WO2005103453A1

WO2005103453A1 - System for recovering heat energy from a heat engine vehicle

Info

Publication number: WO2005103453A1
Application number: PCT/FR2005/050225
Authority: WO
Inventors: Denis Clodic; Rody El Chammas
Original assignee: Armines
Priority date: 2004-04-09
Filing date: 2005-04-08
Publication date: 2005-11-03
Also published as: FR2868809A1; FR2868809B1

Abstract

The invention relates to a system and a method for recovering heat energy from a heat engine vehicle, using a Rankine cycle producing mechanical energy and/or electrical energy by means of a turbine (8) associated with an alternator (12). Said system comprises a coolant circuit (5) using a coolant fluid to heat a re-heating generator (6) of the Rankine cycle, and to recover the heat energy by directly cooling the cylinders and the cylinder head (4) of the heat engine and of the exhaust gases (3) of the vehicle in an exchanger located upstream of a catalyst container (2) of the vehicle. The thermodynamic fluid of the Rankine cycle is determined in such a way as to generate an expansion ratio of 4 to 6 for boiling temperatures between 130 and 150 °C and a condensation temperature of between 60 and 70 °C. The high pressure of the Rankine cycle varies between 1,500 and 2,000 kPa. The inventive method enables the energy recovery to be regulated by controlling a circulating flow of the coolant fluid.

