Dli Witf121

where </„„</i, and da are piston or cylinder diameters as shown in big. 12.11.

The success of the rolling seal was absolutely dependent on the material used. The requirements were a high fatigue strength, high creep resistance, and resistance to chemical attack by oil or hydrogen. Promising results were obtained with a polyurethane rubber. In rig tests it was found that endurance was largely dependent cm three parameters, temperature. pressure difference across the seal, and the ratio of the diaphragm thickness and the piston/cylinder wall clearance. Temperature was found lo be a critical parameter. Seals running at 1500 revolutions per minute would endure for over a year (10 000 hours) at a temperature of 25 °C (77 °F) but would fail at 150 hours if the temperature was raised to 100 "C (2I2°F). This was attributed to the strong dependence on temperature of the tensile strength of the seal material. Al 100 °C (212 °F) it had only 20 per cent of the tensile strength at room temperature.

Basic designs of displacer-type Stirling engines with rhombic-drive mechanisms and using rolling diaphragm seals are shown in Fig. 12.12 (Rietdijk ci al 1965). The single-cylinder machine required four seals

Fig. 12.11. Rolling diaphragm seal with fluid support in n stepped system.

because of the need to provide a high-pressure 'buffer' space below the piston to reduce the mechanical loading on the drive mechanism. In the two-cylinder-opposcd design there was no requirement for a buffer space anil therefore only two seals per cylinder were required.

General Motors licence

The invention of the rhombic drive and the rolling seal provided an apparently invincible combination for the development of successful Stirling engines. The pace of development at Philips was greatly stimulated and was no doubt enhanced by the association with General Motors in the United States following the licence agreement in 1958. Single cylinder prototype engines of 7.4 kW (III hp: the Philips Type I-9S engine) and of 65 kW (90 hp: designated GM Type 1-51050) were developed in addition to the original 30 kW (40 hp) engine. The photograph shown in Fig. 12.13 of this trio of prototype engines was given by Mcijer in a review paper (Meijer 1969c). lite four-cylinder 265 kW (360 hp) engine (designated GM Type 4-S12I0) shown in Fig. 12.14

Rhombic Engine System

I 11». 12.1?. Displacer-type engine with rhombic drive: (a) single-cylinder version, (b) iwo-

cylindcr-opposcd version.

I 11». 12.1?. Displacer-type engine with rhombic drive: (a) single-cylinder version, (b) iwo-

cylindcr-opposcd version.

incorporated four 65 kW (9(1 hp) single-cylinder engines into a common crankcase. Il was designed and built by Philips for the F.lectromotive Division of General Motors and subsequently was tested by the U.S. Navy in acoustic (Schab 1964) and performance (Loftus 1964) studies.

The 1-9.S engine

The small single-cylinder Philips Type 1-98 engine became the workhorse foi numerous developments. It most likely provided guidance and inspiration for both the General Motors Ground Power Units (GPU) (I letfner 1966) and the Allison solar space power plant (Parker and Malik

Stirling Engine Prototype
i ig. 12.13. Trio of prototype engines (nftci Mcijcr 1969c).

1962). A considerable number, perhaps as many as thirty (Michels 1976), 1 -98 engines were built at Philips. They were much used in rig testing for seals and other component developments. In 1969 they were supplied for evaluation to the new licensees. United Stirling of Malmo, Sweden, and the West German group MAN/MWM.

A 1-98 engine was used in the remarkable machine shown in l ig. 12.15. This was built to demonstrate both the perfect dynamic balance of the rhombic-drive mechanism and the omnivorous mullifuel capacity of the Stirling engine. Containers of different fuels were provided along the frame of the generating set including crude oil, lubricating oil. olive oil, salad oil, dicsel fuel, gasoline, and liquid petroleum gas. The engine would run happily on all these individually or as mixtures. On one visit to Eindhoven in 1966 the author witnessed the machine running, at 3000 revolutions per minute, on a mixture of crude oil containing large bubbles of gasoline and alcohol, with one of the multiple-sided English threepenny pieces standing vertically and motionless on the crankcase.

A type 1-98 engine was incorporated as the power unit in a garden tractor, for presentation on his retirement to a senior member of the research laboratory. Another, incorporated in a 2.5 kW (3.4 hp) generating set has been on trial with the Swedish navy for a decade.

Fki. 12.11. iixperimcntnl four-cylinder 36(1 lip engine with iliombic drive.

