CN103968907A - Method and device for measuring supercritical and gaseous hydrocarbon fuel dense flow - Google Patents

Abstract

The invention discloses a device for measuring supercritical and gaseous hydrocarbon fuel dense flow. The device comprises more than two sonic nozzles in serial connection, and each nozzle comprises an isometric straight section, a shrinkage section, a throttling throat portion and an expansion section; the isometric straight section of the first sonic nozzle is connected with an outlet of a hydrocarbon fuel heating device; each sonic nozzle reaches the sonic speed at the corresponding throat portion. The measuring method includes the steps: firstly, heating a to-be-measured fuel to a temperature about To and feeding the heated to-be-measured fuel; secondly, measuring an inlet pressure intensity P'm and a temperature T'm of the isometric straight section of a sonic nozzle m; thirdly, calculating a dense flow value of the to-be-measured fuel under the inlet pressure intensity P'm and the temperature T'm of the isometric straight section of the sonic nozzle m according to an equation: Mm=m/Am, wherein Am refers to the throat area of the sonic nozzle m. Using the device and the method can accurately measure the dense flow of the supercritical and gaseous hydrocarbon fuel reaching a 'choked' state under different state points with low cost.

Description

A kind of above-critical state and the close flow measuring apparatus of gaseous hydrocarbon fuel and method

Technical field

The invention belongs to Aero-Space fields of measurement, be specifically related to fuel system mass flow meter and method.

Background technology

Structural reliability while work for guarantee aircraft farm labourer, scramjet engine and aeromotor need to be carried out cooling to aircraft.The regeneration type of cooling is first using fuel as cooling medium, and then enters burning and participate in burning absorbing propellant spray after heat.Under Ma < 8 conditions, Endothermic Hydrocarbon Fuel is a kind of hypersonic aircraft fuel of excellent combination property.The caloric receptivity of Endothermic Hydrocarbon Fuel changes with flight operating mode is different, and in this process, its state also constantly changes.When fuel temperature and pressure are during respectively higher than its thermodynamics critical temperature and critical pressure, fuel enters above-critical state; Under certain pressure conditions, when fuel temperature higher than this pressure under when saturation temperature, fuel enters gaseous state.Above-critical state and gaseous hydrocarbon fuel have the ideal gas of being similar to diffusion property, but its physical property of some state point is very violent with temperature and pressure change.

Scramjet engine and aeroengine combustor buring constant pressure generally lower (< 6atm) by force.Fuel gas can adopt velocity of sound spray mode.Ideal gas taking specific heat ratio as 1.4 is as example, in the time that spray pressure and combustion chamber pressure meet certain condition when (as spray pressure is greater than 2 times of combustion chamber pressure), in gas spray process, in nozzle, minimum area place can reach the velocity of sound, is generally referred to as to reach " being jammed " state.In the time that ideal gas reaches the velocity of sound, its flow is only relevant with spray temperature with upstream spray pressure, and irrelevant with downstream back pressure, thereby has isolated the impact of downstream back pressure on its flow.Overcritical and gaseous hydrocarbon fuel has and the similar characteristic of ideal gas.For arbitrary combustion chamber pressure, in the time that propellant spray pressure and temperature are enough high, overcritical and gaseous hydrocarbon fuel minimum area place in nozzle reaches the velocity of sound, reaches " being jammed " state.Now, fuel mass flow rates is only relevant with spray temperature with upstream spray pressure, and irrelevant with downstream back pressure.Therefore, can measure its mass rate by making overcritical and gaseous hydrocarbon fuel reach " being jammed " state.The discharge characteristic when spray of the fuel velocity of sound can be propellant spray conceptual design foundation is provided, simultaneously can be for the Gernral Check-up of fuel cut engine working state of system.

For the mass flow measurement of overcritical and gaseous state RP-3 (No. 3 aviation kerosenes of China), model (the Xuejun Fan that learns military affairs, Gong Yu, Jianguo Li and Xinyu Zhang.Investigation of Vaporized Kerosene Injection andCombustion in a Supersonic Model Combustor.Journal of Propulsion and Power.Vol.22, No.1.2006) (mole fraction is respectively 49% in conjunction with the three component alternative models of RP-3 to adopt the supertrapp software package of NIST, 44% and 7% decane, 1, 3, 5 trimethyl-cyclohexanes and propylbenzene), based on one dimensional isentropic flow hypothesis and broad sense corresponding states rule, computing fuel accelerates the density flowing while reaching the velocity of sound, the parameter such as temperature and flow velocity, obtain the close stream (mass rate that unit area is corresponding in velocity of sound cross section, unit is kg/ (m2s)).

