Patent Description:
As it is known, split-cycle engines comprise at least one compression cylinder, which is dedicated to the compression of the oxidizing air, and at least one combustion cylinder or expansion cylinder, which communicates with the compression cylinder through one or more inlet valves so as to receive a charge of compressed air with every cycle, together with a fuel injection. The expansion cylinder is dedicated to the combustion of the air/fuel mixture, to the expansion of the burnt gases to generate mechanical energy and to the discharge of said gases, so that it basically acts like a two-stroke engine, which, in turn, operates the compression cylinder.

In order to improve the efficiency of the compression, the temperature increase and, hence, the work needed during the compression of the air should be limited. To this aim, for example, a liquid substance can be injected into the cylinder so that, during the compression of the air, this substance evaporates, absorbs heat thanks to the phase change and, hence, maintains the temperature of the air at the level of its own boiling temperature.

At the same time, the walls of the compression cylinder/s can be cooled through convection, to a temperature that is as low as possible, in order to remove heat and limit the air temperature increase.

On the other hand, the expansion cylinder needs to be maintained at temperatures that are suitable for its operation, but these temperatures are higher than the ones of the compression cylinder. For the compression cylinder, a traditional cooling system is generally used, with a cooling liquid circulating in the crankcase and in the head of the engine and generally consisting of a mixture of water and ethylene glycol.

In a traditional engine, all cylinders evidently have the same cooling needs, whereas in a split-cycle engine this condition does not apply.

Therefore, the known solutions described above need to be improved, in particular from the point of view of the overall thermodynamic efficiency, keeping the compression work low and exploiting in an ideal manner the residual heat that the heat-exchange fluid managed to remove from the engine.

Known systems are disclosed in <CIT>, <CIT>, <CIT>, <CIT> or <CIT>.

The object of the invention is to provide an engine assembly, which fulfils the above-mentioned need in a simple and economic fashion.

According to the invention, there is provided an engine assembly as claimed in the appended set of claims.

In particular, the engine assembly comprises a split-cycle internal combustion engine, which is cooled by means of a heat exchange fluid comprising at least one phase-change material suited to change phase from liquid to vapour while flowing in the cooling channels of the engine itself, under the temperature and pressure conditions chosen during the cooling channel designing phase.

The invention will be best understood upon perusal of the following detailed description of two preferred embodiments, which are provided by way of non-limiting example, with reference to the accompanying drawings, wherein:.

With reference to what is schematically shown in <FIG>, reference number <NUM> indicates an engine assembly, in particular to drive a motor vehicle (nor show) or for an agricultural machinery.

The assembly <NUM> comprises an internal combustion engine <NUM>, which, in particular, is defined as split-cycle engine.

The engine <NUM> consists of a compression section <NUM> and of an expansion section <NUM>: the compression section <NUM> is dedicated to the compression of air, so that it basically defines a volumetric compressor; the expansion section <NUM> is designed to the receive the air compressed by the compression section <NUM> through at least one connection duct (not shown) and to receive a quantity of fuel from an injection system (not shown) and is dedicated to the combustion of the air/fuel mixture, to the expansion of the gases produced by the combustion and to the discharge of said gases, so that it basically acts like a two-stroke engine.

The compression section <NUM> comprises one or more compression cylinders <NUM>. For example, there are two cylinders <NUM>. Each cylinder <NUM> comprises a respective liner and a respective piston defining, between them, a compression chamber designed to receive an air flow, coming from the outside, in a direct or indirect manner (through a pre-compression stage which is not shown herein, for example). The piston is provided with a reciprocating motion so as to carry out, with every cycle, an intake stroke, during which air flows into the compression chamber through one or more intake valves, and a compression stroke, during which air is compressed and then flows out of the compression chamber through one or more delivery valves in the aforesaid connection duct. The pistons of the compression section <NUM> are preferably operated by a same driven shaft (nor shown), which is defined, in particular, by a crankshaft.

