Fuel Heat Sink Research Articles

Heat transfer and cracking performance of endothermic hydrocarbon fuel when it cools a high temperature channel

Jet fuel is used as a coolant before it is burned in the combustor of the aircraft. Insoluble particles and surface deposits can impair engine performance. Jet fuel thermal oxidation test (JFTOT) defines the standard test method for evaluation of the deposit formed through heating fuels in tubes caused by thermal oxidation (<400°C). At a higher temperature, fuel in the heating process decomposes leading to surface deposits by coking. In this work, we propose a method to evaluate the security of fuel flowing in the tube at high temperatures (>500°C). The heat transfer and cracking performances of two hydrocarbon fuels which are laboratory modified aviation kerosene (Fuel 1 (ρ=0.85g/cm3) and Fuel 2 (ρ=0.78g/cm3)) have been investigated in a heat-exchanger under supercritical conditions (T=700–770°C, p=2.5–5.5MPa, m=0.4–1.0g/s). The temperature and flow rate in this work are much higher than those in JFTOT. The safe run time (SRT) is used to evaluate the heat transfer security of each fuel. As the temperature increases or the flow rate decreases or the pressure increases, the SRTs of Fuel 1 and Fuel 2 decrease clearly. In general, the heat transfer security of Fuel 1 is better than that of Fuel 2. Moreover, the volumetric heat sink of Fuel 1 is larger than that of Fuel 2. So, the overall performance of Fuel 1 is more excellent when it is used as propellant and coolant for hypersonic aircraft. In consideration of the heat transfer security, heat sink and the required driving force for aircraft, the temperature of fuel at the exit of heat transfer passage should be set as 740°C, the flow rate of fuel should be 0.6–1.0g/s, the pressure of heat transfer passage should be 3.5MPa. Based on these results, we find that the modification of a high density fuel is an effective way to prepare an advanced hydrocarbon fuel.

A control method for flow rate distribution of cracked hydrocarbon fuel in parallel channels

With the development of hypersonic vehicles, regenerative cooling becomes an effective method of thermal protection, in which fuel is thus used as coolant. However, it presents the problem of fuel mal-distribution and the waste of heat absorption capacity. In this work, a flow control method based on tandem flow restriction is brought up and experimentally studied with a two-parallel-pipe system. The variation of control effect with different position and corresponding fuel temperature of the restrictors is analyzed. Compared with the single flow restriction, tandem flow restriction method achieves better control effect and allows larger flow restrictors with lower and self-adaptive pressure drop. The fuel heat sink utilization will be improved by proposed effective method for flow rate distribution and corresponding recuperation effectiveness of the engine cycle is improved.

Palmitoyl hyperbranched polyglycerol as a nanoscale initiator for endothermic hydrocarbon fuels

One of hyperbranched polymers is developed as a novel nanoscale initiator to enhance the heat sink of endothermic hydrocarbon fuels to meet the great cooling requirement of hypersonic aircrafts. In this work, the hyperbranched polyglycerol (HPG) is treated with palmitoyl chloride to obtain a fuel-soluble product, palmitoyl-hyperbranched polyglycerol (PHPG). The thermogravimetric analyses show that the long-alkyl chains rupture first from the matrix at about 200°C, and then the HPG core breaks around 400°C during the cracking of PHPG, which indicates a high decomposition temperature for this “macroinitiator”. The cracking processes of n-tridecane with PHPG in different molecular weights and addition quantities are performed in an electrically heated tube reactor under supercritical conditions (3.5MPa, and 600–720°C). PHPG can promote the cracking of n-tridecane with significant improvements of the conversion and heat sink. The conversion of n-tridecane is improved as high as 17.6% at 690°C, and the corresponding heat sink is improved from 3.0MJ/kg to 3.5MJ/kg. Furthermore, the optimum addition quantity and molecular weight range of PHPG are chosen for the practical application to an aviation kerosene under 600–700°C, and the increases of heat sink in comparison with those from the thermal cracking confirm the potential application of PHPG to endothermic hydrocarbon fuels.

Flow rate distribution of cracked hydrocarbon fuel in parallel pipes

A model consisting of two parallel pipes with common inlet and outlet manifolds was established and used to run simulation and experimental study on the flow rate distribution of cracked hydrocarbon fuel in parallel pipes under supercritical pressure. Both simulation and experimental results indicated that mass flow rate and fuel temperature distribution of cracked hydrocarbon fuel in parallel pipes was closely related to the difference in fuel density in pipes. Two deviation amplification mechanisms were found. In addition, the mode of mal-distribution varies with thermal deviation and the distribution was effectively improved by the increase of pressure. And the total mass flow rate could hardly have any effects on the flow rate distribution. All these results could be used to help the full utilization of fuel heat sink and avoid over-temperature.