Description

SYSTEM FOR RECOVERING THERMAL ENERGY FROM A VEHICLE WITH A THERMAL ENGINE

Field of the Invention The increase in electrical demand in motor vehicles, operating with internal combustion engines, brings about a new situation as regards the requirements for converting mechanical energy into electrical energy. In addition, beyond these traditional vehicles, hybrid vehicles with thermal and electric motors have variable electrical powers between 5 and 70 k. The recovery of thermal energy from the heat engine and its conversion into electrical energy then opens up new possibilities for improving the overall energy efficiency of the vehicle. The present invention relates to a Rankine cycle system integrated into the cooling circuit of an internal combustion engine and also recovering energy from the exhaust line. This energy recovery takes place via a heat transfer circuit which transfers the recovered thermal energy to an organic working fluid of a Rankine cycle. State of the art Thermal energy recovery systems on vehicles, are presented in various patents such as US 4901531 and WO 02/031320. The device presented in US 4901531, mainly uses water as thermodynamic fluid, and makes it possible to recover the thermal heat of the lubricating oil, the heat released by the cylinder head, and the energy of the exhaust gases and uses a piston built into the engine to relieve steam. The device presented in WO 02/031320 uses two exchangers mounted respectively on the lubrication oil circuit and on the exhaust line and makes it possible to generate two flows of superheated vapors in two different places, the first vapor flow having a moderate superheat temperature and pressure and the second flow has a much higher temperature and pressure. The two vapor flows expand in the same turbine comprising two successive expansion stages. For an internal combustion engine the exhaust gases can reach high temperatures of the order of 900 ° C. Subsequently an exchanger, for a Rankine cycle, mounted directly on the exhaust line must be able to accept a high pressure and temperature of the working fluid of the Rankine cycle and the high temperatures of the exhaust gases. Such an exchanger has a significant cost and weight, which is a major drawback for an automotive application where the weight alone constitutes an energy penalty. On the other hand, a Rankine cycle using water vapor as thermodynamic fluid and operating with high pressure and temperature levels, complicates the design of the Rankine cycle turbine by expansion in two stages and can lead to a reduced isentropic expansion efficiency, especially for the low powers envisaged. In addition, a Rankine cycle using water vapor as thermodynamic fluid, presents various difficulties linked to the freezing of water in winter and the low condensation pressures encountered. Similarly, for an internal combustion engine, the water pockets surrounding the cylinders and the cylinder head are designed to overcome relatively low pressures; the coolant generally used is glycol water. The working fluid of the Rankine cycle, presents fairly high pressures at the pump discharge and therefore, on a conventional motor,. the introduction of this fluid directly into the pockets of water surrounding the cylinders requires strengthening the tightness of the cooling system. Description of the invention The invention relates to a system making it possible to recover the thermal energy of a vehicle with a thermal engine, and / or of a hybrid vehicle with thermal and electric engines, by implementing a Rankine cycle producing mechanical and / or electrical energy by means of a turbine associated with an alternator, in particular by means of a volumetric turbine. The system includes: a heat transfer circuit using a heat transfer fluid and intended for: heating a boiler heating the Rankine cycle, - recovering thermal energy by direct cooling of the cylinders and the cylinder head of the heat engine and the exhaust gases of the vehicle in an exchanger located downstream of a catalytic converter of the vehicle. The system is such that the thermodynamic fluid of the Rankine cycle is determined so as to generate an expansion rate of 4 to 6 for boiling temperatures between 130 and 150 ° C and a condensation temperature of the order of 60 to 70 ° C. The system is such that the high pressure of said Rankine cycle varies between 1,500 and 2,000 kPa. The invention thus relates to a process for converting the recovered thermal energy into mechanical and / or electrical energy. Thermal energy is recovered both from the engine cooling circuit and from the exhaust gas via a heat transfer fluid which will circulate in the engine cooling circuit, in place of the usual coolant, then which will recover the additional heat on the exhaust line preferably after the catalytic depollution system. In the design of the invention, the heat transfer fluid is chosen so that its temperature varies between 120 and 200 ° C in order to recover this heat at a temperature level which makes the transformation system simple and light. thermal energy into mechanical energy of the Rankine cycle. Indeed, the maximum temperature level of 200 ° C makes it possible to keep all of the components that can be manufactured in light metals such as aluminum, which drastically limits the additional mass associated with the recovery system. It is known in fact that the mass transported constitutes an obstacle even to improving the energy efficiency of rolling vehicles. The principle of the invention is that the thermal energy of the heat engine is recovered at a maximum temperature level of 200 ° C. which makes it possible to design a Rankine cycle using simple turbines, preferably volumetric and having an expansion rate varying between 4 and 6. The overall design is such that the complete energy recovery and transformation system will allow, among other things, to replace the conventional radiator for cooling the heat engine with the condenser associated with the operation of the Rankine cycle. Preferably, according to the invention, the system is such that the heat transfer circuit implements a single-phase heat transfer fluid based on silicone intended to maintain a pressure slightly above atmospheric pressure to recover thermal energy successively: - around the cylinders and the cylinder head of the engine, on the exhaust gases downstream of the catalytic converter, - in a specific exchanger, integrated in the catalytic converter, for temperatures varying between 70 and 220 ° C when the heat engine is hot. The use of a judiciously chosen heat transfer fluid, typically a silicone oil, makes it possible to recover the energy in a suitable manner according to the different operating modes of the engine. In particular when the engine is cold, it is wise not to immediately put the thermodynamic fluid (or fluid of the Rankine cycle) into circulation. Only the heat transfer fluid is circulated to recover the heat of the exhaust gases which is reintroduced again into the engine block to allow the engine to rise as quickly as possible in temperature and thus limit the emissions of pollutants which are extremely significant during cold start. Preferably, according to the invention, the system is such that it further comprises a fan intended to inject a flow of air at ambient temperature in the exhaust gases upstream of the heat recovery exchanger, so as to maintain a temperature level of the order of 220 ° C. at the inlet of the recovery exchanger on the exhaust gases. Advantageously, the system includes a pump for circulating said heat transfer fluid and regulating means for varying its flow rate. The interposition of a heat transfer fluid to recover heat from the engine and part of the heat from the exhaust gases makes it possible to adapt the power recovered to the operation of the engine either in the urban cycle or in the extra-urban cycle. To do this, the flow of the heat transfer fluid must be adaptable, it therefore constitutes a first level of regulation whose purpose is to absorb the sudden variations in heat given off by the heat engine, taking into account the very large variations in engine speed depending on the vehicle's mission profiles. It is also advantageous for the system to be provided with a pump for circulating the thermodynamic fluid and with regulating means for varying its flow rate. The present invention also relates to a method making it possible to recover the thermal energy of a vehicle with a thermal engine, and / or of a hybrid vehicle with thermal and electric engines, by implementing a Rankine cycle producing mechanical energy. and / or electric by means of a turbine associated with an alternator, in particular by means of a volumetric turbine; said method comprising the following steps: heating a boiler reheating said Rankine cycle using a heat transfer fluid, recovering said thermal energy by direct cooling, using the same heat transfer fluid, of the cylinders and of the cylinder head of said engine and exhaust gases from said vehicle in an exchanger located downstream of a catalytic converter of said vehicle - regulate energy recovery by controlling a circulation rate of the heat transfer fluid.

