Method for measuring a gas mass flow through an injector

Abstract

The invention relates to a method for measuring a gas mass flow (2) through an injector (10), wherein a gas (8) is flowed into a measuring chamber (4) while measuring a first gas pressure (P1) until the first gas pressure (P1) assumes a predetermined value (P0), wherein a control valve (15) which is fluidically connected to the measuring chamber (4) is opened to a continuous gas outlet from the measuring chamber (4), wherein the gas (8) is intermittently flowed into the measuring chamber (4) through the injector (10) with the control valve (15) open, and at least during the inflow a second gas pressure (P2) is measured in a time-resolved manner, wherein the control valve (15) is opened in such a way and / or the gas (8) is flowed in through the injector (10) in such a way that the gas (8) continuously flowing out through the control valve (15) has a counterpressure with (P1) has the specified value (P1),and wherein, based on the measured second gas pressure (P2), a pressure curve is determined at least during the inflow, from which the time-resolved gas mass flow (2) through the injector (10) is determined.,

Description

The invention relates to a method for measuring a mass flow of gas through an injector, in particular for an injector of a drive motor, and in particular for the purpose of calibrating the injector for its use in an internal combustion engine.At present, in transit, internal combustion engines still represent the dominant mode of drive in the great majority of means of transport (motor vehicles including. Transport vehicles, aircraft, ships, etc.). In this case, internal combustion engines currently burn almost exclusively fossil fuels which are present in liquid form (that is to say are also put in liquid form and are put in liquid form up to the respective internal combustion engine of the respective means of transport). However, due to the greenhouse gases generated during the combustion of fossil fuels, all CO2on the fly, a departure from fossil energy carriers is also required for the transport, which requires an application of alternative propulsion concepts which have a drastically reduced output (and preferably completely suppressed output, "emission-free") of greenhouse gases compared to the combustion of fossil fuels.While in passenger cars in this context the electric motor and thus the battery-electric vehicle as such seems to be put through an alternative, at least potentially emission-free drive concept, there are areas of the transport and transport industry for which battery-electric operation seems to be barely conceivable for purely physical reasons for the foreseeable time due to the still significantly lower volume and / or mass energy density compared to previous fossil energy carriers, such as, for example, air traffic, ship traffic, or in some cases also heavy load traffic. In the future, particularly in air traffic, as a result of the physical restrictions of alternative drives with respect to their weight, combustion engines will continue to be used with all prospects, which for a reduction of greenhouse emissions are then to be operated with correspondingly alternative fuels (i.e. non-fossil).Such fuels, such as synthetic e-fuels or the like, are often in the gaseous state under the usual conditions (such as room temperature). Such a gaseous fuel must then be introduced into a combustion chamber or a combustion chamber of an internal combustion engine by means of corresponding injection valves, wherein a high precision is required for an efficient (and thus both energy-favourable and residue-free) combustion process in determining a mass flow of the fuel over time. This applies in particular to a mass flow through an injection valve or the like, for which the highest possible time-resolved knowledge is desired.Whereas high-precision measuring devices for the comparable purpose have already been state of the art for a long time for liquid fuels, a development of agents which control an injection process into the combustion chamber as precisely as possible is by far not yet concluded for gaseous fuels. In particular, the calibration of injection valves is used here in order to detect a mass flow which an injection valve for gaseous fuels achieves depending on the setting.The object of the invention is therefore to specify a method for measuring a mass gas flow through an injector which is as precise as possible and by means of which an injector can be calibrated, in particular for use in an internal combustion engine in conjunction with gaseous fuels. The invention is further based on the object of specifying a device for such a measurement, by means of which a gas mass flow through an injector can be determined as precisely as possible.The first object is achieved according to the invention by a method for measuring a mass flow of gas through an injector, wherein a gas is flowed into a measuring chamber while measuring a first gas pressure until the first gas pressure assumes a predefined value, wherein a control valve, which is connected fluidically to the measuring chamber, is opened to a continuous gas outlet from the measuring chamber, wherein the gas is flowed intermittently into the measuring chamber by the injector when the control valve is opened, and a second gas pressure is measured at least during the inflow in a time-resolved manner, wherein the control valve is opened and / or the gas is flowed in through the injector in such a manner that the gas flowing continuously through the control valve has a counterpressure at the predefined value for the first gas pressure, and wherein a pressure profile is determined at least during the inflow on the basis of the measured second gas pressure, from which the time-resolved gas mass flow through the injector is determined. Advantageous and partly per se inventive embodiments are the subject matter of the dependent claims and of the following description.The second-mentioned object is achieved according to the invention by a device for measuring a gas mass flow through an injector which is configured for connection to a gas supply, comprising a measuring chamber which encloses a measuring volume, a number of pressure measurement pickups for measuring a first gas pressure and a second gas pressure in the measuring chamber, a regulating valve which is configured for the outlet of gas located in the measuring chamber, and a control unit. In this case, the control unit is configured to control a gas flow into the measuring chamber on the basis of the measured first gas pressure via said injector and / or at least one auxiliary injector in such a way that the first gas pressure assumes a predefined value, to open the regulating valve in such a way that a continuous gas flow results from the measuring chamber, to actuate an intermittent gas flow into the measuring chamber via said injector when the regulating valve is open and to control a measurement of the second gas pressure, to open the regulating valve in such a way and / or to control the gas flow via the injector in such a way that the gas continuously flowing out through the regulating valve has a counterpressure with the predefined value for the first gas pressure, and to determine, on the basis of the measured second gas pressure, at least when the inflow occurs, a pressure profile from which the time-resolved mass gas flow through the injector is determined.The apparatus according to the invention shares the advantages of the method according to the invention. The advantages specified for the method and for its developments can be transferred analogously to the device. In particular, the device aspects of the invention and the associated developments are also reflected in corresponding method aspects.An injector includes in particular any device which is configured and provided for injecting a gaseous fuel and / or a gaseous fuel-air mixture into a combustion chamber in an internal combustion engine, for which purpose the injector is connected to a fuel supply (as a gas supply). In particular, a needle valve is included under an injector in which a mass flow is controlled in that a needle closes or releases an outflow opening of a nozzle or the like depending on the relative position of the needle, wherein the diameter of the outflow opening is somewhat smaller than the diameter of the needle. In the normal state, the needle is preferably pressed into the outflow opening by means of a spring, wherein a release of the outflow opening is achieved by a mechanical and / or (electro)magnetic actuator which pulls the needle out of the outflow opening mechanically or by magnetic force (by energizing an electromagnet) accordingly counter to the spring force. In another configuration, the injector can be actuated via a piezoelectric crystal.The method is preferably used here to measure the mass flow of gas through the injector in order to characterize it for operation in an internal combustion engine in conjunction with gaseous fuels, that is to say in particular as a function of the activation of the specific valve position of the injector to record the mass flow established by the preferably open injector during a flow through the same as time-resolved as possible. Such a phase of the injector, in which a gas (i.e. for example a gaseous fuel) flows through it during operation, and the gas is correspondingly introduced into a chamber or the like connected to the injector, is also referred to as "injection phase" (in contrast to the "closure time", in which the injector is closed, and therefore does not conduct any gas any further). In particular, the time required by the injector to actually provide a mass flow for opening after a control signal can also be detected here (so-called "dead time").In this case, any suitable gas-tight vessel is included in particular as a measuring chamber, wherein the suitability which can include a design of the material properties and the dimensions or geometry of the measuring chamber can depend in particular on the gas pressure to be maintained and optionally on the measurement volume to be enclosed. Preferably, for the method or in the device of the injector, the gas flows into the measuring chamber without further fluidic non-trivial connecting lines.The predefined value which has to be set for the gas pressure when flowing into the measuring chamber can be predefined in particular by the superordinate application in which the injector is provided and configured for use, that is to say for example by a gas pressure of a combustion chamber of an internal combustion engine which has been determined to be optimum for the combustion process with regard to the energy yield and / or power, or the like.The first gas pressure in the measuring chamber, which can be brought to the predefined value by an inflow of the gas, preferably through the