For verifying the reliability of method of calculating flux above, model (the Xuejun Fan that learns military affairs, Gong Yu, Jianguo Li andXinyu Zhang.Investigation of Vaporized Kerosene Injection and Combustion in a SupersonicModel Combustor.Journal of Propulsion and Power.Vol.22, No.1.2006) adopt in sonic nozzle collected downstream fuel process and carried out the overcritical and gas RP-3 mass rate while reaching " being jammed " state.In certain hour section, keep entrance fuel temperature and pressure substantially constant constant, make overcritical and gas RP-3 reach " being jammed " state in throat (sonic nozzle minimum flow area place) by sonic nozzle, obtain flowing through in this time period the fuel mass of sonic nozzle by collected downstream device, collection obtains fuel mass the time is averaged and obtains fuel mass flow rates, and fuel mass flow rates obtains the close stream of fuel divided by sonic nozzle throat opening area.

Can be found out by above-mentioned, after current main employing alternative model theory is calculated and sonic nozzle throat is jammed, collected downstream is carried out these two kinds of close streams of methods measurement fuel of time average.

The theoretical accuracy of calculating when hydrocarbon fuel is close to flow depends on the accuracy of Calculation of Physical Properties.The fuel used potpourri with thousands of kinds of compositions that is generally of engine, cannot directly calculate fuel physical property under technical conditions at present.General by adopting the representative hydrocarbon composition alternative model of minority, physical property using the physical parameter of alternative model as replaced fuel, because fuel physical property is violent with temperature and pressure change, be difficult to adopt alternative model under all temperature and pressure conditions, accurately to obtain the physical parameter of replaced model.General in physical property with temperature and the quite mild region of pressure change, the accuracy that alternative model calculates is higher, and in physical property with the violent place of temperature pressure change, the accuracy that alternative model calculates is poor.Therefore, the fuel flow rate that adopts theoretical calculation method to obtain in the high region of alternative model Calculation of Physical Properties accuracy has higher precision, and the fuel flow rate error that adopts theoretical calculation method to obtain in the region of alternative model Calculation of Physical Properties poor accuracy is large.

When experiment measuring hot coal oil discharge characteristic owing to adopting time averaging method, its precision and fuel collection time span, consider while collection and need to carry out valve switching, in valve handoff procedure, flow reaches stable state also needs a stabilization time, and the method needs the time in even tens seconds tens seconds just can obtain result comparatively accurately conventionally.Collect the temperature and the invariablenes pressure of liquid that in the process of fuel, need to keep velocity of sound nozzle inlet, fuel is reached and within a period of time, remain on steady temperature fuel upstream heating system to be required very high, especially change violent region in physical property.Use the method simultaneously, can only obtain the close stream under a state point (referring to temperature and pressure) at every turn, efficiency is low, and cost of determination is high.Visible, the method efficiency is low, and cost is high.

Summary of the invention

The present invention solves the technical matters that prior art exists, the close flow measuring apparatus of a kind of above-critical state and gaseous hydrocarbon fuel and method are provided, utilize the lower above-critical state of measurement different conditions point and the gaseous hydrocarbon fuel that these apparatus and method can be accurately, cost is low to reach the close stream under " being jammed " state.

A kind of above-critical state of the present invention and the close flow measuring apparatus of gaseous hydrocarbon fuel, comprise plural series connection sonic nozzle, and described sonic nozzle such as comprises at straight section, contraction section, throttling throat and the expansion segment; The straight section that waits of the 1st sonic nozzle is connected with the outlet of hydrocarbon fuel heating arrangement; Each sonic nozzle all reaches the velocity of sound in throat;

Calculate fuel to be measured at sonic nozzle m import pressure P ' _mwith inlet temperature T ' _mclose flow valuve under state: a _mfor sonic nozzle m throat opening area;

Fuel mass flow rates to be measured $\stackrel{\&CenterDot;}{m}=\stackrel{\&CenterDot;}{M}*\frac{P_N^{\text{'}}}{P}*\sqrt{\frac{T}{T_N^{\text{'}}}}*A_N$

A _nfor sonic nozzle N throat opening area; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state , the actual measurement pressure P ' of sonic nozzle N _nand temperature T ' _n.