Other characteristics and advantages of the invention will appear with the description given below, the latter being carried out for descriptive and non-limiting reference to the drawings below in which: Figure 1 shows an example of architecture of 'a system according to the invention, Figure 2 shows an advantageous example of architecture of a system according to the invention, Figure 3 shows an alternative architecture of a system according to the invention, Figure 4 shows a Ts diagram of a Rankine cycle. As shown in the example of architecture of FIG. 1, the device comprises two distinct circuits: a heat transfer circuit constituted by a circulation pump 5 driven by an electric motor 10 at variable speed, the conventional cylinder cooling circuit and from the cylinder head of the engine 4, the heat recovery exchanger 3, arranged after the catalytic converter 2, and the boiler which is also a heater 6; a thermodynamic circuit allowing the realization of the Rankine cycle consisting of the boiler 6 which recovers thermal energy from the heat transfer circuit, an expansion turbine 8 preferably volumetric driving an alternator 12, a condenser 9 which replaces the conventional radiator of the cooling circuit motor, a pump 7 making it possible to pass the thermodynamic fluid from the low to the high pressure of the cycle, this pump being driven by an electric motor with variable speed 11. The system illustrated in FIG. 1 essentially comprises four components added to the thermal engine . The exchanger 3 where on one side circulates the heat transfer fluid which will enter at a temperature of the order of 120 ° C. when the heat engine is operating in stabilized mode, the temperature of the heat transfer medium will rise to around 200 ° C. that the exhaust gas temperature is around 400 ° C to 600 ° C in the case corresponding to Figure 1 the exchanger 3 is then steel or alloy steel and the temperature difference between the gases exhaust and the heat transfer fluid is large at the hot end of the exchanger since this difference can reach 400K which has the advantage of limiting the size of one exchanger. Advantageously, as indicated in FIG. 2, a fan 15 lowers the temperature level of the exhaust gases leaving the catalytic converter 2 by introducing a flow of fresh air. The fresh air flow from the fan 15 is controlled by a thermostatic train 16 measuring the temperature after the fresh air introduction nozzle 17 in order to maintain a systematic temperature below 220 ° C at the inlet of the recovery exchanger 3. This temperature of 220 ° C maintained at the inlet of the ^Λ exchanger 3 makes it possible to use light alloys such as aluminum alloys and also makes it possible to increase the quantity of energy recovered by increasing the flow rate of gas circulating in exchanger 3. Exchanger 6 is both a boiler of the working fluid of the thermodynamic circuit and a heater of this working fluid since the thermodynamic fluid, after putting under the high pressure of the cycle by the pump 7, the thermodynamic fluid enters at a typical temperature slightly above 60 ° C. and comes out at a saturation temperature of the order of 130 ° C. On the other side of the wall of the exchanger, the heat transfer fluid, for example Syltherm 800, cools from about 200 ° C to a temperature of about 70 ° C by giving its heat to the fluid thermodynamic. Thus cooled, the heat transfer fluid can recover the heat from the heat engine in the engine cooling circuit 4. The operating pressure of the exchanger 6 on the side of the thermodynamic fluid is of the order of 1,500 to 2,000 kPa depending on the thermodynamic fluid chosen. The exchanger 6 can therefore also be constructed from a light alloy. The pump 7 is a commercially available pump, for example a diaphragm pump and driven by a variable speed motor to adapt the flow of the thermodynamic fluid to the thermal power available on the heat transfer circuit. This pump 7 is advantageously controlled by a thermostatic train 13 measuring the temperature of the coolant upstream of the boiler 6. The lower the temperature level of the coolant, the lower the flow rate of this pump. In addition, if the temperature of the coolant is lower than a predetermined temperature, typically 120 ° C., the pump 7 is not put into operation. This mode of regulation accelerates the temperature rise of the heat engine and limits the formation of pollutants during cold start. The turbine 8 is preferably a volumetric turbine either scroll, or piston, or vane. Current technologies of positive