, based on computational fluid dynamics model, investigates the in-cylinder flow, combustion, and emission characteristics under various methanol blending ratios, ignition timings, and equivalence ratios. At the methanol energy blending ratio of 10 %, a more extensive and efficient operating range is observed across different ignition timings and equivalence ratios, attributed to the higher diffusion and combustion rates. An increase in in-cylinder temperature enhances the complete conversion of HC. However, higher proportions of methanol are disadvantageous for the combustion process due to methanol's lower heat value and higher latent heat of vaporization. Thus, the optimal ignition timing was determined to be 30°EA BTDC. At this optimal ignition timing, the cylinder shows higher average turbulent kinetic energy and radical content compared to the ignition timing at 50° EA BTDC. Specifically, the concentrations of OH, H, and O free radicals increase by 12.40 %, 14.77 %, and 13.91 % respectively, leading to more complete initial flame kernel expansion. It is notable that emissions of CO, HC, and NOx are all reduced. The study further explores the influence of the equivalence ratio on the combustion process. At an equivalence ratio of 0.9, there is an earlier peak in the maximum cylinder pressure rise rate and the highest generation of O and OH, with a shorter main combustion period and concentrated heat release. This achieves economically viable operation for rotary engines, indicating a 2.122 % improvement in thermal efficiency and a reduction in fuel consumption to 375.537 g kW−1 h−1.

Effects of operating parameters on start performance of compression ignition engine by using high-pressure direct-injection pure methanol fuel

Methanol was one of the research hotspots in internal combustion engines over recent years. The application of methanol is a promising approach to transport decarbonization due to low carbon content. However, the utilization of methanol in compression ignition (CI) engines faces some challenges as a result of low reactivity and high latent heat of vaporization, such as cold start and operation stability. Furthermore, the impact mechanisms of operating parameters on cold start and operation stability in CI engine have not been understood deeply. In this work, the effects of operating parameters on average cycle of start and coefficient of speed variation (CoVspeed) of idle were studied on a CI engine fueled by pure methanol fuel. Results show that the injection strategy of the minimum average starting cycle number is the pre-main injection, which includes lower injection pressure, −4 °CA ATDC (degree crank angle after top dead center) main timing, smaller pre mass, and larger pre-main interval. The injection strategy of the minimum CoVspeed of idle is the pilot-pre-main injection, which includes lower injection pressure, −4 °CA ATDC main timing, smaller pre mass, larger pre-main interval, smaller pilot mass, and shorter pilot-main interval. Under the same operating conditions, the average cycle of start is 12 and 5 for methanol and diesel respectively. The CoVspeed of idle is 6.72% and 0.53% for methanol and diesel respectively. When coolant temperature is 30 °C, the minimum intake temperature is 120 °C. Upon adjusting the coolant temperature to 80 °C, the minimum intake temperature decreases to 80 °C.

Comparison of Tabulated and Complex Chemistry Approaches for Ammonia–Diesel Dual-Fuel Combustion Simulation

<div>Using ammonia as a carbon-free fuel is a promising way to reduce greenhouse gas emissions in the maritime sector. Due to the challenging fuel properties, like high autoignition temperature, high latent heat of vaporization, and low laminar flame speeds, a dual-fuel combustion process is the most promising way to use ammonia as a fuel in medium-speed engines.</div> <div>Currently, many experimental investigations regarding premixed and diffusive combustion are carried out. A numerical approach has been employed to simulate the complex dual-fuel combustion process to better understand the influences on the diffusive combustion of ammonia ignited by a diesel pilot. The simulation results are validated based on optical investigations conducted in a rapid compression–expansion machine (RCEM). The present work compares a tabulated chemistry simulation approach to complex chemistry-based simulations. The investigations evaluate the accuracy of both modeling approaches and point out the limitations and weaknesses of the tabulated chemistry approach. When using two fuels, the tabulated chemistry approach cannot reproduce misfiring events due to inherent model limitations. By adjusting the model parameters of the tabulated chemistry model, it is possible to reproduce experimental results accurately for a specific case. However, using the adjusted parameters for simulations with changed injection timing or interaction angle between the sprays shows that no predictive calculations are possible. The parameter set is only valid for a single operation point.</div> <div>Further simulations show that the complex chemistry approach can capture the complex interaction between both directly injected fuels for different operation points. It correctly predicts the ignition as well as heat release. Therefore, the approach allows predictive combustion simulations. Furthermore, it reproduces the occurrence of misfiring in cases of unsuitable interaction of both sprays and injection timing.</div>