Preferably, described 0.8P < P ' _n< 1.2P, 0.95T < T ' _n< 1.05T.

Preferably, described close flow valuve acquisition methods be theoretical calculation method or the state sonic nozzle collected downstream fuel process of being jammed.

Preferably, the throat opening area of described sonic nozzle:

1) described N sonic nozzle throat opening area A _n. wherein, for fuel mass flow rates to be measured; be N the close stream of sonic nozzle throat

${\stackrel{\&CenterDot;}{M}}_N=\stackrel{\&CenterDot;}{M}*\frac{P_N}{P}*\sqrt{\frac{T_o}{T}},$

N sonic nozzle import pressure is P _n, P _nbetween 0.5-2.0Mpa, selection, fuel temperature to be measured are T _o; Temperature is that T meets 0.95T < T _o< 1.05T, pressure P meets 0.8P < P _n< 1.2P; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state ;

2) determine upstream sonic nozzle throat opening area A _m:

A _M＝A _N*P _N/P _M

The individual sonic nozzle of M (M=1,2 and N-1); A _nbe N sonic nozzle throat opening area, P _mand P _nbe respectively M and N sonic nozzle import pressure.

Preferably, the flow area of the straight section such as each sonic nozzle is greater than respectively 6 times of its throttling throat flow area.

Utilize above-mentioned device to carry out the method for break bounds state and the close flow measurement of gaseous hydrocarbon fuel, comprise the following steps:

Step 1, fuel to be measured is heated to temperature is about T _oand pass into this device;

Step 2, sonic nozzle m etc. measure its import pressure P ' on straight section _mand temperature T ' _m;

Step 3, calculate fuel to be measured at sonic nozzle m import pressure P ' _mwith inlet temperature T ' _mclose flow valuve under state: a _mfor sonic nozzle m throat opening area;

Fuel mass flow rates to be measured $\stackrel{\&CenterDot;}{m}=\stackrel{\&CenterDot;}{M}*\frac{P_N^{\text{'}}}{P}*\sqrt{\frac{T}{T_N^{\text{'}}}}*A_N$

A _nfor sonic nozzle N throat opening area; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state the actual measurement pressure P ' of sonic nozzle N _nand temperature T ' _n.

Adopt the apparatus and method of multiple throttling throat's series connection measurement above-critical states and gaseous hydrocarbon fuel.Measurement efficiency is high, can obtain the close stream of fuel of multiple state points simultaneously.Fuel only need to keep stable state in the shorter time, has reduced the requirement to fuelizer, has reduced experiment difficulty.

Brief description of the drawings

Fig. 1 double throttle throat sonic nozzle schematic diagram

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in detail.

The present invention, by designing each sonic nozzle throttling throat opening area, makes fuel all reach the velocity of sound at each place of throttling throat, reaches " being jammed " state, measures above-critical state and the gaseous hydrocarbon fuel close stream under different conditions.

Fuel to be measured flows and reaches while stablizing in apparatus of the present invention, identical by the fuel mass flow rates of each throttling throat.Close stream by known fuel to be measured under low pressure (P is between 0.5-2.0Mpa) state, calculates the close stream of fuel to be measured in the 2nd throat, then passes through according to formula calculate the close stream of the 1st throat, i.e. the close stream of fuel to be measured under the 1st sonic nozzle inlet condition.Wherein be respectively by the close stream of sonic nozzle 1 and sonic nozzle 2, A ₁, A ₂be respectively the throat opening area of logical sonic nozzle 1 and sonic nozzle 2, for by the fuel mass flow rates of sonic nozzle.Can set up by this method between the state of fuel to be measured and close stream relation one to one, the close properties of flow of the fuel that obtains can be for the design of engine injection system.

Taking the sonic nozzle that is in series with Liang Ge throttling throat as example, in conjunction with Fig. 1, design process of the present invention is described below.

Step 1: the present invention is made up of two sonic nozzles that straight section, contraction section, throttling throat and the expansion segment such as comprise respectively.Streamwise, upstream sonic nozzle 1 is by waiting straight section 11, contraction section 12, throttling throat 13 and expansion segment 14 to form, and downstream sonic nozzle 2 is by waiting straight section 21, contraction section 22, throttling throat 23 and expansion segment 24 to form.Deng being designed with interface on straight section 11 for being connected with hydrocarbon fuel heating arrangement outlet.Adopt existing hydrocarbon fuel heating arrangement to provide the hydrocarbon fuel of different temperatures for apparatus of the present invention.At present ripe hydrocarbon fuel heating arrangement can realize heated hydrocarbon fuel mass rate and outlet temperature adjustable on a large scale.

