GB2333131A - A externally heated gas engine having two heat loops - Google Patents

Abstract

A externally heated gas engine comprises a piston capable of reciprocating in a cylinder, the cylinder and piston forming a first working chamber and a second working chamber, one on either side of the piston, a first heat loop and a second heat loop for providing working fluid alternatively to either side of the piston and electronic valves for providing unidirectional flow of the fluid. Each heat loop has a heater for providing constant volume heating of the working fluid and a condenser for providing constant volume cooling and both loops are arranged to alternately feed to the first chamber fluid that has undergone constant volume heating while fluid that has undergone constant volume cooling is exhausted from the second chamber. Preferably the fluid is hydrogen. Also the invention may have a catalyst brick shaped for retaining heat in the working fluid pipes (figure 3), a seal that allows lubrication of the piston rod without mixing lubricant with the working fluid (figure 7) and a sliding stabiliser of a con rod link which may be used as an alternator armature (figure 1, reference 14).

Description

COMPACT EXTERNAL HEATING GAS EXPANSION ENGINE This invention relates to a type of engine that controls its working fluids externally between the heat source & cylinder expansion similar to a Stirling Engine but with a major difference of having two heat loops working by adding pressure and abstracting pressure above and below the piston in the form of a double acting piston. The hot blow time is significantly improved over Stirling engines and there is no working fluid reversal, but working fluid flows in one direction only. This prevents high aerodynamic flow resistance and therefore improves thermal efficiency. This arrangement with electronic valves allows for a completely hermeticaly sealed unit. It has duplication of seals between the expanding and contracting volumes and also the crank case with the introduction of a mushroom seal which completely excludes these volumes between the working gas expanding volumes and crankcase thus ensuring no migration of working fluid into the crankcase. All moving elements of the engine have maximum utilization particularly the conrod guide which also acts as a alternator armature by utilizing the oscillating movement to induce alternating current generation. The crankshaft also drives two generators which are hermetically sealed from atmosphere. Hydrogen gas can be used as a working fluid with high pressure producing high outputs than helium which is normally prefered because of the safety aspects, but because of the micro size of the engine these safety concerns have been reduced to that of any engine type because of a small amount of hydrogen used.

If more power capacity is required then it is only necessary to add more engine units which are autonomous and can be controlled or shut down individually according to various energy requirements. The engine contains its own heat exchanger using fine tubing for maximising sureface area to heat exchanger size density for optimum heat capacity to cooling fluid. see Fig. 8 A specific embodiment of this invention will now be described with reference to drawings and graphs in which Fig. 1 Illustrates the invention in the form of a single cylinder double acting piston.

Fig. 2 Shows a schematic diagram of the invention.

Fig. 3 Illustrates in section the close proximity of the heater to base engine.

Fig. 4 Shows detail of the heat recuperation by means of gas throttling.

Fig.5 Illustrates the method of combustion with catalytic lining in relation to base engine for one heat loop only.

Fig. 6 Illustrates the inventions electronically activating valves with gas servo assist.

Fig. 7 Illustrates the piston mushroom seal and piston conrod lubrication.

Fig. 8 Shows heat exchanger tube diameter relationship to surface area.

Fig. 9 Shows thermodynamic laws used in one heat loop.

Description: Refering to the invention Fig.l The engine comprises of two heat loops 1 & 2 expanding & contracting gas either side of a double acting piston 3 in a cylinder 4 rigidly connected by rod 7 see Fig. 2. This conrod 7 slides coaxially in a tube structure 8 which intrudes halfway into the cylinder entering the piston 3 centrally. The piston 3 is sealed from the top of the tube 8 to the base of the piston 3 which also has a seal 9 which completely seals the underside of the piston 3 and cylinder 4 volumes ensuring complete separation of expanding volumes to crankcase.

