TURBOGENERATOR DEVICE WITH GAS RECIRCULATION FOR VEHICLES

Abstract

A turbogenerator device (8) comprising at least one first stage (ET1) which includes a first compressor (CP1) and a first turbine (TB1), a first combustion chamber (CC1) delivering a first gas stream (F1) to the first turbine via a hot line (5), a recuperative heat exchanger (1) interposed between the outlet of the first compressor (CP1) and the inlet of the first combustion chamber, a first supply line (3) for compressed air from the first compressor to an inlet of the first combustion chamber, passing through the recuperative heat exchanger, the device comprising a recirculation line (2) extending from a first branch (54) in the hot line (5) to a second branch in the first supply line, and a recirculation means is provided for circulating exhaust gases from the hot line to the first supply line. Figure 3

Description

Title of the invention: TURBOGENERATOR DEVICE WITH GAS RECIRCULATION FOR VEHICLES

[0001] This disclosure generally relates to the field of gas turbine cycle type turbogenerator devices, otherwise known as "turbomachines." Here, we are in the context of a motor vehicle, where the turbomachine is involved in a range extender system for an electric or hybrid vehicle.

[0002] The present invention relates more specifically to the optimization of efficiency and the optimization of heat exchanges involved in the architectures of turbogenerator devices.

[0003] The invention is more particularly concerned with the sizing of a heat exchanger called a recuperative exchanger, which makes it possible to heat compressed intake air by heat exchange with the hot exhaust gases that exit the combustion chamber.

[0004] This recuperative exchanger makes it possible to improve the overall efficiency of the turbomachine, in the case of a turbomachine with two compression stages, and also in the case of a turbomachine with a single compression stage.

[0005] However, this heat exchanger proves to be an expensive part to manufacture. Furthermore, this heat exchanger is bulky and difficult to integrate into a vehicle design.

[0006] The inventors sought to propose alternative solutions to obtain a sufficient air temperature at the inlet of the combustion chamber, while reducing the size of the heat exchanger or even eliminating it.

[0007] To achieve this objective, the invention proposes a turbogenerator device, comprising a first stage which includes a first compressor and a first turbine linked together via a first shaft, a first combustion chamber delivering a first gas flow to the first turbine via a hot pipe, a recuperative heat exchanger interposed between the outlet of the first compressor and the inlet of the first combustion chamber, a first compressed air supply pipe which extends from the outlet of the first compressor, to an inlet of the first combustion chamber, passing through the recuperative heat exchanger, characterized in that the device includes a recirculation pipe extending from a first branch in the hot pipe to a second branch in the first supply pipe, and a recirculation method is provided to circulate exhaust gases from the hot pipe back to the first feed pipe.

[0008] Whereupon, a quantity of gas circulating in the hot pipe is drawn up to the supply pipe via the recirculation pipe and helps to warm the compressed air before its admission into the first combustion chamber.

[0009] It is noted that the recirculated gases mix with the fresh compressed air before entering the first combustion chamber.

[0010] Thanks to these provisions, it is therefore possible to consider downsizing the heat exchanger. In certain sizing scenarios, the recirculation technique even allows the heat exchanger to be eliminated.

[0011] It is noted that the recirculation line takes exhaust gases from the combustion chamber and reinjects them at the inlet of the combustion chamber in parallel with fresh compressed air.

[0012] It should be noted that the heat exchanger extracts heat from the turbine outlet flow and transfers it to the air flow exiting the compressor and to the first combustion chamber via the first supply line.

[0013] It should be noted that the recuperating exchanger can also be called a 'regenerator' or simply a 'recuperator'.

[0014] According to an advantageous option, the recirculation means is formed by a section restriction arranged on the first supply line at the location of the second branch.

[0015] The section restriction generates a Venturi effect with a local static depression at the location of the section restriction. This results in a suction phenomenon in the recirculation duct due to the depression within the section restriction.

[0016] According to one embodiment, the recirculation means is formed by a pump. The use of a pump makes it possible to generate forced recirculation in cases where the relative pressures do not allow the Venturi solution to be used easily.