Step 2: select to need the fuel state scope to be measured of measurement, comprise temperature range and pressure range, the intermediate value of temperature and pressure range is labeled as respectively to T _oand P _o.

Step 3: obtain the accurate close flow valuve that hydrocarbon fuel to be measured is jammed under state in the time that pressure P (P is between 0.5-2.0Mpa) and temperature are T .For RP-3, can adopt supertrapp software to calculate its close flow valuve by aforementioned three component alternative models, the method has obtained experimental verification in the time that pressure is lower.The hydrocarbon fuel that temporarily cannot calculate by this kind of method reliable close flow valuve for other, utilize background technology introduction pass through in the mode of state sonic nozzle collected downstream fuel of being jammed, obtain its accurate close flow valuve under dbjective state.

Step 4: select sonic nozzle 2 throat opening area A ₂.Pass through formula determine downstream sonic nozzle throat opening area.Wherein, the fuel mass flow rates to be measured providing for hydrocarbon fuel heating arrangement.Pass through formula calculating pressure is P ₂, temperature is T _oclose stream when state like this known p, T and T _ocondition under, by select P ₂can calculate A ₂.Preferably, P ₂between 0.5-2.0Mpa, select.

Step 5; Select sonic nozzle 1 throat opening area A ₁.By formula A ₁=A ₂* P ₂/ P _ocalculate upstream sonic nozzle throat opening area.For ensureing that fuel all reaches the velocity of sound in Liang Ge sonic nozzle throat, preferably, the A selecting in step 4 ₂and P ₂should ensure A ₂> 1.3A ₁.

Step 6: select selections wait straight section 11 with and etc. the flow area of straight section 21.Preferably, Deng straight section 11 with and wait the flow area of straight section 21 to be greater than respectively 6 times of throttling throat 13 and 23 flow areas, make fuel to be measured be less than 0.15 at the Mach number (ratio of flow velocity and the velocity of sound) that waits straight section 11 and 21, now on straight section 11 and 21, record pressure and directly import stagnation pressure and the stagnation temperature at sonic nozzle 1 and 2 as fuel of temperature waiting.Preferably, the angle of throat of contraction section 12 and 22 is selected respectively between 20 ° to 60 °, and the angle of flare of expansion segment 14 and expansion segment 24 is selected respectively between 6 ° to 30 °.Above-mentioned parameter is the general range of choice in this area.

Step 7: select expansion segment 14, etc. the volume of straight section 21 and contraction section 22.In the actual hydrocarbon fuel heating arrangement course of work be difficult to control make the fuel temperature of its outlet and invariablenes pressure of liquid constant.Suppose t and within the t+ Δ t moment fuel mean mass flux to be measured by sonic nozzle 1 and sonic nozzle 2 be respectively in Δ t time span, due to hydrocarbon fuel heating arrangement, cause fuel to be measured in the present invention in flow process its state have in time small size variation.Expansion segment 14 is designated as V with the volume that waits straight section 21 and contraction section 22, and it is designated as at t and the average density in t+ Δ t moment according to mass conservation theorem, in Δ t time span, fuel mass to be measured by sonic nozzle 1 and 2 is poor to be met and can pass through formula calculate.The precision of the present invention's measuring method used can be passed through formula $({\stackrel{\&OverBar;}{\stackrel{\&CenterDot;}{m}}}_1-{\stackrel{\&OverBar;}{\stackrel{\&CenterDot;}{m}}}_2)/{\stackrel{\&OverBar;}{\stackrel{\&CenterDot;}{m}}}_2=(\stackrel{\&OverBar;}{\mathrm{\&rho;}}(t+\mathrm{\&Delta;t})-\stackrel{\&OverBar;}{\mathrm{\&rho;}}\left(t\right))*V/({\stackrel{\&OverBar;}{\stackrel{\&CenterDot;}{m}}}_2*\mathrm{\&Delta;t})$ Calculate, can find out, in measured time range, expansion segment 14 and straight section 21 such as grade and contraction section 22 fuel state temporal evolution amplitudes are less ( / Δ t is less), the volume of expansion segment 14 and straight section 21 such as grade and contraction section 22 is less, and the fuel mass flow rates that hydrocarbon fuel heating arrangement provides is larger, and measuring accuracy of the present invention is higher.Suppose that fuel mass flow rates is 0.1kg/s, Measuring Time is Δ t=1s, and average density is changed to 10kg/m3 (RP-3 density when 700K, 1Mpa is about 25kg/m3, and when fuel state omits microvariations, variable density can not exceed 10kg/m3), V=5*10 ^-5when m3, (be equivalent to the pipe volume of the long internal diameter 20mm of about 160mm), measuring error is about 0.5%.Visible, as long as the flow through fuel state of apparatus of the present invention of guarantee is more stable during short time (1s time scale), the present invention has very high measuring accuracy.In actual use, by fuel to be measured rate of change of the density and fuel flow rate in time, select expansion segment 14 and wait the volume of straight section 21 and contraction section 22 to make measuring error be less than 1%.