Similarly, the expansion section <NUM> comprises one or more expansion cylinders (or combustion cylinders) <NUM>. For example, the cylinders <NUM> are twice the cylinders <NUM>. Each cylinder <NUM> comprises a respective liner and a respective piston defining, between them, a combustion chamber designed to receive the air under pressure coming from the aforesaid connection duct, through one or more inlet valves, together with the fuel injected by the injection system. The piston makes a reciprocating motion having an expansion stroke, during which air and fuel flow into the combustion chamber and form a mixture, which is ignited (in a controlled manner or spontaneously) in order to then produce an expansion of the burnt gases and generate mechanical energy, and an exhaust stroke, during which the burnt gases are discharged through one or more outlet valves in an exhaust system, which is not shown and is provided with exhaust gas treatment devices.

The pistons of the cylinders <NUM> preferably operate a same driving shaft (not shown), which is defined, for example, by a crankshaft and operates, in turn, the driven shaft of the compression section <NUM> in a direct or indirect manner. In the example schematically shown herein, the cylinders <NUM> and <NUM> are aligned with one another and the shafts of the sections <NUM> and <NUM> are aligned with one another along the same rotation axis.

The engine <NUM> comprises a crankcase, which, for example, is shared by both sections <NUM> and <NUM>. In other words, the crankcase comprises two distinct portions where the compression cylinders and the expansion cylinders are respectively arranged; alternatively, separate crankcases are provided for the sections <NUM> and <NUM>. The engine <NUM> also comprises two distinct heads or two portions that are part of a same head and are associated with the sections <NUM> and <NUM>, respectively.

The assembly <NUM> further comprises a cooling circuit <NUM>, which conveys a heat-exchange fluid along one or more closed loops and comprises at least one pump <NUM>. In particular, the circuit <NUM> comprises a portion <NUM>, which extends through the compression section <NUM> (in the crankcase and/or in the respective head), a portion <NUM>, which extends through the expansion section <NUM> (in the crankcase and/or in the respective head), and a portion <NUM>, which extends on the outside of the components to be cooled in the engine <NUM> and connects an outlet of the portion <NUM> to an outlet of the portion <NUM>, so that the sections <NUM> and <NUM> are cooled in series by at least part of the heat-exchange fluid.

Therefore, the inner cooling channels defining the portions <NUM> and <NUM> of the circuit <NUM> extend in the material of the crankcase (around the cylinders) and/or in the material of the head (around the ducts and valves feeding air to the cylinders and/or around the outlet ducts and valves that allow exhaust gases to be discharged from the cylinders <NUM>).

The circuit <NUM> preferably comprises a further pump <NUM>, which is distinct from the pump <NUM>, so as to independently feed respective fractions of the heat-exchange fluid to the sections <NUM> and <NUM>. In other words, the pump <NUM> has a delivery mouth 43a connected to portion <NUM> (in a direct manner or through a duct <NUM>), whereas the pump <NUM> has a delivery mouth 48a connected to the portion <NUM> (in a direct manner or through a duct). The portion <NUM> can end downstream of the pump <NUM>, namely in the area of the duct <NUM> (as shown by the continuous line), so that the pumps <NUM> and <NUM> are arranged in parallel, or can end upstream of the pump <NUM> (as shown by the broken line), so that the pumps <NUM> and <NUM> are arranged in series along the circuit <NUM>.

According to an aspect of the invention, the heat-exchange fluid circulating in the circuit <NUM> comprises a phase-change material having a boiling temperature that is such as to cause it to change phase from liquid to vapour when, in use, it flows in the portion <NUM>, namely flows through the expansion section <NUM>, under a given pressure and temperature condition of the engine <NUM> (in a steady state). At the same time, the cooling circuit <NUM> is controlled so as to let at least a fraction of the heat-exchange fluid in the portion <NUM> reach its boiling temperature under the pressure conditions present in the portion <NUM>, unlike what happens in traditional engines, where controls are provided (for example to turn on a fan associated with the radiator) in order to lower the temperature of the cooling liquid before it reaches its boiling temperature.