Experimental study on heat transfer performance of high temperature heat pipe under axial non-uniform heat flux

Non-uniform high-temperature large heat flux is commonly encountered in engineering applications, posing challenges to heat transfer processes and affecting system performance. High temperature heat pipes offer an effective solution to mitigate the adverse effects of non-uniform heat flux by leveraging the unique characteristics of their inner alkali metal (or alloy) working fluid, such as high latent heat of vaporization, strong heat flux density, and ability to operate at elevated temperatures. These features enable high temperature heat pipes to achieve excellent isothermal and uniform heat transfer performance, thereby improving overall thermal management in heat transfer systems. Building upon the investigation of the original high temperature heat pipe, this study designed and fabricated a specially shaped high temperature heat pipe with a spherical crown surface as the evaporator. Experimental research was conducted to assess its frozen start-up performance and heat transfer characteristics under the influence of axial non-uniform heat flux. The results were also analyzed theoretically, providing valuable insights into the frozen start-up performance and heat transfer performance of the high temperature heat pipe in the presence of non-uniform heat flux conditions. The analysis results reveal several important findings: (1)The high temperature heat pipe demonstrates its capability to convert axial non-uniform high-temperature large heat flux into a uniform heat flux, thus achieving excellent uniform heat transfer performance. (2)The theoretical solution obtained through the lumped heat capacity analysis method shows satisfactory agreement with the actual frozen start-up process of the high temperature heat pipe. This theoretical reference can aid in the transient analysis of the frozen start-up process under the influence of axial non-uniform high-temperature large heat flux. (3)The experiment investigated the influence of heating power on heat transfer performance and temperature uniformity. The results indicate that the temperature uniformity of the high temperature heat pipe exhibits a trend of initially increasing and then decreasing. Specifically, the best temperature uniformity is achieved when the heating power is 1084.7 W. Moreover, when the heating power is 1197.9 W, the high temperature heat pipe exhibits the lowest equivalent thermal resistance of 0.0265 K/W, indicating the best heat transfer performance. (4) The variable power heating approach demonstrates that increasing the heating power leads to an extension of the effective length of the heat pipe. The most favorable heat transfer performance and temperature uniformity are observed when the heating power is set to 1133.7 W, allowing the full length of the condenser of the high temperature heat pipe to participate actively in the heat transfer process. These results can provide quantitative experimental data and theoretical references for improving the thermal shock of non-uniform high-temperature large heat flux.

Effects of methanol direct injection and high compression ratio on improving the performances of a spark-ignition passenger car engine

The high octane number and high latent heat of vaporization of methanol are beneficial to suppress knock and consequently increase compression ratio (CR) of spark ignition engines, and thus improve the thermal efficiency. Few preious research on methanol engine combuston and performances have been conducted based on spark-ignition passenger car engines with a CR greater than 14. In this study, a 1.5-liter spark ignition passenger car engine with miller cycle was used to explore the potentials of high CR and methanol direct injection (MDI) on improving engine performances. First, the engine was tested under stoichiometric combustion using methanol and gasoline at BMEPs of 1.1 MPa and 1.5 MPa with CR11.5, CR13.8, and CR15.3. Then, the performances of the CR11.5 case with gasoline and the CR15.3 case with methanol were compared under lean burn combustion. The results show that for gasoline, increasing CR from 11.5 to 15.3 results in decreased fuel economy under stoichiometric combustion, whereas the exact opposite tendency is shown for methanol. Integrating a high CR of 15.3 and MDI improves brake thermal efficiency (BTE) to 43.3 % at an excess air/fuel ratio (λ) of 1.0, when compared with 37.4 % of gasoline at CR11.5. Applying lean burn can further improve the BTE of methanol at CR15.3 to 44.9 %. The main causes of the improvement of BTE by high CR and MDI are the reduced exhaust heat loss resulted from earlier combustion phasing. However, high CR and MDI also extend combustion durations at all specified λs, and emit more THC and CO emissions than low CR with gasoline at high λs because of higher surface/volume ratio and flame quenching. The extended combustion duration and the incomplete combustion are the main barriers to greater BTE for MDI sprak ignition engine with high CR.

