ARRANGEMENT OF A STEAM ENGINE PLANT

Abstract: The invention relates to a device on a steam engine plant comprising a steam generator (3), a steam buffer (6) and a valve (2) adjustable for various cut offs and forward and backward motion for supplying steam to a steam engine (1) of displacement type. In order to obtain a powerful engine braking, the valve is designed to be set for opposite direction of driving and to open the inlet to a cylinder (5) when its piston is moving up towards the top dead centre, at the same time as injection of feed water (10, 11) into the cylinder (5) or its inlet is performed until the piston has reached the top dead centre.

Description: Arrangement of a steam engine plant The present invention relates to a device on a steam engine plant comprising a steam generator , a steam buffer and an adjustable valve for various filling and for forward- and backward motion and supply of steam to a steam engine of displacement type, especially an axial piston engine. For a steam engine as for other engines it is desirable to have the possibility of some kind of engine braking. For conventional engines the engine braking is obtained by the pump losses , which does not exist at a steam engine, and the mechanical losses, which are consider¬ ably higher than for the steam engine. Consequently it is important to provide a steam engine with an engine braking function . The steam engine plant of the introductorily mentioned type is equipped with a steam buffer and 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 " ( SE 9402181-3), 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 con¬ nection for feed water and there between 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 connections. It has been shown that an energy density of 500 kJ/kg and a power density of 100 kW kg is possible to obtained with this design, which can be compared with corresponding values for a lead-acid battery for instance with the energy den¬ sity of 100 kJ/kg and power density of only 100 W/kg. The object of the invention is to accomplish for a device according to the introductorily mentioned type an efficient and preferably also regenerative engine braking which is simple and uncomplicated, and hence safe to operate. This has been achieved according to the invention in that the device has obtained the characteristics measures defined in claim 1. By shifting the inlet valve for driving the engine in the opposite direction of rotation than the current direction of rotation, high pressure steam will start flowing into a cylinder in which the piston is moving up to the top dead centre. Hereby it is possible to obtain a very powerful engine braking , but the steam will pass through a process that , if no measures are taken, should result in a heavy overheating and a rapid melt¬ ing down of the steam engine plant. The solution of the overheating problem is to cool the high pressure steam during its admission to the cylinder to nominal steam buffer temperature by injection of cold or at least 80 °C feed water, that is available, whereafter the steam is per¬ mitted to flow into the steam buffer, which has large capacity to absorb the energy content of the this steam for later use when needed. Hereby a very effective braking function is obtained, which also is controllable from zero to a very high power , and works in both directions of rotation of the engine. The invention is described in the following in more detail with reference to the attached drawings, which schematically illustrate one embodiment of a device according to the inven¬ tion , on which figure 1 illustrates a simplified perspective view of the parts of interest of the device , figures 2 and 3 are indicator diagrams at driving and braking, respectively, and figure 4 and 5 show the flow diagrams for two different braking processes. Figure 1 shows the main engine 1 in a steam engine plant and the other components to which it is directly connected. The engine 1 , which is of axial piston type has a central rotating valve 2, which controls the steam supply with the pressure of 250 bar and the temperature of 500 °C from a steam generator 3 via a pipe 4 to all the cylinders 5 in turn in the steam engine 1. The steam buffer 6 is connected between the pipe 4 and the pipe 7, which leads the feed water with a temperature of about 80 °C and the pressure of 250 bar to the steam generator 3. The rotating valve 2 rotates synchronized with the engine shaft and is axially displaceable by a control device ( not illustrated) which makes it possible to select that hole 8 or 9 or neither of them rotates in line with the inlet holes to the individual cylinders 5. The high pressure steam is supplied in the centre of the rotating valve 2. The steam supply at normal operation forward to each cylinder 5 will take place when respective piston reaches the top dead centre. When the piston in a cylinder has reached the top dead centre the vertical edge of the triangular hole 8 of the valve 2 has reached exactly the inlet hole of the cylinder in question, and hence gives access of the high pressure steam to the cylinder in question. When the engine shaft and the valve rotates further the piston starts to leave the top dead centre and during its movement to the bottom dead centre the other edge of the hole 8 of the valve will shut off the supply of steam. The process from the steam starting entering the cylinder to closing the inlet valve is called the filling process and the fraction cal¬ culated as a percentage of the total stroke as the piston has been moved until it is closed is called the cut off. After the end of filling process the expansion process of the trapped steam takes place until the outlet ports in the cylinder liner are uncovered ( not illustrated) at the end of the stroke. The valve 2 is axially displaceable which makes it possible to utilize different parts of the hole 8 which gives different cut offs. Another hole 9 in the valve gives different cut offs at backward rotation. Driving forward at the shaft speed of 3000 rpm gives an indicator diagram according to figure 2 with the surface Yd which is positive, because the process takes place clock wise and with a magnitude which is dependent on the position of the valve 2 or the speed. When the valve is set for braking, that is, rotation in the opposite direction than the cur¬ rent direction of rotation, the high pressure steam will enter a cylinder 5 when the piston is on its way upward towards the top dead centre and feed water is injected with a temperature of approximately 80 °C into cylinder inlet and the cylinder 5 via the inner of the valve 2, to which a pipe 10 leads from an outlet port of a dosage pump 11. The inlet of the pump 11 is by a pipe 12 connected to the feed water pipe 7 and the pump 11 is driven in synchronism with the braking adjustment of the valve 2 and is active during the braking. The steam will be cooled by the water and flows together with the vaporized water back to the steam buffer 6 with a temperature equal to the nominal temperature of the steam buffer and its energy content is stored in the steam buffer simultaneously as the feed water is pressed away in corresponding amount from the steam buffer and is fed out to the pipe 7 and further to the dosage pump 11. The stored energy corresponds to the work Yb in figure 3. Since the process proceeds counter¬ clockwise in figure 3 the work is negative and consequently gives a braking torque on the engine shaft. The braking work of the engine corresponds with other words to the energy stored in the steam buffer 6. The energy flow is schematically illustrated in figure 4. Thus, the axial displacement of the rotating valve 2 gives a complete so called four quadrant control of the steam engine torque. It will give both driving and braking for forward as well as backward motion. Notable is that the quality ( steam data ) of the steam which is supplied from the steam engine at braking, is equal with the nominal existing steam in the steam buffer. Concerning that this engine brake function must not be confused with a so called exhaust brake, where the brake energy is throttled away and therefore can not be regenerated. According to the inven¬ tion the thermodynamic function of the device at braking can be said to imply that the braking energy is transferred into the injected water. The maximum torque when braking is about 70 %of the maximum driving forward torque. A steam engine of described type will have an extraordinary high torque per displace¬ ment volume . Therefore even a small steam engine can give a such high braking as the fric¬ tion against the road permits until the wheels are locked. The regeneration of the braking energy is possible only as far as the steam buffer can receive the braking energy. When the steam buffer is fully loaded the braking energy is fed to the condenser system 13 via a special pipe 14 including a throttle valve 15, as illustrated sche¬ matically in figure 5. The condenser system has an endurance to cool which depends on the velocity of the vehicle and specially the temperature of the conventional air cooled condenser. When driving it is important to keep the condenser temperature as low as possible - nominal at 80 °Q on grounds of efficiency. When braking, this reason is of course not relevant. Therefore the condenser temperature may in this case be allowed to increase, in which case the air cooled condenser will give a strongly, increased cooling capacity.

