WO2008087685A2

WO2008087685A2 - Open-cycle gas turbine engine system having power and modulation sections

Info

Publication number: WO2008087685A2
Application number: PCT/IT2008/000023
Authority: WO
Inventors: Mauro Palitto; Marcello Palitto
Original assignee: Mauro Palitto; Marcello Palitto
Priority date: 2007-01-18
Filing date: 2008-01-16
Publication date: 2008-07-24
Also published as: WO2008087685A3; ITRM20070023A1

Abstract

An open-cycle gas turbine system comprising a power section (5, 6, 7, 8, 9), a modulation section (1, 2, 3, 4), and a regeneration section (10, 11) for recovering heat from the exhaust gases. The turbines (6, 7) of the power section operate at a substantially constant maximum temperature, also in the regulation mode (partial load), up to the time a burner (3) of the modulation section is switched off. During the continuous modulation of the delivered power, which is mainly performed by modulating the amount of fuel injected into the burner (3), the efficiency constantly remains at high levels. The system can be sized in such a way to attain a maximum of the efficiency in the regulation mode. The system has rapid response times since the power modulation obtained through the variation of the density of the working fluid maintains unaltered the rpm value and the temperature of the power section, until reduced power values are reached.

Description

Open-cycle gas turbine system Technical Field

The present invention relates to the technical field of internal combustion engines or systems, and more particularly it relates to an open-cycle gas turbine system, that is, a system having the suction inlet and discharge outlet of the working fluid in communication with the atmosphere. The open-cycle turbine system according to the invention has several advantages both compared with internal combustion engines of the reciprocating kind, and with respect to already known gas turbine systems. The main advantage consists in insuring a greater efficiency both at high powers and at medium-low powers (partial load operation), not facing higher production costs as compared with already known technologies. The gas turbine system of the present invention can be used not only in the automotive industry but also for the construction of motor pumps (advantage of light weight), electric generators, and in the aeronautical and marine propulsion fields.

Background Art

Since the first half of the 20-th century, gas turbine based engines have been realised for motor vehicles. This type of engines has not replaced the reciprocating combustion engines on motor vehicles, for the following reasons:

- the poor efficiency, especially in the partial load operation; - the delay in accelerator response;

- the higher production cost.

On the other hand, turbine systems have several advantages compared with reciprocating combustion engines:

* the extremely low emissions (NO_x, CO, HC, dusts) at all loads; being the gas turbine an inherently clean engine, whereas reciprocating engines used for propulsion purposes (automotive industry), even when equipped with a catalytic converter system for the exhaust gases treatment, heavily increase pollutant emissions for operating conditions not foreseen by the NEDC cycle (New European Drive Cycle);

* the noiselessness and absence of vibrations; * a favourable torque curve for propulsion systems (maximum torque when the power turbine is stationary);

* a low weight to power ratio;

* a cooling circuit limited to an air/gas intercooler;

* the possible absence of a lubrication circuit which, even if provided in the system, will be in any case "minimal" and will absorb a very small power;

* they can operate with several kinds of fuels, without consequences for their efficiency and power;

* they have reduced dimensions which - in case of front drive vehicles - allow the gearbox to be placed in the middle, with the consequence that the axle shafts can have equal lengths and there is no need for transmission links; moreover there is the possibility to effect a flanged connection of the compressor of the air-conditioning system and of the motor-alternator, to the propulsion system, without resorting to belts and additional gears. In the last decades, substantial technical and technological improvements have been made, allowing to overcome the aforementioned problems (-) which downgraded the turbine systems in comparison with the reciprocating engines:

* the efficiency of compressors and turbines has increased considerably due to the knowledge gained both in the aeronautical sector and in the automotive sector (turbocharged engines); • the cost of turbo-compressors has decreased since they have been realised in mass production for the supercharging of reciprocating combustion engines;

* the cost of inverters and motorgenerators has decreased due to the commercialisation of hybrid electric and reciprocating combustion engines. The availability of these new opportunities allows to reconsider the utilisation of a turbine also in the automotive sector.

Hybrid vehicles, of the electrical/gas-turbine kind, are capable of overcoming the problems of response times, and only partially those of efficiency in the partial load operation, since they are in any case adversely affected by the presence of an electric shaft and by the need of storing a noticeable amount of energy in their battery, this giving rise to losses because of the multiple energy conversions. Efficiency problems in the regulation mode (partial load operation) of gas turbine systems, that is, at medium-low powers, have been partially solved by a gas turbine system operating in an open cycle, as disclosed in US Patent 6,606, 864, issued to MacKay on August, 19, 2003. This patent discloses a system of gas turbines which can operate in more than one pressure level. Valves are provided for the control of a particular operation mode associated with a corresponding discrete, average pressure level of the working fluid. During switching from one of the discrete levels of average working pressure, to another discrete level of average working pressure, the efficiency value is substantially maintained, although discontinuities arise in the regulation mode. The gas turbine system preferably uses catalytic combustors (burners) with an associated preheating section (preheater); it has, moreover, advantages during starting of the system, since starting is performed at subatmospheric pressure.