The effect of acetone-butanol-ethanol and gasoline blends on the knocking performance of spark-ignition engine

In this study, the effect of acetone-butanol-ethanol (ABE) and gasoline blends on knocking performance was investigated experimentally in a four-stroke, high-speed spark-ignition engine. Four types of fuels were used in this study: pure gasoline, gasoline mixed with 10%, 20% and 30% ABE. The knocking factor is introduced to evaluate the knocking tendency of the experiential fuels. The results show that the threshold for knock identification is 1.100 when the width of the reference window and the knock window are set to the same length. The more ABE that is added to gasoline, the weaker the tendency of the engine to knock. The high latent heat of vaporization of ABE helps reduce the temperature of the combustion start point, thereby suppressing knocking. The spark timing of the engine can be advanced when the gasoline is blended with ABE. The spark timing can be advanced 5.34° crank angle at 3000 r/min, 30% throttle position when the engine is fuelled by gasoline blended with 30% ABE compared to the pure gasoline engine. This paper has shown that ABE can be used as a blended fuel to suppress the knocking tendency in spark-ignition engine.

Combustion Parametric Investigations of Methanol-Based RCCI Internal Combustion Engine and Comparison with the Conventional Dual Fuel Mode

Reactivity-controlled compression ignition (RCCI) is an advanced combustion mode. Its uses two fuels with different physical and chemical properties to form a combustible mixture with active stratification. RCCI can flexibly control the combustion process by changing the concentration and activity of the combustible mixture. It can also reduce the emission of NOx and particulate matter in the engine without significantly reducing the thermal efficiency. Among various fuel combinations, methanol as an oxygen-containing fuel, has a high latent heat of vaporization, which is conducive to reducing combustion temperature and achieving low-temperature combustion. This experimental study explores the potential of Methanol-Diesel Reactivity Controlled Compression Ignition (RCCI) in achieving low emissions and high thermal efficiency and compares this with the conventional dual fuel mode. Low-temperature combustions such as Reactivity Controlled Compression Ignition (RCCI) have been shown to be a promising way to reduce pollutants at the exhaust, i.e. NOx and soot emissions. and increase the thermal efficiency of future engines. The methanol to diesel energy share (MDES) could be enhanced to 56% in the RCCI mode with proper setting of the injection parameters from 45% in the dual fuel mode. A higher quantity in the second diesel pulse that occurred close to TDC led to higher thermal efficiency and good combustion stability. Engines working in a dual-fuel mode need special conditions to ignite an air-fuel mixture without a spark plug in a good moment with high combustion efficiency.

Enhanced capillary-driven thin film boiling on cost-effective gradient wire meshes for high-heat-flux applications

As high-power electronics continue to advance rapidly, the pursuit of efficient thermal management has emerged a critical challenge for their further high-performance and large-scale applications. Capillary-driven thin film boiling phase-change cooling, harnessing the high latent heat of vaporization, presents an effective strategy to efficiently dissipate waste heat and meet the escalating cooling requirements of high-heat-flux applications. In this study, a cost-effective gradient wicking structure was proposed to enhance the thermal performance of the wick by promoting bubble dynamics and optimizing the balance between capillary pressure and permeability in homogeneous wicks. The comprehensive capillary properties of the homogeneous wicks were analyzed through theoretical calculations, and the capillary-driven thin film boiling heat transfer performance of four wick samples was systematically studied experimentally. Additionally, the effects of reduced pressures on the thermal performance of the gradient wick were investigated. Notably, the gradient porous wicking structure demonstrated exceptional thermal performance, with a critical heat flux reaching as high as 202.8 W/cm2 and a maximum heat transfer coefficient of 121.9 kW/m2·K achieved at 88.5 W/cm2. The findings of this study offer valuable design guidelines for the wick structures utilized in phase change equipment, with potential wide-ranging applications in advanced thermal management.