Claims: Claims 1. A device on a steam engine plant comprising a steam generator (3) a steam buffer (6) and an adjustable valve (2) for various filling for forward- backward motion and supply with steam to a steam engine (1) of displacement type , especially an axial piston engine, character¬ ized in that, to accomplish an engine brake, the valve (2) is positioned for driving the engine in the opposite direction of rotation than the current direction of rotation, so that it opens the steam admission to a cylinder (5) when its piston is moving up to top dead centre, and simul¬ taneously a device (11) is active injecting water into the cylinder (5) or its inlet until the piston has reached top dead centre. 2. A device according to claim 1. characterized in that steam from the inlet of the cylin¬ der leads to the steam buffer (6) for regeneration of the braking energy, and the injected water consist of the feed water, which is pressed away from the steam buffer (6). 3. A device according to claim 1, characterized in that the steam from the inlet of the cylinder is fed to the condenser system (13) of the steam engine plant via a pipe (14) including a throttle valve (15). 4. A device according to claims 1 or 2 , characterized in that the water injection is arranged to take place by feed water from the steam buffer (6) with a dosage pump (11) depending on braking power. 5. A device according to any of claims 1 to 4 with a steam engine of axial piston type, characterized in that the valve (2) is a rotating sleeve synchronized with the engine, which is axially displaceable and has two axially separated inlet ports (8,9) in the wall of the sleeve for supply of the steam to the cylinders (5) of the steam engine in turn for the driving of the engine in forward and backward direction respectively and with a filling dependent of the axial position of the valve.

Inventors: PLATELL OVE, PLATELL, OVE
Applicants: PLATELL OVE, RANOTOR UTVECKLINGS AB, PLATELL, OVE
Application year: 1995
Main classification: F01B25
IPC codes: F01B25, F01K3