The present invention differs from this MacKay patent in that the power supplied by turbine system can be controlled to have a continuous variation, and this results in a regular behaviour of the efficiency, which efficiency - moreover - increases in the partial load operation, since in the turbines of the power section, the velocities and temperature of the working fluid at the inlet to these turbines (maximum temperature of the cycle) remain substantially constant up to the moment when the burner of the modulation section is switched off (see the description given below), and for this reason the system always works at high efficiency levels. In particular (see the following description and claim 4), the gas turbine system of the present invention can be realised in such a way to enhance its basic abovementioned feature, by obtaining the maximum efficiency at medium-low powers (that is, in the regulation phase/mode), at which the maximum cycle temperature remains constant during the variation of the delivered power. Since in practice high powers, or extremely high powers of motor vehicle engines, are never used, an exception being during the acceleration phase and (rarely) on straight stretches in the absence of speed limits, the invention is advantageous under the aspect of fuel consumption efficiency and manufacturing costs, because the aforementioned principle allows a reduction of the size of the regenerator (recuperator) for exhaust gas heat recovery.

Disclosure of Invention

The present invention solves the abovementioned efficiency and cost problems of gas turbine systems, by providing an open-cycle turbine system as defined by the features contained in claim 1.

In substance, the open-cycle gas turbine system according to the present invention includes a power section, from which the power absorbed by a mobile or stationary user unit is drawn, a modulation section, for modulating in a continuous way the average pressure of the working fluid used to operate the power section, and a regeneration section, for the recovery of heat from the exhaust gases. The fundamental point of the invention is that power control is performed by varying, in a continuous manner, the pressure/density of the working fluid, while the turbines of the power section are operating at a substantially constant temperature of the working fluid, up to the moment when a burner - which is included in the modulation section - is switched off. The modulation section also includes a turbine- compressor assembly (named 'first turbine-compressor assembly' in claim 1), and a system (e.g. an intercooler; see claim 6) for lowering the temperature of the compressed air coming out of the compressor of the turbine-compressor assembly belonging to the modulation section. The function of the burner of the modulation section is essential, because it controls the pressure of the fluid (comburent air) entering the power section, by heating the gas coming out of the power section; this gas expands within the turbine of said first turbine-compressor assembly, and this, in turn, drives the compressor of the first turbine-compressor assembly of the modulation section. Thus, a person skilled in the art immediately realises that since the pressure of the fluid entering the power section is controlled in a continuous manner, in the above described way, when the thermal energy supplied by the burner of the modulation section to the working fluid is increased (or respectively decreased), there will be an increased (or respectively a decreased) mass flow rate of working fluid travelling through the system, and therefore, it will never be necessary to reduce the maximum temperature of the cycle, till the moment the burner of the modulation section is switched off (see also the following part of the description and the preferred embodiment). It follows that the system efficiency is always maintained at a high level, up to the moment the burner of the modulation section is switched off, which will however occur only at low or extremely low powers, for which the architecture of the system will anyway insure good efficiencies. The compressor of the modulation section sucks comburent air from the atmosphere and feeds it to the power section, while the burner of the modulation section is supplied with the gas discharged from the power section and modulates the temperature of this gas by adding fuel to it; then, this gas is guided to the turbine of the turbine-compressor assembly belonging to the modulation section, inside which an expansion occurs substantially until the atmospheric pressure is reached. Briefly, by means of the modulation section, the operating pressure (and thus the mass flow rate) of the working fluid is modulated in a continuous manner, by substantially maintaining at a constant value the volumetric flow rate of the working fluid that flows through the power section, for a given rotational speed of the of said power section. The power output varies as a function of the mass flow rate of the working fluid, and the amount of fuel to be supplied to the power section varies proportionally to this mass flow rate, but the efficiency remains constantly high since it depends from the maximum temperature of the cycle and from the velocity of the working fluid, which is substantially constant.