Study on the mechanism of influence of cetane improver on methanol ignition

Methanol has attracted much attention because it can realize carbon neutral cycle. Methanol is difficult to use in compression ignition engines because of its low cetane number and high latent heat of vaporization. 2-ethylhexyl nitrate (EHN) is a widely used cetane number improver, which can effectively promote the ignition of methanol. Therefore, a reduced mechanism of methanol and EHN containing 61 species and 479 reactions is proposed in this paper, and it has been verified to fit well with the original mechanism and experimental date. Then, chemical kinetic analysis is carried out using CHEMKIN PRO. Results show that after adding EHN, the ignition delay is significantly shortened. As the EHN ratio increases, the effect of EHN on shortening the ignition delay period does not increase nonlinearly, but shows a slowing trend. The reaction with higher positive temperature sensitivity changes from R133 (CH3OH + HO2 = CH2OH + H2O2) to R307 (CH2O + NO2 = HONO + HCO), and the reaction with higher negative temperature sensitivity changes from R18 (2HO2 = H2O2 + O2) to R305 (HCO + NO2 = HONO + CO). The reaction time of H, OH and HO2 is advanced and the peak values decrease. In the methanol dehydrogenation pathway, the proportions of reactions involving HO2 decrease significantly and the proportions of reactions involving NO2 and OH increase. The methanol consumption rate increases significantly after adding EHN. With the addition of 3% EHN, the reaction time of methanol was reduced by 99.8% compared to pure methanol.

Incorporating Chaotropic/Kosmotropic Chemistries onto Plasmonic Nanoheater to Boost Steam Generation Beyond its Photothermal Property.

Photothermal steam generation promises decentralized water purification, but current methods suffer from slow water evaporation even at high photothermal efficiency of ≈98%. This drawback arises from the high latent heat of vaporization that is required to overcome the strong and extensive hydrogen bonding network in water for steam generation. Here, light-to-vapor conversion is boosted by incorporating chaotropic/kosmotropic chemistries onto plasmonic nanoheater to manipulate water intermolecular network at the point-of-heating. The chaotropic-plasmonic nanoheater affords rapid light-to-vapor conversion (2.79kgm-2 h-1 kW-1 ) at ≈83% efficiency, with the steam generation rate up to 6-fold better than kosmotropic platforms or emerging photothermal designs. Notably, the chaotropic-plasmonic nanoheater also lowers the enthalpy of water vaporization by 1.6-fold when compared to bulk water, signifying that a correspondingly higher amount of steam can be generated with the same energy input. Simulation studies unveil chaotropic surface chemistry is crucial to disrupt water hydrogen bonding network and suppress the energy barrier for water evaporation. Using the chaotropic-plasmonic nanoheater, organic-polluted water is purified at ≈100% efficiency, a feat otherwise challenging in conventional treatments. This study offers a unique chemistry approach to boost light-driven steam generation beyond a material photothermal property.

Parametric evaluation of neat methanol combustion in a light-duty compression ignition engine