Measuring method:

Step 1: by hydrocarbon fuel heating arrangement, fuel to be measured is heated to temperature and is about T _oand pass into apparatus of the present invention.

Step 2: in the time that sonic nozzle 1 and 2 inlet temperatures and pressure all reach steady state (SS), waiting the import pressure P ' that measures respectively sonic nozzle 1 and 2 on straight section 11 and 21 ₁, P ' ₂and temperature T ' ₁, T ' ₂.

Step 3: pass through formula calculate by the fuel mass flow rates to be measured of sonic nozzle 2.

Wherein, P ' ₂and T ' ₂for testing sonic nozzle 2 import pressure and the temperature that record, be P, the temperature close stream of fuel to be measured while being T for obtaining at pressure in step 3, A ₂for sonic nozzle 2 throat opening areas.For ensureing experiment measuring precision, preferably, 0.8P < P ' in parameter selection course ₂< 1.2P, 0.95T < T ' ₂< 1.05T.Pass through formula calculate fuel to be measured at P ' ₁and T ' ₁close flow valuve under state.As T ' ₁not in the time of dbjective state temperature range, by regulating hydrocarbon fuel heating arrangement to regulate fuel temperature to be measured that it is dropped in dbjective state temperature range.Work as P ₁not in the time of dbjective state pressure range, make P ' by the fuel mass flow rates to be measured that regulates hydrocarbon fuel heating arrangement to provide ₂fall in dbjective state pressure range.

Preferably, for improving the dirigibility of combining between the different sonic nozzles of use procedure, each sonic nozzle entrance and exit is all designed with interface for being connected with other sonic nozzle or hydrocarbon fuel heating arrangement etc.

In apparatus of the present invention, hydrocarbon fuel to be measured experiences following flow process: the straight section 11 such as to enter lower than 0.15 Mach number; In contraction section 12, constantly accelerate and reach the velocity of sound at 13 places of throttling throat, realization is jammed; In expansion segment 14, there is shock wave, shock wave front fuel by the velocity of sound continue accelerate, after shock wave fuel flow rate by supersonic speed be reduced to subsonic speed, static pressure raises, in expansion segment 14 after shock wave fuel along current method flow velocity continue reduce, static pressure continue raise; Waiting in straight section 21 fuel Mach number lower than 0.15; In contraction section 22, constantly accelerate and reach the velocity of sound at 23 places of throttling throat, in expansion segment 24, continuing to accelerate to reach supersonic speed.

In addition, the present invention can also, by the multiple throttling of employing throat sonic nozzle, obtain the close flow valuve of fuel to be measured under near different pressure target temperature in once testing.While thering is the sonic nozzle of N throttling throat as adopted, can set N-1 nozzle inlet state, the temperature range of the N-1 setting a nozzle inlet state should be identical, by the setting of throat opening area, make N-1 nozzle inlet pressure, by these target, pressure called after target, pressure 1,2 and N-1 successively from high to low.All reach the velocity of sound for making to be flowing in all throttlings throat, these pressure should have certain intervals, and every two close pressure values minimums differ 30%.Selectable highest pressure should be lower than the highest pressure allowable of hydrocarbon fuel heating arrangement, to ensure that hydrocarbon fuel heating arrangement normally works.Each sonic nozzle is also respectively by waiting straight section, contraction section, throttling throat and expansion segment, and its expansion segment and contraction section angle are followed the example of identical with described in step 1.Streamwise, by the sonic nozzle at each throttling throat place called after sonic nozzle 1,2 and N respectively.The throat opening area computing method of N sonic nozzle are identical with step 4.The throat opening area A of the individual sonic nozzle of M (M=1,2 and N-1) _mcomputing method and step 5 are similar, by formula A _m=A _n* P _n/ P _mdetermine upstream sonic nozzle throat opening area.Wherein, A _nbe N sonic nozzle throat opening area, P _mand P _nbe respectively target, pressure M and selected N sonic nozzle import pressure.

