The Development of the Single Sleeve Valve Two-Stroke Engine Over the Last 110 Years

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Review The Silent Path: The Development of the Single Sleeve Valve Two-Stroke Engine over the Last 110 Years

Robert Head * and James Turner

Mechanical Engineering, Faculty of Engineering and Design, University of Bath, Bath BA2 7AY, UK; [email protected] * Correspondence: [email protected]; Tel.: +44-0789-561-7437

Abstract: At the beginning of the 20th century the operational issues of the Otto engine had not been fully resolved. The work presented here seeks to chronicle the development of one of the alternative design pathways, namely the replacement for the gas exchange mechanism of the more conventional poppet valve arrangement with that of a sleeve valve. There have been several successful engines built with these devices, which have a number of attractive features superior to poppet valves. This review moves from the initial work of Charles Knight, Peter Burt, and James McCollum, in the first decade of the 20th century, through the work of others to develop a two-stroke version of the sleeve- valve engine, which climaxed in the construction of one of the most powerful piston aeroengines ever built, the Rolls-Royce Crecy. After that period of high activity in the 1940s, there have been limited further developments. The patent efforts changed over time from design of two-stroke sleeve-drive mechanisms through to cylinder head cooling and improvements in the control of the thermal expansion of the relative components to improve durability. These documents provide a foundation for a design of an internal combustion engine with potentially high thermal efficiency. Keywords: two-stroke; sleeve valves; patents Citation: Head, R.; Turner, J. The Silent Path: The Development of the Single Sleeve Valve Two-Stroke Engine over the Last 110 Years. 1. Introduction Energies 2021, 14, 616. https:// doi.org/10.3390/en14030616 If the internal combustion engine is to play any part in combating the environmental pressures on personal mobility in the third decade of the 21st Century it will require Academic Editor: that automotive engineers review all technologies likely to produce low-cost engines Andrzej Teodorczyk which do minimum harm to the environment. One way forward in this was suggested Received: 17 September 2020 by Gaplin et al. [1] with their work in two-stroke diesel engines with forward and reverse Accepted: 23 November 2020 uniflow scavenging air flows. However, their results were greatly affected by the gas Published: 26 January 2021 exchange limits imposed by the use of poppet valves in their designs. Fortunately, there is another way to address the problem of the valve heads at low valve lifts interfering with Publisher’s Note: MDPI stays neutral the in-cylinder air motion. with regard to jurisdictional claims in Poppet valves have been the default technology for gas exchange in internal combus- published maps and institutional affil- tion engines for the last 110 years. However, there were many other technologies tried in the iations. past. Sometimes a re-evaluation of these systems can help resolve long-standing problems. This can help in keeping the IC engine competitive as an option for an effective means of powering cars in a CO2 constrained world. One such technology worth considering is the sleeve-valve in either a 4-stroke or two-stroke configuration. Copyright: © 2021 by the authors. The sleeve valve is a thin-walled cylinder located between the piston and the engine Licensee MDPI, Basel, Switzerland. cylinder liner. This cylinder is designed to move relative to both the liner and piston so This article is an open access article that a number of slots cut into it at appropriate points can be aligned with the gas passages distributed under the terms and of the engine at a suitable interval in the engine cycle allowing gas exchange to take place. conditions of the Creative Commons There are a number of sound engineering reasons why the sleeve valve is superior to Attribution (CC BY) license (https:// the poppet valve arrangement in engines. These include: creativecommons.org/licenses/by/ 1. Larger valve flow areas for the same bore and stroke than a poppet valve engine [2]. 4.0/).

Energies 2021, 14, 616. https://doi.org/10.3390/en14030616 https://www.mdpi.com/journal/energies Energies 2021, 14, 616 2 of 21

2. There is no valve, valve stem, or valve guide to affect air flow at small port openings. 3. Higher effective compression/expansion ratios than that of poppet valve engines are possible at the same knock limit for a common fuel quality (RON or MON) [2]. 4. Complete flexibility in the design of combustion chamber shape, injector, or spark plug position, as there are no valve discs to consider. 5. Removal of many of the hot spots in the cylinder head i.e., components such as the exhaust valves. 6. Desmodromic valve operation is simple to achieve (and indeed the norm), leading to reduced limitations on gas exchange and engine speed. 7. Reduction in number of engine parts, including the elimination of valves, valve spring, followers, and associated paraphernalia. 8. Quieter operation. 9. Reduced engine height for a given engine stroke length (as there is no valve train mechanism above the cylinder head to consider). 10. Potentially better heat transfer behaviuor. 11. Simple cylinder disablement, depending on the valve drive mechanism. 12. Reduced component wear. 13. Potentially lower running friction. 14. The possibility of supercharging and/or Atkinson cycle operation on a two- stroke engine. For this technology, it is possible to use a patent history to show how it developed over time until the “commercial” will to move forward stopped. The reason why the concept was not commercialised more, is a subject in itself. However, in summary, during the war years, the engine manufacturers and the oil industry developed an understanding on how to solve a number of the major poppet valve engine problems. These included optimising of cam profiles, the use of sodium-cooled exhaust valves, and understanding of fuel knock behaviours to improve engine knock limits. These were partly achieved with the introduction of leaded gasoline blends which allowed higher compression/expansion ratios to be used in the engines for the same boost level and hence lower exhaust gas temperatures. This reduced the likelihood of exhaust valve failures and preignition at the same time. Hence, after the war, it was cheaper for the automotive manufacturers of engines to develop what they already knew, than to build new engine plant for a design concept known to only a few. In addition, in the pre-war period, the aero engine manufacturers had pioneered technologies which then disseminated to the auto industry. However, with their change in direction into gas turbines post-war, this link was broken. due to the fact that gas turbines have operating characteristics that are generally unsuited to automotive applications. No new automotive sleeve valve engines were produced after the war and the technology has been partly forgotten.

2. Birth of Sleeve Valve Technology: The First Decade of 20th Century It was Charles Yate Knight who ﬁrst suggested a possible alternative gas exchange process control system for the four-stroke engine. Which up to that time had either used steam-engine-like slide valves or the poppet valves that are ubiquitous today. The ﬁrst of these was his vertical moving sleeve arrangement shown (Figure1) as per patent US968166 of April 1904 [3]. He further improved his ideas in his patent US1090991 of 4 June 1906 [4] (Figure2) proposing that the poppet valves be replaced by a pair of thin sliding liners which surrounded the piston, these nested inside each other and were driven up and down by separate cranks at half engine speed. These sleeves having slots in them which allow for gas exchange to take place at suitable times in the Otto cycle. Determined by the operation of the sleeve crank drive mechanism. This coordinated both the opening and closing of the ports making it much quieter in operation compared with the cam operated poppet valve engines of the era. Energies 2021, 14, 616 3 of 21 Energies 2021, 14, x FOR PEER REVIEW 3 of 22

Energies 2021, 14, x FOR PEER REVIEW 3 of 22 Furthermore, without hot exhaust valves, the knock performance of the engine was superior to that of the poppet valve engine when run on the same lower octane fuels as well.

