Liquid Turbine Research Articles

Flow Investigation and Optimization Design of a Radial Outflow Liquid Turbine Expander for Liquid CO2 Energy Storage System

Abstract The radial outflow liquid turbine expander (LTEROF) draws increasing attention for enhancing the efficiency of the liquid CO2 energy storage (LCES) system. However, the detrimental cavitation deteriorates the flow behavior, which demands an in-depth study of the flow physics and then effective attenuation. This study aims to effectively mitigate thermosensitive fluid cavitation and reduce energy dissipation. First, a preliminary expander design methodology taking into account the large specific volume variation of working fluid is implemented. Next, the entropy production analysis method (EPAM) is proposed to characterize energy dissipation and cavitation. Furthermore, the improved cavitation and turbulence models are validated through simulating Hord's liquid hydrogen hydrofoil. To suppress the cavitation and energy dissipation, the optimization design method based on the particle swarm optimization (PSO) algorithm together with the Kriging-based adaptive surrogate model is developed. Among them, the nonuniform relational B-splines and free form deformation (NURBS-FFD) method is applied to flexibly deform the profiles of nozzle and rotor, and a novel objective function incorporating vapor volume fraction and local entropy production rate (LEPR) is constructed to capture the cavitation and energy dissipation. During optimization, the optimizer is driven by the objective function to search globally toward the cavitation-resistance and low-dissipation geometry. With the optimization, the LEPR region shrinks and the cavitation is obviously weakened, the performance significantly improves both under design condition and under off-design conditions.

Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units

Cryogenic liquid turbine expanders have emerged quite recently as a replacement for traditional Joule-Thomson valves in cryogenic processes for energy saving purpose. However, introducing a liquid turbine expander into the cryogenic air separation unit (ASU) can influence the operating points of ASU components, and the maximum benefits arising from the liquid turbine expander have not yet been reported. To fill such a gap, thermodynamic models are first established for ASU components, including the main air compressor, booster air compressor, cryogenic gas and liquid turbine expanders, main heat exchanger, cryogenic pump, and distillation column. To achieve the best possible use of the liquid turbine expander, an optimization method is developed by incorporating the thermodynamic models with the particle swarm optimization algorithm, in which the total minimization power consumption of ASU is the optimization goal while the flow rates and pressures of the high pressure air stream and the air stream drawn from the booster air compressor middle section together with the temperature of the medium pressure air stream exiting the main heat exchanger midway act as the optimization variables. Then, energy, exergy and economic analyses are conducted and the corresponding indexes are chosen to quantitatively evaluate the influence of the liquid turbine expander on the air separation process. For the case study, ASUs of 35000 Nm3/h oxygen production capacity with and without a cryogenic liquid turbine expander are optimized, respectively. The results show that the ASU total power saving through the use of liquid turbine expander is 4.2-fold its output shaft power; thus, the energy consumption of unit oxygen decreases by 2.12% and the overall exergy efficiency increases by 1%. In addition, the economic analysis shows that the period of return of the liquid turbine expander in the ASU is estimated to be 1.75 years.

Influence of tooth geometrical shape on the leakage and rotordynamic characteristics of labyrinth seals in a cryogenic liquid turbine expander

Cryogenic liquid turbine expanders have been used in many refrigeration systems to save energy, and rotor stability is a top concern in their development. The present study focuses on the influence of tooth geometrical shape on the leakage and rotordynamic characteristics of labyrinth seals in a cryogenic liquid expander, whose rotordynamic characteristics are typically special because of the thermodynamic effect of cryogenic liquid and a large pressure drop. Computational fluid dynamics (CFD) simulations are conducted in thirteen-teeth labyrinth seals with isosceles trapezoid shaped teeth and two types of right-angle trapezoid shaped teeth for a given geometric parameter through the whirling rotor method and total energy model. The flow behavior in the three labyrinth seals with different tooth geometrical shapes is explored, and their influence on the leakage and rotordynamic characteristics of the labyrinth seal is obtained. The results show that the leakage flow rate of the labyrinth seal with front right angle trapezoid shaped teeth is 1.1% and 0.6% less than that with rear right angle trapezoid shaped teeth and isosceles trapezoid shaped teeth, respectively, because of a larger divergence angle and more leakage flow involved in dissipation, while the labyrinth seal with isosceles trapezoid shaped teeth produces a larger fluid-induced tangential force opposite to the direction of whirling velocity and is more favorable for rotor stability. In addition, a parametric study is conducted to analyze the influence of clearance, tooth height, tooth thickness and inclination angle on the leakage and rotordynamic characteristics of the three labyrinth seals.