The MacKay patent discusses similar concepts, but in any case its disclosure is totally different both under structural and functional aspects (see above). Specific embodiments of the invention result from the dependent claims and from the detailed description of preferred embodiments. Preferably, as follows from claim 3, the regeneration section for recovering heat from the exhaust gases includes a reforming device arranged upstream of a heat exchanger with reference to the gas flow outputted by the modulation section. The regeneration section for recovering heat from the exhaust gases increases the efficiency of the system because of the presence of the exchanger and as a result of the operation of the reforming device. The latter receives as input the fuel to be fed to the turbine system, and water, and these substances are converted into H₂, CO₂, CO, HC, H₂O (steam) etc. through a catalysed endothermic reaction; these gaseous (reaction) products make up the fuel fed to the burners of the modulation and/or power sections. The utilisation of the reforming process also allows to use cheaper materials for the construction of the heat exchanger of the heat regeneration section, since the temperature of the discharged fluid entering the hot side of the exchanger, has already been reduced by the endothermic reforming process to such a level which is also acceptable by an economic exchanger type (meaning one not manufactured with superalloys or other expensive materials).

With regard to other preferred embodiments and advantages of the invention, attention is drawn to the following detailed description and to the remaining dependent claims. Brief Description of Drawings

The present invention will now be described below for illustrative but not limitative or binding purposes, by referring to some specific embodiments thereof, some of which are based on the architecture of a turbine system schematically shown in the only figure (Fig. 1) annexed to the present patent application.

Description of Some Preferred Embodiments of The Invention

Figure 1 and the preferred embodiments of the invention are illustrated in detail only to put a person of average skill in this field in a condition to practically apply the invention.

Therefore, Fig. 1 should not be interpreted as a general limitation of the architecture of the open-cycle gas turbine system according to the present invention. In order to overcome the abovementioned problems (-) of known architectures of turbine vehicles (compare the architectures realised on the Ford model 705 in the 1960's and US Patent No. 6,606,864 B2 of 19/08/2003, to MacKay), a new turbine engine architecture has been conceived which, in a broad power control interval (e.g. 15%- 100%), maintains very high efficiencies, by continuously modulating the mass flow rate of the working fluid and by maintaining near to their maximum value the velocities and temperatures of two (in the present embodiment of Fig. 1) of the three turbines making up said architecture. This is due to the fact that the power delivery section operates with a variable average pressure, because of the superposition of a modulation section (1, 2, 3, 4), which, by means of a specific compressor-turbine assembly (1, 2) and a third burner 3, modulates the pressure increment of the air entering the power section and uses the discharge gas of the latter as power fluid. The architecture of Fig. 1 is designed in particular for the automotive industry, both for automobiles and industrial vehicles, like trucks etc., but it is also applicable as engine in any "mobile application" (e.g. airplanes, boats, etc.) or "stationary application" (e.g. generators, pumps, etc.). Description of the propulsion system in the embodiment of Fig. 1

The new propulsion system (see Fig. 1) is based on a system including:

- two turbo-compressors 1, 2 and 5, 6;

- a free turbine 7 which delivers the useful power; - three burners 3, 8, 9;

- a reforming system 10 of the fuel, in case the latter differs from H₂;

- an electric resistance, if any, (not shown), used to activate (to trigger) the reforming process during starting; an exchanger or recuperator 11 ; - an intercooler 4, if any;

- a fuel injection circuit (not shown), a duct of which (not shown) passes through the reformer 10;

- a plant for conveying to the outside the exhaust gases (not illustrated);

- a lubrication circuit - if any - for the turbines (not shown); - a recuperator (regenerator) for recovering heat from the exhaust gases, to heat the interior compartment (not shown);

- a gearbox 12;

- a compressor 13 for the air-conditioning system;

- a motor- generator 14, if any, on the transmission; - a system of electric energy accumulators (not illustrated);

- an electronic control system used to control/govern the propulsion system (not shown);

- injection systems (not shown), if any, for injecting water (overboost and reforming); - systems, if any, which are not shown and serve to recover and collect the condensate from the exhaust gases.

The invention practically consists in defining an architecture (e.g. the architecture of Fig. 1) that allows to practically use "off-the-shelf turbo-compressors together with a low-cost exchanger, and in inserting known devices - e.g. the reforming 10 - in this particular context, besides an electric machine (motor generator 15) mounted one (5, 6) of the turbo-compressors. This allows to realise operating conditions that are extremely competitive compared with the most promising engines present today on the market.