Figure 1. C.Y. Knight patent for internal combustion engine US patent 968166 filed 4 April, 1904. Figure 1. C.Y. Knight patent for internal combustion engine US patent 968166 ﬁled 4 April 1904. ReproducedReproduced with with permission permission from from US US Pa Patenttent Office. Ofﬁce. Copyright Copyright Publisher, Publisher, 1910. 1910. Figure 1. C.Y. Knight patent for internal combustion engine US patent 968166 filed 4 April, 1904. Reproduced with permission from US Patent Office. Copyright Publisher, 1910.

Figure 2. C.Y. Knight patent for internal combustion engine US patent 1090991 ﬁled 4 June 1906. FigureReproduced 2. C.Y. Knight with permission patent for from internal US Patentcombustion Ofﬁce. engine Copyright US patent Publisher, 1090991 1914. filed 4 June 1906. Reproduced with permission from US Patent Office. Copyright Publisher, 1914. Figure 2. C.Y. Knight patent for internal combustion engine US patent 1090991 filed 4 June 1906. Reproduced with permission from US Patent Office. Copyright Publisher, 1914.

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These sleeves having slots in them which allow for gas exchange to take place at suitable times in the Otto cycle. Determined by the operation of the sleeve crank drive mechanism. This coordinated both the opening and closing of the ports making it much quieter in operation compared with the cam operated poppet valve engines of the era. Further- Energies 2021, 14, 616 more, without hot exhaust valves, the knock performance of the engine was superior 4to of 21 that of the poppet valve engine when run on the same lower octane fuels as well. However, this new invention was not without its own set of shortcomings, which included problems with cylinder (or “junk”) head cooling, liner sleeve seizure, and high However, this new invention was not without its own set of shortcomings, which oil consumption. This final item was even highlighted by the inventor himself, in his later included problems with cylinder (or “junk”) head cooling, liner sleeve seizure, and high patent of November 1908 [5], in which he conceded that there was an issue with the lubri- oil consumption. This ﬁnal item was even highlighted by the inventor himself, in his cation of the two nested sleeves and that the lubricant tended to escape into the combus- later patent of November 1908 [5], in which he conceded that there was an issue with tion space or into the exhaust system where it produced oil smoke. the lubrication of the two nested sleeves and that the lubricant tended to escape into the Notwithstanding this, several automakers of the period did take up the idea for pro- combustion space or into the exhaust system where it produced oil smoke. duction, two of note being the Willy’s Car Company in the US and Daimler of Coventry Notwithstanding this, several automakers of the period did take up the idea for in England [6]. Engines of this type were produced into the early 1930s. However, it was production, two of note being the Willy’s Car Company in the US and Daimler of Coventry the inin Englandfollowing [6 ].year, Engines 1909 ofthat this two type independent were produced designers into the disclosed early 1930s. similar However, ideas that it was addressedthe in following the shortcomings year, 1909 of that the two Knight independent double-sleeve designers arrangement disclosed similar within ideas three that monthsaddressed of each the other. shortcomings of the Knight double-sleeve arrangement within three months ofThese each other.were Peter Burt, [6] a Scottish inventor, and James McCollum, [7] from Canada. They independentlyThese were Peter invented Burt, [the6] amono- Scottish or inventor, single-sleeve and James valve McCollum, mechanism, [7 ]which from Canada.as a resultThey of the independently combination invented of their individual the mono- design or single-sleeve characteristics valve came mechanism, to become which known as a as theresult Burt–McCollum of the combination sleeve of valve. their individual(Figures 3 and design 4) show characteristics their original came patents. to become known as the Burt–McCollum sleeve valve. (Figures3 and4) show their original patents.

FigureFigure 3. James 3. James McCollum, McCollum, 29 May 29 May 1909, 1909, internal internal comb combustionustion engine, engine, Patent Patent US US 1212653. 1212653. Repro- Reproduced ducedwith with permission permission from from US US patent pate ofﬁcent office Copyright Copyright Publisher, Publisher, 1917. 1917.

The major step forward in this device was the motion of the single sleeve. Knight’s twin moving sleeves operated in a pure vertical motion at half engine speed in the case of 4-stroke operation. The Burt–McCollum single sleeve arrangement manages to achieve this by a combination of vertical and rotational movement of the sleeve. This can be achieved by a crank, ﬁtted with a peg which slides in and out of a drive ball in a socket attached to the sleeve. While knight design the exhaust port activate only when slots in both of the inlet and exhaust sleeves were lined up with the necessary external port in the cylinder wall, the Burt–McCollum single sleeve with correctly positioned and proﬁled slots can, if its motion is suitable, be used to control both the inlet and exhaust events. This arrangement can be considered to have the same degrees of freedom as a single overhead camshaft arrangement in a conventional engine. In the single sleeve four-stroke the drive apparatus Energies 2021, 14, 616 5 of 21

operates at half crankshaft speed in a manner similar to a camshaft drive in a poppet valve Energies 2021, 14, x FOR PEER REVIEW 5 of 22 engine. However, for two-stroke engine applications the mechanism needs to operate at crankshaft speed.

FigureFigure 4. 4. PeterPeter Burt, Burt, Argyll Argyll Limited, Limited, 5 5August August 1910, 1910, an an improved improved inte internalrnal combustion combustion engine engine CA CA 133050A.133050A. Reproduced Reproduced with with permissi permissionon from from US Patent Office Ofﬁce,, Copyright Publisher, 1910.