[0017] According to one embodiment, the second branch is located downstream of the recuperating exchanger.

[0018] The pressures prevailing on both sides of the combustion chamber are substantially similar, and the depression created by the restriction of the cross-section is sufficient to draw burnt gases into the recirculation line from the hot line.

[0019] According to one embodiment, the second branch connection is located upstream of the heat exchanger. This constitutes an alternative to the previous solution, which works also taking into account the pressure loss caused by the circulation in the recuperative exchanger (upward part).

[0020] According to one embodiment, the recirculation rate is between 5% and 35%. This recirculation rate depends on the geometry of the cross-sectional restriction and, in particular, on the ratio of the cross-sections. The recirculation rate can be adapted to the specific configuration of the turbogenerator device according to the other parameters: pressure, temperature, and fuel flow rate injected into the combustion chamber.

[0021] The recirculation rate is defined by the ratio F2 / F4 where F4 is the mass flow entering the first combustion chamber, and F2 is the mass flow circulating in the recirculation duct, which in fact forms part of the mass flow entering the first combustion chamber.

[0022] According to one embodiment, the device may further include a second stage comprising a second compressor and a second turbine linked together via a second shaft, a second combustion chamber receiving the gases from the first turbine and delivering at the outlet a flow of gas to the second turbine, the second stage forming a low pressure stage and the first stage forming a high pressure stage, the second compressor delivering compressed air to the first compressor.

[0023] The use of two stages makes it possible to achieve a higher thermodynamic efficiency than in the single-stage configuration.

[0024] According to one embodiment, the device may further include a first electric machine linked to the first shaft, if a second stage is present a second electric machine linked to the second shaft.

[0025] Each electric machine can be used as a motor for starting the turbogenerator device, and then in established operation, each electric machine is used as a generator to produce electricity, in particular for the vehicle battery or a traction motor.

[0026] According to one embodiment, the pressure difference denoted P1-P2, between a first pressure PI prevailing in the first supply line upstream of the section restriction and a second pressure P2 prevailing at the location of the section restriction, is between 100 millibars and 500 millibars.

[0027] It is noted that the pressure PI is in the order of 5 bars to 10 bars.

[0028] The present invention also relates to a motor vehicle comprising a turbogenerator device as defined above.

[0029] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates a turbomachine system, otherwise called here a turbogenerator device, for a motor vehicle, in a single-stage compression version, with a recirculation device according to the present invention; - [Fig.2] schematically illustrates a section restriction zone causing a Venturi effect; - [Fig.3] schematically illustrates a turbomachine system for motor vehicles, in a two-stage compression version, with a recirculation device according to the present invention; - [Fig.4] schematically illustrates an example of a variant of a turbomachine system with a recirculation pump; - [Fig.5] schematically illustrates another example of a turbomachine system variant with recirculation injection upstream of the recuperator exchanger.

[0030] In the various figures, the same reference numerals designate identical or similar elements. For the sake of clarity, some elements are not necessarily shown to scale.

[0031] Gas turbine-type energy converters are considered as possible range extender solutions in electric or hybrid vehicles. These converters are also more simply called "turbomachines".

[0032] This type of converter can operate in APU (Auxiliary Power Unit) mode, where its role is to recharge the batteries of an electric vehicle. It is thus mechanically decoupled from the powertrain and operates at its maximum efficiency point.

[0033] The gas turbine cycle with cooler, recuperator and reheater is a cycle with high potential for automotive applications. This cycle makes it possible to achieve high efficiency but also high power density (high specific net work).

[0034] This technology offers the following advantages: low emissions, low noise emissions, and the ability to operate with several types of fuel. These turbogenerators are attractively compact, except for the heat exchanger.

[0035] The turbomachine system proposed here, otherwise called a turbogenerator device, may comprise two compression stages or a single compression stage.

[0036] Figure 1 shows a turbomachine system 8 according to the present invention, with a single stage for this first embodiment.

[0037] The system includes a first stage ET1 which includes a first compressor CPI and a first turbine TB1 linked together by means of a first shaft Al. The system includes a first combustion chamber CCI delivering a first gas flow Fl to the first turbine TB1 via a hot pipe 5.