Numerical analysis of flowing cracked hydrocarbon fuel inside cooling channels in view of thermal management

Thermal management of fuel is very important for the cooling system of an advanced engine. In order to study the 3-D phenomena of fuel flow with cracking reaction in the cooling channels and their effect on the utilization of fuel heat sink, numerical models of cracking fuel flow in an asymmetrically heated rectangular tube are built on the basis of the real fuel thermophysical properties using commercial software and validated through experiments in a conversion range from 0% to 76%. The simulation results indicate that the velocity, temperature and conversion of fuel flow exhibit a clear nonuniformity in the cross-section of the rectangular tube, causing the nonuniformities of physical and chemical heat sinks. Compared to the situation without chemical reaction, due to the fact that chemical reaction can slightly reduce the nonuniformity of temperature field, the nonuniformity of physical heat sink resulting from the temperature field can be slightly reduced. However, the nonuniformity of total heat sink can be dramatically reduced by chemical reaction because the chemical heat sink is one of the major components of total heat sink, and unlike physical heat sink, chemical heat sink shows much less nonuniformity under the influence of both temperature and velocity.

Experimental study on effect of pressure on heat sink of n-decane

The heat sink is one of the key indicators of the development of endothermic hydrocarbon fuels, and the total heat sink of endothermic hydrocarbon fuels can be increased by enhancing the chemical heat absorption capacity to meet the cooling requirements for future high-performance aircraft. The supercritical pyrolysis and endothermicity capacity of n-decane (a major component in endothermic hydrocarbon fuels) are studied under different pressures. Experimental results indicate the main gas products are small molecular hydrocarbons (methane, ethane, ethylene, etc.), ethylene and propylene are the most abundant components at current experimental conditions. It is noticed that the influence of pressure on the production of ethylene is greater than that of any others. The increase in pressure increases the conversion of fuel to enhance its endothermicity, but the increase in pressure also decreases the alkene/alkane ratio, which has negative effect on the improvement of the chemical heat sink of fuel. So the influence of pressure on the endothermicity of n-decane is not a simple effect of promotion or inhibition, the regularity is different in different temperature ranges.

Thermal management method of fuel in advanced aeroengines

The method to improve the heat sink utilization of fuel is the primary issue for thermal management of advanced aeroengines. In order to study the methods to control the fuel heat sink utilization, a one dimensional model of flow and heat transfer process in a single cooling channel of endothermic hydrocarbon fuel cooled scramjet in terms of endothermic reaction is developed, which is validated by corresponding experimental data. Different methods are put forwarded to control the utilization level of fuel heat sink and effective residence time of fuel during fuel cooling process is defined to distinguish global method and local method. The control of fuel mass flow rate or the height of cooling channel can be regarded as a global method, while the control of operating pressure in the cooling process can be considered as a local method. Analytical results indicate that the control methods can effectively improve the fuel heat sink utilization. However, the efficiency of the global method is limited by the allowable wall temperature. In contrast, the local method can be used not only to control the utilization of fuel heat sink, but also to improve the heat transfer and pressure drop performance of fuel.

Off-Design Condition Cooling Capacity Analysis of Recooling Cycle for a Scramjet

Many methods have been widely carried out to increase fuel heat sink to meet the cooling requirement of an airbreathing hypersonic vehicle. In particular, the recooling cycle has been newly proposed for an actively cooled scramjet to increase fuel heat sink. Fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink through secondary cooling in recooling cycle. The performance of recooling at off-design conditions is evaluated based on a coupled heat transfer and flowmodel of a scramjet with recooling cycle. The design principle of the recooling cycle under off-design conditions with a great range of Mach numbers and equivalence ratios is determined. The results show that the recooling cycle possesses variable heat sink increment capacities, and it can meet heat sink requirement at all conditions.

Effect of recooling cycle on performance of hydrogen fueled scramjet

Abstract Hydrogen fueled scramjet is a candidate for use as the engine of the aerospace plane. Many methods to increase the fuel heat sink (cooling capacity) are widely carried out to meet the cooling requirement of scramjet engine. Especially, recooling cycle (RCC) has been newly proposed for actively cooled scramjet to increase fuel heat sink for cooling. With the working process of fuel cooled scramjet defined as a recuperated cycle, the difference between regenerative cooling (RC) and RCC in the characteristics of heat recovery, heat extraction and heat reinjection are compared first, and the scramjet performance of under RC and RCC mode is compared through off-design comparison analysis at different Mach numbers and equivalence ratios to evaluate the effect of recooling cycle on the performance of scramjet using a coupled heat transfer and flow model. It can be seen through analysis and comparison that recooling cycle can save the fuel mass flow rate for cooling, and make maximum use of the recovered heat. And the specific impulse of a scramjet can be greatly promoted as well.