TheThe major application step forward was first in used this indevice the Argyll was the motor motion vehicle of the of 1911.single sleeve. Knight’s twin movingUnfortunately, sleeves the operated Argyll in motor a pure company vertical went motion bankrupt at half inengine 1914 speed (caused in inthe part case by of a 4-strokelawsuit relatedoperation. to the The sleeve Burt–McCollum valve engine sing technology)le sleeve arrangement [8]. The rights manages to the sleeve to achieve valve thisengine by werea combination then bought of by vertical Continental and rotational Motors of Englandmovement (part of ofthe the sleeve. greater This Continental can be achievedgroup) in by 1926, a crank, after fitted which with the a major peg which site of slides patent in activity and out moved of a drive across ball to in Detroit a socket in attachedthe USA. to After the sleeve. this, there While was knight a great design deal ofthe patent exhaust activity port activate as the 4-stroke only when engine slots was in bothdeveloped. of the inlet but thatand exhaust is another sleeves story. were lined up with the necessary external port in the cylinderThe wall, first ofthe the Burt–McCollum two-stroke sleeve-valve single sleeve engine with patents correctly actually positioned appeared and in 1915.profiled slots can, if its motion is suitable, be used to control both the inlet and exhaust events. This arrangement2.1. History of can the be Two-Stroke considered Engine to have Sleeve the Valve same Arrangement degrees of freedom as a single overhead camshaft2.1.1. Early arrangement Developments in a conventional engine. In the single sleeve four-stroke the drive apparatusThe idea operates that aat sleeve half crankshaft valve could speed be applied in a manner to the similar two-stroke to a camshaft engine architecture drive in a poppetcame early. valve It engine. allows However, the symmetric for two-stroke gas exchange engine timing applications of a simple the piston-portedmechanism needs two- tostroke operate engine at crankshaft to be modified speed. allowing an extra degree of freedom, enabling asymmetric timing.The Byapplication this means was the first amount used ofin timethe Argyll the exhaust motor port vehicle is open of 1911. after the inlet port has shutUnfortunately, is reduced which the moderates Argyll motor the freshcompany charge went short-circuiting bankrupt in at1914 the (caused end of the in exhaustpart by agas lawsuit scavenging related event.to the Insleeve the extremevalve engine case, te thechnology) inlet port [8]. could The evenrights be to closed the sleeve before valve the engineexhaust were port. then This bought allows by for Continental either, expelling Moto unrequiredrs of England air (part at light of the load greater or allowing Continen- extra talair group) to be forced in 1926, in underafter which pressure the whenmajor necessarysite of patent at high activity load. moved across to Detroit in the USA. After this, there was a great deal of patent activity as the 4-stroke engine was developed. but that is another story. The first of the two-stroke sleeve-valve engine patents actually appeared in 1915.

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2.1. History of the Two-Stroke Engine Sleeve Valve Arrangement 2.1.1. Early Developments The idea that a sleeve valve could be applied to the two-stroke engine architecture came early. It allows the symmetric gas exchange timing of a simple piston-ported two- stroke engine to be modified allowing an extra degree of freedom, enabling asymmetric timing. By this means the amount of time the exhaust port is open after the inlet port has Energies 2021, 14, 616 shut is reduced which moderates the fresh charge short-circuiting at the end of the exhaust6 of 21 gas scavenging event. In the extreme case, the inlet port could even be closed before the exhaust port. This allows for either, expelling unrequired air at light load or allowing extra air to be forced in under pressure when necessary at high load. In Hunt’sIn Hunt’s invention invention of 1915 of 1915 [9] (Figure [9] (Figure 5), 5the), the first ﬁrst concept, concept, the the sleeve sleeve motion motion was was controlledcontrolled by a by cam a cam on onthe the crank crank and and a large a large return return spring spring mounted mounted in in the the junk junk head. head. In In all all probability,probability, this this latter component would have been extremely unhelpful for coolingcooling the the head,head, but but the the engine engine used used a a wet wet sump, sump, unlike unlike the the crankcase crankcase scavenged scavenged 2 2stroke stroke engines engines of of thethe period. period.

Figure 5. W.H. Hunt 13 December 1915, valve mechanism for two-stroke gas engine US 1292322. FigureReproduced 5. W.H. Hunt with 13 permission December from 1915, US valve Patent. mechan Copyrightism forPublisher, two-stroke 1919. gas engine US 1292322. Reproduced with permission from US Patent. Copyright Publisher, 1919. In his patent of 1916 [10] (Figure6) Stokes moved the spring from the junk head to theIn his area patent above of the 1916 crankcase. [10] (Figure In this6) Stok case,es moved the sleeve the wasspring driven from either the junk by head a cam-lobe to the areaor an above eccentric the crankcase. circle drive In onthis the case, crankshaft. the sleeve was In his driven concept, either the by bottom a cam-lobe of the or sleevean eccentricalso functions circle drive as anon annularthe crankshaft. piston inIn ahi scavenges concept, pump the bottom unit. This of the allowed sleeve thealso wet func- sump tionsarrangement as an annular to piston be maintained in a scavenge for piston pump lubrication. unit. This allowed the wet sump arrangement to be maintained for piston lubrication. 2.1.2. 1930s and the War Years

These ideas then lay dormant until the 1930s. The ﬁrst of the true sleeve-valve two- strokes was patented by Bischof (Figure7) in 1931 [ 11] for a low-speed diesel engine application. The drive followed a quite different concept. The mechanism was complex with the drive taken directly from the crank via a pin-and-slider arrangement (which in turn was likely to be speed limited) but the principles were determined with the asymmetric gas exchange events potential clearly disclosed. Additionally, the ports were arranged with the exhaust close to the head and the inlet at the crankshaft end, in a manner which could be considered to become the norm in later two-stroke sleeve-valve applications. This was followed by Kipfer [12] (Figure8) who simpliﬁed the concept and produced a design with an elliptical (Burt–McCollum-type) [6,7] drive mechanism for a smaller diesel engine. The asymmetric timing potential of a two-stroke in the design is clearly shown in the patent. EnergiesEnergies 20212021, 14, 14, x, FOR 616 PEER REVIEW 7 of7 of22 21

Figure 6. C.L Stokes, 2 April 1916, internal combustion engine US 1308560. Reproduced with

permission from US Patent Ofﬁce. Copyright Publisher, 1919. Figure 6. C.L Stokes, 2 April 1916, internal combustion engine US 1308560. Reproduced with permission from US Patent Office . Copyright Publisher, 1919.

2.1.2. 1930s and the War Years These ideas then lay dormant until the 1930s. The first of the true sleeve-valve two- strokes was patented by Bischof (Figure 7) in 1931 [11] for a low-speed diesel engine application. The drive followed a quite different concept. The mechanism was complex with the drive taken directly from the crank via a pin-and-slider arrangement (which in turn was likely to be speed limited) but the principles were determined with the asymmetric gas exchange events potential clearly disclosed. Additionally, the ports were arranged with the exhaust close to the head and the inlet at the crankshaft end, in a manner which could be considered to become the norm in later two-stroke sleeve-valve applications.

Figure 7. B. Bischof, 9 February1931, two-stroke internal combustion engine US 2022841. Reproduced with permission from US patent Ofﬁce. Copyright Publisher, 1935.

This was improved further by Kammer [13] who combined this with his work on drive mechanisms for 4-stroke sleeve valve engines and introduced a secondary set of “boost” ports part way up the sleeve. (Figure9) These boost ports would only operate under speciﬁc high load conditions. Due to this fact, the cylinder volume above the piston rapidly reduces during the compression phase accordingly. Consequently, the later the inlet ports were left open, the higher the boost pressure would have had to be to overcome this pressure to increase the fresh charge mass. In turn, this would increase the work required of the inlet scavenge pump system to provide the extra pressure.

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Figure 8. Kipfer 20 May 1936, two-stroke internal combustion engine US 2134286. Reproduced with permission from US patent Ofﬁce. Copyright Publisher, 1938.