[0038] The system includes a recuperative heat exchanger 1 interposed between the outlet of the first compressor CPI and the inlet of the first combustion chamber CCI. The recuperative heat exchanger 1 comprises a rising portion 11 and a falling portion 12. In the rising portion 11, the temperature increases. In the falling portion 12, the temperature decreases.

[0039] The system includes a first compressed air supply line 3 from the first compressor CPI, to an inlet of the first combustion chamber CCI, passing through the rising part 11 of the recuperator exchanger.

[0040] The conduit 18 directs the output of the first turbine TB 1 towards the descending part of the recuperator 12.

[0041] The air temperature is T2 at the outlet of the compressor and at the inlet of the recuperator 1. The air temperature is T3 at the outlet of the recuperator 1. T3 is substantially higher than T2, by an additional value typically between 100°C and 300°C.

[0042] Advantageously according to the present invention, a burnt gas recirculation flow is joined to the fresh air flow, the temperature of the resulting mixture is denoted T4.

[0043] At the outlet of the combustion chamber CCI, the burnt gases have a temperature T5. T5 is typically between 800°C and 950°C. At the outlet of the first turbine TB1, the burnt gases have a temperature T6 slightly lower than T5.

[0044] The system comprises a first electric machine MG1 connected to the first shaft, i.e., fixed in rotation with the first shaft AL

[0045] According to the present invention, a recirculation line 2 is provided extending from a first branch 54 in the hot line to a second branch 34 in the first supply line.

[0046] A section restriction 33 is provided arranged on the first supply line at the location of the second branch 34.

[0047] As illustrated in [Fig. 2], the passage section in the section restriction is denoted S2, while the passage section in the current section upstream 31 and downstream 32 of the restriction is denoted SL

[0048] We have SIxV 1 = S2xV2 where VI is the flow velocity in the current section upstream 31 and downstream 32 of the restriction, and where V2 is the flow velocity in the restriction of section 33.

[0049] The sum of the flow rates gives F4 = F3 + F2.

[0050] The recirculation rate is defined by the ratio F2 / F4 where F4 is the mass flow rate entering the first combustion chamber, and F2 is the mass flow rate circulating in the recirculation pipe. The flow rate F3 represents the outlet flow of the recuperative exchanger 1.

[0051] The recirculation rate (F2 / F4) is between 5% and 35%.

[0052] The pressure PI is the pressure prevailing in the first supply line upstream of the section restriction. The second pressure P2 is the pressure prevailing in the section restriction.

[0053] In a typical embodiment, the pressure difference denoted PI - P2 is between 100 millibars and 500 millibars.

[0054] It is noted that, as known in itself, P1-P2 is inversely proportional to the ratio S2 / S1.

[0055] The target temperature T4 at the inlet of the first combustion chamber CCI is around 450°C.

[0056] A desired heating of the compressed air towards this target temperature can be dimensioned with the contribution of the recuperative exchange on the one hand and the contribution of the supply of recirculated gas which arrives at a temperature close to the outlet of the combustion chamber, i.e. at least 800°C.

[0057] A person skilled in the art understands that the higher the recirculation rate, the more the heat recovery exchanger can be sized down.

[0058] Figure 3 shows a system diagram of a turbomachine according to a second embodiment with two compression stages.

[0059] All the elements that have been commented on in relation to the first embodiment are assumed to be identical or similar and are not described again here.

[0060] A first stage ET1, here referred to as high-pressure, is similar to that described previously; it comprises a high-pressure compressor CPI ('first' compressor) and a high-pressure turbine TB1 ('first' turbine), these two entities being linked together via the first shaft AL

[0061] A second stage ET2, referred to as low pressure, comprises a low pressure compressor CP2 ('second' compressor) and a low pressure turbine TB2 ('second' turbine), these two entities being linked together by means of a second shaft A2. This second shaft A2 drives a second electrical machine MG2 which is used mainly as a generator and secondarily as a motor for the start-up phase of the second stage.