In particular, the heat-exchange fluid is defined by a mixture of at least two components, one of said components being defined by the aforesaid phase-change material, whereas the remaining part of the heat-exchange fluid is chosen so that a second fraction remains liquid under the temperature and pressure conditions in which the first fluid fraction boils. In other words, this mixture is chosen so as to form an azeotrope.

The remaining liquid fraction of the heat-exchange fluid prevents the cooling channels, in particular areas of the engine (for example, the head), from being full of sole vapour. The presence of a given quantity of liquid in the cooling channels in the engine maintains the heat exchange under ideal conditions.

The phase-change material is preferably defined by ethanol or ethyl alcohol, which boils at a temperature of approximately <NUM> at a pressure of approximately <NUM> bar.

The value of the operating pressure in the circuit <NUM> is kept at a threshold value by means of a known device, which is not shown herein and is arranged downstream of the portion <NUM>. This threshold value determines the boiling temperature of the heat-exchange fluid in the portion <NUM>.

For example, it is possible to use an azeotrope consisting of ethanol and water, having a percentage that is smaller than <NUM>% and greater than <NUM>%, respectively. In particular, ethanol is used in a percentage ranging from <NUM>% to <NUM>%.

Once the boiling temperature of the azeotrope is reached under the temperature and pressure conditions that were set (for example, a pressure of approximately <NUM> and a pressure of approximately <NUM> bar), a first fraction consisting of a mixture of the two substances (containing approximately <NUM>% of water and <NUM>% of ethanol) starts evaporating. When there is no more ethanol left, the remaining liquid fraction is defined by the sole water (which, at a pressure of <NUM> bar, has a boiling temperature of approximately <NUM>, so that, under operating conditions of <NUM>, it remains liquid).

According to variants which are not described in detail, an azeotrope with three substances can be used, for example ethanol, water and ethylene glycol.

At the same time, the circuit <NUM> comprises a vapour turbine, which is indicated with reference number <NUM> and is arranged downstream of the portion <NUM> so as to receive the vapour generated in the portion <NUM> after said vapour has been separated from the liquid fraction by means of a separator <NUM>, as explained more in detail below. The separated vapour expands in the turbine <NUM> and, as a consequence, produces mechanical energy (which can be extracted in the area of a rotary shaft of the turbine <NUM>), for the recovery of energy. The mechanical energy is preferably turned into electrical energy (by means of a generator, which is not shown, connected to the rotary shaft of the turbine <NUM>).

The circuit <NUM> further comprises a heat exchanger defining a condenser <NUM>, which has an inlet <NUM> connected to an outlet <NUM> of the turbine <NUM> so as to receive the vapour subjected to the expansion and turn it into liquid (thus transferring heat from said vapour to another fluid, for example ambient air, in a known manner which is not shown herein).

The sizing, during the designing phase, of the condenser <NUM> is such as to obtain a condensate having a temperature that is as low as possible. For example, the sizing is carried out in such a way that the temperature difference between the condensate and the ambient air (used to cool the vapour flowing out of the turbine <NUM>) is in the range of approximately ten degrees, in order to have an efficient heat exchange. At the same time, the condensation pressure (corresponding to the pressure at the outlet of the turbine <NUM>) must be such as not to cause an exaggerated vacuum in the condenser <NUM>.

Ethanol, which was mentioned above by way of example, at a pressure of approximately <NUM> bar, condenses at approximately <NUM>, a temperature that meets the heat exchange needs, even in the presence of ambient temperatures of <NUM>-<NUM>.

As already mentioned above, ethanol can be replaced by a different phase-change material, which is chosen so as to boil under the desired temperature and pressure conditions and/or under the temperature and pressure conditions set, during the designing phase, for the cooling channels on the inside of the engine <NUM> (in steady engine state). To this regard, in the cooling channels of the portion <NUM>, a relatively high operating pressure is needed in order to have a good enough pressure drop in the area of the turbine <NUM> and, hence, a greater mechanical energy extracted from the turbine <NUM>.

The choice of the ideal substance for the phase-change material and for the composition of the azeotrope is made by taking into account its pressure/temperature map and the relative liquid/vapour balances.