Figure 9. G.S Kammer 21 February 1939, two-stroke cycle US 2197107. Reproduced with permission Figure 9. G.S Kammer 21 February 1939, two-stroke cycle US 2197107. Reproduced with permis- from US Patent Office. Copyright Publisher, 1940. sion from US Patent Office. Copyright Publisher, 1940. Scott’s design [14] Figure 10 was the first to locate the inlet ports near the junk head and theScott’s exhaust design ports [14] close Figure to the10 was crank the shaft. first Heto locate also introduced the inlet ports a variable-stroke near the junk sleeve head anddrive the to exhaust allow variation ports close in to gas the exchange crank shaft. events. He also However, introduced the sleevea variable-stroke motion does sleeve not driverotate to now. allow variation in gas exchange events. However, the sleeve motion does not rotate now.By this point in time major engineering companies were beginning to take an interest in two-stroke sleeve-valve engines such as Rolls Royce. The patent by Rowledge of Rolls-Royce of 1939 [15] (Figure 11) shows one route to provide a single central drive to operate two cylinders simultaneously in a V engine arrangement, significantly reducing complexity in the architecture.

Figure 10. L.L. Scott GM, 13 July 1939: Internal combustion engine US 2261156. Reproduced with permission from US Patent Office. Copyright Publisher, 1941.

By this point in time major engineering companies were beginning to take an interest in two-stroke sleeve-valve engines such as Rolls Royce. The patent by Rowledge of Rolls-Royce of 1939 [15] (Figure 11) shows one route to provide a single central drive to operate two cylinders simultaneously in a V engine arrangement, significantly reducing complexity in the architecture.

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Figure 9. G.S Kammer 21 February 1939, two-stroke cycle US 2197107. Reproduced with permission from US Patent Office. Copyright Publisher, 1940.

Scott’s design [14] Figure 10 was the first to locate the inlet ports near the junk head and the exhaust ports close to the crank shaft. He also introduced a variable-stroke sleeve Energies 2021, 14, 616 drive to allow variation in gas exchange events. However, the sleeve motion does not ro- 9 of 21 tate now.

Energies 2021, 14, x FOR PEER REVIEW Figure 10. L.L. Scott GM, 13 July 1939: Internal combustion engine US 2261156. Reproduced10 of 22 with Energies 2021, 14, x FOR PEERFigure REVIEW 10. L.L. Scott GM, 13 July 1939: Internal combustion engine US 2261156. Reproduced with 10 of 22 permission from US Patent Ofﬁce. Copyright Publisher, 1941. permission from US Patent Office. Copyright Publisher, 1941.

FigureFigure 11. A.J. 11. RowledgeA.J. Rowledge Rolls-Royce Rolls-Royce 2 February 2 February1939: two-stroke 1939: two-strokesleeve drive sleeve of V engine-config- drive of V engine- Figure 11. A.J. Rowledge Rolls-Royce 2 February 1939: two-stroke sleeve drive of V engine-config- urationconﬁguration engines GB engines524642A. GB Reproduced 524642A. Reproduced with permission with from permission GB Patent from Office GB Patent Copyright Ofﬁce Pub- Copyright lisher, uration1934. engines GB 524642A. Reproduced with permission from GB Patent Office Copyright Pub- Publisher,lisher, 1934. 1934.

This wouldThis would be further be further refined reﬁned from froma separate a separate drive drive shaft shaftto a mechanism to a mechanism which which ran ran directly offThis the wouldcrank withbe further a lost refined motion from slave a separatepiston arrangement drive shaft toas a used mechanism in the laterwhich ran directlydirectly offoff thethe crankcrank withwith aa lostlost motionmotion slaveslave pistonpiston arrangementarrangement asas usedused inin thethe laterlater Rolls-Royce Crecy engine which also had a 90° V engine◦ architecture (Figure 12). Rolls-RoyceRolls-Royce CrecyCrecy engine engine which which also also had had a a 90 90°V V engine engine architecture architecture (Figure (Figure 12 12).).

Figure 12. The Rolls-Royce Crecy sleeve valve drive arrangement. Reproduced with permission from NewFigureFigure Zealand 12.12. TheThe Rolls-Royce Rolls-Royce & Crecy Bentley sleeve sleeve Club valve valveInc Copyright drive drive a arrangement.rrangement. Publisher, Reproduced2007. Reproduced with with permission permission fromfrom New New Zealand Zealand Rolls-Royce Rolls-Royce & & Bentley Bentley Club Club Inc Inc Copyright Copyright Publisher, Publisher, 2007. 2007. In Britain, Harry Ricardo, who was ever a strong advocate of the sleeve-valve engine produced hisIn Britain, own drive Harry design Ricardo, [16] (Figurewho was 13). ever He a also strong built advocate a number of ofthe single-cylinder sleeve-valve engine researchproduced engines, his which own weredrive used design to support[16] (Figure the efforts 13). He of also Rolls-Royce built a number [17] and of D. single-cylinder Napier & Son,research who produced engines, their which own were twin-cylin used to supportder experimental the efforts engine, of Rolls-Royce the E.113 [17] [18]. and D. Napier & Son, who produced their own twin-cylinder experimental engine, the E.113 [18].

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In Britain, Harry Ricardo, who was ever a strong advocate of the sleeve-valve engine Energies 2021, 14, x FOR PEER REVIEW produced his own drive design [16] (Figure 13). He also built a number of single-cylinder11 of 22 research engines, which were used to support the efforts of Rolls-Royce [17] and D. Napier & Son, who produced their own twin-cylinder experimental engine, the E.113 [18].

FigureFigure 13. H 13.RicardoH Ricardo 11 June 11 1943, June Two 1943, stroke Two strokesleeve sleevevalve engine valve engineUS 2367963. US 2367963. Reproduced Reproduced with with permissionpermission from US from Patent US Patent Office. Ofﬁce. Copyright Copyright Publisher, Publisher, 1943. 1943.