Operation of the propulsion system (turbine system) of the present invention In the embodiment of Fig. 1, the air sucked by the compressor 1 is compressed and then conveyed first to the intercooler 4, which is provided with a fan and is cooled by the ambient air, and thereafter to another compressor 5 which further compresses this air. This flow of compressed air then passes through an exchanger 11, where it is heated by the exhaust gases discharged by the whole system. Then, this air is further heated inside a burner 8 and delivered to a turbine 6, inside which it expands to provide the mechanical work needed for the sole actuation of the compressor 5 and generator 15 integrated in the turbo-compressor assembly (5, 6). Thereafter, the discharge gases of the turbine 6 are heated in the burner 9 and are delivered to the power turbine 7, whose discharge gases are further heated inside the burner 3, before being conveyed to the turbine 2, where they expand and provide the mechanical work needed for the sole actuation of compressor 1. The turbine 2 discharge gases flow first into the fuel reforming device 10 and then into the exchanger 11, to be finally discharged in the atmosphere 16. The reforming device 10 receives as input the fuel fed to the turbine system, as well as water, and these substances - through an endothermic reaction promoted by a catalyser - are converted into H₂, CO₂, CO, HC, H₂O, etc., and these gaseous products make up the fuel which is then fed to the combustors 3, 8, 9. By way of example, the whole methane reforming reaction (x variable between 0 and 1) is:

CH₄ + (2-x) H₂O = xCO + (1-x) CO₂ + (4-x) H₂. It is possible to realise an overboost function by introducing, for a few seconds, nebulized H₂O both into the air sucked by the compressor 1 and into the air sucked by the compressor 5, as well as into the colder side of the exchanger 11. The injection ofH₂O can be pushed as far as the oversaturation level, to thereby reduce the work done by the compressors 1, 5 without adversely affecting the duration (life) of the exchanger.

The turbine system, in this embodiment shown in Fig. 1, is characterised by:

- a specific architecture, comprising: a power section 5, 11, 8, 6, 9, 7 (as specified by the working fluid direction), a modulation section 1, 4, 3, 2 for continuously modulating/varying the working fluid average pressure, and a heat recovery/regeneration section 10, 11 for recovering heat from the exhaust gases, which is formed by the fuel reforming device 10 and the exchanger 11, connected in series in the above mentioned order;

- multiple heating operations successively carried out on the working fluid by means of the burners 8, 9, 3 (in the order specified by the working fluid flow entering the compressor 1 at 17);

- that part (if any) of the reforming device, which is provided with an electrical heating resistance used during cold start (not shown);

- the second turbo-compressor assembly (5, 6), having a motor-generator 15 of adequate power integrated/mounted on the compressor-turbine shaft, which: 1. operates like a motor during the start function and also for obtaining an increment in the acceleration of the turbo-compressor 5, 6 during transient states, to thereby reduce the response time

2. operates like a generator to satisfy the needs of electric apparatuses on the automobile, in case there is no motor-generator 14 on the transmission or in case the electric apparatuses of the automobile require very high power peaks;

- the specificity of the burners 8, 9, 3 provided with apparatuses for preventing NO_x formation belonging to the state of the art, these apparatuses effecting air/fuel premixing and/or the combustion on a porous, catalytic or non catalytic septum. The fuel injector may be of the type suited to perform the injection of a liquid or of a gaseous substance.

- Depending on the kind of fuel being used, these types of injectors can also be present at the same time, since in this case, during cold start, only a liquid fuel will be available (if no electrical heating is provided that is capable of activating immediately the reforming device);

- the burners may also be provided with an injector of water or steam, that may be located in proximity of the outlet of the premixing chamber. In order to adapt the burner with premixed flame to variable loads, it is possible to provide a shutter device in the outlet section of the premixing chamber, to insure that the outflow velocity of the fluid from said chamber is always greater than the velocity of the flame front. This device may be formed by a conical outlet of the premixing chamber, choked by an axially displaceable conical pin;