Cavitation Suppression and Design Optimization in a Cryogenic Liquid Turbine Expander Based on Thermodynamic Cavitation and Entropy Production Analysis

Abstract Cryogenic liquid turbine expanders have emerged quite recently as a replacement of J–T valve for enhancing energy efficiency of industrial systems, such as air separation units (ASUs) and Supercritical Compressed Air Energy Storage systems. In the liquid turbine expander, the rotating impeller-induced swirling flow and cavitation are essentially significant and intensive, which requests some in-depth work toward a thorough understanding flow physics and then effective attenuation. This study aims at effectively mitigating the swirling flow and cavitation. The entropy production analysis method (EPAM) is proposed to characterize the swirling flow and cavitation. It is then incorporated with the improved cavitation and turbulence models and validated through the simulation of the Hord's liquid nitrogen hydrofoil. To mitigate the swirling flow and subsequent cavitation, the design optimization method is developed, in which a novel optimization objective function is constituted by incorporating the local entropy production rate and vapor volume fraction to capture the mechanical energy dissipation and cryogenic cavitating flow physics; the non-uniform relational B-Splines and free form deformation (NURBS–FFD) parametric method is used to facilitate a flexible variation in impeller blade and diffuser vane geometries. It is solved within cfx frame by means of the particle swarm optimization (PSO) algorithm coupling the Kriging-based adaptive surrogate model. With the design optimization, the impeller and vaned diffuser tube geometries are collaboratively fine-tuned, and the mechanical energy dissipation and cavitating flow across both the impeller and vaned diffuser tube is effectively mitigated.

Performance and flow characteristics of the liquid turbine for supercritical compressed air energy storage system

• Geometrical models of liquid turbines affect the accuracy of predicted efficiency. • The model with a nozzle and a rotor predictes the efficiency with 15.8% error. • The total pressure loss of the rotor accounts for the largest portion among all parts. • The nonuniform flow in the nozzle and the rotor is significant at low flow rates. The liquid turbine can replace throttling valves during the depressurization process of high-pressure liquid or supercritical fluid and improve the system efficiency of many industrial systems. However, there is no research about studying the internal flow and total pressure loss of liquid turbines, which can affect the turbine performance significantly. In this paper, performance and flow characteristics in a liquid turbine were analyzed for supercritical compressed air energy storage (SC-CAES) systems in the first time. Three typical topology models (C1, C2 and C3) of the tested liquid turbine were simulated and their performances were compared with experimental results. The deviation of the turbine efficiency between C3 and the experiment was less than 2%, while C1 had a constant increment of the turbine efficiency about 15.8% with the experiment. The total pressure loss in each part was evaluated and the flow characteristics in the nozzle and the rotor were analyzed. Nonuniform flow affected the nozzle’s total pressure loss significantly, while the rotor’s total pressure loss was related to the development of low energy regions. The results obtained in this paper provides guidance for optimizing liquid turbines and improving the turbine performance for various industrial systems with throttling valves installed.