[0062] The second stage ET2 includes a second combustion chamber CC2. In the two-stage configuration, the outlet of the first turbine is directed to the second combustion chamber CC2.

[0063] The second combustion chamber CC2 delivers a gas flow to the second turbine TB2 at temperature T7. The outlet of the second turbine TB2 delivers a flow F8 which is directed towards the descending part of the recuperating exchanger 1 via the pipe 18.

[0064] In addition, an AF air filter is arranged upstream of the low-pressure compressor CP2. The air filter admits fresh air at temperature Tl.

[0065] In addition, an IC cooling exchanger ('intercooler') cools the air taken from the outlet of the low pressure compressor and brought to the inlet of the high pressure compressor CPI.

[0066] The first combustion chamber CCI and the second combustion chamber CC2 are each supplied with a hydrocarbon fuel. The hydrocarbon fuel is, for example, methanol or ethanol.

[0067] The heat recovery exchanger takes heat from the outlet flow F8 of the second turbine TB2 and transfers it to the outlet flow of the first compressor CPI.

[0068] [Fig.5] differs from [Fig.3] in that the section restriction is replaced by an active pump 27 on the recirculation circuit.

[0069] Consequently, it can be stated that, in a generic way, a means of recirculation (Venturi or pump) is provided to circulate burnt gases from the hot line 5 to the first supply line 3.

[0070] [Fig. 4] differs from [Fig. 3] in that the recirculation flow inlet point is located upstream of the regenerative heat exchanger instead of downstream of it. A 33' Venturi restriction or a pump can be used as the recirculation means.

Claims

Demands

1. Turbogenerator device (8), comprising a first stage (ET1) which includes a first compressor (CPI) and a first turbine (TB1) linked together via a first shaft (Al), a first combustion chamber (CCI) delivering a first gas flow (Fl) to the first turbine via a hot line (5), a recuperative heat exchanger (1) interposed between the outlet of the first compressor (CPI) and the inlet of the first combustion chamber (CCI), a first compressed air supply line (3) extending from the outlet of the first compressor (CPI), to an inlet of the first combustion chamber (CCI), passing through the recuperative heat exchanger, characterized in that the device includes a recirculation line (2) extending from a first branch (54) in the hot line (5) to a second branch (34) in the first supply line (3),and a recirculation means is provided to circulate exhaust gases from the hot pipe (5) back to the first supply pipe (3).

2. Turbogenerator device according to claim 1, characterized in that the recirculation means is formed by a section restriction arranged (33) on the first supply line at the location of the second branch (34).

3. Turbogenerator device according to claim 1, characterized in that the recirculation means is formed by a pump (27).

4. Turbogenerator device according to any one of claims 1 to 3, characterized in that the second branch (34) is located downstream of the recuperator exchanger (1).

5. Turbogenerator device according to any one of claims 1 to 3, characterized in that the second branch (34) is located upstream of the recuperator exchanger.

6. Turbogenerator device according to any one of claims 1 to 5, characterized in that the recirculation rate (F2 / F4) is between 5% and 35%.

7. A turbogenerator device according to any one of claims 1 to 6, further comprising a second stage (ET2) which includes a second compressor (CP2) and a second turbine (TB2) linked together via a second shaft (A2), a second combustion chamber (CC2) receiving the gases from the first turbine (TB1) and delivering at the outlet a flow of gas to the second turbine (TB2), the second stage (ET2) forming a low pressure stage and the first stage (ET1) forming a high pressure stage, the second compressor (CP2) delivering compressed air to the first compressor (CPI).

8. Turbogenerator device according to claim 7, further comprising a first electric machine (MG1) linked to the first shaft (A1), a second electric machine (MG2) linked to the second shaft (A2).

9. Turbogenerator device according to claim 2, characterized in that the pressure difference denoted P1-P2, between a first pressure PI prevailing in the first supply line upstream of the section restriction and a second pressure P2 prevailing at the location of the section restriction, is between 100 millibars and 500 millibars.

10. Motor vehicle comprising a turbogenerator device according to any one of claims 1 to 9.

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