displacement compressors make it easy to create turbines based on these same technologies, in particular to have turbines made of light materials, in particular cast aluminum. This is because temperatures of the order of 130 ° C and a maximum pressure of 2,000 kPa remain reasonable. In addition, the relaxation rate is fixed at around 5, which corresponds to many available technologies. The pump 5 of the heat transfer circuit is of the same type as the circulators used for the cooling circuit of conventional engines. Its only special feature is that it has a variable speed electric motor 10. This pump 5 is controlled by a thermostatic train 14 which adapts the flow rate of the pump as a function of the temperature of the heat transfer fluid at the outlet of the heat engine. A variant is presented in Figure 3 where the heat transfer circuit after passing through the heat exchanger 3 circulates in an exchange surface 19 integrated around the catalytic converter 2 in order both to maintain the temperature of the catalytic converter 2 in its optimal zones operating, for example around 500 ° C, the passage or not of the heat transfer fluid in this exchange surface 19 is controlled by a 3-way valve 18, itself controlled by a thermostatic train 20 disposed inside the pot catalytic 2 in order to control its temperature. This variant provides a double benefit, increasing the amount of thermal energy recovered when the catalytic converter is at a temperature above its optimum operating threshold and controlling the optimal operating temperature of the catalytic converter. Thus, the object of the invention is to design a system for recovering thermal energy which does not entail modification of the engine cooling circuit by the use of a heat transfer fluid generating a low overpressure for a recovery temperature level varying between 120 and 200 ° C and on the other hand to operate a Rankine cycle with a single expansion stage with an appropriately chosen organic working fluid and a sufficiently high condensation temperature level, around 60 ° C. The choice of these temperature levels aims to recover thermal energy and partially transform it into electrical energy by means of steel exchangers for large temperature differences and light alloys typically based on aluminum for heat exchangers. moderate temperature. The turbine, preferably volumetric, is also made of light alloy derived from scroll or piston compressor techniques. The proposed system minimizes the number of components added and their weights, in particular the Rankine cycle condenser replaces the conventional engine cooling radiator. The total number of components added is four: an exchanger on the exhaust line, an organic fluid boiler using the heat from the heat transfer circuit, an organic fluid pump from the Rankine cycle, and an expansion turbine driving an alternator. The thermal drawing circuit on the thermal engine replaces the usual cooling circuit, passing through the water pockets surrounding the cylinders and the cylinder head. This cooling is carried out by means of a heat transfer fluid, the pressure of which will remain below 150 kPa absolute for the temperature levels chosen between 120 and 200 ° C. such as the SYLTHERM 800 or the DYALENE 600 which are fluids based on silicones. After recovering the engine cooling heat, the heat transfer fluid recovers an additional amount of heat from the exhaust gases. The heat is recovered downstream of the catalytic converter at a variable temperature level between 600 and 400 ° C. One of the options to maintain a temperature level at around 220 ° C at the entrance to the exchanger between the coolant and the exhaust gases is to use a fan taking outside air to mix it with the exhaust gases at 600 ° C to lower the temperature while maintaining a level of thermal power recovered high. This device makes it possible to increase the energy recovered by increasing the flow rate circulating in the recovery exchanger. The working fluid of the Rankine cycle is preferably an organic fluid having an acceptable critical temperature and a normal boiling temperature (saturation temperature of the fluid at atmospheric pressure), such as for example those presented in Table 1: R- 123, R-245ca, pentane and isopentane which will generate moderate pressures for the target temperature levels of this Rankine cycle, namely a boiling temperature around 130 ° C and a condensation temperature around 60 ° vs. In these cases, and for most of these fluids, the expansion rate is of the order of 5.