Preliminary design and performance analysis of the liquid turbine for supercritical compressed air energy storage systems

• The preliminary design method and experiment of the liquid turbine is presented. • The predicted and experimental performance of the turbine validates the method. • Reasonable parameter ranges for liquid turbines are different from other turbines. Liquid turbines can replace throttling valves to recover waste energy and reduce vaporization in various industrial systems, such as liquefied natural gas, air separation, supercritical compressed air energy storage (SC-CAES) systems, et al. However, there were few studies about differences in the preliminary design method between general radial inflow turbines and liquid turbines. In this paper, a preliminary design method of liquid turbines was presented, and the performance of liquid turbines was predicted using CFD methods which were validated with experimental results. The efficiency of the designed liquid turbine was 92% and the output power was 65.7 kW. The performance of the turbine predicted by the preliminary method could agree with simulation results of prototype and model turbines near the design working condition, while there was a certain deviation when the flow rate was less than 70%. Through analyzing the presented preliminary design method, it could be found that distinctive differences in thermal properties of working fluids caused that typical design parameters for liquid turbines, like ratios of the blade height, the hub radius and the area, should be selected differently from empirical values for gas radial turbines. The results obtained in this paper could help guide the design of liquid turbines for various systems to promote energy conservation and improve system efficiencies significantly.

Investigating the Influence of Impeller Axial Thrust Balance Holes on the Flow and Overall Performance of a Cryogenic Liquid Turbine Expander

Abstract An excessive rotor axial thrust in any turbomachine can cause critical operational problems, and rotor axial thrust balancing has always attracted much attention. The present numerical study is focused on axial thrust balancing for a cryogenic liquid turbine expander, whose axial thrust balancing is typically challenging because of its small impeller size and large axial thrust. A computational fluid dynamics (CFD) simulation is conducted in a real turbine expander environment constituted by main and gap flow domains with allowing for the thermodynamic effect of liquefied air. The balance hole influential mechanism on the main and gap flows is explored, and its influence on the expander axial thrust and overall performance is quantified. The results show that the use of balance holes creates a highly swirling gap flow, and the static pressure over the impeller disk back-side surface decreases to produce a small axial component force and axial thrust, but the turbine expander overall efficiency drops by 1.1 and 2.8 points at 100% and 50% design flow, respectively, due to an increased internal leakage loss and distorted impeller flow. In addition, a parametric study is conducted to analyze the effect of balance hole diameter, circumferential position, and radial position on expander axial thrust and overall performance. The results indicate that the axial thrust is sensitive to both the balance hole diameter and circumferential position but less sensitive to its radial position, while the overall efficiency is influenced by all three parameters.

Black Hole-Inspired Optimal Design of Biomethane Liquefaction Process for Small-Scale Applications

Biomethane is regarded as a promising renewable energy source, with great potential to satisfy the growth of energy demands and to reduce greenhouse gas emissions. Liquefaction is a suitable approach for long distances and overseas transportation of biomethane; however, it is energy-intensive due to its cryogenic working condition. The major challenge is to design a high-energy efficiency liquefaction process with simple operation and configuration. A single mixed refrigerant biomethane liquefaction process adopting the cryogenic liquid turbine for small-scale production has been proposed in this study to address this issue. The optimal design corresponding to minimal energy consumption was obtained through the black-hole-based optimization algorithm. The effect of the minimum internal temperature approach (MITA) in the main cryogenic heat exchanger on the biomethane liquefaction process performance was investigated. The study results indicated that the specific energy consumption of modified case 2 with MITA of 2°C was 0.3228 kWh/kg with 21.01% reduction compared to the published base case. When the MITA decreased to 1°C, the specific power of modified case 1 reduced to 0.3162 kWh/kg, which was 24.96% lower than the base case. In terms of exergy analysis, the total exergy destruction of the modified cases 1, 2, and 3 was 31.28%, 22.27%, and 17.51% lower than the base case, respectively. This study’s findings suggested that introducing the cryogenic liquid turbine to the single mixed refrigerant-based biomethane liquefaction process could reduce the specific energy consumption and total exergy destruction significantly. Therefore, this study could provide a viable path for designing and improving the small-scale biomethane liquefaction process.