- the specificity of the burner 3, which is provided with an oxidative catalyser; - the specificity of the duct used to convey to the outside the exhaust gases (not shown), which is provided with an exchanger for recovering heat from these exhaust gases to perform the heating of the passenger compartment, and which may also be provided with a device for recovering a portion of condensate water that will be collected in a specific tank. Referring again to Fig. 1, the power turbine 7 is connected to the gearbox 12 through an electromagnetic coupling or servocontrolled clutch, 18, which gearbox 12 may be conventional. The maximum rpm of the power turbine is reduced to about 10000 rpm by a first reduction device 19. Using an electromagnetic coupling 20, the following components are connected (in case of front drive vehicles possibly on the same axis) to the main shaft of the transmission whose rpm reaches the aforesaid value: the motor-generator 14, if any, and the compressor 13 of the air-conditioning system, which is of the clutchless or conventional kind, and which in the latter alternative can be disconnected by means of an electromagnetic coupling 21. As known in the art, a differential gear 22, used to transmit the motion to the wheels 23, is further connected to the gearbox 12. The gearbox 12 may be of any kind: manual or automatic (conventional, robotised or CVT). A Stop & Start (S & S) function could be activated also in relation with the release of the gas pedal when the vehicle is moving, that is, when the gas pedal is released, the injection of fuel is interrupted and the electromagnetic coupling 18 is opened, thus realising a freewheel; in this manner the working fluid is stationary and the temperatures of the system remain at high levels during a certain period of time, since the propulsion system is insulated. Assuming that the motor-generator 14 on the transmission is actually provided, it may be sized in such a way (e.g. 4 kW) to actuate the compressor 13 when the vehicle stops and the turbines are switched off; in this case the assembly 14 + 13 is isolated from the transmission by means of the electromagnetic coupling 20. In this way, when the car is moving and the driver does not step on the gas pedal, the assembly 14 + 13 is normally driven by the transmission and is able to recuperate - at least partially - the kinetic energy of the car. The motor-generator 14 on the transmission, if provided, is also used to eliminate the operation of the turbines at extremely low powers, corresponding to unfavourable efficiencies. If a power is required which is less than that provided by the motor-generator 14 (e.g. 4kW), and assuming that the compressor 13 of the air- conditioner is not operating, or if the latter does not draw all the power furnished by the motor-generator 14, the car will be driven by the sole power of the motor- generator 14 within a period limited by the capacity and charge of the battery and also by the temperature threshold of the hot components of the system, since below this threshold level the turbine system needs to be switched-on again. If the function of the motor-generator 14 on the transmission is not available, either because this motor-generator is not present, or the electric energy accumulated so far is insufficient, then, if the car is stationary, the compressor 13 of the air-conditioning system will be actuated by the power turbine 7 by putting the gearbox 12 in neutral. Assuming that the motor-generator 14 is present on the transmission and assuming also that the energy stored so far is insufficient, then the compressor 13 of the air- conditioner - in the car stationary state - may be actuated, notwithstanding this, by the motor-generator 14, in which case the latter will be driven by an electric shaft of the motor-generator 15 mounted on the shaft of the second turbo-compressor (5, 6) , provided the latter is delivering an adequate power.

Each time the gas pedal is actuated, either when the car is moving or when it is stationary, the turbine system is operated through the activation of the starter or motor-generator 15 of the turbo-compressor (5, 6). The above described turbine system, besides allowing to obtain high efficiencies at maximum power, is also capable of obtaining even higher efficiencies in the regulation phase (partial load), since also in the latter condition it is able to maintain the inlet velocities and temperatures of the turbines (6, 7) of the power section near their maximum values, as a consequence of the fact that the control is performed mainly by varying the mass flow rate of the working fluid (air), using the modulation assembly 1, 4, 3, 2 for the modulation of the average working pressure. Starting from the maximum power (e.g. 100 kW), a first modulation is carried out by modulating the fuel injection into the burner 3; this modulation causes a relevant variation of air flow rate and, as a result, a modulation of the fuel injected in the burners 8, 9 is also effected so as to maintain at their maximum levels the temperatures at the inlet of the turbines 6 and 7. When the burner 3 is switched off, the power available on the power turbine 7 falls - for instance - below 15% of the maximum power (e.g. 12 kW). In these conditions the efficiency will be even greater than the efficiency at maximum power, since the recuperator 11 is oversized in case of low load, and its size could in fact be reduced/limited to obtain a desired cost reduction, in such a way to maintain high efficiencies in the regulation phase (partial load) and lower efficiencies at high power values, which in fact are used for very short periods, usually of the order of some seconds. The further or remaining regulation involves only the modulation of the burners 8 and 9, according to operation modalities that may vary and depend on a specific design. When the power is modulated below the threshold at which the burner 3 is switched off, the efficiencies drop, but if the turbine system is provided with a motor-generator 14 on the transmission, it is possible - below the threshold of maximum power of this motor generator (e.g. 4 kW) - to switch off the turbine system and to use instead the motor generator 14 as 'engine'. The battery will be recharged during the next start of the turbine system. In case of high power systems (e. g. 300 kW) it will always be possible to obtain limited powers associated with high efficiencies, using the following options: compressors 1 and 5 with high compression rations (e.g. 5) and/or a doubling of the power section, by the use of smaller components. In the latter case one of the assemblies will be smaller in size (e.g. 50 kW), since also larger cars need limited power in urban cycle and in order to not exceed speed limits - if any - on highways. On the other hand, the second assembly/section may be arbitrarily large (to reach high powers is much easier with turbines than with a reciprocating engine). The two turbines for delivering (low and high) power will be connected to the main shaft of the gearbox 12, either in series or in parallel, by a respective reduction and a corresponding coupling (claim 22). In order to reduce thermal stresses in the larger turbine system, exhaust gases flowing out of the exchanger of the smaller turbine system may be conveyed to the inlet of the burner of the larger turbine system and be discharged in the atmosphere after passing through the corresponding turbine (claim 23). To insure the proper flow direction, special not-return devices are adopted, which are located at the outlet of the compressor of the larger turbine system and of the exchanger (claim 24).