The designThe design shows shows the use the of use a slave of a slave joint jointand eccentric and eccentric drive drive of the of crankshaft the crankshaft that that was successfulwas successful in the in Rolls-Royce the Rolls-Royce Crecy Crecy engine. engine. They Theyalso continued also continued to place to place the inlet the inletport port at theat bottom the bottom with withthe exhaust the exhaust at the at junk the he junkad headend, which end, which enabled enabled increased increased blow blowdown down performanceperformance at the at expense the expense of ultimate of ultimate efficiency, efﬁciency, blow blow down down being being the period the period from fromwhen when the exhaustthe exhaust port opens port opens to the to point the point at which at which the cylinder the cylinder pressure pressure reduces reduces to that to of that the of the exhaustexhaust manifold. manifold. The Rolls-RoyceThe Rolls-Royce Crecy Crecy(Figure (Figure 14) can 14 effectively) can effectively be considered be considered the swansong the swansong for the for two-strokethe two-stroke sleeve-valve sleeve-valve concept as concept it was asthe it la wasst to the be lastbuilt to even be built in prototype even in prototype numbers. num- This engine,bers. This a 24-litre engine, V12, a 24-litrewas built V12, and was the builtinitial and running the initial was promising, running was as was promising, docu- as mentedwas by documented Nahum, et al. by [18] Nahum, and Hiett et al. and [18 Robs] andon Hiett [17]. andIt was Robson also tested [17]. in It supercharged was also tested in and turbo-compoundedsupercharged and turbo-compoundedforms, the latter with forms, an exhaust the latter turbine with geared an exhaust into the turbine super- geared chargerinto drive. the supercharger Originally it drive.was intended Originally for interceptor it was intended fighters, for interceptorwhere extremely ﬁghters, high where power-to-weightextremely high ratios power-to-weight take priority over ratios fuel take consumption. priority over However, fuel consumption. its fuel consump- However, its tion wasfuel actually consumption good wasin compound actually good form. in Ne compoundvertheless, form. with Nevertheless, the exigencies with of war, the exigencies and of war, and Rolls-Royce’s increasing involvement in gas turbine propulsion for aircraft, Rolls-Royce’s increasing involvement in gas turbine propulsion for aircraft, development development was ultimately halted, and all of the test engines were destroyed in 1946 [18]. was ultimately halted, and all of the test engines were destroyed in 1946 [18].

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Figure 14. Rolls-Royce Crecy engine 12-cylinder two-stroke sleeve valve direct fuel injection 90

degree V aircraft piston engine. Reproduced with permission from WW2 aircraft.net Copyright FigurePublisher,Figure 14. 14. Rolls-Royce Year1989.Rolls-Royce Crecy Crecy engine engine 12-cylinder 12-cylinder two-stroke two-stroke sleeve sleeve valve valve direct direct fuel fuel injection injection 90 degree 90 Vdegree aircraft V pistonaircraft engine. piston Reproducedengine. Reproduced with permission with permission from WW2 from aircraft.net WW2 aircraft.net Copyright Copyright Publisher, Publisher, Year1989. Year1989.Towards the end of the war, other designs were patented. Halsing [19] (Figure 15) considered an arrangement where the sleeve was controlled by a pair of connecting rods drivenTowardsTowards off the thecrank.the endend This ofof the thereturns war,war, other theother sleeve designs designs motion were were to patented. patented.a simpler Halsing Halsingreciprocating [[19]19] (Figure(Figure type. The 1515)) consideredphasingconsidered of the anan arrangementsleevearrangement is still some wherewhere degrees thethe sleevesleeve advanced waswas controlledcontrolled of the crankshaft byby aapair pair and of of connecting theconnecting exhaust rods portrods drivenremainsdriven offoff at the the crank. crank.head end. ThisThis The returnsreturns novel thethe feature sleevesleeve wasmotion motion thatto tothe a a simpler inletsimpler ports reciprocating reciprocating were broken type. type. up The intoThe phasingthreephasing sub-ports, of of thethe sleevesleeve which isis were stillstill some someopened degreesdegrees and closed advancedadvanced progressively of of thethe crankshaftcrankshaft by the piston and and the the motion exhaustexhaust during port port remainstheremains compression atat thethe headhead phase. end.end. TheThe novelnovel featurefeature waswas thatthat thethe inletinlet portsports werewere brokenbroken upup into into threethree sub-ports, sub-ports, which which were were opened opened and and closed closed progressively progressively by by the the piston piston motion motion during during thethe compressioncompression phase. phase.

Figure 15. K Halsing GM 24 February 1945, sleeve valve engine US 2409761. Reproduced with permissionFigure 15. K from Halsing US Patent GM 24 Ofﬁce. February Copyright 1945, sleeve Publisher, valve 1946. engine US 2409761. Reproduced with

permission from US Patent Office. Copyright Publisher, 1946. FigureThis 15. enabledK Halsing different GM 24 February swirl levels 1945, to sleeve be imparted valve engine to the US incoming 2409761. Reproduced charge through with the ducts,permission as each from set US had Patent a different Office. Copyright inlet channel Publisher, angle 1946. relative to the bore, thus helping to scavenge residual gas and to control rates of combustion.

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Energies 2021, 14, 616 This enabled different swirl levels to be imparted to the incoming charge through12 the of 21 ducts, as each set had a different inlet channel angle relative to the bore, thus helping to scavenge residual gas and to control rates of combustion. There was also an embodiment of the patent with a secondary inlet port control sleeve (i.e.,There a cuff) was alsooutside an embodiment of the liner to of further the patent control with gas a secondary exchange inlet timings. port control sleeve (i.e.,The a cuff)work outside by Meulien of the [20] liner (Figure to further 16) retains control the gas original exchange Burt–McCollum timings. motion but The work by Meulien [20] (Figure 16) retains the original Burt–McCollum motion but allows for variable stroke length in the sleeve drive to further adjust gas exchange events. allows for variable stroke length in the sleeve drive to further adjust gas exchange events. In this design, the effective time area is changed as well as the opening and closing of the In this design, the effective time area is changed as well as the opening and closing of ports. the ports.

Figure 16. H. Meulien et al. SNECMA 1 August 1951, Valve US 2714879. Reproduced with Figure 16. H. Meulien et al. SNECMA 1 August 1951, Valve US 2714879. Reproduced with permissionpermission e 1951. e 1951. Sparmann [21] proposed an alternative design (Figure 17) achieved by the introduction Sparmann [21] proposed an alternative design (Figure 17) achieved by the introduc- of an additional driven element which modified the input motion to the sleeve. This tion of an additional driven element which modified the input motion to the sleeve. This delivers more vertical movement to the sleeve when aligned with the ports for gas exchange delivers more vertical movement to the sleeve when aligned with the ports for gas ex- (increasing the effective port open duration) but then generates increased radial velocity change (increasing the effective port open duration) but then generates increased radial during the compression and expansion strokes when the piston is moving faster. velocity during the compression and expansion strokes when the piston is moving faster. However, after World War 2 the aero engine two-stroke work rapidly tailed off, as the gas turbine engine took over the role for propulsion in aircraft. Nevertheless, while at Rolls- Royce Tresilian proposed a very highly compounded sleeve-valve engine developed from the Crecy arrangement. (Figure 18) It was an “X” configuration of four banks each at 90◦ to each other. Its sleeve drive was to have been an evolution of the Ricardo arrangement, with the two opposing sleeves in a crankcase bay. These were driven by a drive rod assembly off an eccentric cut into the crankshaft cheeks with the assembly having a swinging slave link grounded to the crankcase [17]. The other two cylinders in the bay at 90◦ to the first pair had a similar arrangement driven from the crankshaft cheek. Overall, this gave an extremely compact engine. His calculations suggested that his “X-engine” would have significantly better fuel consumption than contemporary gas turbines and would have been ideal for what would now be thought of as the small turboprop market. Ultimately, Energies 2021, 14, x FOR PEER REVIEW 14 of 22

Energies 2021, 14, 616 13 of 21

Energies 2021, 14, x FOR PEER REVIEW 14 of 22 though, it came to naught, although it does still suggest a direction for highly compact engine architectures.