injector itself, and / or through one or more auxiliary injectors, thus preferably represents the counterpressure against which the injector must blow the gas into a combustion chamber or the like in use. The inflow process can be effected here by a continuous or an intermittent, in particular pulsed, injection through the injector or the injectors.The first gas pressure is measured during the inflow of the gas into the measuring chamber, preferably by a first pressure measuring transducer of the device, which is preferably designed as an absolute or relative pressure measuring transducer, in order to be able to detect the attainment of the predefined value by the first gas pressure as precisely as possible. The relative pressure measuring sensor is configured here to indicate the measured gas pressure relative to an ambient pressure, while the absolute pressure measuring sensor is configured to indicate the measured gas pressure with reference to a reference pressure of a closed reference volume.After the first gas pressure in the measuring chamber has thus reached the predefined value, the regulating valve is opened in such a way that a continuous gas flow from the measuring chamber is thereby produced. In this case, gas is intermittently introduced into the measuring chamber through the injector, so that gas flows out of the regulating valve at a counterpressure (counter to the subsequent application or arrangement) which has the predefined value for the counterpressure in the measuring chamber. The control valve is preferably closed during the inflow of the gas into the measuring chamber up to the predetermined value for the counterpressure, or is only slightly open.During the intermittent gas inflow through the injector, i.e. preferably at least during each individual phase in which the gas is respectively flown through the injector into the measuring chamber, the second gas pressure is now measured in a time-resolved manner, preferably by a second pressure measuring transducer of the device, which particularly preferably has a measurement frequency of at least 1 kHz. In particular, the first pressure measuring transducer for measuring the first gas pressure has a measurement frequency of less than 100 Hz, preferably less than 10 Hz and particularly preferably less than 1 Hz.In this case, the continuous gas outlet from the measuring chamber is controlled by means of the control valve on the basis of the first gas pressure in such a way that the gas continues to flow out of the measuring chamber at the value predefined for the first gas pressure, while the gas is intermittently flowed into the measuring chamber by the injector. This operation is controlled in the device by the control unit. During the individual inflow phases of the injector, the second gas pressure is measured in each case in a time-resolved manner, preferably with a measurement frequency of at least 1 kHz and particularly preferably at least 10 kHz.On the basis of the second gas pressure, it is now possible to determine a pressure curve p(t) during the individual inflow phases, from which pressure curve, in particular on the basis of the formula given in equation (i), it is possible to determine the mass gas flow m(t) through the injector: where V mess indicates the measurement volume enclosed by the measurement chamber, R s,Gas indicates the specific gas constant of the gas used, T indicates the temperature in the measurement volume and κ(T) indicates the isentropic exponent of the gas used at the temperature prevailing in the measurement volume.In this case, the time-resolved gas mass flow is preferably determined on the basis of a plurality of individual inflow phases of the intermittent inflow process, in that in particular a statistical evaluation of the individual measurements of the respective inflow phases takes place, for example by averaging the respective values for the gas mass flow at the respective measurement time of the inflow phase.For a measurement of the gas mass flow through the injector, in particular for a characterization of the injector, a discharge of the gas from the measurement volume is necessary, since otherwise the pressure in the measurement chamber would increase continuously, whereby the correct measurement point (i.e. the value of the first gas pressure predefined by the application of the injector) would not be kept sufficiently long to obtain a meaningful measurement statistic (e.g. 100 or 200 or 1000 measurements in individual inflow processes).A pulsed or otherwise intermittent opening of the control valve for said discharge of the gas from the measurement volume, which appears a priori as the logical variant as a result of the intermittent inflow, would however lead to pressure oscillations in the measurement chamber and additionally to structure-borne noise, which would be superimposed on a measurement signal of the gas mass flow. Those pressure oscillations which are caused by an opening of the injector cannot be avoided on the basis of the principle (since the behavior during the opening of the injector forms the object to be measured), and can thus be eliminated from the associated measurement signal of the second gas pressure by computational methods such as smoothing and / or notch filters. Further physical influences on the measurement of the second gas pressure, such as even pressure waves in the measuring chamber as a result of intermittent opening of the regulating valve, are