Preliminary Design Method and Performance Analysis of the Liquid Turbine for Supercritical Compressed Air Energy Storage Systems

Liquid turbines can replace throttling valves to recover waste energy and reduce vaporization in various industrial systems, such as liquefied natural gas, air separation, supercritical compressed air energy storage (SC-CAES) systems, et al. However, there were few studies about differences in the preliminary design method between general radial inflow turbines and liquid turbines. In this paper, a preliminary design method of the liquid turbine for the SC-CAES system was presented, mathematical models for correlating geometrical and flow parameters were derived, and the model test method of the liquid turbine was proposed. The experimental performance of the liquid turbine was carried out and the internal flow was analyzed numerically. Ranges of geometrical parameters were also discussed, and modifications were made for the liquid turbine. The results obtained in this paper indicated that the presented preliminary design method could be applied to liquid turbines for various systems with high accuracy and reliability.

Cavitating Flow Suppression for a Two-Phase Liquefied Natural Gas Expander Through Collaborative Fine-Turning Design Optimization of Impeller and Exducer Geometric Shape

Abstract Cryogenic liquid turbine expanders have been increasingly used in liquefied natural gas (LNG) production plants to save energy. However, high-pressure LNG commonly needs to be throttled to or near a two-phase state, which makes the LNG turbine expander more vulnerable to cavitation. Although some work has been reported on cryogenic turbomachine cavitation, no work has been reported on designing a cavitation-resistant two-phase LNG liquid turbine expander. Motivated by the urgent requirement for two-phase liquid turbine expanders, an effective design optimization method is developed that is well-suited for designing the cavitation-resistant two-phase liquid turbine expanders. A novel optimization objective function is constituted by characterizing the cavitating flow, in which the overall efficiency and local cavitation flow behavior are incorporated. The adaptive-Kriging surrogate model and cooperative coevolutionary algorithm (CCEA) are incorporated to solve the highly nonlinear design optimization problem globally and efficiently. The former maintains high-level prediction accuracy of the objective function but uses much reduced computational fluid dynamics (CFD) simulations while the later solves the complex optimization problem at a high convergence rate through decomposing them into some readily solved parallel subproblems. By means of the developed optimization method, the impeller and exducer blade geometries and their axial gap and circumferential indexing are fine-tuned. Consequently, cavitating flow in both the impeller and exducer of the two-phase LNG expander is effectively mitigated.

Cryogenic Cavitation Mitigation in a Liquid Turbine Expander of an Air-Separation Unit through Collaborative Fine-Tuned Optimization of Impeller and Fairing Cone Geometries

An air-separation unit (ASU) uses atmospheric air to produce essential pure gaseous and liquid products for many industrial sectors but requires intensive power consumption. In recent years, cryogenic liquid turbine expanders have been used to replace the traditional J-T valves in air-separation units to save energy. In this paper, an effective design optimization method is proposed to suppress swirling flow and mitigate cavitation in liquid turbines. A flexible tuning of the impeller and fairing cone geometries is simultaneously realized, where the optimization variables are identified via a geometric sensitivity study. A novel objective function is deliberately established by allowing both swirling flow and cavitation characteristics, driving the optimizer to search for deswirling and cavitation-resistant geometries. A kriging surrogate model with an adaptive sampling strategy and a cooperative co-evolution algorithm (CCEA) are incorporated to solve the highly nonlinear optimization problem, where the former reduced the costly evaluations but simultaneously maintained the model prediction accuracy and enabled the aim-oriented global searching (the latter decomposes the problem into several readily solved sub-problems that could be solved in parallel at a high-convergence rate). The optimized impeller and fairing cone geometries were quite favorable for suppressing swirling flow and mitigating cavitation. The impeller cavitation was significantly reduced, with the maximal vapor volume fraction reduced from 0.365 to 0.17 at the blade surface; the diffuser tube high-swirl flow was significantly deswirled and the intensive vapor fraction around the centerline largely reduced, with the maximal vapor volume fraction in the diffuser tube reduced from 0.387 to 0.121. As a result, the isentropic efficiency of the liquid turbine expander was improved from 88.4% to 91.43%.