Marine engines

A 30 kW (40 hp) single-cylinder engine (the Philips Type 1-365) was installed iti the motor yacht Johan de Win, to gain experience on pleasure-boat installations and for the development of engine auxiliary equipment. Following this, the four-cylinder opposed-piston (Philips Type 4-235 Boxer) engine shown in l igs. 12.16 and 12.17 was designed and built (Meijcr 1965). This engine was intended as an undcrfloor engine for pleasure boats or other marine installations. It was designed to produce 85 kW (115 hp) at 300 revolutions per minute and to have a maximum thermal eflicicticy of 41 per cent. Research on this engine was suspended when the need appeared for a four-cylinder in-line engine (van Bcukering et id. 1973), for bus and truck propulsion.

Fig. 12.15. Philips Type l-'jk Stirling engine with eleciric-pow.-r generator, built to demonstrate the perfect dynamic balance of the rhombic-drive mechanism and the omnivorous multifucl capacity of the Stirling engine (after Meijer 1969c).

Vehicle engines: /he new licensees The cylinder module of the opposed-piston engine was incorporated into the new four-cylinder (Type 4-235 In-line) engine. This development was undertaken at the request of the new licence holder. United Stirling, to assess the suitability of the Stirling engine for vehicular applications, II

Rhombic Drive

I'iG. 12.16. Cross-section of four-cylinder opposed piston-displaccr engine (lloxcr> for undcrfloor marine installation (after Mcijer 196,1).

was about this time the German consortium MAN/MWM also negotiated a licence agreement with Philips.

Up to that lime. Philips appeal to have given little serious attention to the use of Stirling engines in vehicles. In a wide ranging comprehensive review paper directed principally to the potential for applications with a radioisotope power source van Witteveen (1966) listed a variety of civil and military uses for Stirling engines. He did not emphasize vehicular applications to any degree but mentioned the possibilities for heavy traction.

Once started, work on the in-line 4-235 engine proceeded apace and progress was reported by de Wilde dc Ligne (1971) and by Neelen ci al. (1971). The engine shown in Fig. 12.18 had four cylinders, a bore of 8.28 cm (3.26 in), stroke of 5.00 cm (1.97 in) and operated at 300 revolutions per minute with a mean pressure of 21.6 MN/m2 (3140 lb per sq in) to produce 147 kW (200 hp). The engine was installed in a rear-mounted flat underfloor arrangement in a DAF bus chassis model S3200 as shown in Fig. 12.19.

The original radiator (front surface area 0.42 m2) (651 in2) of the bus was retained along with the existing electrically driven fans. It was supplemented with additional radiator capacity (0.67 nr/1038.5 in2) fitted al the rear above the engine, but fans were not fitted to the supplementary radiator. The mean water temperature was calculated to be 62 eC (143.6 °F) at an air temperature of 25 °C (77 °F.) with the engine at the full power of 120 kW (163 hp) and maximum speed 25.5 iii/s (57 rnph). Neelen el al. (1971) provide many other interesting details about the installation including the power and fuel control system and the bus

Pig. 12.17. Four-cylinder opposed piston-displacei engine (Boxer) lot under floor marine installations (courtesy Philips Research Laboratory).

gearbox and transmission particulars. Van Beukering et <il. (1973) indicated that commencing in 1971 the bus had undergone extensive testing in respect to cooling, power control, and vehicle 'drive-ability' characteristics.

Similar engines of this type were supplied to United Stirling for installation in a MAN bus and a motor yacht. According to llallare and Rosenqvist (1^77) the Swedish engines were rated at only half power because the hot parts were constructed of stainless steel rather than the superior heal-rcsisting steels necessary for the full pressure and high temperature to achieve the rated 147 kW (200 hp). It is likely thai the

Bus Philips Stirling Engine
Imo. 12.18 Four-cylinder in-line Philips Type 4.235 vehicle engine (courtesy Philips Research I ahoratory)

engine of I lie Philips bus installation was similarly restricted. No substantial report of Ihe bus performance and operation has been given, but hearsay has it that the rolling seals have been a persistent source of difficulty.

The Philips Type 4-235 in-line engine was the last major multiple-cylinder development of the rhombic-drive displacer-type engine, but Meijer (1970a) described extensive studies of advanced displacer engines for city buses with hydrogen and lossil fuel and with thermal storage systems.