advantageously avoided within the scope of the invention, so that the computational post-processing of the measurement of the second gas pressure for the purpose of measuring the gas mass flow is simplified, since only the influences of the intermittent inflow through the injector have to be corrected, and thus the precision of the measurement is improved.During the continuous outflow of the gas through the control valve, the gas is preferably flowed through the injector into the measuring chamber in periodic pulses. A periodically pulsed inflow of the gas has the advantage that the pressure oscillations formed in the measuring chamber in this case are also periodic (with the same frequency) and can thus be identified more easily and thereby eliminated in a measurement signal of the second gas pressure.Advantageously, a sound wave corresponding to the incoming pulses is determined in the measuring chamber from the measured second gas pressure, and the pressure change about the sound wave is corrected for determining the mass gas flow. This makes use of the fact that periodic pressure oscillations, i.e. a sound wave in the measuring chamber, result from the periodicity of the pulsed inflow through the injector. The correction can be effected here on the level of the measured second gas pressure, that is to say directly in the corresponding measurement signal, or else on the level of the calculated, time-resolved gas mass flow.For this purpose, the pressure change is advantageously transformed into the frequency domain, wherein a fundamental frequency of the sound wave is determined, and wherein the frequency spectrum of the pressure change around the sound wave is corrected by means of a notch filter having the fundamental frequency. Eliminating the signal contributions in the measurement signal of the second gas pressure, which correspond to said sound wave, can be carried out particularly easily and at the same time precisely in the frequency domain, especially since the sound wave usually cannot expect any appreciable contributions due to harmonic oscillations.It has proven to be further advantageous if a speed of sound in the measuring chamber is estimated or determined for the correction of the pressure change about the sound wave, and a frequency of the sound wave is estimated or determined on the basis of the speed of sound, wherein the estimated or determined frequency of the sound wave is used for said correction. Preferably, the frequency of the sound wave estimated in particular on the basis of the speed of sound of the gas in the measuring chamber is used to determine the exact frequency of the sound wave, which is then corrected on the basis of a notch filter of the corresponding frequency or by means of comparable methods in the measurement signal of the second gas pressure or in the finished time-resolved signal for the mass gas flow.The gas is expediently injected through the injector with pulses having a pulse duration of 0.1 ms to 100 ms, preferably 0.2 ms to 10 ms, and / or a pulse frequency of 0.1 Hz to 100 Hz, preferably 0.4 Hz to 20 Hz. The aforementioned values for pulse durations represent the realistic application, while the values for pulse frequencies, on the one hand, allow a sufficient distance between the pulse processes in measuring chambers of the usual size (corresponding to the associated injector) in order not to influence each other, and, on the other hand, allow a sufficiently rapid measurement with corresponding measurement statistics.It has proven to be further advantageous if the second gas pressure is measured in each case in a time window around the pulses of the injector, which has a length of at least 100% of the pulse duration and / or at most 1000% of the pulse duration. This means in particular that during the closure times in which no gas at all flows into the measuring chamber through the injector, no measurement of the second gas pressure takes place, or only in direct temporal proximity to an inflow process. This takes into account the fact that for the gas mass flow essentially only pressure changes directly at or in direct temporal proximity (max. 10 pulse durations and preferably 5 pulse durations) for the inflow process are of interest.Advantageously, for determining the gas mass flow from the pressure change, the measured second gas pressure is smoothed over time, a time derivative for determining the pressure change is formed by the smoothed second gas pressure, and the pressure change is smoothed over time again in order to filter any additionally occurring data noise in this case. The time derivative can be formed in particular as a difference quotient. By smoothing the measurement of the second gas pressure, it is possible in particular to filter geometric effects of the measuring chamber, which could lead to excessive fluctuations in the second gas pressure and thus to "artifacts" in its time derivative.Advantageously, for setting the predetermined gas pressure, the gas is flowed into the measuring chamber through the injector. As a result, further auxiliary injectors and their control or regulation can be dispensed with, which reduces both the measuring method and the associated device in terms of their complexity.An exemplary embodiment of the invention is explained in more detail below with reference to drawings. Here, in each case, diagrammatically show: FIG. 1 is a block diagram of a device for measuring a mass flow of gas through