Back to <FIG>, the condenser <NUM> has an outlet <NUM>, which is connected to a suction port 48b of the pump <NUM>. According to a variant, alternatively to or in combination with the connection to the pump <NUM>, the outlet <NUM> could communicate with a suction port 43b of the pump <NUM> by means of a connection line <NUM> provided with a properly controlled valve.

The circuit <NUM> comprises the liquid/vapour separator <NUM> mentioned above, which has an inlet <NUM> connected to an outlet of the portion <NUM>, so as to receive the heat-exchange fluid immediately after the latter has removed heat from the head and/or the crankcase of the expansion section <NUM>, and is configured so as to separate the liquid fraction left in the flow flowing out of the portion <NUM>, in order to prevent said liquid fraction from damaging the turbine <NUM>. Hence, the separator <NUM> has a vapour outlet <NUM>, which is connected to an inlet <NUM> of the turbine <NUM>, and a liquid fraction outlet <NUM>, which is connected to the inlet <NUM> of a heat exchanger <NUM> in order to lower the temperature of said liquid fraction.

The exchanger <NUM> is preferably sized, during the designing phase, so as to lower the temperature of the liquid fraction by a few degrees, thus maintaining a great temperature difference between said liquid fraction and the ambient air used to cool the radiator <NUM>. In this way, a high efficiency is obtained, which minimizes the energy spent for this cooling and tends to at least partly make up for the energy requested for the cooling in the area of the condenser <NUM>.

The exchanger <NUM> is defined by a conventional radiator, if the pressure of the circuit is below <NUM> bar. In this case, using an ethanol and water azeotrope, the maximum temperature in the circuit is controlled so as to reach the boiling temperature of the azeotrope (approximately <NUM>, at the set operating temperature of <NUM> bar) and avoid reaching the boiling temperature (approximately <NUM>) of the remaining liquid fraction (water). If, on the other hand, a greater operating temperature is set, for example in the range of <NUM> bar as suggested above by way of example, the exchanger <NUM> needs to be capable of resisting this operating pressure, so that a liquid cooling could be necessary, namely a cooling with an "indirect" heat exchange, instead of using a conventional radiator.

The exchanger <NUM> has an outlet <NUM>, which is connected to the suction mouth 43b of the pump <NUM> in order to reintroduce the liquid fraction in the circulation of the expansion section <NUM> (together with the fraction that condensed in the condenser <NUM> and flew through the compression section <NUM>).

Furthermore, one or more valves (for example, pressure limiting valves and/or flow control valves associated with possible bypass branches which are not shown herein) can be arranged along the circuit <NUM>.

The closed-loop configuration comprising the engine <NUM>, the turbine <NUM>, the condenser <NUM> and the pump <NUM> allows the circuit <NUM> to be used as a Rankine cycle. However, according to a variant, it is possible to provide a heating device <NUM> (shown with a broken line) between the separator <NUM> and the turbine <NUM>, so as to overheat the vapour fraction fed to the turbine <NUM>, in order to increase the conversion efficiency thereof. The heating device <NUM> is electrically powered and/or uses the heat of the exhaust gases produced by the engine <NUM>.

In the embodiment of <FIG>, the circuit <NUM> is dedicated to the expansion section <NUM>, so that it is not provided with the pump <NUM> and with the portions <NUM> and <NUM>; furthermore, the outlet <NUM> of the condenser <NUM> is connected to the suction mouth 43b of the pump <NUM>, together with the outlet <NUM> of the exchange <NUM>.

At the same time, there is a cooling circuit <NUM>, which is separate from the circuit <NUM>; the circuit <NUM> comprises a pump <NUM>, which is distinct from and independent of the pump <NUM> and conveys a heat-exchange fluid of its own (different from or equal to the substance used in the circuit <NUM>), so that the two fluid cannot be mixed or meet. The circuit <NUM> extends through the compression section <NUM> (in the crankcase and/or in the head), so that it is dedicated to removing heat from the crankcase and/or from the head of the compression section <NUM>, and comprises a heat exchanger <NUM>, which is defined, for example, by a conventional radiator. If needed, the exchanger <NUM> and <NUM> can be integrated in one single radiator, though keeping the two heat-exchange fluids separate.