The small turbine system may be a standard assembly usable on all kinds of cars, that is, on normal, powerful, and very powerful cars. The same assembly can then be used as main driving assembly on small cars (e.g. on a "citycar").

By injecting H₂O, the disclosed turbine system allows to realise the following: an overboost, which even during the few seconds of its activation does not lead to a worsening of the NO_x levels (claim 13). The overboost may be adopted as an alternative or in combination with the larger turbine system (claim 25).

The injection OfH₂O may be performed alternatively or concurrently at various points of the circuit (claim 13):

- in anyone of the burners 3, 8, 9; - concurrently, in two burners, or in all three burners;

- in the colder side of the exchanger 11;

- at the suction inlet of the compressor 1;

- at the suction inlet of the compressor 5; and, assuming the presence of the larger turbine system,

- in the burner of this larger turbine system (not shown); - at the suction inlet of the compressor of this larger turbine system (not shown) (claim 25).

The increase in power ensuing the water injection depends on several factors: the greater available mass of fluid due to the added H₂O mass, the increase in the mass of sucked air due to the increased power delivered by the turbo-compressors involved, and the lower power absorbed by the compressors.

The water required for the overboost, if any, or for fuel reforming, if provided, is made available by an appropriate tank which is fed/supplied from outside the system, or by the condensation of the steam contained in the exhaust gases from which it is possible to separate part of the flow , which is cooled in order to obtain said condensation.

The turbine system described above can be realised in such a manner to enclose inside a warm (that is, insulated) enclosure all components which need to be thermally insulated in the best possible way (these are the turbines, the burners, and the reforming devices). At least one, and preferably each one of these components, will have in any case its own specific compartment.

Industrial Applicability It is not necessary to repeat once again the features which show the advantages of the turbines and which have already been listed in the discussion of the background art. Instead, we stress the fact that the illustrated architecture, in combination with the technical and technological developments of the background art, allow to overcome those problems which have prevented the turbines up to now from replacing the reciprocating combustion engines.

For what concerns the costs of a turbine system according to the present invention, they are similar to those of a reciprocating combustion engine, when including in the cost of the latter, those systems needed for the elimination of noxious emissions. The limitation of costs for the present innovative system is based on the use of the following:

• turbo-compressors already commercialised by the "automotive mass production"; ceramic-made turbines are also available on the market;

• preferably, an exchanger/recuperator of the static kind, entirely made of metal without resorting to superalloys (the maximum inlet temperature is about 70O⁰C)₅ produced using completely automatic processes;

• the size of the exchanger and of the intercooler can be optimised for intermediate power values and not for the maximum power.

For what concerns the response times, they have been reduced, because:

• the turbo-compressor (5, 6) of the power section rotates at the maximum rpm and at the maximum temperature, up to the power threshold determined by the switching- off of the burner 3 ;

• light materials are employed for manufacturing the turbines (for instance ceramics) and possibly also for the rotors of the compressors (for instance reinforced plastics); • the electric starter (starting motor) 15 is used in order to accelerate the rpm increase of the turbo-compressor (5, 6) of the power section;

• the turbine 7 from which power is drawn is of the free turbine type and benefits from the inherent properties of turbines: the stall torque is about 2,5 times higher than the torque at maximum rpm and it delivers the maximum power up to 25% of the maximum rpm, the efficiency being reduced only by 5%;

• during the first period of acceleration of the car, the motor generator 14 - mounted on the transmission - is also used, and this is also helpful even in case it has a limited power. At all power levels, efficiencies for the illustrated architecture are higher than those of reciprocating combustion engines, and also in comparison with turbodiesel engines, since the power section maintains the velocity and temperature values, existing at the inlet of the turbine, always equal to those corresponding to the maximum power operating condition, up to the moment when the burner 3 is switched off; moreover, a possible endothermic fuel reforming with water increases the heat regeneration capacity of the system and allows to use high temperatures at the turbine inlet, while maintaining a temperature threshold at the inlet to the exchanger which is critical for its low cost. The present invention has been described mainly with reference to the architecture of Fig. 1 and its possible variants - e.g. the doubling of the power section etc. -. However, it is evident that a skilled person is capable of realising innumerable further embodiments included in the same inventive concept based on the main claim, that is, claim 1 of this patent application. For instance, as mentioned in claim 2, the power section can be realised with a two-shaft scheme (see Fig. 1) or with a one-shaft scheme (the power is drawn directly from the turbine 6 of the turbo-compressor (5, 6); this case is not shown in he figure), and with one or two burners (8, 9).