I lowcver, detailed work by United Stirling, MAN/MWM, by General Motors, and perhaps by Philips themselves, all combined to show that double-acting engines would have a size, weight, and cost of one half or less than multiple-cylinder rhombic-drive displacer-type machines. The principal saving was, of course, in the simplified drive and the need for only one reciprocating element per cylinder. Thus as the sixties drew to a close there was a concerted movement by Philips and the three licensees away from rhombic-drive engines, and a resumption of work on double-acting engines.

The fifteen years of development effort on rhombic-drive engines had advanced the technology of Stirling engines immeasurably beyond Ihe

l-'io. 12.1U Philips Type 4.235 Stirling-engine installation in a DAI-' bus (after Neclen rf ul.

l-'io. 12.1U Philips Type 4.235 Stirling-engine installation in a DAI-' bus (after Neclen rf ul.

small air engines of the early Philips programme. The rhombic-drive engines were nearly ready for work. They were comparable in size and weight to diesel engines, were low in noise and emission products, had an omnivorous fuel capacity, good torque characteristics and excellent part-load performance, lint the cost was high, perhaps three times the cost of a diesel, and there was simply no means in prospect to halve the cost.

The Swash-plate drive Van Beukcring el ai (1973) have disclosed that a return to the double-acting engine was made at Philips in 1968 with the design of the Type 4-65 D.A. engine shown in Fig. 12.20 and conceptually in Fig. 12.21.

Elsewhere, Percival (1974) identifies 1965 as the date of the revival of interest in double-acting engines at General Motors, specifically as a propulsion unit for torpedo motors, and probably with liquid metal combustion, li is clear from big. 12.21 that the swash-plate engine has a configuration well suited to torpedoes. At General Motors a six-cylindei

Civil Engineering Laboratory Design

Flo. 12.21» Philips I'ypc 4-65 double-acting engine. (Courtesy Philips Research laboratory).

Swashplate Engine

Piston rod Swash plate

Expansion space

Compression

I Icatcr tubes Burner !

\ Cylinder sP*ce

Air inlel for burner

Burner exhaust outlet

Oil pumps

Cooler lubes Regenerator

I'rcbeatei

C onnecting ducts

Fie». 12.21 Conceptual view oi Philips Type 4-65 double-acting engine. (Courtesy Philips

Research Laboratory).

370 kW (500 hp) design was completed in 1966. and by 1967 experimental work was under way on swash-plate drive components. This suggests that Philips were somewhat delayed in their return to double-acting engines and, as with thermal energy systems, followed the lead ol their licensee. General Motors. A measure of support loi this view comes. Indirectly, from their use of nomenclature. Whereas early (1940s) double-acting air engines were said (van Beukering et al. 1973) to have wobble-plate drive mechanisms the later (1960s) double-acting engines were described as having a swash-plate drive mechanism. A distinction between a swash-plate and a wobble-plate is sometimes hard to make. Many dictionaries make no distinction and treat the two terms as interchangeable. Maki et al. (1971) define a true swash-plate drive mechanism as one that features an inclined disc rigidly attached to the rotating shaft whereas the wobble-plate does not rotate with the shaft bill merely rotates. In any event. Philips have now adopted 'swash-plate' to describe the drive on recent engines and, interestingly, retain the term 'wobble-plate' for the older engines (van Beukering et al, 1973). Further support loi the view that General Motors initiated and led a return to double-acting engines comes in a discussion on the Philips Type 4-65 DA engine by v;iu Beukering et al. (1973) from the references to work on swash-plate drives and bearings by Maki et al. (1977) and I lays et al. (1971), both these papers emanating from General Motors.

The Philips Type -1-65 DA engine is a four-cylinder double-acting engine designed foi 44 kW brake power (60 brake hp) and in 1973 was said (van Beukering et al. 1973) to have been running over 2000 hours on test. No other details of performance have been disclosed in the literature and the engine probably served as a workhorse for the development of subsequent engines ol the same form but of larger capacity.

Termination of General Motors licence

In 1970 the three licensees, General Motors. United Stirling, and MAN/MWM were all working on double-acting engines with crank/connecting drives of one form or another while Philips concentrated on double-acting engines with the swash-plate drives. Then, in early 1970, General Motors did not renew their licence agreement and their programme was suddenly and unexpectedly terminated. It is not difficult to imagine the consternation this must have aroused al Philips, for General Motors had been a partner in development since I95K.