Figure 17. E.E.K. Sparmann 26 November 1946, two-cycle engine sleeve valve control of scavenging US 2523599. Reproduced with permission from US Patent Office. Copyright Publisher, 1950.

However, after World War 2 the aero engine two-stroke work rapidly tailed off, as the gas turbine engine took over the role for propulsion in aircraft. Nevertheless, while at Rolls-Royce Tresilian proposed a very highly compounded sleeve-valve engine developed from the Crecy arrangement. (Figure 18) It was an “X” configuration of four banks each at 90° to each other. Its sleeve drive was to have been an evolution of the Ricardo arrangement, with the two opposing sleeves in a crankcase bay. These were driven by a drive rod assembly off an eccentric cut into the crankshaft cheeks with the assembly having a swinging slave link grounded to the crankcase [17]. The other two cylinders in the bay at 90° to the first pair had a similar arrangement driven from the crankshaft cheek. Overall, this gave an extremely compact engine. His calculations suggested that his “X- engine” would have significantly better fuel consumption than contemporary gas turbines and would have been ideal for what would now be thought of as the small turbo- propFigure market. 17. E.E.K. Ultimately, Sparmann 26 though, November it 1946, came two-cycle to naught, engine although sleeve valve it controldoes still of scavenging suggest a direc- tionUS 2523599. for highly Reproduced compact with engine permission architectures. from US Patent Ofﬁce. Copyright Publisher, 1950.

Figure 17. E.E.K. Sparmann 26 November 1946, two-cycle engine sleeve valve control of scavenging US 2523599. Reproduced with permission from US Patent Office. Copyright Publisher, 1950.

engine” would have significantly better fuel consumption than contemporary gas tur- ◦ binesFigure and 18. wouldRolls-Royce have been Pennine ideal 24-cylinder for what sleevewould valve now 2be stroke thought 90 X of Engine as the 1945. small Reproduced turbo- propwith market. permission Ultimately, from Old though, Machine it Press].came Copyrightto naught, Publisher, although 2018. it does still suggest a direction for highly compact engine architectures. After that, patent activity slowed down until the turn of the 21st century. The next design by Chen et al. [22] (Figure 19) suggests an arrangement in which the sleeve is forced down against a spring by the piston during the expansion stroke, which then causes the sleeve to open the gas exchange ports. The large diameter spring then returns the sleeve to its original position as the piston rises again. Unfortunately, there is no consideration for asymmetric gas exchange timing with this design.

Energies 2021, 14, x FOR PEER REVIEW 15 of 22

Energies 2021, 14, x FOR PEER REVIEW 15 of 22 Figure 18. Rolls-Royce Pennine 24-cylinder sleeve valve 2 stroke 90°X Engine 1945. Reproduced with permission from Old Machine Press]. Copyright Publisher, 2018.

Figure 18.After Rolls-Royce that, patent Pennine activity 24-cylinder slowed sleeve down valv untile 2 strokethe turn 90°X of Enginethe 21st 1945. century. Reproduced with permissionThe next from design Old byMachine Chen Press].et al. [22] Copyright (Figure Publisher, 19) suggests 2018. an arrangement in which the sleeve is forced down against a spring by the piston during the expansion stroke, which thenAfter causes that, the patent sleeve activity to open slowed the gasdown exchan until gethe ports. turn ofThe the large 21st century.diameter spring then returnsThe next the sleevedesign to by its Chen original et al. position [22] (Figure as the 19) piston suggests rises an again. arrangement Unfortunately, in which there the is sleeveno consideration is forced down for againstasymmetric a spring gas byexchange the piston timing during with the this expansion design. stroke, which then causes the sleeve to open the gas exchange ports. The large diameter spring then returns the sleeve to its original position as the piston rises again. Unfortunately, there is Energies 2021, 14, 616 14 of 21 no consideration for asymmetric gas exchange timing with this design.

Figure 19. Y.Chen 6 November 2003, two-stroke engine US 6662764B2. Reproduced with permission from US Patent Office . Copyright Publisher, 2003. Figure 19. Y. Chen 6 November 2003, two-stroke engine US6662764B2. Reproduced with permission Figure 19.Infrom Y.ChenBeninca’s US Patent 6 Ofﬁce. November patent Copyright [23] 2003, Publisher, (Figure two-stroke 2003. 20) the engi drivene US train 6662764B2. for the Reproducedsleeve is modified with permis-, with the sionintroduction from USIn Patent Beninca’s of aOffice patentpair . [ofCopyright23] (Figuredrives. 20 Publisher,)This the drive impa train 2003.rts for a the compound sleeve is modiﬁed, motion with to the single sleeve the introduction of a pair of drives. This imparts a compound motion to the single sleeve whichwhich gives gives improved improved port port opening opening and closing and dynamics closing thus dynamics allowing asymmetric thus allowing gas asymmetric gas exchangeIn exchangeBeninca’s timing timing patent to be be achieved [23] achieved (Figure again withagain 20) the thewith engine. drive the engine.train for the sleeve is modified, with the introduction of a pair of drives. This imparts a compound motion to the single sleeve which gives improved port opening and closing dynamics thus allowing asymmetric gas exchange timing to be achieved again with the engine.

FigureFigure 20. J 20. BenincaJ Beninca 26 26 August August 2010, 2010, compound compound drive for drive the sleeve for the valve sleeve of an engine valve WO of an engine WO 2010094078A1.2010094078A1. Reproduced Reproduced with with permission permission from World from Intellectual World Property Intellectual Organization. Property Copy- Organization. Cop- right Publisher, 2010. yright Publisher, 2010. Figure 20. J TheBeninca nextarrangement 26 August by2010, Cleeves compound [24] (Figure drive 21) allowsfor the the sleeve junk head valve internal of an engine WO surfaces to move relative to the piston, which changes the geometric compression and 2010094078A1.Theexpansion next Reproduced ratios, arrangement while still with allowing bypermission Cleeves the sleeve from movement[24] Wo(Figurrld to controlIntellectuale 21) the allows gas exchangeProperty the junk in Organization. head internal Cop- sur- yrightfaces Publisher,the to portsmove via, 2010. relative a collar and to lever the drive piston, device which which produces changes a linear the motion geometric on the sleeve. compression and expan- The design offered by Ellis [25] (Figure 22) is a complex design in which a pair of sion cylindersratios, while have opposed still allowing pistons in them. the These sleeve act onmovement a pair of double-sided to control cam ringsthe gas exchange in the portsThe via, next a collararrangement and lever by drive Cleeves device [24] whic(Figurh eproduces 21) allows a linear the junk motion head on internal the sleeve. surfaces to move relative to the piston, which changes the geometric compression and expan-

sion ratios, while still allowing the sleeve movement to control the gas exchange in the ports via, a collar and lever drive device which produces a linear motion on the sleeve.