Owing to the above, a person skilled in the art clearly understands the advantages of the assembly <NUM>. In particular, the circuit <NUM> allows energy to be recovered from the heat-exchange fluid in an efficient manner and with a relatively small number of components, exploiting the ability of the phase-change material to turn into vapour inside the engine <NUM> and to store a large quantity of energy in the form of latent heat in the engine <NUM> itself.

In the embodiment of <FIG>, one single mixture flows in the circuit <NUM> for the cooling, but the flow rates and/or the heat exchanges are different for the two sections <NUM> and <NUM> depending on operating conditions, namely based on the actual percentage of fluid turning into vapour while flowing through the engine <NUM>. For example, during the starting phases, the azeotrope has not reached its boiling temperature yet and, therefore, is still in the liquid state and circulates from the separator <NUM> to the pump <NUM> together with remaining part of the heat exchange fluid. In this case, the outlet <NUM> of the separator <NUM> is preferably connected to the suction port 48b by means of the connection line <NUM>, so as to deflect the heat-exchange fluid towards the pump <NUM>, with the control of one or more valves (not shown). On the other hand, under steady state conditions, the azeotrope reaches its boiling temperature in the expansion section <NUM>, so that the vapour flows from the separator <NUM> to the turbine <NUM>, thus recovering residual heat and turning it into mechanical (and, if necessary, electrical) energy. At the same time, all condensate flows to the compression section <NUM>, where it is pre-heated before being mixed again with the remaining (non-evaporating) part of the heat-exchange fluid.

As mentioned above, the operating temperature should not exceed a predetermined temperature, which is greater than or equal to the boiling temperature of the azeotrope, so as to allow it to evaporate, but smaller than the boiling temperature of the fraction that has to remain liquid. To this aim, there are one or more possible solutions to remove heat, which operate according to known control logics that are not described in detail (for example: an increase in the fluid flow introduced into the expansion section <NUM>, in particular adjusting the pump <NUM>; a deflection of a flow of condensate, which has a relatively low temperature, through the line <NUM> towards the suction port of the pump 43b, if necessary providing an additional tank (not shown) in the area of the line <NUM>; an activation of a fan in the area of the radiator defining the exchanger <NUM>; etc.).

In the configuration of <FIG>, on the other hand, the two circuits <NUM> and <NUM> can be managed in a completely independent manner to set/adjust the heat exchange of the two sections <NUM> and <NUM>, without them affecting one another.

Furthermore, it is particularly advantageous to use the circuit <NUM> in a split-cycle engine, due to the relatively high and constant temperatures available in the expansion section <NUM>.

Owing to the above, it is evident that assembly <NUM> can be subjected to changes and variants, without for this reason going beyond the scope of protection set forth in the appended claims.

In particular, in the solution of <FIG>, a suitable phase-change material, with a relative vapour turbine, could be used also in the heat-exchange fluid of the compression section <NUM>.

Claim 1:
An engine assembly (<NUM>) comprising:
- a split-cycle internal combustion engine (<NUM>) comprising a compression section (<NUM>) and an expansion section (<NUM>); characterized in that the engine assembly (<NUM>) comprises
- a cooling system comprising a first circuit (<NUM>) configured so as to circulate a heat-exchange fluid along at least one closed loop, the first circuit (<NUM>) comprising a first pump (<NUM>) and a first circuit portion (<NUM>) extending through the crankcase and/or the head of said compression and expansion sections in order to remove heat from said crankcase and/or head;
wherein said heat-exchange fluid has a boiling temperature such that at least a fraction of the heat-exchange fluid changes phase, in use, from liquid to vapour in said first circuit portion (<NUM>), in an operating condition of the engine (<NUM>); and in that said first circuit (<NUM>) comprises a turbine (<NUM>) arranged along said closed loop downstream of said first circuit portion (<NUM>) in order to receive vapour generated in said first circuit portion (<NUM>) and produce mechanical energy by the expansion of the vapour.