ENGINE ASSEMBLY COMPRISING AN INTERNAL COMBUSTION ENGINE AND A STEAM ENGINE

Abstract: The invention relates to an engine assembly comprising an internal combustion engine (1) and a steam engine (7) connected to a driving assembly (23), and a heat exchanger (4), by which the heat losses from the internal combustion engine (1) is utilized for generation of steam to the steam engine (7). In order to obtain an engine assembly with small weight and size and small environmental harmful emission, but still being able to give high power output when required, the steam engine (7) is of displacement type, and excessive steam from the heat exchanger (4) which is not required for driving the steam engine (7) is arranged to be fed to a steam buffer (20), which is designed to emit a heavy flow of steam for short time periods, when required, to the steam engine (7).

Description: Engine Assembly comprising an internal combustion engine and a steam engine. The present invention refers to an engine assembly comprising an internal combustion engine and a steam engine connected to a driving assembly e.g. by a common driving axle, and a heat exchanger by which the heat losses, as exhaust gases and/or cooling water, from the internal combustion engine is utilized for generation of steam to the steam engine. Since long time ago it is known to utilize the combustion gases from the internal com¬ bustion engine in order to improve the efficiency, and here internal combustion engine refers to otto- and diesel engines. The most common device today is an exhaust driven turbo turbine driving a turbo compressor for supercharging of the combustion air, which will give an improvement at high shaft speeds of the engine. In large ships it is also customary to use steam turbines in order to utilize the heat from the exhaust gases of diesel engines. It also has been discussed to use exhaust gas heat from an internal combustion engine in a Rankine cycle proc¬ ess with the purpose to increase the engine efficiency. However, with conventional steam tech¬ nology the steam engine with its auxiliary system will be too bulky and heavy. Therefore it has not been considered as a realistic alternative in vehicles where weight and space demands are of great importance. From a thermodynamic point of view a piston steam engine would be a possible solution to utilize the heat losses in an internal combustion engine. However, in that case the weight and space demand must be considerably more reduced compared to present steam technology. The object of the invention is to accomplish an engine assembly of the introductorily mentioned type, with essentially smaller dimensions and weight and which optimizes the flex¬ ibility which is built-in in a rational steam engine system. This has been obtained according to the invention by the fact that the steam engine is of displacement type with built-in engine braking capacity, that excess steam from the heat exchanger which is not required for driving the steam engine is fed to a steam buffer, which is designed to supply steam for short periods to the steam engine with high power density. The invention is based on the utilization of a steam buffer of that type which is described in detail in an application filed together with this application, called "Steam buffer for a steam engine plant ", to which is referred regarding details about the steam buffer. This steam buffer is equipped with a high temperature connection for steam, preferably with the temperature 500 °C and the pressure 250 bar, and a low temperature connection for feed water and therebe¬ tween a solid heat exchanging material with a large number of pressure resistant flow channels with a hydraulic diameter less than 0.5 mm for the steam and feed water between the two con¬ nections. It has been shown that an energy density of not less than 500 kJ kg and a power den¬ sity of 100 kW/kg is possible with this design, which can be compared with a lead-acid battery with the energy density of 100 U kg and power density of only 100 W/kg. Almost all vehicle engines are used at very low power output compared to the maximum power output, which has to be available in some situations and in that case mostly during short periods of time. The fuel consumption for a vehicle will therefore be determined by the effi¬ ciency at low loads. The invention is also based on the knowledge that an internal combustion engine has its highest efficiency at high loads whereas a steam engine of displacement type has the highest efficiency at low loads. A diesel engine with an efficiency of 45 % at these conditions will get an additional efficiency of 10-15 percentage units from the steam engine, and hence the total efficiency can be increased to approximately 55-60 %. The diesel engine shall be designed so small that it will operate at full load in normal driving cycles. The steam engine will be designed such that it will operate at very low load when it uses the energy from the diesel exhaust gases, and the' total driving system operates in normal driving cycles. Short requirements of high power output can be supplied overwhelmingly by the steam buffer, which can immediately increase the power output from the steam engine e.g. from 30 kW at 5 % load at normal driving to 600 kW at 100 % load. Due to the high contribution from the steam engine to the power performance, but small contribution to the total weight and space demand, a very high power density of the total engine assembly is achieved. One of the reasons that the steam engine should be of displacement type is that such a steam engine can be designed to give an effective engine brake capacity, which is of great importance in many vehicles. The braking energy can also be regenerated in the steam buffer. The very high braking capacity of the displacement steam engine will save or maybe replace the conventional brakes in applications were overheating problems exist. The engine assembly according to the invention is specially suitable for propulsion of heavy vehicles like trucks and long freight trains or boats, and especially boats that require high power output for short periods of time in order to obtain planing velocity rapidly. The invention is described in more detail in the following with reference to the attached drawing, which schematically illustrates an example of an embodiment of the engine assem¬ bly for a heavy vehicle application according to the invention. The drawing illustrates an internal combustion engine 1 of diesel type ( can also be a Otto type which has larger exhaust heat losses to regenerate) with an exhaust pipe 2, which is connected to the exhaust pipe 3 via a heat exchanger 4. The heat from the cooling water can also be utilized especially if the water is pressurized. For a marine application , where the feed water shall be heated from approximately 20 °C the cooling water can be used for preheating the feed water to about 80 - 100 °C, and after that the exhaust gases can be used. The illus¬ trated heat exchanger has a heat absorbing part 5 forming a part of a pipe for steam 6, which is dimensioned for high pressure as 250 bar and a steam temperature of 500 °C and leads to a steam engine 7 of axial piston type. From the outlet of the steam engine leads a pipe 8 to a condenser 9, which is connected to a cooler 10 by the pipes 11. From condenser 9 there is a pipe 12 arranged to a feed water pump 13, which pressurizes the water to 250 bar in a pipe 14 to a circulation pump 15, from which a pipe 16 leads the feed water to the heat absorbing part 5 of the heat exchanger 4, where the feed water is vaporized and heated to 500 °C by the heat exhaust gases from the pipe 2. Between the pipe 6 with the steam temperature 500 °C and the pipe 14 with the feed water temperature of approximately 80 °C is the above mentioned steambuffer 20 connected, and to the pipe 14 is further a pressure vessel 21 connected contain¬ ing feed water and a gas cushion. The steam engine 7 is by a transmission 22 connected to a driving shaft 23, which is connected with the crankshaft of the engine 1. The diesel engine 1 is dimensioned to operate at full load at normal driving cycles and drive the drive shaft 23, to which even the steam engine 7 is connected. The steam engine is dimensioned to operate at low loads at normal driving cycles. Both engines will then operate at almost their optimum efficiency. The steam to the steam engine 7 is generated in the heat exchanger 4 in an amount that is slightly larger than what is required at normal driving cycles. The excess steam is fed to the steam buffer 20, and the feed water in the steam buffer is pressed back to the pipe 14 and then further to the pressure vessel 21, where the gas cushion is compressed. When a high power output is required, e.g. at overtaking or at a strong upward slope, a control valve 24 will be opened in the pipe 6 to the steam engine 7 from a position corresponding to low load to a position corresponding to full load. Steam will then flow from the steam buffer 20 to the steam engine 7 with the highest or a required power capacity. For an application as a heavy truck where the average power at normal driving is about 80 kW would e.g. the diesel engine be designed to give 70 kW at 100 % load and the steam engine to give 30 kW at 5 % load. At normal driving - 80 kW - both engines will work at almost optimal effi¬ ciency and simultaneously a continuous charging of the steam buffer will take place if not fully charged. Since the steam engine has a maximum power output of 600 kW, the engine assembly can, if the steam buffer is charged, give 670 kW instantaneously. For how long time it is possible to obtain this power depends of course on the size of the steam buffer, which as mentioned can have an energy density of 500 kJ/kg. The invention is of course not restricted to this shown and described example but can be modified in several ways within the scope of the inventive idea defined by the claims. The two engines can for instance be connected to different drive shafts of some kind of driving assem¬ bly. Further, a small steam generator can of course be connected to the steam pipe 6 for gener¬ ation of steam as complement to the heat exchanger 4, if required , e.g. to keep the steam system warm when there is freezing hazard. As already mentioned the steam buffer has a very high energy density of 500 kJ kg , and with a proper heat insulation there will be possibilities to store heat energy for long time periods. Hence, there are possibilities to run the engine assembly for a limited time period without running the internal combustion engine, i.e. with¬ out emission of exhaust gases.