Methanol is currently considered a promising alternative fuel for energy de-fossilization due to its simplicity and adequacy for renewable production. This study investigates the feasibility of using neat methanol in high-efficiency compression ignition engines, with a focus on its potential to reduce CO2 emissions compared to conventional diesel. However, achieving efficient combustion of neat methanol in compression ignition engines presents challenges due to its low ignition capability, requiring higher compression ratios, intake temperatures, and pressures than diesel for autoignition. Furthermore, the high latent heat of vaporization contributes to significant cycle-to-cycle combustion variability. This work evaluates the combustion characteristics of neat methanol in a light-duty multi-cylinder compression ignition engine with a 19:1 compression ratio, examining its suitability for commercial applications. Performance indicators such as engine efficiency, fuel consumption, and engine-out pollutant emissions are assessed. The findings contribute to advancing research and implementation of methanol fuel as an energy source for internal combustion engine vehicles, addressing both the advantages of the fuel and the challenges that need to be overcome, particularly with respect to its low auto-ignition characteristics. Notably, despite methanol's lower energy density compared to diesel, the achieved combustion efficiency is comparable, with remarkable improvements in NOx and soot emissions trade-off.The study reveals that neat methanol combustion poses difficulties, especially at low loads, speeds, and during engine startup, due to its high ignition energy requirement and long ignition delay. Even with modifications such as increased compression ratio, and the addition of intake heaters and glow plugs, sustaining combustion at low load conditions remains a challenge. However, once the engine is warmed up, methanol combustion can be sustained at medium to high loads without additional heating accessories, although the use of such accessories improves combustion stability.

Blending n-octanol with biodiesel for more efficient and cleaner combustion in diesel engines: A modeling study

Biodiesel has become a popular alternative fuel to fossil diesel. However, compared to conventional diesel engines, the adoption of pure biodiesel often leads to higher NOx though soot emissions can be reduced. In this study, the alcoholic fuel n-octanol was chosen as the blending fuel in biodiesel. The modeling study was carried out to investigate the effects of blending n-octanol on the combustion characteristics and emissions formation process in a diesel engine. At first, a multi-component reaction mechanism involving 115 species and 489 reactions was constructed to better predict the combustion process of biodiesel and n-octanol. This mechanism was then coupled with KIVA-CHEMKIN to implement a three-dimensional simulation of the engine. The developed mechanisms and adopted models were validated under a variety of conditions. At last, to examine the effects of n-octanol, simulations were carried out by gradually increasing the percentage of n-octanol from 0% to 100% with an interval of 10%. Analysis of the simulation results revealed that blending more n-octanol with biodiesel could lead to a prolonged ignition delay. Due to the high latent heat of vaporization of n-octanol, the temperature at the initial stage of combustion can be reduced which subsequently mitigated the formation of NOx. The higher oxygen content of n-octanol was beneficial for the improvement in power output and the decrease of soot emissions. Overall, B20/O80 blends were found to be capable of achieving more efficient and cleaner combustion in the diesel engine at both speeds.

An Experimental Investigation on the Characteristics of a Compression Ignition Engine Fuelled by Diesel-Palm Biodiesel–Ethanol/Propanol Based Ternary Blends

Issues such as rising fuel prices, fuel costs, and lowering reserves highlight the importance of research into sustainable fuels derived from biological sources. This study is focused on experiments on a CI engine using ethanol and propanol-based ternary blends. Palm biodiesel is kept constant at 40% volumetric concentration, while diesel and ethanol/propanol are varied in different batches. The results obtained with ternary blends were compared with reference fuel diesel, pure palm biodiesel, and a palm biodiesel–diesel binary blend. The ternary blends exhibit lower brake thermal efficiency and higher brake specific energy consumption than diesel and binary blends due to their lower calorific value. Despite in-fuel oxygen presence, lower brake specific oxides of nitrogen and smoke opacity were observed for engine operation with a ternary blend due to the predominant role of higher latent heat of vaporization and volatility of alcohols, but unburned hydrocarbon and carbon monoxide emissions increased due to the interactive effect of a lower cetane number, higher latent heat of vaporization, and lower kinematic viscosity of alcohols when compared to reference fuels. Among the tested fuels, in-cylinder pressure was observed to decrease with ternary blends due to their lower calorific value, but a raised heat release rate was attributed to lower viscosity and faster burning of alcohols.