The present invention is the close flow measurement for above-critical state and gaseous state RP-3 and decane in National University of Defense technology's experiment outfield, has obtained good effect.

Claims (6)

1. an above-critical state and the close flow measuring apparatus of gaseous hydrocarbon fuel, comprise plural series connection sonic nozzle, described sonic nozzle such as comprises at straight section (11,21), contraction section (12,22), throttling throat (13,23) and the expansion segment (14,24); The straight section (11) that waits of the 1st sonic nozzle is connected with fuelizer outlet; Each sonic nozzle all reaches the velocity of sound in throat;

Fuel to be measured is at sonic nozzle m (m=1 to N, N is nozzle number) import pressure P ' _mwith inlet temperature T ' _mclose flow valuve under state for: a _mfor sonic nozzle m throat opening area;

Fuel mass flow rates to be measured $\stackrel{\&CenterDot;}{m}=\stackrel{\&CenterDot;}{M}*\frac{P_N^{\text{'}}}{P}*\sqrt{\frac{T}{T_N^{\text{'}}}}*A_N$

A _nfor sonic nozzle N throat opening area; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state the actual measurement pressure P ' of sonic nozzle N _nand temperature T ' _n.

2. a kind of above-critical state as claimed in claim 1 and the close flow measuring apparatus of gaseous hydrocarbon fuel, is characterized in that described 0.8P < P ' _n< 1.2P, 0.95T < T ' _n< 1.05T.

3. a kind of above-critical state as claimed in claim 1 and the close flow measuring apparatus of gaseous hydrocarbon fuel, is characterized in that described close flow valuve acquisition methods be theoretical calculation method or the state sonic nozzle collected downstream fuel process of being jammed.

4. a kind of above-critical state as claimed in claim 1 and the close flow measuring apparatus of gaseous hydrocarbon fuel, is characterized in that the throat opening area of described sonic nozzle:

1) described N sonic nozzle throat opening area A _n, wherein, for fuel mass flow rates to be measured; be N the close stream of sonic nozzle throat

${\stackrel{\&CenterDot;}{M}}_N=\stackrel{\&CenterDot;}{M}*\frac{P_N}{P}*\sqrt{\frac{T_o}{T}},$

N sonic nozzle import pressure is P _n, P _nbetween 0.5-2.0Mpa, selection, fuel temperature to be measured are T _o; Temperature is that T meets 0.95T < T _o< 1.05T, pressure P meets 0.8P < P _n< 1.2P; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state

2) determine upstream sonic nozzle throat opening area A _m:

A _M＝A _N*P _N/P _M

The individual sonic nozzle of M (M=1,2 and N-1); A _nbe N sonic nozzle throat opening area, P _mand P _nbe respectively M and N sonic nozzle import pressure.

5. a kind of above-critical state as claimed in claim 1 and the close flow measuring apparatus of gaseous hydrocarbon fuel, the flow area that it is characterized in that the straight sections such as described each sonic nozzle (11,21) is greater than respectively 6 times of its throttling throat (13,23) flow area.

6. utilize device described in right 1 to carry out the method for break bounds state and the close flow measurement of gaseous hydrocarbon fuel, comprise the following steps:

Step 1, fuel to be measured is heated to temperature is about T _oand pass into this device;

Step 2, sonic nozzle m (m=1 to N) etc. upper its import pressure P ' that measures of straight section (11,21) _mand temperature T ' _m;

Step 3, calculate fuel to be measured at sonic nozzle m import pressure P ' _mwith inlet temperature T ' _mclose flow valuve under state: a _mfor sonic nozzle m throat opening area;

Fuel mass flow rates to be measured $\stackrel{\&CenterDot;}{m}=\stackrel{\&CenterDot;}{M}*\frac{P_N^{\text{'}}}{P}*\sqrt{\frac{T}{T_N^{\text{'}}}}*A_N$

A _nfor sonic nozzle N throat opening area; The hydrocarbon fuel to be measured close flow valuve in the time that pressure P and temperature are T of being jammed under state , the actual measurement pressure P ' of sonic nozzle N _nand temperature T ' _n.