The Ford licence

Vigorous negotiation resulted in the announcement in August 1972. of a licence and development programme with the Ford Motor Company, Dearborn, Michigan (Ford, 1972). Under the terms of the agreement

Bus Philips Stirling Engine

l i<]. 12.22. Schematic view of two heavy-duty Philips Stilling engines with swash-plate drive mechanisms (A) Type 4-M00D..A, enpine tn> Type H-500 D.A. engine (after van

Beukering <■! al. 1973), l i<]. 12.22. Schematic view of two heavy-duty Philips Stilling engines with swash-plate drive mechanisms (A) Type 4-M00D..A, enpine tn> Type H-500 D.A. engine (after van

Ford obtained

'exclusive worldwide licence rights for Philips know-how and patents for ear, truck, tractor, bus, miliiaty vehiele, industrial and surfucc vessel Stirling engines,t and a non-exclusive licence for rill other Stirling engines. Doth licences are subject lo lights reserved for ccrtain European countries. An initial three year joint development program of a seven year plan was initiated with Philips to design and build experimental engines for l ord.'

Hard on the heels of this agreement came the important review paper of van Beukering ct al. (1973) emphasizing the suitability of the Stirling engine for automotive use. Three double-acting Stirling engines with swash-plate drive were discussed in addition to the 4-1 kW (60 hp) Philips Type 4-65 DA engine mentioned above.

The three engines were a car engine and two heavy-duty truck or coach engines:

(a) Philips Type 4-215 DA Passenger car engine of 125 k\V (170 hp).

(b) Philips Type 4-1400 DA engine of 295 kW (400 hp).

(c) Philips Type 8-500 DA engine of 295 kW (400 hp). Schematic views of I he two heavy-duty engines are shown in Fig. 12.22. One was a double-acting four-cylinder swash-plate unit and the other was t Note omission of underwatei power systems (author).

an cight-cylinder twin swash-plate unit. Both engines were designed for long life and high eflicicncy at full load.

Some projected characteristics for the 4-140(1 engine are torque at maximum power of 2.1 kN.m (1590fl-lbf) at 1300 revolutions pei minute and a maximum torque of 2.6 kN.m (1900 ft-lbf) at 400 revolutions pci minute with the maximum efficiency near 40 per cent. For the 8-500 engine a torque at maximum power of 1.5 kN.m (1090 ft-Jbf) at 1900 revolutions per minute and maximum torque of 1.8 kN.m (1302ft-lbf) at 400 revolutions per minute with the maximum efficiency neat 40 per cent. These data were calculated for a coolant temperature of 70 ®C (I58°lv), a working fluid pressure of 22 MN/m" (3200 lb per sq in) of hydrogen, and heater-tube wall temperatures of 700 X 11292 T) with no allowance made for the auxiliary power consumption for fan. alternator, and power steering. A 10-15 per cent allowance for these would therefore reduce the peak thermal efficiency to about 35 per cent. No other details of the heavy-duty engines have been published.

The Philips Type 4-215 double-acting engine

Most work has been done on the Philips Type 4-215 DA engines for passenger cars shown in Fig. 12.23. Some aspects of the design of this

Bus Philips Stirling Engine
I'ia. 12.23. Philips Type4-215 D.A. engine with swash-pin tc ilrivc for passenger cat application. (Courtesy Foril Motor Company).
Ford Torino Stirling

l ie 12.24. Insinuation sketch for Philips 4-215 engine in .i 1973 Ford Torino (after

Postma rr al 1973).

l ie 12.24. Insinuation sketch for Philips 4-215 engine in .i 1973 Ford Torino (after

Postma rr al 1973).

engine have been reviewed by van Giessel and keinink (1977). big. 12.24 is an installation sketch of Ihe engine in a 1975 Ford Torino car and Fig. 12.25 is a photograph of the engine compartment of the actual Torino test vehicle. Fig. 12.26 shows the predicted performance characteristics for the Type 4-215 l)A engine reproduced from Postlna ct ul. (1973).

The review paper by Postma ci ul. (1973) disclosed thai the lirsl meeting of Ford and Philips was held in late 1970 (it will be recalled the General Motors program was terminated in early 1970). Following that meeting, a joint technical program was undertaken to investigate the applicability of the Stirling engine to cars. More specifically, the aim was to replace the Ford 5752cm* (351 in3) displacement V8 gasoline engine in the Ford Torino passenger car of intermediate size. The result of that initial joint program was a decision announced in August P>72 to continue with a second phase lo design, build, and develop Stirling engines for cars.