Process design and economic optimization of boil-off-gas re-liquefaction systems for LNG carriers

Recent LNG carriers are equipped with high pressure gas injection engines. However, there has been a lack of research on liquefaction processes for boil-off gas (BOG) on LNG ships driven by high pressure fuel. Thus, this paper investigates the economic feasibility of the additional BOG liquefaction facilities in the high pressure fuel supply system on the vessels. To utilize the existing BOG compressor for fuel production, the liquefaction was conducted by the Joule Thomson (JT) cycle, which can use the pressurized BOG as a working fluid. For the comparison of the fuel supply system and its variations with BOG liquefaction, they are optimized with respect to total annual cost (TAC) as the objective function. With an LNG price of 5 USD/MMBtu, the optimization results show that the use of BOG liquefiers on LNG vessels reduces the TAC by at least 9.4% compared to the high pressure fuel supply system. The use of a liquid turbine in the liquefaction configurations also resulted in 2.4% savings in TAC compared to the JT cycle based process. However, a sensitivity analysis with different LNG prices indicates that the liquefaction systems are not economical compared to the fuel supply system when the LNG price is lower than 4 USD/MMBtu.

Measurement uncertainty of turbine flow meter calibration used in conformity assessment for water management

Water management is a relevant activity for society, for industry and for consumers, requiring transactions based on measurement. To ensure confidence to all users, a high level of measurement quality is required to enable conformity assessment to be acceptable in the definition of market conditions by the stakeholders. The practical implementation of conformity assessment to equipment requires the definition of decision rules, on acceptance or rejection of its performance, depending on the accuracy of measurements. Liquid turbine flow meters are common equipment used to measure flow velocity and volume of water in many water supply systems. To approve the use of this type of equipment it is necessary to provide measurement traceability and to evaluate and use the measurement uncertainty in the applied decision rules. This paper describes a new framework to use measurement uncertainty obtained by calibration in the definition of decision rules for conformity assessment.

Experimental investigation of a liquid turbine in a full performance test rig

In traditional industrial systems, a liquid expander can be used as a substitute for a throttling valve to improve system efficiency and economy. In this paper, the research and development of liquid expanders was reviewed. A set of experimental procedures were presented and an experimental test rig was built to examine the performance of a liquid turbine, which is a model machine of the liquid expander used in the supercritical compressed air energy storage system. At the rated condition, the flow rate of the liquid turbine is 60.7 kg/s, the differential pressure is 0.662 MPa, the output power is 30.44 kW, and the efficiency is 75.16%. The experimental results indicate successful construction of the test rig, which fully demonstrates the advantages of a semi-open and semi-closed system. The experimental results of the liquid turbine are of practical value for verification and development of the liquid expander in supercritical compressed air energy storage system.

Blade shape optimization of liquid turbine flow sensor

Based on the characteristic curve analysis, the method using Δ(K2) square difference of meter factor at different flow rates was developed to evaluate the performance of turbine flow sensor in this study. Then according to the distribution of entrance velocity, it was supposed that reducing the blade area near the tip could decrease the linearity error of a sensor. Therefore, the influence of different blade shape parameters on the performance of the sensor was investigated by combining computational fluid dynamics(CFD)simulation with experimental test. The experimental results showed that, for the liquid turbine flow sensor with a diameter of 10 mm, the linearity error was smallest, and the performance of sensor was optimal when blade shape parameter equaled 0.25.

Feasibility Demonstrations of Liquid Turbine Power Generator Driven by Low Temperature Heats