Experimental study on the performance of recooling cycle of hydrocarbon fueled scramjet engine

Recooling cycle (RCC) has been newly proposed as a new cooling method to increase fuel heat sink (cooling capacity). A testing system is established and an experimental study is conducted on the operating characteristics and performance of RCC with different flow, heat transfer and cracking conditions. Experimental results indicate that the utilization of fuel heat sink is restricted by the allowable material temperature of heated tube; RCC provides another chance for the continued use of fuel chemical heat sink and the repeated use of fuel physical heat sink in the secondary cooling by reducing the fuel temperature by doing work to turbine, and the total heat sink of fuel can be increased to 0.7MJ/kg when n-Decane is used as the fuel. RCC can also improve the “olefin/paraffin ratio” of cracking reaction, which facilitates the improvement of the combustion performance of fuel.

Heat transfer characteristic modelling and the effect of operating conditions on re-cooled cycle for a scramjet

Abstract A re-cooled cycle has been proposed for a regeneratively cooled scramjet to reduce the hydrogen fuel flow for cooling. Upon the completion of the first cooling, fuel can be used for secondary cooling by transferring the enthalpy from fuel to work. Fuel heat sink (cooling capacity) is thus repeatedly used and fuel heat sink is indirectly increased. Instead of carrying excess fuel for cooling or seeking for any new coolant, the cooling fuel flow is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. A performance model considering flow and heat transfer is build. A model sensitivity study of inlet temperature and pressure reveals that, for given exterior heating condition and cooling panel size, fuel heat sink can be obviously increased at moderate inlet temperature and pressure. Simultaneously the low-temperature heat transfer deterioration and Mach number constrains can also be avoided.

Power generation and heat sink improvement characteristics of recooling cycle for thermal cracked hydrocarbon fueled scramjet

In order to further investigate how much fuel heat sink could be increased and how much power generation could be obtained by using recooling cycle for a regeneratively cooled scramjet, the energy conversion from heat to electricity and the fuel heat sink increase in recooling cycle are experimentally investigated for fuel conversion rate and components of gas cracked fuel products at different fuel temperatures. The results indicate that the total fuel heat sink (i.e., physical+chemical+recooling) of a recooling cycle is obviously higher than the heat sink of fuel itself, and the maximum heat sink increment is as high as 0.4 MJ/kg throughout the recooling cycle. Furthermore, the cracked fuel mixture has a significant capacity of doing work. The thermodynamic power generation scheme, which adopts the cracked fuel gas mixture as the working fluid, is a potential power generation cycle, and the maximum specific power generation is about 500 kW/kg. Turbine-pump scheme using cracked fuel gas mixture is also a potential fuel feeding cycle.

Flow and heat transfer characteristics in fuel cooling channels of a recooling cycle

Developing fuel with higher heat sink is widely carried out to meet the cooling requirement for an air breathing hypersonic vehicle. Especially, a recooling cycle has been newly proposed for an actively cooled scramjet to reduce the fuel flow for cooling. Fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink in a recooling cycle. The variation of fuel thermal property related with heat transfer and flow as temperature and pressure is added to the one-dimensional analytical fin-type model for rectangular ducts. Heat transfer performance comparison between recooling cycle and regenerative cooling is carried out, and detailed discussion about the variation and influence of heat transfer and flow characteristics caused by the introduction of the recooling process are discussed. Performance comparison between a recooling cycle at supercritical pressure and it at subcritical condition is also investigated.

Irreversible cycle analysis of a re-cooled cycle for a scramjet

In this article, a re-cooled cycle (RCC) has been proposed for a regeneratively cooled scramjet to decrease the hydrogen fuel flow for cooling. In this method, the fuel heat sink (cooling capacity) is indirectly increased, and the fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle; this is done instead of carrying excess fuel for cooling or looking for a new coolant. Heat transfer effectivenesses of the cooling passage and pressure loss are introduced in the cycle, and cycle parameters are recomputed. An investigation of the effects of various irreversible losses on the RCC performance is carried out.

