Investigation Of Endothermic Hydrocarbon Fuel Flow Distribution Characteristics And Flow Deviation Control

The regenerative cooling of scramjet engines is of great significance to the safety and performance of the engine structure.However,the unreas onable flow distribution of fuel in parallel cooling channels leads to serious waste of fuel cooling capacity and even local over-temperature,which results in the thermal protection failures and threatens the safety of the engine structure.In order to ensure the cooling effect and structural safety of the engine,it is urgent to develop proper channel design method and flow distribution control scheme.The coupling relationship between the distribution of hydrocarbon fuel flow and the geometric parameters of the channel is an important support for related designs and methods.This thesis focuses on the above mentioned issues:The experimental study shows that there is a double deviation amplification mechanism in the hydrocarbon fuel flow distribution problem.Through the sensitivity analysis of hydrocarbon fuel properties and operating conditions,the double deviation amplification mechanism is explained.The problem is classified according to the leading factors: distributor induced case and heat flux induced case.The flow distribution characteristics in 3D-multi-parallel-channel system are studied.When the geometry factor dominates,it directly causes the initial flow mal-distribution.Then the sharp and complex variations of hydrocarbon fuel properties with heating amplify the initial flow mal-distribution greatly.When the non-uniform heat flux dominates,the thermal coupling effect of the transcritical area channel has a significant impact on flow distribution.The non-uniform heat flux causes severe thermal stratification in the channels with higher heat flux.As a result,the flow rate and fuel temperature distribution are worse.Further,in the pyrolysis zone,besides thermal stratification,chemical reaction emerges to become the new factor,which finally leads to significant changes in the distribution mechanisms.Based on the basic distribution characteristics,the influence of channel parameters on flow distribution is studied.In distributor induced cases,no matter with chemical reaction or not,the flow distribution is optimized as the aspect ratio of the channel increases.However,increasing the aspect ratio causes severe thermal stratification,which results in higher wall temperature and cannot be applied.While in the non-uniform heat flux dominated cases,the flow distribution optimizes with the channel aspect ratio increase in the non-pyrolysis zone.So are the fuel temperature and fuel heat sink utilization distributions.Compared with the results of the single-channel study,when considering the effects of flow distribution,the upper limit of the cooling channel aspect ratio is higher.In the cracking zone,it is generally suitable for a small aspect ratio design.The increase of channel aspect ratio does not affect the flow distribution.But it causes the distribution of fuel temperature and fuel conversion rate to deteriorate.The wall temperature rises.Compared with the single channel study,the upper limit of the channel aspect ratio of the cracking zone is lower.This thesis also proposes a parallelogram channel design that can effectively increase the heat transfer area,reduce the flow deviation,and optimize the cooling effect in the non-pyrolysis zone.In addition,the parameters such as the flow area ratio of inlet and outlet headers and the aspect ratio of header also have significant impacts on the flow distribution.In order to alleviate the flow mal-distribution,a method for adjusting flow distribution based on variable cross-section channel design is proposed.It reduces the sectional area in the low-temperature zone and increases the sectional area in the high-temperature zone.Together with proper heat transfer enhancement,this method cuts off the relationship between the temperature deviation and the flow resistance deviation,and finally optimizes the flow distribution.Based on the idea of the allocating the ratio of flow resistance,this thesis also proposes a more specific method adjusting the flow distribution.A two-stage throttling structure is set in the temperature zone below the pseudo-critical point.The stable flow resistance is increased,which helps to control flow deviation.This method has been verified on the high-temperature hydrocarbon fuel flow distribution test bench,which highlights its advantages in terms of control effect and practicality.It also proves the idea of allocating the flow resistance ratio is valid.It provides a solution to help solve the problem of flow mal-distribution.At last,by comparing the heat flow conditions of different Mach numbers,the overtemperature risk and the severe limit on the speed range of the engine caused by the flow deviation are presented.The threaten of the flow deviation to the engine is analyzed.The effect of the flow mal-distribution control on the engine is also studied.It is proved that the control of flow mal-distribution helps to expand the engine velocity range.