Ihe initial program was most likely a joint exploratory venture with Ford and probably involved no cash royalty or fee payments. The objectives of the program were to demonstrate Stirling engine emission capability, to investigate installation in cars, to predict vehicle performance and fuel economy, and lo identify the major unknowns requiring further elfort.

According lo Postma e.l ul. (1973) each company assumed specific tasks:

'Ford provided specifications for engine design, conductcd package studies, projected vehicle performance and fuel cconomy, designed the ucccssory systems and provided customer acceptance criteria.

Fio, 12.25. Photograph of I lie* engine cornpiirtnicnl <if 1973 Ford Torino car with Philips I vpe -1-215 double-acting Stirling engine installed. (Courtesy Ford Motor < 'ompany).

Hngine speed (rpm)

l2S(kW)

Ftct. 12.20. Perfoiinnnce characteristics ol the Philips Type 4-215 H.A. engine (after

Philips designed die engine, provided engine drawings, conducted simulated California Vehicle Standards (CVS) emission tests, provided basic engine performance and specific fuel consumption and furnished information 011 general engine operating characteristics."

The results achieved in this preliminary phase were sufficiently encouraging for Philips and Ford to undertake the development of a prototype installation in a 1975 Ford Torino car. Philips' task was to design, build, test and develop the basic engine while l ord designed and built the accessory and cooling systems, supplied the vehicle, installed the engine, and performed vehicle tests and evaluations.

At the start of the second phase of the program there was a note of cautious optimism in the paper by Post ma et a I. (1973) but some concern was evident about the size of the cooling system, the use of hydrogen as a working fluid, the feasibility of maintaining low emission levels over the projected life of 80 467 km (50 000 miles) and the cost of manufacturing.

Progress in the development of this program has been well documented in the semi-annual contractors coordination meetings for advanced automotive power systems organized by the U.S. Department of Energy (formerly the Energy Research and Development Administration). At the meeting in May 1975. Ford were able to announce that the Type 4-215 engine had been under extensive test and development al Philips for the past year, had been installed in the Torino tesl car and would be in the United States before the end of 1975. In the subsequent report (November 1975) il was confirmed that the Stirling powered car was received 011 schedule from Philips. In addition, a feasibility study was sponsored by ERDA for a Stirling engine of 60 to 73 kW (SO to 100 hp) for use in a passenger car of I 134-1361 kg (2500 -3000 pound) weight. Preliminary data was included for this smaller engine obtained by scaling the 4-215 engine. Ambitious plans were projected for the extensive development of Stirling engines for automotive and oilier applications under joint Ford-ERDA-othcr sponsorship.

The subsequent report (May 1976) described the progress of design studies for the small engine. An important development was that:

The assembly, difficulty, cosl and possible reliability problems with the roll sock seal used lo contain the high pressure hydrogen al the piston rod/block mtcrfacc has prompted a look at an alternative system'.

About this time Ford had been working also with United Stirling of Sweden with the installation of one of their engines in a Ford Taunus estate car. The Ford report of May 1976 briefly discussed the United Stirling sliding seal and also disclosed that the material of the seal was Rulon, a proprietory filled PTFF. (tellon) plastic with exceptional wear properties. By May 1976, 'some 2 300 miles (322-483 km) of driving on the cars (sic) had been accumulated but "they have not yet been in a satisfactory enough condition to obtain meaningful test data". .. Problems to be resolved before serious testing can begin were general engine durability, power control stability and air/fuel control stability.' A major mechanical problem had been 'the eccentric crosshead rotation with consequent noise and friction'. T he same report also noted that the DAP bus with the Type 4-265 in-line rhombic drive engine had been brought to the United States for demonstration purposes and press review.

The Philips type 4-98 double-acting engine In the October 1976 report on passenger car trials, the small engine referred to six months earlier had become identified as the Philips Type 4-98 DA engine of 60 kW (84 hp) shown in big. 12.27. The projected performance characteristics of the engine are shown in Fig. 12.28. I lie working fluid was hydrogen at 20.2 MN/nr (200 aim) mean pressure with a heater inside wall temperature of 750 "C (I382CF) a cooler temperature of 80 °C (176°F) and a maximum engine speed of 5400 revolutions per minute. The engine had four cylinders, a swash-plate angle of rr/\0 radians (18°), swept volume per cylinder of 98cnr (5.98 in *) a volumetric ratio of expansion/compression of 1.10 and a regenerator lilling factor of 38 per cent. Further work was described on the development of a sliding seal as an alternative to the rolling seal. Another interesting aspect was the comparison made between two engines having identical Type 4-98 parts, one with a swash-plate drive and the other with a dual crank drive (similar to contemporary United Stirling engines). I'lte comparison was made for installation in a 1976 Ford Pinto car. The dual crank engine with front-wheel drive was contained in the existing engine compartment

Fig. 12.27 Philips Type4-98 D.A. engine for use in a Ford Pint« (after Kitzncr 1977a).