an injector; and FIG. 2 shows a gas mass flow measured with the device according to FIG. 1 with and without correction of a sound wave in the measurement volume caused by pulsed operation of the injector.Mutually corresponding parts and sizes are each provided with the same reference numerals in all figures.FIG. 1 schematically shows a block diagram of a device 1 which is configured to measure a mass gas flow 2 through an injector 10 for its characterization. The device 1 comprises a measuring chamber 4 which encloses a measuring volume 5 and to which the injector 10 to be characterized is connected in terms of flow. This can comprise, in particular, the injector flowing a gas directly into the measuring chamber 4 without further, fluidic non-trivial connecting lines. The measuring chamber 4 can also have a domed or widened bulge or the like (not shown) at the location at which the injector 10 is connected (so that, in particular when gas flows into the region of the bulge, the flow equations to be applied in the measuring chamber remain valid).The injector 10 is connected to a gas supply 6, from which the injector 10 draws a gas 8. The gas 8 can be provided in particular by a fuel for an internal combustion engine, for example a synthetic fuel. The device 1 moreover has a first pressure measurement pickup 11 and a second pressure measurement pickup 12. The first pressure measuring transducer 11 is configured to measure a first gas pressure P 1 in the measurement volume 5, while the second pressure measuring transducer 12 is configured to measure a second gas pressure P 2 in the measurement volume.Furthermore, the device 1 comprises a control valve 15 which is configured to derive a gas contained in the measuring chamber 4 from the measuring chamber 4, and a control unit 20.The injector 10 can be designed in particular as a needle valve or the like, wherein in a possible configuration of the present injector 10 of the exemplary embodiment, the latter has only two controllable states, namely closed (that is to say no gas flow through the injector) and (completely) opened, but no intermediate states (such as, for example, an opening with a reduced gas rate or the like) can be controlled. However, in addition to the present exemplary embodiment, the invention also permits time-resolved detection of a mass current through an injector with such intermediate states.In order to measure a mass gas flow 2 through the injector 10 for characterizing the flow properties of the injector 10, a gas 8 is first of all introduced into the measuring chamber 4 by the gas supply 6 through the injector 10, and the first gas pressure P 1 is measured by the first pressure measuring transducer 11. For this purpose, the injector 10 is controlled by the control command 14 by the control unit 20, wherein the control unit 20 controls the injector 10 as a function of the first measurement signal 21 to further flow the gas 8 into the measurement chamber 4 until the first gas pressure P 1 measured by the first pressure measuring transducer 11 in the measurement chamber 4 has reached a predefined value P 0. The control command 14 can in particular contain direct electrical signals which cause an actuator of the injector 10 to open the latter.The first pressure measuring sensor 11 is configured here in particular for measuring absolute pressures (absolute pressure gauge) and / or pressures relative to the environment (relative pressure gauge). The inflow of the gas 8 until the predetermined value PO is reached by the first gas pressure P 1 can additionally or alternatively also be effected by one or more auxiliary injectors (not shown), which are each controlled by the control unit 20 by corresponding control commands.When the first gas pressure P 1 has reached the predefined value P 0 as a result of the gas 8 flowing into the measuring chamber 4, the control valve 15 is controlled by the control unit via the corresponding control command 17 to allow gas 8 to escape continuously from the measuring chamber 4, while at the same time the injector 10 is controlled via the control command 14 to allow the mass gas flow 2 to flow into the measuring chamber 4 in a pulsed manner. In this case, the control valve 15, preferably by way of a corresponding actuation of an associated actuator by the control command 17, is opened in such a way that, through the continuous outlet of the gas 8 from the measuring chamber 4 with simultaneous pulsed inflow of the mass gas flow 2 through the injector, the first gas pressure P 1 continues to maintain the predefined value PO.In particular, the first pressure measuring transducer 11 measures here with a measurement frequency which is at most in the range of the pulse frequency of the injector 10 for the intermittent inflow of the gas mass flow 2. Thus, the damping effect of the gas 8 in the measurement volume 5 can prevent pressure oscillations, which arise as a result of the pulsed inflow, from entering into the first measurement signal 21, which would otherwise lead to a continuous readjustment of the control valve 15. If, for example, the pulse frequency of the injector for the individual inflow phases is 1 Hz (with a length of, for example, 1 Hz. 5 ms or 10 ms of each inflow phase), the measurement frequency of the first pressure measurement sensor 11 is preferably not more than 1 Hz. The smoothing achieved in the first measurement signal 21 by the selection of the measurement frequency