Claims

1. An open-cycle gas turbine system, having a plurality of inlets or inputs, one of them (17) being provided for the comburent air and one or more for the fuel, and with two outputs, of which one (16) serves for the exhaust gases and another one for the mechanical drive power absorbed by a mobile or stationary served user unit, said gas turbine system comprising a power section, from which the power required by said mobile or stationary served user unit is drawn, a modulation section, used to modulate in a continuous way the average operating pressure of the working fluid which drives the power section, and a regeneration section, for recovering heat from the exhaust gases, said gas turbine system being characterised in that the turbines (6, 7) of the power section operate at a maximum, substantially constant temperature, also at partial load, till the moment a burner (3) of the modulation section is switched off, the latter including a first turbine-compressor assembly (2, 1), a system (4) for lowering the temperature of compressed comburent air, and said burner (3) located upstream of the turbine (2) of the first turbine-compressor assembly (2, 1) with reference to the gas stream coming from the power section, wherein, the compressor (1) of the modulation section is apt to suck comburent air from the atmosphere and to feed it to the power section; said burner (3) receiving the gas stream leaving the power section and modulating its temperature by the addition of fuel, and finally feeding it to the turbine (2) of the first turbine-compressor assembly (2, 1), in which said gas stream is expanded substantially to atmospheric pressure, to thereby actuate said compressor (1) by means of the generated power.

2. An open-cycle turbine system according to claim 1, characterised in that the power section is realised according to the two-shaft scheme or the one-shaft scheme, and with one or two burners (8, 9).

3. An open-cycle turbine system according to claim 1 or 2, characterised in that said output for the exhaust gases of the turbine system is associated with the regeneration section (10, 11) for recovering heat from the exhaust gases, which includes a reforming device (10) located upstream of a heat exchanger (11) with reference to the exhaust gas stream coming from the modulation section; said regeneration section (10, 11) for recovering heat from the exhaust gases being apt to recover part of said heat and to transfer it to the gas or comburent air flowing out of a compressor (5) of said power section; the regeneration section for recovering heat from the exhaust gases being capable, by means of its reforming device (10), of maintaining a temperature threshold at the input to the hot side of the heat exchanger (11), which is compatible with an economic construction of the latter, and at the same time, of allowing a high maximum operating temperature of the turbine (2) belonging to the first turbine-compressor assembly (2, 1), thereby increasing the efficiency of the turbine system as a whole.

4. An open-cycle turbine system according to claim 1, 2 or 3, characterised in that said turbines and compressors (1, 5; 2, 6, 7) belonging to the power section and to the modulation section, and said heat exchanger (11), are sized in such a way to realise the maximum of efficiency at medium-low powers, for which the maximum cycle temperature remains approximately constant during the variation of the power outputted by the system.

5. An open-cycle turbine system according to anyone of the preceding claims, characterised in that after the switching-off of the burner (3) of the modulation section, a further power reduction is obtained by modulating the fuel amount fed to the burners (8, 9) of the power section, according to modalities which depend on the relative sizing of the turbines (6, 7) of the power section.

6. An open-cycle turbine system according to anyone of the preceding claims, characterised in that the system (4) for lowering the temperature of comburent air, belonging to said modulation section, is an intercooler (4) arranged downstream of said compressor (1) of the modulation section with reference to the comburent air flow that passes through said input ( 17) of comburent air.

7. A turbine system according to anyone of the preceding claims, characterised in that said power section comprises a motor-generator (15) usable for starting and accelerating a second turbine-compressor assembly (6, 5) included in the power section.

8. A turbine system according to claim 7, characterised in that said motor-generator (15) usable for the starting and the acceleration, is mounted on a shaft of the second turbine-compressor assembly (6, 7) included in the power section.

9. A turbine system according to anyone of the preceding claims, characterised in that the power section comprises a free turbine (7) from which the mechanical power, required by said mobile or stationary served user unit, is drawn.

10. A turbine system according to claim 9 which in turn depends on claim 8, characterised in that the power section includes two burners (8, 9), of which one (8) is arranged upstream of the turbine (6) of said second turbine-compressor assembly (6, 5), and the other (9), is arranged upstream of said free turbine (7) from which the mechanical power, required by said mobile or stationary served user unit, is drawn.

11. A turbine system according to anyone of the claims 3 to 10, characterised in that the reforming device (10) includes an electrically heated portion to perform the reforming process during the start phase of the turbine system.