Experimental investigation on the thermal performance of a novel thermosyphon heat pipe with truncated cone for heat recovery systems

A Thermosyphon Heat Pipe (THP) is an effective heat transfer device primarily deployed in the field of energy conversion and heat recovery systems. Among the various working fluids, deionized (DI) water exerts higher latent heat of vaporization making it suitable for efficient performance testing of THPs. The novel design of a THP in a non-uniform geometry-based truncated cone structure is suggested to recover waste heat from various sources. A detailed parametric study is carried out on the non-uniform structure THPs to analyze the thermal performance. This study examines the thermal performance of the Convergent Truncated Cone (CTC) THP and the effect of modifying the influencing factors of its diameter, length, heat flux, inclinations, and mass flow rate. Based on the experimental results, it is seen that the CTC helps to reduce the overall thermal resistance by 48.94 %, 35.15 %, and 34.69 % for 90°, 60°, and 30° inclinations, respectively. Similarly, the temperature difference between the evaporator and the adiabatic sections shows an average thermal resistance reduction of 36.38 %, 30.3 %, and 55.82 % under the same operating conditions. Additionally, the results of the current investigation indicate that there are two positive outcomes for the supplied heat input range of 30–300 W. It is observed that the THP is 2.54 % more efficient than a conventional THP at an angle of 90° for a heat input range of 30–150 W. The maximum augmentation of thermal efficiency is noted to be 4.12 % and is attained at 30° inclination for the input range of 180–300 W.

Effect of mixed nonionic surfactants on microemulsion phase boundary, fuel property, and engine performance of biofuels

Microemulsion biofuels can become one of alternative biodiesels using suitable nonionic surfactants and cosurfactant to emulsify vegetable oil and ethanol with the appropriate formulae. Without the further chemical improvement, the low volatility and high viscosity because of triglycerides in vegetable oil can cause a serious problem in engine operation. This work proposed a systematic investigation of microemulsion biofuel prepared from rice bran oil and ethanol using mixed nonionic surfactant systems (Dehydol LS7, Tween 80, and Span 80) as surfactant (S) and 1-octanol as a cosurfactant (C) at molar ratio of 1:30. Microemulsion phase behaviors can be examined through the ternary phase diagram of rice bran oil, ethanol, and S:C. It was observed that Dehydol LS 7 was poor in solubilization of rice bran oil and ethanol because of their preference in hydrophilic compounds rather than lipophilic compounds. Introduction of Tween 80 or Span 80 into the biofuels using Dehydol LS 7 enhanced the solubilization of these systems as the extent of single-phase boundary was significantly enlarged because of the hydrophilic–lipophilic balance of the mixture and chemical structure of surfactants. The fuel properties of microemulsion biofuel were investigated through kinematic viscosity, specific gravity, flash point, cloud point, pour point, and higher heating value. It was found that mixed surfactant also improved some fuel properties due to additional surfactants contain many oxygenated functional groups, however, some parameters were slightly substandard. The combustion characteristics and exhaust emission were investigated in CI diesel engine. It was observed that the in-cylinder pressure was lower under the combustion of microemulsion fuel mainly due to the high latent heat of vaporization of alcohols. The start of combustion was more retarded with the addition of Span 80, especially at low load condition. It was observed that the significant reduction in nitrogen oxides was achieved with the combustion of microemulsion fuel while unburnt hydrocarbon emissions were higher compared to diesel fuel. The obtained experimental data showed that microemulsion biofuels can be a promising alternative biodiesel although the individual usage in engine was slightly less efficient than commercial diesel fuel.

Experimental investigation and performance prediction of gasoline engine operating parameters fueled with diisopropyl ether-gasoline blends: Response surface methodology based optimization