Lower temperature waste heats less than 373 K have strong potentials to supply additional energies because of their enormous quantities and ubiquity. Accordingly, reinforcement of power generations harvesting low temperature heats is one of the urgent tasks for the current generation in order to accomplish energy sustainability in the coming decades. In this study, a liquid turbine power generator driven by lower temperature heats below 373 K was proposed in the aim of expanding selectable options for harvesting low temperature waste heats less than 373 K. The proposing system was so simply that it was mainly composed of a liquid turbine, a liquid container with a biphasic medium of water and an underlying water-insoluble low-boiling-point medium in a liquid phase, a heating section for vaporization of the liquid and a cooling section for entropy discharge outside the system. Assumed power generating steps via the proposing liquid turbine power generator were as follows: step 1: the underlying low-boiling-point medium in a liquid phase was vaporized, step 2: the surfacing vapor bubbles of low-boiling-point medium accompanied the biphasic medium in their wakes, step 3: such high momentum flux by step 2 rotated the liquid turbine (i.e. power generation), step 4: the surfacing low-boiling-point medium vapor was gradually condensed into droplets, step 5: the low-boiling-point medium droplets were submerged to the underlying medium in a liquid phase. Experiments with a prototype liquid turbine power generator proved power generations in accordance with the assumed steps at a little higher than ordinary temperature. Increasing output voltage could be obtained with an increase in the cooling temperature among tested ranging from 294 to 296 K in contrast to normal thermal engines. Further improvements of the direct current voltage from the proposing liquid turbine power generator can be expected by means of far more vigorous multiphase flow induced by adding solid powders and theoretical optimizations of heat and mass transfers.

Swirling and cavitating flow suppression in a cryogenic liquid turbine expander through geometric optimization

A single-stage cryogenic liquid turbine expander is developed as a replacement of Joule–Thompson valve in the internal compression air separation unit for energy-saving purpose. Flow analysis and optimization is conducted for the turbine expander. With the original geometry, static pressure drops gradually from the nozzle to impeller together with a 2.7 K temperature drop, which exhibits simultaneously a smooth throttling characteristic and cryogenic refrigeration effect. However, similar to the conventional hydraulic turbine, a vortex-rope is apparently formed around the draft tube centerline. It leads to considerable mechanical energy dissipation and, subsequently, a local pressure drop and temperature rise, which have made the turbine expander vulnerable to cavitation. The draft tube vortex swirling flow has been found to be sensitive to exit geometric shape of rotating impeller. To suppress the swirling flow and cavitation, design optimization of impeller geometric shape is further conducted with an efficient global optimization method developed by the authors, where in particular, an innovative optimization objective function and a simultaneous tuning of both impeller meridian profile and blade shape are incorporated. The former is a linear combination of the draft tube loss factor and normalized impeller exit static pressure. It depicts the draft tube swirling flow behavior and also captures somehow the cavitation flow physics. The latter permits a very flexible variation of the impeller geometry. Such a highly nonlinear problem is solved by the global optimization algorithm, in which the Kriging surrogate model is used but updated through adaptive sampling. It is demonstrated that with the optimized geometry, the vortex-rope like characteristics has diminished apparently and both scale and intensity of swirling region are reduced significantly. As a result, the low static pressure region has shrunk and the local temperature rise is reduced and, subsequently, the cavitation is effectively suppressed.

Experimental study of cryogenic liquid turbine expander with closed-loop liquefied nitrogen system

A cryogenic liquid turbine expander is developed as a replacement for traditional Joule–Thomson valves used in the cryogenic systems for the purpose of energy saving. An experimental study was conducted to evaluate the performance of the turbine expander and is the subject of this paper. The test rig comprises a closed-loop liquefied nitrogen system, cryogenic liquid turbine expander unit, and its auxiliary and measuring systems. The test operating parameters of the turbine expander are determined on the basis of flow similarity rules. Pre-cooling of the liquid nitrogen system is first performed, and then the tests are conducted at different flow rates and speed ratios. The turbine expander flow rate, inlet and outlet pressure and temperature, rotational speed and shaft torque were measured. Experimental results and their uncertainties were analyzed and discussed. The following are demonstrated: (1) For both test cases, turbine expander peak isentropic efficiency is respectively 78.8% and 68.4% obtained at 89.6% and 92% of the design flow rate. The large uncertainties in isentropic efficiency are caused by the large enthalpy variations subjected to small measurement uncertainties in temperature and pressure. (2) Total efficiency and hydraulic efficiency of the turbine expander are obtained. They are essentially the same, since both include flow-related effects and also bearing losses. Comparisons of total efficiency and hydraulic efficiency were used to justify measurement uncertainties of different quantities, since the former involves the measured mass flow rate and enthalpy drop (being dependant on inlet and outlet temperature and pressure), while the latter involves the actual shaft power, volume flow rate, and inlet and outlet pressure. (3) Losses in flow passages and the shaft-bearing system have been inferred based on the measured turbine expander total efficiency, isentropic efficiency, and mechanical efficiency, which are respectively 57.6–74.8%, 62.1–78.8% and 89.5–96.4%. Uncertainty analysis is conducted for experimental isentropic efficiency, hydraulic efficiency, and total efficiency. The hydraulic efficiency seems to be the best measure for assessing the performance of cryogenic liquid turbine expander. (4) Isentropic efficiency versus speed ratio is obtained from the experimental data. The experimental isentropic efficiency increases with the speed ratio, and it reaches 78.8% at the largest experimental speed ratio. A higher efficiency would be achieved if the speed ratio could reach a larger value. This provides some guidance for an optimal operation of the turbine expander in the future.