Effect of cooling channel geometry on re-cooled cycle performance for hydrogen fueled scramjet

Developing fuel with higher heat sink is widely carried out to meet the cooling requirement for an airbreathing hypersonic vehicle. However, a Re-Cooled Cycle has been newly proposed for a regeneratively cooled scramjet to reduce the fuel flow for cooling. Fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink. Parametric sensitivity analysis of Re-Cooled Cycle of a hypersonic aircraft is explored. An analytical fin-type model for incompressible flow in smooth-wall rectangular ducts in terms of hydrodynamic, thermal, power balance and Mach number constraints is proposed. Based on this model, the difference of the cooling channel structure design between Re-Cooled Cycle and regenerative cooling is discussed, and a new optimization index is introduced for Re-Cooled Cycle. The sensitivity of the cycle performance to cooling channel geometry is investigated, and the optimal performance of a Re-Cooled Cycle is obtained by satisfying constraints. The differences of the effect of channel design variables between Re-Cooled Cycle and regenerative cooling are also discussed.

Thermodynamic optimization for a scramjet with Re-cooled Cycle

A new Re-cooled Cycle has been proposed for a regeneratively cooled scramjet to reduce the fuel flow for cooling, fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. Parametric analysis of the Re-cooled Cycle carried out in previous study shows the potential for the cycle to be optimized. A thermodynamic optimization analysis of Re-cooled Cycle for a scramjet is obtained by satisfying hydrodynamic, thermal, and Mach number constraints. The optimal cycle parameters and length allocation between the first and second cooling passages are obtained.

Thermodynamic analysis and parametric study of a closed Brayton cycle thermal management system for scramjet

A closed Brayton cycle thermal management system is proposed for a regeneratively cooled scramjet to reduce the hydrogen fuel flow for cooling, through converting part of the heat from fuel to other forms of energy to decrease the heat that must be taken away by hydrogen fuel. Fuel heat sink (cooling capacity) is thus indirectly increased. Instead of carrying excess fuel for cooling or seeking for any new coolant, the fuel flow for cooling is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. A parametric study of an irreversible closed Brayton cycle thermal management system for scramjet has been performed with external as well as internal irreversibilities. It is known through performance analyses that closed Brayton cycle thermal management system has excellent potential performance over conventional regenerative cooling, due to the reduction in fuel flow for cooling and additional power output.

Parametric performance analysis of multiple Re-Cooled Cycle for hydrogen fueled scramjet

A Re-Cooled Cycle is newly proposed for a regeneratively cooled scramjet to reduce the hydrogen fuel flow for cooling. Upon the completion of the first cooling, hydrogen fuel can be used for secondary cooling by transferring the enthalpy from fuel to work. Fuel heat sink (cooling capacity) is thus repeatedly used to indirectly increase the fuel heat sink. Instead of carrying excess fuel for cooling or seeking for any new coolant, the cooling fuel flow is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. Two new performance parameters are defined combining the characteristics of scramjet, differences between RCC and expander cycle is discussed, and pressure loss in cooling passage is also considered. Performance comparison is carried among multiple RCCs, and preliminary application limit and real possibility of RCC for scramjet is discussed.

Performance cycle analysis of an open cooling cycle for a scramjet

In a conventional regeneratively cooled scramjet, fuel directly enters the combustor after cooling. It is proposed in this article that high-temperature and high-pressure fuel out of the first cooling passage can be used for secondary cooling after expanding through the turbine and transferring enthalpy from fuel to work. A fuel heat sink (cooling capacity) is thus repeatedly used to indirectly increase the fuel heat sink. Instead of carrying excess fuel for cooling or looking for any new coolant, the fuel flow for cooling is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. First are defined cooling and expansion and, second, cooling an open cooling cycle (OCC) for the scramjet. This article provides a brief description of the assessment of the performance potential and scientific feasibility of a scramjet with OCC using fundamental thermodynamic principles. The results show that OCC yields higher performance gain over regenerative cooling, because of the increase in the fuel heat sink and additional power output.

Additives to Improve Fuel Heat Sink Capacity in Air/Fuel Heat Exchangers

Hypersonic air-breathing vehicles travel at high speeds and generate heat loads that are greater than can be met from sensible heating of the fuel. However, the fuel can provide about 50% more heat sink capacity if it undergoes endothermic thermal cracking reactions before combustion. Unfortunately, thermal cracking reactions require high temperatures, in excess of 100°F, to obtain useful reaction rates. However, a fuel additive has been identified that increases the rate of thermal cracking reactions, allowing the same chemical endotherm to be obtained at lower fuel temperatures. This paper describes work in which we conducted extensive laboratory bench-scale calorimetric tests to directly measure the effectiveness of the cracking initiator compound with several prospective fuels, including JP-7 and normal decane. We then used the data obtained from the laboratory experiments to generate rate models, which we then used in the design of a pilot scale fuel/air heat exchanger. Finally, we tested the pilot scale unit at heat fluxes approaching 100,000 Btu /ft 2 ·h with JP-7 and n-decane with and without the initiator. At each test point, the data clearly indicated that the initiator produced significant increases in the rate of cracking and fuel heat sink capacity.