Energies 2021, 14, 616 15 of 21

located at either end of the engine which drives a central shaft. The gas exchange events are controlled by sleeves which are in turn driven off another pair of cam rings. The Pattakos device [26] (Figure 23) uses a toothed gear built on the outer diameter of Energies 2021, 14, x FOR PEER REVIEW 16 of 22 the liner to cause it to rotate at crank speed allowing the opening and closing of the engine ports, at the required timings. This however limits the size of the engine as the number of teeth on the crank driving gear must match those on the driven gear on the liner.

Figure 21. J. Cleeves 16 May 2017, Single piston sleeve valve with optional variable compression ratio Figurecapability 21. US 9650951.J. Cleeves Reproduced 16 May with 2017, permission Single from piston US Patent sleeve Ofﬁce valve Copyright with Publisher, optional 2017. variable compression ratio capability US 9650951. Reproduced with permission from US Patent Office Copyright Pub- lisher,This 2017. is the last fully mechanical system found to date. The work of Turner et al. of Lotus [27] (Figure 24) where the sleeve motion is controlled via a yoke plate in one embodiment and electronic controlled hydraulic actuators in another.The This design allows bothoffered directions by Ellis of motion [25] of(Figure the sleeve 22) to beis drivena complex and controlled design in which a pair of cylindersindependently have of the opposed crankshaft pistons motion, in allowing them. all These three degrees act on of a freedom pair of in double-sided gas cam rings locatedexchange at to beeither covered, end port of area,the engine event timing, which and driv duration.es a Itcentral is further shaft. possible The to gas exchange events programme the motion to be adjustable for both speed and load when connected to an areelectrical controlled variable-speed by sleeves compression which or scavenge are in turn pump. driven Thus, all off forms another of engine pair control of cam rings. would be possible, including full cylinder deactivation and skip-ﬁring in any order and frequency as required.

2.1.3. Engine Design Issues As with any engine design, there have been several areas of concern. These have included the following: 1. Seizure of the engine caused by thermal expansion of different components 2. Junk head cooling 3. Piston cooling 4. Sleeve roundness (a speciﬁc issue for sleeve valves)

Energies 2021, 14, 616 16 of 21

Energies 2021, 14, x FOR PEER REVIEWFigureFigure 22. P. Ellis 22. 12P. January Ellis 12 2017, January sleeve 2017,valve engine sleeve US valve 2017/ engine009617A1. US Reproduced 2017/009617A1. with Reproduced18 of with 22

permissionpermission from US from Patent US Offi Patentce. Copyright Ofﬁce. Copyright Publisher, 2017. Publisher, 2017.

Figure 23. Pattakos December 2018 rotary sleeve valve for asymmetric timing in two strokes Figure 23. Pattakos December 2018 rotary sleeve valve for asymmetric timing in two strokes GB GB 2563685. Reproduced with permission from GB Patent Ofﬁce Copyright Publisher, 2018. 2563685. Reproduced with permission from GB Patent Office Copyright Publisher, 2018. Energies 2021, 14, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/energies This is the last fully mechanical system found to date. The work of Turner et al. of Lotus [27] (Figure 24) where the sleeve motion is controlled via a yoke plate in one embodiment and electronic controlled hydraulic actuators in another. This allows both directions of motion of the sleeve to be driven and controlled independently of the crankshaft motion, allowing all three degrees of freedom in gas exchange to be covered, port area, event timing, and duration. It is further possible to programme the motion to be adjustable for both speed and load when connected to an electrical variable-speed compression or scavenge pump. Thus, all forms of engine control would be possible, including full cylinder deactivation and skip-firing in any order and frequency as required.

Figure 24. J. Turner Lotus 18 November 2005, sleeve valve engine 2005 GB 2432398A. Reproduced with permission from GB Patent Office. Copyright Publisher,.2005.

2.1.3. Engine Design Issues As with any engine design, there have been several areas of concern. These have included the following: 1. Seizure of the engine caused by thermal expansion of different components 2. Junk head cooling

Energies 2021, 14, x FOR PEER REVIEW 18 of 22

Figure 23. Pattakos December 2018 rotary sleeve valve for asymmetric timing in two strokes GB 2563685. Reproduced with permission from GB Patent Office Copyright Publisher, 2018.

This is the last fully mechanical system found to date. The work of Turner et al. of Lotus [27] (Figure 24) where the sleeve motion is controlled via a yoke plate in one embodiment and electronic controlled hydraulic actuators in another. This allows both directions of motion of the sleeve to be driven and controlled independently of the crankshaft motion, allowing all three degrees of freedom in gas exchange to be covered, port area, event timing, and duration. It is further possible to programme the motion to be adjustable for both speed and load when connected to an electrical variable-speed compression or scavenge pump. Thus, all forms of engine control Energies 2021, 14, 616 would be possible, including full cylinder deactivation and skip-firing in any order and17 of 21 frequency as required.

Energies 2021, 14, x FOR PEER REVIEW 19 of 22

3. Piston cooling Figure4.Figure 24.Sleeve 24.J. TurnerJ. roundness Turner Lotus Lotus 18 (a November 18specific November issue 2005, 2005, forsleev sleeve sleevee valve valvevalves) engine engine 2005 2005 GB 2432398A. GB 2432398A. Reproduced Reproduced withwith permission permission from from GB GBPatent Patent Office. Office. Copyright Copyright Publisher,.2005. Publisher, 2005. The first of these was a specific issue with high-performance air-cooled engines, where the heat rejection requirement is high. This would also be the case in any two-stroke 2.1.3. EngineThe first Design of these Issues was a specific issue with high-performance air-cooled engines, where engine.the heat It rejection was found requirement that specific is high. locations This wouldon the alsosleeve be thewere case exposed in any two-stroketo high tempera- engine. turesAs forwith different any engine durations design, this there led to have dissimilar been several localised areas increases of concern. in thermal These expansion. have in- cludedIt was the found following: that specific locations on the sleeve were exposed to high temperatures for Itdifferent was resolved durations by careful this led tolerancing, to dissimilar flaring localised the external increases diameter in thermal of theexpansion. sleeve by a Itsmall was 1. amount,resolvedSeizure and byof usingthe careful engine sleeve tolerancing, caused materials by flaringther whichmal thehave expansion external similar of expansion diameter different of coefficomponents thecients sleeve as by other a small key 2. components,amount,Junk head and namelycooling using sleeve the piston, materials junk which head, haveand cylinder similar expansion block [28]. coefficients as other key components,Junk head namely cooling the on piston,a sleeve junk valve head, two-stroke and cylinder engine block is considered [28]. doubly challeng- ing dueJunk to the head increased cooling frequency on a sleeve of valve the heat two-stroke flux events engine and is the considered more complex doubly heat challeng- path. Muching due work to the was increased done on frequency developing of thesuitable heat fluxstrategies events for and temperature the more complex control heat during path. theMuch 1930s, work with was a number done on of developing patents being suitable written strategies on how to for achieve temperature the required control level during of cooling.the 1930s, An with example a number of this of being patents the being work writtenby Mayer on (Figure how to achieve25). the required level of cooling. An example of this being the work by Mayer (Figure 25).