Kariintor lop water temperature — 50°C Healer insiile wall temperature — 750°(

Kariintor lop water temperature — 50°C Healer insiile wall temperature — 750°(

Fig. 12.28. Performance characteristics of the Philips Type 4-98 D.A. engine (niter Kiuncr

1977b).

Fig. 12.28. Performance characteristics of the Philips Type 4-98 D.A. engine (niter Kiuncr

1977b).

without modification. To accommodate the swash-plate drive engine it was necessary to increase the length of the vehicle by 8.1 cm (3.2 in).

The Torino rests

In the October 1976 report no details of the Torino tests were given but il was disclosed that the program 'had not proceeded as quickly as originally hoped, because a variety of... failures have prevented running a sequence of engine calibration tests.' The design of the swash-plate drive mechanism had been modified and. more importantly, to permit early resumption of the engine development lest program the rolling seals were replaced by the piston rod seals used for the smaller engine although rolling seals were 'still believed to be a possibly proper approach for production*.

A year later the October 1977 (Kil/.ncr 1977a) report contained an extensive review of the work on the Philips Type4-215 engine. The major innovations of the engine were identified as:

1. 20.2 MN/nr (200 aim) instead of 15.2 MN/m2 (150 atm) Tor working gas pressure.

2. first engine with a rotary regenerative ceramic preheatei system.

3. new air/fuel control system to satisfy dynamic requirements.

4. new power control system for automobile demands.

5. three times larger than previous swash-plate engines.

6. half the specific weight of previous Stirling engines.

7. packageable within existing engine compartments.

8. 4000 rev/min capability instead of the 2000-3000 rev/min with rhombic-drive.

9. first engine with exhaust gas recirculation.

10. unique coolant flow through cooling units.

11. new lubrication system.

12. first engine designed to diive lull range of automotive type accessories.

The major technical problems encountered in the engine both in dynamometer and in the Torino vehicle tests were divided between problems resolved and problems unresolved. The problems resolved were identified as:

1. swash-plate surface galling.

2. drive system noise due to non-concentric crossheads.

3. regenerator end-plate bending.

4. crankcase failure.

5. engine out of balance.

6. piston attachment failure.

7. insufficient exhaust gas recirculation.

8. unstable air-fuel control system.

9. corrosion of check valves.

10. unstable combustion and power control contamination. The problems unresolved were identified as:

1. roll sock seal system failure.

2. prcheatcr leakage.

3. prcheatcr binding.

4. fuel burning on preheater core.

5. heater-head temperature distribution.

6. excessive warm-up time.

7. insufficient burner air supply.

8. power control instability.

9. heater-head cracking.

DOE-sponsored work

Kitzner (1977b) have reported comprehensively on a feasibility study for a 60 lo 73 kW (80 to 100 hp) automotive Stirling engine, conducted jointly by Ford and Philips, and commissioned by the U.S. Department of Energy. This report puts into the public domain a good deal of technical data and information not previously available. It is recommended for close study by anyone interested in advanced Stirling engine systems. Earlier. Kitzner (1977a) gave some details of a comprehensive cost-shared Ford/ERD A/NASA Stirling-engine development program extending over eight years with fundings at Ihe level of $160 million. A program of similai magnitude is being undertaken by United Stirling/Ml'!/American Motors with ERDA or. as it is now, Department of Energy (DOE) backing. Thus, ¡1 would appear, forty years alter the initial effort by Philips. Stirling engines are finally to be given the benefit of adequate funding to permit comprehensive development to be undertaken.

related work

Since the laic 1960s the main thrust of Philips's efforts seems to have been directed to automobile applications. Mcijer (1970a) discussed applications of heavy-duty Stirling engines to buses. At the same time he introduced the concept for vehicle applications ol the combination of Stirling engines and thermal storage systems (heal buffer) for completely pollution-free operations. He also introduced the possibility of using hydrogen as the fuel for engines following I he discovery at Philips of the means to 'store' large quantities of hydrogen in hexagonal intermetallic compounds of rare-earth metals and nickel or cobalt (van Vucht cr aL 1970). 11 had been found, for example, that in the material LaNis the density of hydrogen absorbed at 0.25 MN/m3 (2.5 atm) pressure and at room temperature was nearly twice as high as the density of liquid hydrogen.

