HEAT ENGINE

Abstract: A free-piston engine in which combustion gas is conducted around a piston (11) via inertial channel (19) for a short time during the expansion stroke. The resulting lowered pressure enables intaking in the final part of this stroke. Pressure from the gas conducted around the piston (11) via inertial channel (19) and ports (25, 26) provide the piston rebounding force and the engine output.

Description: This invention relates to a heat engine for pumping gas according to claim 1 and a process for effecting a thermodynamic cycle according to claim 7. This application corresponds to US-Patent No. 49 20 928. Heat engines and processes for effecting thermodynamic cycles are known for instance from Marks Standard Handbook for Mechanical Engineers, 7th Ed., Baumeister, McGraw-Hill, New York 1958, pages 9-170 and 9-171. Such free piston engines have output gas from their combustion chamber at the end of the expansion stroke and utilize supercharging to force gas into the combustion chamber against the output pressure in a conventional two-stroke cycle. These engines have also generally required a separate bounce chamber to rebound the piston at the end of the stroke. The need of supercharging and bounce chamber have added significantly to the complexity of these engines. It is an object of the invention to improve the abovementioned heat engine and the process for effecting a thermodynamic cycle. The problems are solved by: a) the heat engine for pumping to claim 1; and b) the process for effecting a thermodynamic cycle according to claim 7. There are many advantages offered by the invention such as: a high efficiency engine; an engine cycle, wherein the combustion chamber is exhausted part-way into the expansion stroke; a high compression engine which applies only easily managed stresses to its component parts; an engine capable of durable operation without conventional oiling or cooling; an engine readily made from non-metallic materials; and so on. Embodiments of the invention are described with reference to drawings, in which: Figure 1 is a schematic cross-sectional illustration of a single piston engine; Figure 2 is a pressure-volume-curve of the engine of Figure 1; Figure 3 is a schematic cross-sectional illustration of a dual-piston engine; Figure 4 is a cross-section view A-A of the channel 39 of Figure 3; Figure 5 is a pressure-volume curve of the engine of Figure 3; and Figure 6 is a partially sectioned outline view of another embodiment the engine of Figure 3. Referring to Figure 1, the piston 11, which is attached to rod 20, is fitted to the cylindrical casing 12. Starting air jet 14 provides an aerosol of fuel from the fuel jet 15, through the reed check valve 16, and into the combustion chamber 17. Spark plug 18 is fired on the opening of the breaker points 23 by the inward travel of the rod head 24. Inertial channel 19 and ports 25 and 26 can also be composed of a slot in the casing 12 when passed over by the piston 11. Such a slot can be spiraled around inside the casing 12 to achieve the desired length. Rings 27 limit leakage of gas across the piston 11. Receiver 21 collects and smooth pressure fluctuations of the gas, which are then delivered by pipe 22 to the turbine 29, whose work output is from the rotating shaft 30. Starting is accomplished by forcing the rod head 24 inward, driving the piston 11 to compress fuel air mixture in the combustion chamber 17, and opens breaker 23, firing the spark 18. The high pressure of combustion, C in Fig. 2 causes the piston 11 to move outward and opening the port 25 at D in Fig. 2, where the gas pressure DE causes flow through the inertial channel 19. The work available to cause this high speed flow is the area DGE. This flow once set in motion continues causing a further drop in pressure from E to F. The work done in this pumping is the area HEF. Area DGE is greater than area HEF to make up for throttling and flow losses and at high power levels shock losses. At point F, the continued travel of the piston 11 closes port 26 and further expansion FA is carried on by the piston 11 until the pressure is lowered below P-in, opening valves 16, admitting new air. The piston 11 stops its outward travel when the kinetic energy acquired by the piston 11 in the initial expansion CDEI is used up in traveling against P-out, area EFAJ. The piston 11 then begins the compression stroke driven by the work represented by the area JAB, which then becomes the compression work BIC. Combustion then occurs completing the cycle. The volume of the inertial channel 19 is sufficient that the pumping work HEF can be a achieved by the kinetic energy of the gas mass in this channel's volumn traveling at less than the local speed of sound. The length of the inertial channel 19 is such that the time taken to accelerate and decelerate the gas column is equal to the time between the opening of port 25 by the piston 11 and the closing of port 26 by the piston 11. The piston speed crossing the ports is determined by the mass of the piston 11 and rod 20 acted on by the expansion work ICDE. To minimize throttling losses, the port 25 should extend along the opening edge of piston 11 as far as possible consistent with a shape having low flow losses. This enables an abrupt valving action, which quickly bring the whole pressure DE to bear, accelerating the gas in the inertial channel. Referring to Fig. 3, ceramic cylindrical casing 31 contains the heavy ceramic piston 32 and the light ceramic piston 33. The velocity and stroke of the counter-balancing, oppositely moving pistons are inversely proportionate to their masses. Spring 47, whose force is light when compared to the air pressure forces, maintains the reciprocating pistons in the same lengthwise position in the casing 31. Intake port with non-return reed valve 50 and conduit 40 for valves 41, 42, and 44 pass through the casing 31. For starting, air from tank 45 through valve 41 enters the combustion chamber 49 side of the pistons driving the pistons apart, which engage pawls 34 and 35. Valve 42 then releases air from between pistons. With valve 40 closed, valves 43 then pressurizes receivers 36 and 37 through pipe 46. Pipe 46, which keeps the pressure in the receivers 36 and 37 equal, can also be equipped to utilize pressure fluctuation to apply a relatively small pressure differential between receivers 36 and 37 moving the combustion position in the casing 31. Pawls 34 and 35 then release pistons which accelerate inward. Electrical fuel pumping means not shown receives a signal from sensor 48 measuring the inwardness of piston 32 to determine the point for fuel pumping through the injector 38. Channel 39 permits flow bypassing the piston 33. Non-return valve 44 enables recharging of the tank 45. Fig. 4 shows the cross-section of the channel 39 which is adapted to fast valving action by the piston 33. Referring to Fig. 5, arrow 53 represents the starting pressurization of the receivers 36 and 37. The initial inward movement of the pistons which compresses 55 air between the pistons continues till the channel 39 opens, when air flows around piston 33 through the channel 39. The channel 39 is open for flow when the volume between pistons is between the dotted lines 61a. This flow is represented by curve 56, which inertially continues below P-out the pressure of receiver 37 utilizing the kinetic energy of the flow. This spill 56 of gas from the combustion chamber 49 serves to stabilize the quantity of gas compressed for combustion. The momentum of the pistons continues the compression 57, fuel is injected at 58 from the injector 38, combustion further increasing the pressure. The pressure due to compression and combustion stops and turn the pistons into the initial expansion 59 which continues until the channel 39 opens and blowdown-scavenge 60 results. The outward momentum of the piston continues 61. Piston 32 uncovers the intake 50 at 63 and air is drawn in when the pressure between the pistons goes below P-in 62. This intaking continues until the outward momentum of the pistons is exhausted 54; aid the whole cycle repeats. Output of gas at pressure P-out is available from valve 40 to such as a turbine. Fig. 6 shows a spiral slot 73 in the casing 74, which when covered by the piston 33, forms a channel to permit flow around the piston 33. The spiraling about the casing of a channel lessens flow losses due to turning gas out and back into the casing while achieving the desired length. To reduce side-force on the piston, a second channel 180 degrees around the casing from the first can be employed to balance pressure on the piston. Similarly, groves circling the outside of the pistons will equalize pressure side-forces. The channel can also be annularly extended completely around the casing.