Expanding working gas entry into the cylinder 4 expansion spaces above & below piston 3 is controlled by valves 15,16 volumes above piston 3 and by valves 17,18 below the piston 3 & cylinder 4 volume spaces. Exit of expanding gas into loop 1 is forced by return stroke of above piston 3 volume closing & depression of working fluid caused by cooling loop 1 through orifice plate 32 in the upper cylinder 4 at the same time working fluid is flowing through valve 17 entering and expanding on the underside of piston 3 volume. Once the gas passes through orifice plate 32 heat is given up to a metal matrix 26 (metal plated lost foam process) and conducted away through copper plate 24 to revitilise previously cooled gas just before entry into heater 20. This forms part of the heat recuperation of the cycle. Equally the underside volume of piston 3 which just when the working gas has completed its work expansion stroke is then also forced through orifices in plate 33 on return stroke giving up heat to matrix 28 & copper plate 25 which conducts heat away to fluid just entering heater 21 thus recovering heat from an exhausted cycle.

Fig. 2 Hot expanding gas from loop 2 enters cylinder 4 through valve 16 when piston 3 is at TDC. forcing piston 3 downwards.

Piston 3 & conrod 7 is connected via a link rod 10 to a crankshaft 39 running on bearings Fig. 1. Conrod 7 is stabilized by a guide 11 which also acts as an armature oscillating up & down the cylinder 4 centre line. This armature oscillates past a coil or field winding 14 causing alternating current to flow. The rotary movement of crankshaft 39 drives two DC. generators one acting as a starter are hermetically sealed eitherside of crankshaft 39 Fig.l. Located alongside of the base engine Fig.3 are the heater with heat loops 1 & 2 composed of stainless steel tubes coiled inside the heater running in channels formed in substrate brick 40 with flame heater located centrally to it.

Positioned at one end of the heater is the combustion chamber 41 which has liquid fuel injected 44 into it ignited by heater starter coil. At the other outer end of the brick 40 air is induced to pass over the whole outside length of the brick 40 picking up residual heat wasted from the brick 40 before forced draught by fan 43 into the combustion chamber 41. The flame is developed in the chamber 41 and is flowed down a steel tube 42 to the end of the substrate brick 40 where it is directed onto the heat loops 1 & 2 tubes for their full length afterwhich it is exhausted out through the stack 45. The substrate brick 40 forms a catalyst action to ensure most of all the contaminants are burnt off and its heat contributing to the heat loops 1 & 2.

Fig. 8 electronic valve tiiming can be triggered by a rotating disc 48 with slots to indicate piston 3 position in cylinder 4 timing for valves 15,16,17,18,19 & 22 opening and closing.

These valves Fig. 6 15,16,17,18,19, & 22 are composed of a plunger shaft & piston 50 which has a diagonal hole passage across it shown Fig. 3 sectioned through. This hole shown Fig. 3 can align with gas passages routed to & from from cylinder 4 to heaters 20 & 21 controlling gas to pass from the cylinder 4 to heaters 20 & 21. This has an shut & open control to these valves 15,16,17,18,19 & 22 electronically controlled from the slotted disc 48 for piston 3 position and valve timing see Fig. 6 To servo assist these valves a small gas passage is aligned once the valve initially opens so that gas pressure can assist in the opening of these valves whilst the return spring assists in closing.

Fig. 2 CYCLE OPERATION: Hot expanding gas from heat loop 2 enters the upper cylinder 4 volume through valve 16 whilst exhausted gas in lower cylinder 4 volume below the piston is induced to exit valve 18 to cool in loop 2. When the piston 3 arrives at BDC. valve 18 & valve 22 closes trapping gas in the heater volume loop 2.valve 16 shut after the crank has rotated 180 degrees to BDC. When the crank rotates a further 180 degrees to TDC. with the gas being heated in the heater loop 2 then valve 16 opens allowing hot expanding gas to enter cylinder 4 thus completing one revolution. Simily when the piston 3 arrives at BDC. hot expanding gas from loop 1 enters the lower cylinder 4 with piston 3 at BDC.through valve 17 expanding gas in the lower cylinder 4 volume forcing the piston 3 upwards valve 15 opens allowing expanded gas to enter heat loop 1 completing 180 degrees & arriving at TDC.

After 180 degrees at 360 degrees crank position both valves 19 & 17 loop 1 are closed trapping the gas in the heater 20 after which this gas is heated at constant volume for 180 degrees crank cycle time ready for when valve 17 to open at BDC. allowing expanding gas to enter lower cylinder 4 forcing the piston upwards.