can, however, alternatively also be achieved by a subsequent filtering (i.e. in particular a software solution) of the first measurement signal 21 recorded at a higher measurement frequency.In a time window during said pulsed inflow through the injector, which can preferably begin in a short period of time up to a maximum of 10 ms (i.e. for example preferably 2 ms or 1 ms) before the beginning of the gas pulse through the injector, and which can preferably end in a short period of time up to a maximum of 100 ms and particularly preferably up to a maximum of 10 ms (i.e. for example also 5 ms) after the end of the gas pulse, the second gas pressure P 2 is now measured by the second pressure measurement pickup 12 with a measurement frequency of preferably more than 1 kHz and particularly preferably more than 10 kHz (i.e. for example with 20 kHz or 50 kHz or 100 kHz). The corresponding second measurement signal 22 is subjected to a smoothing 24 in the control unit 20, which may be carried out, for example, on the basis of recursive averaging or via a (for example exponentially) decaying filter or the like. The time derivative d / dt is now formed by the smoothed second gas pressure P 2, and the resulting pressure changes dP 2 are subjected to a further smoothing 26.In parallel, the second gas pressure P 2 (or alternatively the smoothed gas pressure P 2) is subjected to a Fourier transformation FFT. On the basis of a signal of the second gas pressure P 2 in the frequency domain resulting therefrom, a fundamental frequency f 0 of a sound wave is determined, which is formed from the periodic pressure waves in the measuring chamber 4, which are caused by the periodic inflow processes of the injector 10. For ascertaining the fundamental frequency f0, it is also possible in particular to estimate and use a speed of sound csin the measurement volume.A notch filter 28 is now formed on the basis of the fundamental frequency f0, which notch filter precisely eliminates the fundamental frequency f0in the frequency domain. However, notch filter 28 is preferably implemented in the time domain and applied to the output signal of smoothing 26 (i.e., to the once again smoothed pressure change dP 2 of second gas pressure P 2). As a result, in the pressure change dP 2 of the second gas pressure P 2, the said acoustic wave of the pressure oscillations, which are generated by the periodic inflow of the mass gas flow 2 through the injector 10, is largely corrected.From the signal k (dP2) corrected in this way, the gas mass flow 2 is now calculated according to equation (i). Since the calculation according to equation (i) consists only in the multiplication by scalar factors which are independent of time for the duration of the measurements, this multiplication can also be carried out at any other arbitrary point in the internal measurement sequence of the control unit 20.The significance of the correction of the sound wave is apparent from FIG. 2. There, the gas mass flow 2 (solid line) corrected by the said sound wave is shown schematically in a diagram together with a preliminary gas mass flow 2' (dashed line) in which no such correction has taken place, against a time axis t in ms. In the preliminary gas mass flow 2', the individual oscillations 30 corresponding to the sound wave are embodied with a period duration of just less than 1 ms to be clearly recognizable. The associated fundamental frequency f0in this case clearly does not correspond to the pulse frequency of the inflow (which lies in the range of 1 Hz), but rather also substantially depends on geometric factors of the measurement volume. In the gas mass flow 2, these oscillations are completely suppressed; the local maxima and local minima, after a peak at the beginning, clearly no longer correlate with those of the preliminary gas mass flow 2'. This demonstrates that the influence of the pulsed inflow through the injector can be eliminated mathematically from the second gas pressure P 2. In the case of intermittent, in particular pulsed, opening of the control valve 15 for discharging the gas 8 from the measuring chamber 4 according to FIG. 1, two pressure oscillations would have been able to be eliminated significantly more difficultly from the second measurement signal 22 or the variables derived therefrom as a result of possible interferences.Although the invention has been illustrated and described in more detail by the preferred exemplary embodiment, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.List of reference characters1 Device 2(') (preliminary) gas mass flow 4 measuring chamber 5 measuring volume 6 gas supply 8 gas 10 injector 11 first pressure measuring transducer 12 second pressure measuring transducer 14 control command (at injector) 15 control valve 17 control command (at control valve) 20 control unit 21 first measuring signal (of the first gas pressure) 22 second measuring signal (of the second gas pressure) 24 smoothing 26 smoothing 28 notch filter 30 oscillations cs sonic velocity d / dt derivative dP2 pressure change (of the second gas pressure) f0 fundamental frequency (of the sonic wave) FFT Fourier transformation k corrected signal P0 of predefined value (for the first gas pressure) P1 / 2 first / second gas pressure P2 smoothed second gas pressure second gas pressure in the frequency domain t time axis

Claims