Composition-Explicit Distillation Curves of Alternative Turbine Fuels

In recent years, environmental considerations, the potential for supply disruptions, and rising fuel prices have led to the development of turbine fuels produced from non-petroleum feedstocks. To determine the suitability of an alternative turbine fuel, it is important to characterize the fuel properties and assess the degree of departure of the alternative fuel characteristics from those of petroleum-derived fuels. One very important property to use for this purpose is the volatility, as expressed by the distillation curve. In this paper, we present advanced distillation curve measurements of three prototype alternative turbine fuels and compare the distillation curve, composition, and combustion enthalpy to those of the petroleum-derived turbine fuels JP-8 and JP-10. We studied a hydrotreated fuel derived from chicken fat, a fuel composed of hydrogenated pinene dimers derived from turpentine, and a gas–liquid fuel produced from natural gas via the Fischer–Tropsch process. We found that the distillation curves of the chicken-fat-derived fuel and the gas–liquid turbine fuel were similar to those of JP-8, deviating the most at high distillate volume fractions. The chicken-fat-derived fuel deviated by at most 17 °C from the distillation curve of JP-8, and the gas–liquid turbine fuel deviated by at most 36 °C. The hydrotreated turpentine dimer fuel was much less volatile than JP-10, a fuel with which the turpentine dimer fuel shares some structural similarities. The shape of the distillation curves of these two fuels was similar, however. The major components of all fuels were determined, and these were used to calculate the enthalpy of combustion for several distillate volume fractions of the alternative turbine fuels. The gas–liquid turbine fuel was most similar to petroleum-derived fuel in its energy content, and the turpentine dimer fuel had a high volumetric enthalpy of combustion value similar to that of JP-10.

Natural Convection Effect on the Droplet Ignition in High Pressure Condition

A simulation of the droplet combustion in the high-pressure environment is very important in understanding the fundamental phenomena of liquid rocket, gas turbine and diesel engine combustion. Therefore, a more reliable ignition model of a droplet under high pressure condition is highly desirable in developing a useful tool for design. In this paper, the ignition model of the n-heptane droplet is suggested for high pressure environment and solved for the ignition delay. Its variations with the change in the ambient pressure and temperature are discussed for the cases with/without gravity so that the natural convection effects on the droplet ignition delay time are also examined. The Redlich-Kwong equation of state is used for calculating the phase equilibrium at the droplet surface under high pressure. The natural convection effects are considered by introducing so-called the time scale correction method. The results show that the logarithmic ignition delay time linearly decreases with the inverse of the ambient temperature, and its decreasing slope is independent of the ambient pressure. Thereby, the overall activation energy is found not to be affected by the pressure variation. As the pressure increases, the ignition delay time gets shorter since the droplet vaporization rate is enhanced. But, at a higher ambient pressure, the reduction rate in the ignition delay time becomes smaller. The natural convection effect is also found to make the ignition delay time shorter due to the improved heat feedback to the droplet.