The use of electronic controlled valves 15,16,17,18,19 & 22 has made it possible to advance & retard their opening & closing and change their phase opening relationships to each other which will maximise the engines torque output for varying speed conditions.

Lubrication is made by drawing oil from the crank case 51 or a deposit by the deflection of mushroom seal 49 causing a small depression drawing oil through the tube structure 8 to lubricate connecting rod 7. The cylinder bore 4 walls do not require lubricating because it has a self lubricated piston ring 52 and the piston 3 walls have no contact with the cylinder mainly to prevent heat loss from the expansion volume but also frictional losses between the piston 3 & cylinder wall 4. Any side thrust is taken by piston conrod 7 which is completely enclosed by the tube structure 8 which is lubricated and sealed.

Claims (8)

1. CLAIMS 1) A compact external heating gas expansion engine as Fig. 1 comprising of two heat loops alternately feeding expanding gas from constant volume heating and exhausting contracting gas from constant volume cooling either side of a double acting piston to effect efficient torque & power generation. An engine completely hermeticaly sealed with electronic controlled valves enabling constant direction flow of working fluids reducing aerodynamic flow loses which reflect in this engines high efficiency and compact output.
2. 2) A compact external heating gas expansion engine as Claimed in Claim 1 wherein the flexible location of these electronic valves either side of the heater dead volume has enabled high compression ratios to be used than current Stirling engine practice.
3. 3) A compact external heating gas expansion engine as Claimed in Claim 1 & 2 wherein the gas working fluid flow through two separate heat loops has permitted one direction gas flow & has avoided gas flow reversals cycle as in the case of the Stirling Engine which slows down the heat transfer for an efficient cycle.
4. 4) A compact external heating gas expansion engine as Claimed in Claim 1 where there are no sliding sealing surfaces to atmosphere as the working volumes are completely hermetically sealed thus allowing Hydrogen as a working gas at very high installation pressures to be used enabling the engines output density to be very high & thermally efficient.
5. CLAIMS 5) A compact external heat engine as Claimed in Claim 1 where because of small heat loop volumes using hydrogen as a working fluid presents less of a safety problem than the usual case of a large bore size as used in Stirling Engines.
6. 6) A compact external heat engine as Claimed in Claim 3 wherein the gas flow through two separate heat loops has provided more cycle time than the SE cycle in heating working gas fluids at constant volume thus extracting more useful heat from the heater and resulting in more thermal efficiency than the SE.
7. 7) A compact external heat engine as Claimed in Claim 1 whereby enclosing the piston rod in a tube structure and introducing improved sealing ie. mushroom seal has allowed lubrication of the piston rod without mixing lubricants with the working fluids thus reducing the problems of lubrication migration to the heater causing burning and contamination of the working fluid.
8. 8 An engine substantially as here in described & illustrated in the accompanying drawings.

   8) A compact external heat engine as Claimed in Claim 1 whereby utilizing the piston 3 conrod link to crankshaft sliding stabilizer used as a alternator armature passing a field winding producing alternating current thereby maximising component elements contained within this engine.

   9) A compact external heat engine as Claimed in Claim 1 which has a heater composed of a catalyst brick best shaped for retaining heat arround the working fluid tubes but also burns off contaminents which contribute to the overal heat contribution to the engine.

   CLAIMS 5 An engine as claimed in any proceeding claim whereby having two independent heat loops provides more time of the cycle for heating & cooling the gas so that air may be used as a working fluid (gas) with a less demanding sealing requirement.

   6 An engine as claimed in any proceeding claim where the location of heat recuperators in the cylinder outlets facilitates heat transfer recovery through the transfer plate to the heater on the exhaust stroke with increasing back pressure & temperature loss thus recovering some of this energy.

   7 An engine as claimed in any proceeding claim whereby throttling gas through an orifice located in the cylinder both loops has produced diffusion of hot molecules from the gas to be trapped & held in a high conducting labyrinth and conducted through the heat transfer plate to the heater for energy recovery.