In this research, gasoline engine performance and emission characteristics were studied when powered by diisopropyl ether-gasoline blends. The main objective of this study is to determine the behavior of diisopropyl ether-gasoline blends at various engine speeds and compression ratios. Further, the engine parameters were optimized using the response surface methodology. Enriched oxygen, higher latent heat of vaporization, and the readily volatile nature of the fuel enhanced the brake thermal efficiency and lowered the hydrocarbons and carbon monoxide due to a better combustion rate. The developed model exhibited superior R2 values with a 0.957 desirability factor. The optimum parameters such as speed, compression ratio, and fuel-blend concentrations were found at 2250 rpm, 10:1, and D25 (75% gasoline and 25% diisopropyl ether), respectively. The responses for the optimal input parameters were brake thermal efficiency (31.53%), specific fuel consumption (0.2923 kg/kWh), carbon monoxide (0.14% by Vol.), hydrocarbons (31 ppm), and oxides of nitrogen (708 ppm). The predicted values for optimum engine parameters were validated with the experimental data, and their percentage of absolute error was found to be less than 5%. Thus, the study concludes that diisopropyl-ether gasoline blends can be used as an alternative fuel to enhance the brake thermal efficiency and reduce the pollution level, and the proposed numerical model can predict the responses with high accuracy.

Effects of second hydrogen direct injection proportion and injection timing on combustion and emission characteristics of hydrogen/n-butanol combined injection engine

Hydrogen and n-butanol are superior alternative fuels for SI engines, which show high potential in improving the combustion and emission characteristics of internal combustion engines. However, both still have disadvantages when applied individually. N-butanol fuel has poor evaporative atomization properties and high latent heat of vaporization. Burning n-butanol fuel alone can lead to incomplete combustion and lower temperature in the cylinder. Hydrogen is not easily stored and transported, and the engine is prone to backfire or detonation only using hydrogen. Therefore, this paper investigates the effects of hydrogen direct injection strategies on the combustion and emission characteristics of n-butanol/hydrogen dual-fuel engines based on n-butanol port injection/split hydrogen direct injection mode and the synergistic optimization of their characteristics. The energy of hydrogen is 20% of the total energy of the fuel in the cylinder. The experimental results show that a balance between dynamics and emission characteristics can be found using split hydrogen direct injection. Compared with the second hydrogen injection proportion (IP2) = 0, the split hydrogen direct injection can promote the formation of a stable flame kernel, shorten the flame development period and rapid combustion period, and reduce the cyclic variation. When the IP2 is 25%, 50% and 75%, the engine torque increases by 0.14%, 1.50% and 3.00% and the maximum in-cylinder pressure increases by 1.9%, 2.3% and 0.6% respectively. Compared with IP2 = 100%, HC emissions are reduced by 7.8%, 15.4% and 24.7% and NOx emissions are reduced by 16.4%, 13.8% and 7.9% respectively, when the IP2 is 25%, 50% and 75%. As second hydrogen injection timing (IT2) is advanced, CA0-10 and CA10-90 show a decreasing and then increasing trend. The maximum in-cylinder pressure rises and falls, and the engine torque gradually decreases. The CO emissions show a trend of decreasing and remaining constant. However, the trends of HC emissions and NOx emissions with IT2 are not consistent at different IP2. Considering the engine's dynamics and emission characteristics, the first hydrogen injection proportion (IP1) = 25% plus first hydrogen injection timing (IT1) = 240°CA BTDC combined with IP2 = 75% plus IT2 = 105°CA BTDC is the superior split hydrogen direct injection strategy.

Hybrid nanofluid spray cooling performance and its residue surface effects: Toward thermal management of high heat flux devices

• Hybrid nanofluid spray system.shows critical heat flux enhancement up to 126%. • Critical heat flux enhancement may be due to residue wetting and wicking effects. • Hybrid nanofluid sprays show higher heat transfer coefficient than existing fluids. • Existing fluid sprays fail to effectively cool electric vehicle power electronics. • Hybrid nanofluid sprays can effectively cool electric vehicle power electronics. In recent years, heat dissipation in high heat flux devices remarkably increased and it is anticipated to reach unprecedented levels in future devices, mainly due to increased power density, compact packaging and high-performance requirements. To address this challenge, in current research, we initially investigate the spray cooling performance and spray residue surface effects of the next generation thermal fluid, called hybrid nanofluid. Subsequently, we investigate the hybrid nanofluid spray cooling potential to address heat dissipation issues in a high heat flux application, that is, the electric vehicle (EV) high power electronics. Our results demonstrate that the critical heat flux (CHF) enhancement up to 126% can be achieved using the hybrid nanofluid spray cooling compared to water spray cooling. The hybrid nanofluid and its spray residue characterization further suggest that high CHF in hybrid nanofluid spray cooling may be due to high latent heat of vaporization and residue wetting and wicking effects. Moreover, the spray cooling efficiency and Nusselt number obtained for hybrid nanofluid spray cooling is more than twice that of water spray cooling. Furthermore, our results indicate that the hybrid nanofluid spray cooling can keep high power electronics of current and future electric vehicles below their failure temperatures, while the same cannot be achieved using water and dielectric fluid spray cooling.