Claims: Heat engine for pumping gas comprising: a casing (12,31,74) fitting a movable piston (11,33), said casing together with said piston forming a chamber (17,49), the movement of said piston expanding and compressing gas in said chamber; means to increase the pressure of the gas so as to impart kinetic energy into the piston (11,33); a bypass channel (19,39,73) opened and later closed by said piston (11,33) while said piston is expanding said chamber (17,49), said bypass channel (19,39,73) releasing gas around said piston to (11,33) the casing (12,31,74) on the side of said piston away (11,33) from said chamber (17,49); an inlet (16,50) for entry of gas into said chamber (17,49) when the further movement of the piston (11,33) after closure of the bypass channel (19,39,73) causes the pressure in the chamber (17,49) to be less than the inlet pressure (Pin) and; means to maintain the pressure (Pout) in the casing (12,31,74) on the side of said piston (11,33) away from said chamber (17,49) sufficiently greater than the inlet pressure (Pin) to be able to rebound the piston (11,33) back over the bypass channel (19,39,73), said engine pumping being the work in drawing of gas into said chamber (17,49) from said inlet at the inlet (16,50) pressure (Pin) and passing (D-F,60) of gas from said chamber (17,49) to the casing (31) on the side of said piston (11,33) away from said chamber (17,49) at the greater pressure (Pout) therein. Heat engine according to claim 1, characterized in that a receiver (21,37) connects to a point on said casing (12,31,74) on the side of said piston away from said chamber (17,33). Heat engine according to claim 1 or 2, characterized in that the bypass channel (19,39) is an inertial channel (19,39) tuned to pump gas from the chamber (17,49). Heat engine according to one of the claims 1 to 3, characterized in that said bypass channel (73) is formed between said piston (11,33) and said casing (12,31,74). Heat engine according to one of the claims 1 to 4, characterized in that a second piston (32) is movably arranged in said chamber (49) opposite to said piston (33). Heat engine according to claim 5, characterized in that the second piston (32) has a greater mass than said piston (33) thereby counterbalancing vibration due to said piston (33). Process for effecting a thermodynamic cycle as accomplished by the apparatus defined in claim 1, characterized by the utilization of expansion work of a cycle to subsequently compress gas (A-C,55,57) for a new cycle; the increase of the pressure of said compressed gas (C,58); an initial expansion after said pressure increase (C-D,59); the releasing of part of the gas (D-F,60); and a further expansion drawing in gas (F-A,62) after the completion of said release (D-F,60). Process according to claim 7, characterized in the said release (D-F,60) of a part of said gas including a tuned pumping of gas (E-F,60 below Pout).

Inventors: HAMMETT, ROBERT B.
Applicants: HAMMETT, ROBERT B.
Application year: 1988
Main classification: F02B71
IPC codes: F02B71, F02B75