In a paper published about the same time (Mcijer 1970b) the prospects foi application of the Stirling engine to vehicles were further discussed with firs I mention of the new double-acting swash-plale engines. The discussion included a review of the advantages of indirect heating using heal pipes and a heal storage system using lithium fluoride. Further details of the hydrogen storage system for vehicle fuels were also given. I'lie results of calculations were presented for a variety of vehicles: cars, vans, taxis, and buses operating with Stirling engines in combination with thermal storage systems or hydrogen fuel. Conclusions were that both systems were well suited for vehicular application except in Ihe large American cars requiring a wide radius of operation.

More recently, Asselman at al. 11977) have contributed further work on the Stirling automotive engine with thermal energy storage. Roser (1(>77) has discussed some aspects of safety with high-temperature thermal storage systems. 1'he vehicle Stirling engine with thermal energy storage is believed to have an important part to play in Ihe future when fossil fuels are no longer so readily available. Clearly Philips believe this and are at Ihe forefront of research in this important field. Various oilier papers, important to the literature of Stirling engines, have been contributed by Philips workers.

Asselman el ol. (1972) reported on the development of a high-performance radiator. A design called Ihe 'folded front' radiator was described that was found to be lighter in weight, smaller, and with better heat-transfer properties with less fouling than conventional radiators. This work was stimulated by the handicap of the very large cooling-system load that is characteristic of vehicles equipped with Stirling engines. Use of an improved radiator or other cooling system is of course not confined to Stirling engines. It could be just as easily adopted with great advantage for dicsel engine use, and so the penalty of double-sized cooling systems would remain with the Stirling engine.

Michels (1972) presented the results of studies of the emission characteristics of the combustion systems used on Stirling engines in support of the development of the Type 4-215 DA engine. Earlier. Michels (1971) had reported on the theoretical and experimentally measured effects of exhaust gas recirculation on the NOx content of exhaust gases from a Stirling engine.

Utter, Michels (1976) presented interesting data in a study of the elfect of temperature and different working lluids on the efficiency of a Stirling engine with particular reference to the Philips 1-98 displacer engine with rhombic drive. Some of these results are reproduced in Chapter 8.

Hermans cf u I. <1972) and Uhleinann et a I. (1974) reported on the possibilities for the combination of a nuclear isotope heat source and Stirling engine for remote unattended power generation.

In the field of thermal energy storage systems in combination with Stirling engines, Asselman and Green (1973a and b) discussed the technology of heat pipes and their application at Philips to Stirling engines. Gawron and Schrocder (1972) presented information on the thermal storage aspects of eutectic fluoride mixtures, and van der Sluys (1975) and Bicrman (1975) presented experimental data about lithium sulphurhcxafluoridc heat sources in combination with Stirling engines for underwater propulsion systems. Design studies for underwater power systems and for total-energy systems were described by Jaspers and du Pre (1973).

Under ERDA contract the Philips Laboratories in North America investigated the application of Stirling engine prime movers to total-energy power-generation systems in hospitals, office buildings, and a residential complex. The results of this study were reported by Lehrfeld (1977). Asselman (1976) described experimental work with lluidized bed coal combustion to provide heat to a Stirling engine with a heat pipe.

In addition to all the above work, major research and development programs on Stirling engines as cryogenic cooling machines have been carried out continuously since 1948 at the Philips Research Laboratories at Eindhoven and. later, at the North American Philips Laboratories in New York. None of the cryogenic work has been reviewed here but is included in the companion volumet. I! should he understood there was much interchange between the different groups working on prime movers and refrigerating machines with developments in one field finding their application in another.

Another important program not covered here is the joint North American Philips/Westinghouse program to investigate the feasibility of the radioisotope artificial heart under contract to the U.S. Atomic Energy Commission (AEC), and later the Energy Research and Development Administration. This program is reviewed in Chapter 17.

1 Kegencrative Cryogenic Cooling Engines—in preparation.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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