Research on combustion and emission characteristics of a hydrous ethanol/hydrogen combined injection spark ignition engine under lean-burn conditions

Ethanol, as one of the carbon-neutral fuels for spark ignition (SI) engine, has been widely used. Dehydration and purification of ethanol during production process will lead to high energy consumption. If hydrous ethanol can be directly applied to the engine, the cost of use will be greatly reduced. Due to the high latent heat of vaporization of ethanol and water, it is necessary to consider the performance of atomization, evaporation and combustion stability when hydrous ethanol is used in engine. As a zero-carbon fuel, hydrogen has excellent characteristics such as low ignition energy, fast flame propagation speed and wide combustion limit. The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance. Therefore, this study explores the performance of hydrous ethanol/hydrogen in SI combined injection engine. The hydrous ethanol is injected into the intake port and the hydrogen is directly injected into the cylinder during the compression stroke. In this study, we firstly analyze the optimal water blending ratio (ω) of hydrous ethanol, which including 0, 3%, 6%, 9% and 12%. The experimental results show that the hydrous ethanol with 9% water ratio has the best performance without hydrogen addition. Based on the 9% water ratio, the effects of hydrogen blending ratio (0, 5%, 10%, 15% and 20%) on the combustion and emission under different excess air ratio (λ) (1, 1.1, 1.2, 1.3, 1.4). Hydrogen addition can increase the degree of constant volume combustion, so that the maximum cylinder pressure and temperature increase with the increase of the hydrogen blending ratio (HBR). When λ = 1.3 and HBR = 20%, the maximum in-cylinder pressure can be increased by 108.64% compared to pure hydrous ethanol. Hydrogen effectively increases the indicated mean effective pressure (IMEP) and reduces the coefficient of variation of IMEP (COVIMEP). Adding hydrogen can reduce CO and HC emissions, while NOx emissions will increase. When λ = 1.2 and HBR increasing from 0 to 20%, the NOx emissions increase by 106.75%, but it is still less than the NOx emissions of pure hydrous ethanol at λ = 1. On the whole, hydrogen direct injection can improve the combustion performance of hydrous ethanol and achieve stable combustion under lean-burn conditions.

Combustion and emission performance of isopropanol-butanol-ethanol (IBE) mixed with diesel fuel on marine diesel engine with nano YSZ thermal barrier coating

The effect of piston coating on the combustion and emission performance of IBE and diesel blended fuel was experimental studied. The experimental conditions were set to be a orthogonal matrix of three loads from low to high, coated and uncoated, IBE20 fuel and D100 fuel. The heat release rate, ignition delay periods and combustion duration were calculated by the cylinder pressure curves. The break thermal efficiency was calculated by the fuel consumption rate, and the concentration of soot, NOx and CO in the exhaust was collected. It was found that Nano-YSZ thermal barrier coating (TBC) can effectively reduce heat transfer loss, increase in-cylinder combustion temperature, and effectively solve the problems of high latent heat of vaporization and ignition delay of alcohol fuel. The experimental results showed that the Nano-YSZ coating could effectively reduce the brake specific fuel consumption, which was reduced by 5% when using pure diesel under 25% load, and was reduced by 7.3% for IBE20 fuel. Furthermore, TBC_IBE20 (IBE20 used in TBC Engine) exhibited the highest thermal efficiency under the three working conditions. Under all operating conditions, IBE20 had the potential to reduce soot emissions but increase NOx emissions, and thermal barrier coatings could amplify this potential.