Table 1

For example, for R-245ca, the boiling temperature of 130 ° C (403 K) in the boiler results in a pressure of 1750 kPa and for a condensation temperature of 60 ° C (333 K), the pressure is 328 kPa, the expansion rate is therefore 5.33. The diagram Ts represented in FIG. 4 shows such a Rankine cycle with the heating and boiling represented by the segment DA, the isentropic expansion represented by the segment AB, the desuperheating and the condensation represented by the segment BC and the compression by the pump. represented the very short CD segment. Given the shape of the vapor saturation curve of this fluid shown in Figure 4, the isentropic expansion is dry and therefore, a fortiori, expansion with a generation of entropy will bring the turbine outlet point to the right of point B isentropic output, in the direction of increasing entropies. This type of fluid therefore has an important advantage compared to a fluid such as water where the outlet point of the turbine is found in the two-phase domain. A fluid like R-245ca or for that matter R-123, pentane or 1 'isopentane makes it possible to create a liquid-vapor exchanger between the outlet of the turbine, segment BB' and the inlet of the boiler for reheating the thermodynamic fluid, segment DD ', under high pressure. For a typical expansion efficiency of the turbine of 0.75, the efficiency of the Rankine cycle is of the order of 10%, which allows on a conventional engine, for example with a mechanical power of 75 kW, to recover a mechanical power of the turbine varying between 0.8 and 7.5 kW, which therefore makes it possible to improve the overall conversion efficiency of the heat engine by 15 to 30%, which is quite significant. The present invention also aims to provide simple and effective means of regulating the cooling of the engine and the mechanical power supplied by the turbine. The system presented has means of regulation, in particular electric motors with variable speed, to vary the flow rates delivered by the pumps of the heat transfer and thermodynamic circuits. To accelerate the temperature rise of the engine, during the cold start phases, the flow of the thermodynamic circuit pump is stopped while the heat circuit pump is running. So when the engine starts, the heat of the exhaust gases is recovered by the heat transfer fluid and reintroduced back into the engine block and is used to heat the cylinder head and the cylinders, which accelerates its temperature rise and limits the production of pollutants. cold engine. Once the heat engine has reached its nominal operating temperature, the thermodynamic circuit pump is started and the flow rates of the two circuits are regulated in order to maximize the recovery of thermal energy.

Claims

1. System making it possible to recover the thermal energy of a vehicle with a thermal engine, and / or of a hybrid vehicle with thermal and electric engines, by implementing a Rankine cycle producing mechanical and / or electric energy by means of a turbine (8) associated with an alternator (12), in particular by means of a volumetric turbine; said system comprising: - a heat transfer circuit (5) using a heat transfer fluid and intended for: heating a heating boiler (6) of said Rankine cycle, recovering said thermal energy by direct cooling of the cylinders and of the cylinder head (4) of said engine thermal and exhaust gas (3) of said vehicle in an exchanger located downstream of a catalytic converter (2) of said vehicle; said system being such that the thermodynamic fluid of said Rankine cycle is determined so as to generate an expansion rate of 4 to 6 for boiling temperatures between 130 and 150 ° C and a condensation temperature of the order of 60 to 70 ° C; said system being such that the high pressure of said Rankine cycle varies between 1,500 and 2,000 kPa.

2. System according to claim 1; said system being such that said heat transfer circuit (5) implements a silicone-based heat transfer fluid intended to maintain a pressure slightly higher than atmospheric pressure to recover thermal energy successively: - around the cylinders and the cylinder head (4 ) of said heat engine, - on said exhaust gas (3) downstream of said catalytic converter (2), - in a specific exchanger, integrated in said catalytic converter (2), for temperatures varying between 70 and 220 ° C when said heat engine is hot.

3. System according to any one of claims 1 or 2; said system being such that it further comprises a fan intended to inject a flow of air at room temperature into said exhaust gases (3) upstream of said heat recovery exchanger, so as to maintain a temperature level of the order of 220 ° C at the inlet of said recovery exchanger on said exhaust gases (3).

4. System according to one of the preceding claims; said system including a pump for circulating said heat transfer fluid and regulating means for varying its flow rate.

5. System according to one of the preceding claims; said system including a pump for circulating said thermodynamic fluid and regulating means for varying its flow rate.

6. Method for recovering thermal energy from a vehicle with a thermal engine, and / or from a hybrid vehicle with thermal and electric engines, by implementing a Rankine cycle producing mechanical and / or electric energy by means of a turbine (8) associated with an alternator (12), in particular by means of a volumetric turbine; said method comprising the following steps: heating a boiler (6) of said Rankine cycle using a heat transfer fluid, recovering said thermal energy by direct cooling, using the same heat transfer fluid, of the cylinders and of the cylinder head (4) of said heat engine and of the exhaust gases (3) of said vehicle in an exchanger located downstream of a catalytic converter (2) of said vehicle - regulating energy recovery by controlling a circulation rate heat transfer fluid.