Claims: Claims 1. An engine assembly comprising an internal combustion engine (1) and a steam engine (7) connected to a driving assembly (23), e.g. a common driving shaft, and a heat exchanger (4), by which the heat losses of the internal combustion engine from exhaust gases and/or cooling water is utilized for generation of steam to the steam engine , characterized in that, the steam engine (7) is of displacement type with built-in engine braking capacity, that excess steam from the heat exchanger (4), which is not required for driving the steam engine is sup¬ plied to a steam buffer (20) , which is designed to supply to the steam engine steam of high power density for short time periods. 2. An engine assembly according to claim 1. characterized in that the internal combus¬ tion engine (1) is a diesel engine and the steam engine (7) is a multi cylinder axial piston engine designed for a steam pressure of 250 bar and a steam temperature of 500 °C. 3. An engine assembly according to claim 1 or 2, characterized in that the internal com¬ bustion engine (1) is designed to operate at full load or close to full load at normal driving cycles and, simultaneously the steam engine (7) is designed to operate at low load. 4. An engine assembly according to claim 3, especially for propulsion of heavy vehicles as trucks, freight trains or boats, characterized in that the internal combustion engine (1) is designed to operate at full load when the steam engine (7) is operated at 5 % load.

Inventors: PLATELL OVE, PLATELL, OVE
Applicants: PLATELL OVE, RANOTOR UTVECKLINGS AB, PLATELL, OVE
Application year: 1995
Main classification: F01K3
IPC codes: F01K3, F01K23