12. A turbine system according to anyone of claims 3 to 11, characterised in that, in case the fuel is a liquid, the reforming device (10) will be fed with a water-fuel mixture, and in case the fuel is an alcohol, said mixture will be obtained only by mixing, whereas, if a hydrocarbon is employed, it will be necessary to use an

5 emulsifier.

13. A turbine system according to anyone of the preceding claims, characterised in that it realises an overboost function through the injection OfH₂O, by performing this alternatively or in combination in different parts of the turbine system, in one or

10 more burners, and/or in the colder side of the exchanger, and/or in the suction inlet of the compressor of the modulation section, and/or in the suction inlet of the compressor of the power section.

14. A turbine system according to anyone of the preceding claims, characterised in 15 that there is provided a plant for conveying the exhaust gases outside the system, which plant includes a heat exchanger for recovering heat from the exhaust gases, to allow the heating of an interior compartment.

15. A turbine system according to anyone of the preceding claims, characterised in 20 that there is provided a duct for conveying the exhaust gases outside the system, which duct is equipped with an exchanger to allow the condensation of steam contained in the exhaust gases and the recovery of the condensate, which thereafter is conveyed into an apposite, specific tank.

25 16. A turbine system according to anyone of the preceding claims, characterised in that the burner(s) (3, 8, 9) is (are) equipped with conventional apparatuses for preventing the formation of NO_x.

17. A turbine system according to anyone of the preceding claims, characterised in that the burner (3) of the modulation section is equipped with an oxidative catalyst.

18. A turbine system according to anyone of the preceding claims, characterised in that the turbine (7) of the power section, which delivers the power, is provided with a reduction system (19) for reducing the rpm, to allow the transmission of the power so generated to a conventional gearbox (12) for motor vehicles.

19. A turbine system according to anyone of the preceding claims, characterised in that there is provided a stop/start function extended to the car moving condition, whereby a control system of the turbine system interrupts fuel supply to the burners (3, 8, 9) of the turbine system each time a gas pedal is released, this interruption lasting for a period of time which insures that the temperatures of the turbines (2, 5, 6) will not drop below a threshold that would determine an unacceptable thermal shock on restart.

20. A turbine system according to anyone of the preceding claims, characterised in that an insulated enclosure/casing is provided, in which all components (2, 5, 6; 3, 8, 9; 10, 11) requiring an effective thermal insulation are enclosed, wherein, one or more of said components (2, 5, 6; 3, 8, 9; 10, 11) is also enclosed and insulated inside its specific insulation means; said components (2, 5, 6; 3, 8, 9; 10, 11) including the turbines of the power section and the turbine of the first turbine- compressor assembly, the burners, and the section (10, 11) for recovering heat from the exhaust gases.

21. A turbine system according to anyone of the preceding claims, characterised in that especially for applications concerning motor vehicles, the turbine-compressor assembly/assemblies (2, 1, 6, 5) is/are selected or derived from those used for the supercharging of reciprocating combustion engines.

22. An engine employing gas turbines, characterised in that it comprises two gas turbine systems, one of which is smaller, has a high efficiency and a limited power, and is realised according to anyone of the preceding claims, and the other is larger, more powerful, has a lower efficiency, is combined with the former one, is conceived in accordance to economical/lightness/compactness requirements, and consequently is limited to a single turbo-compressor and a single burner, without necessarily including the heat recovery from the exhaust gases, and is connected to the main shaft of a gearbox of the smaller turbine system by means of a rpm reducer and a coupling/servocontrolled clutch, the latter being interposed between the gearbox and the connection to the gearbox of the smaller turbine system.

23. An engine employing gas turbines, according to claim 22, characterised in that the exhaust gases of the smaller turbine system are conveyed to the larger turbine system and then are discharged in the atmosphere through the turbine of the larger turbine system, in order to reduce thermal shocks in the larger turbine system.

24. An engine employing gas turbines, according to claim 23, characterised in that in order to insure the correct direction of flow of hot fumes, or exhaust gases, not-return systems are used between said two turbine systems, that is, between the smaller and larger systems.

25. An engine employing gas turbines, according to anyone of claims 22-24, characterised in that the larger turbine system has an overboost function.

26. An engine employing gas turbines, according to anyone of claims 22-25, characterised in that the burner of the larger turbine system is provided with an oxidative catalyst.

27. An engine employing gas turbines, according to anyone of claims 22-26, characterised in that the burner of the larger turbine system is provided with apparatuses for preventing the formation OfNO_x.

28. An engine employing gas turbines, according to anyone of claims 22-27, characterised in that the burner and/or the turbine of the larger turbine system are thermally insulated and are located inside the same thermally insulating enclosure/casing that receives the components of the smaller turbine system.