Method for measuring a gas mass flow (2) through an injector (10), wherein, while measuring a first gas pressure (P1), a gas (8) is flowed into a measuring chamber (4) until the first gas pressure (P1) assumes a predefined value (P0), wherein a control valve (15), which is connected fluidically to the measuring chamber (4), is opened to a continuous gas outlet from the measuring chamber (4), wherein the gas (8) is intermittently flowed into the measuring chamber (4) by the injector (10) when the control valve (15) is opened, and a second gas pressure (P2) is measured at least during the flowing in in in a time-resolved manner, wherein the control valve (15) is opened in this way and / or the gas (8) is flowed in by the injector (10) in this way, the gas (8) continuously flowing out through the control valve (15) has a counter pressure with the predetermined value (P1) for the first gas pressure (P1), and wherein a pressure curve is determined at least during the inflow on the basis of the measured second gas pressure (P2), from which the time-resolved gas mass flow (2) through the injector (10) is determined.Method according to claim 1, wherein during the continuous outflow of the gas (8) through the control valve (15), the gas (8) is inflowed through the injector (10) into the measuring chamber (4) in periodic pulses.Method according to claim 2, wherein a sound wave corresponding to the incoming pulses is determined in the measuring chamber (4) from the measured second gas pressure (P2), and wherein the pressure curve around the sound wave is corrected for determining the mass gas flow (2).Method according to Claim 3, wherein a pressure change (dP2) resulting from the pressure profile is transformed into the frequency domain, wherein a fundamental frequency (f0) of the sound wave is determined, and wherein the frequency spectrum of the pressure change (dP2) around the sound wave is corrected with the fundamental frequency (f0) by means of a notch filter (28).Method according to claim 3 or claim 4, wherein for the correction of the pressure change (dP2) around the sound wave a sound velocity (cs) in the measuring chamber (4) is estimated or determined, and based on the sound velocity (cs) the fundamental frequency (f0) of the sound wave is estimated or determined, and wherein the estimated or determined fundamental frequency (f0) of the sound wave is used for said correction.Method according to one of Claims 2 to 5, wherein the gas is injected through the injector (10) with pulses having a pulse duration of 0.1 ms to 100 ms and / or a pulse frequency of 0.1 Hz to 100 Hz.Method according to one of Claims 2 to 6, wherein the second gas pressure (P2) is in each case measured in a time window around the pulses of the injector (10), which time window has a length of at least 100% of the pulse duration and / or at most 1000% of the pulse duration.Method according to one of the preceding claims, wherein, in order to determine the mass gas flow (2) from the pressure change (dP2), - the measured second gas pressure (P2) is smoothed over time, - a time derivative (d / dt) for determining the pressure change (dP2) is formed from the smoothed second gas pressure (P2), and - the pressure change (dP2) is smoothed over time.Method according to one of the preceding claims, wherein, in order to set the predefined value (P0) for the first gas pressure (P1), the gas (8) is flowed into the measuring chamber (4) through the injector (10).Device (1) for measuring a gas mass flow (4) through an injector (4) which is configured for connection to a gas supply (6), comprising: - a measurement chamber (4) which encloses a measurement volume (5), - a number of pressure measurement pickups (11, 12) for measuring a first gas pressure (P1) and a second gas pressure (P2) in the measurement chamber (4), - a control valve (15) which is configured for the outlet of gas (8) located in the measurement chamber (4), and - a control unit (20), wherein the control unit (20) is configured - on the basis of the measured first gas pressure (P1), via said injector (10) and / or at least one auxiliary injector, to control a gas flow into the measurement chamber (4) in such a way, the first gas pressure (P1) assuming a predefined value (P0), the control valve (15) being opened in such a way that a continuous gas flow results from the measuring chamber (4), the control valve (15) being opened to actuate an intermittent gas flow into the measuring chamber (4) via the injector (10) and thereby to control a measurement of the second gas pressure (P2), the control valve (15) being opened in such a way and / or the gas flow via the injector (10) being controlled in such a way that the gas (8) continuously flowing out through the control valve (15) has a counterpressure having the predefined value (P0) for the first gas pressure (P1), and the measured second gas pressure (P2) being used, at least during the inflow, to determine a pressure profile from which the time-resolved mass gas flow (2) is determined by the injector (10).The device according to claim 10, wherein the number of pressure measurement pickups (11, 12) comprises a first pressure measurement pickup (11) for measuring the first gas pressure (P1) and a second pressure measurement pickup (12) for measuring the second gas pressure (P2), wherein the first pressure measurement pickup (11) is configured as an absolute or relative pressure measurement pickup, and wherein the second pressure measurement pickup (12) has a measurement frequency of at least 1 kHz.

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