Figure 25. Junk Head Cooling A.J. Mayer. 8 October 1931 Continental Engine US 2016680. Repro- duced with permission from US Patent Ofﬁce Copyright Publisher, 1935. Figure 25. Junk Head Cooling A.J. Mayer. 8 October 1931 Continental Engine US 2016680. Repro- duced with permission from US Patent Office Copyright Publisher, 1935.

Mayer showed the need for extensive finning and deep air-cooled passages in his patent of 1935 [29] Figure 25 to remove the heat from the head area. In addition, it is interesting to note the number of bolts used to hold the junk head in place. It is suggested this helped with minimising distortion of the sleeve pocket under compression. helping to maintain operational clearance under load. The extreme version of these ideas can be seen in the patent of Fedden of the Bristol Engine Company [30] (Figure 26) where the ducting around the junk head is extensive to ensure the directionality of the high flow rates of air (the cooling medium) required to reduce overheating of the head. The many vanes mounted inside the junk head are used to stop air shortcutting from its predetermined path.

Energies 2021, 14, 616 18 of 21

Mayer showed the need for extensive ﬁnning and deep air-cooled passages in his patent of 1935 [29] Figure 25 to remove the heat from the head area. In addition, it is interesting to note the number of bolts used to hold the junk head in place. It is suggested this helped with minimising distortion of the sleeve pocket under compression. helping to maintain operational clearance under load. Energies 2021, 14, x FOR PEER REVIEW 20 of 22 The extreme version of these ideas can be seen in the patent of Fedden of the Bristol Engine Company [30] (Figure 26) where the ducting around the junk head is extensive to ensure the directionality of the high ﬂow rates of air (the cooling medium) required to reduce overheating of the head. The many vanes mounted inside the junk head are used to stop air shortcutting from its predetermined path.

Figure 26. A.H.R Fedden, Bristol Aeroplane Company Cylinder head for internal combustion engine 28 August 1931, US 1962987. Reproduced with permission from US Patent Ofﬁce. Copyright Publisher, 1934. Figure 26. A.H.R Fedden, Bristol Aeroplane Company Cylinder head for internal combustion en- The above applied to air-cooled arrangements used in the Bristol aeroengines. As gineliquid 28 cooling August was used1931, on someUS 1962987. designs (e.g., Reproduced the Crecy and the with Napier permission Sabre) liquid- from US Patent Office. Copyright Publisher,cooled junk heads1934. were designed and used. The designers even considered evaporative cooling designs [31] which were also patented. However, this appears to have been a dead end and was not taken further at that time. An example can be seen in Niven’s patent US1820628.The (Figureabove 27). applied to air-cooled arrangements used in the Bristol aeroengines. As liquid cooling was used on some designs (e.g., the Crecy and the Napier Sabre) liquid- cooled junk heads were designed and used. The designers even considered evaporative cooling designs [31] which were also patented. However, this appears to have been a dead end and was not taken further at that time. An example can be seen in Niven’s patent US1820628. (Figure 27).

Figure 27. A.M. Niven Continental, cylinder head 25 August 1931, US 1820628. Reproduced with permission from US Patent Office Copyright Publisher,.1931.

3. Conclusions The single-sleeve-valve engine underwent a great deal of refinement in the first half of the 20th century, initially in four-stroke cycle configurations where its greatest success

Energies 2021, 14, x FOR PEER REVIEW 20 of 22

Figure 26. A.H.R Fedden, Bristol Aeroplane Company Cylinder head for internal combustion engine 28 August 1931, US 1962987. Reproduced with permission from US Patent Office. Copyright Publisher, 1934.

The above applied to air-cooled arrangements used in the Bristol aeroengines. As liquid cooling was used on some designs (e.g., the Crecy and the Napier Sabre) liquid- cooled junk heads were designed and used. The designers even considered evaporative cooling designs [31] which were also patented. However, this appears to have been a dead end and was not taken further at that time. An example can be seen in Niven’s patent Energies 2021, 14, 616 US1820628. (Figure 27). 19 of 21

Figure 27. A.M. Niven Continental, cylinder head 25 August 1931, US 1820628. Reproduced with Figurepermission 27. A.M. from US Niven Patent Continental, Office Copyright cylinder Publisher, head 1931. 25 August 1931, US 1820628. Reproduced with permission3. Conclusions from US Patent Office Copyright Publisher,.1931. The single-sleeve-valve engine underwent a great deal of refinement in the first half of 3.the Conclusions 20th century, initially in four-stroke cycle configurations where its greatest success was foundThe in thesingle-sleeve-valve high-performance British engine aeroengines underwent of Bristol a great and deal Napier, of refinement during World in the first half ofWar the 2. 20th Moreover, century, two-stroke initially engine in four-stroke variations were cycle developed configurations at this time. where These showed its greatest success the potential, of the engine arrangement to generate even larger amounts of power from small displacements but the designs do have their shortcomings. The use of the sleeve valve in two-stroke engines enables the easy adoption of asymmetric gas exchange timings which can improve their volumetric and thermodynamic efficiency [32].The later patents with adjustable sleeve axial motion and variable angular velocity outline even greater potential to achieve class leading levels of fuel economy [33]. Ultimately, full active control of the sleeve could perhaps give fully flexible engine cycle operation combined with a level of confidence in operation which is unavailable in a poppet-valve engine with fully variable valve control. The systems are also 100% valve safe at all valve event timings. To achieve modern emission levels these sleeve valve arrangements could be married to gasoline compression ignition combustion systems for NOx emission reduction. The use of direct fuel injection could be used to stop fuel shortcutting and with the characteristic of a permanent lean exhaust stream. The application of the latest generation of electrical heated catalysts and gasoline particulate filters with low light-off temperature substrates could allow the possibility of increased levels of oxidation to remove any hydrocarbons, soot particles, and additional carbon monoxide gases present in the exhaust stream. As a consequence, these two-stroke sleeve-valve engine technologies could perhaps be an alternative to the conventional four-stroke engine in vehicles of the future as they too will need additional equipment to meet impending environment targets. Many of these will be made much simpler to adopt in the two-stroke. Due to the moving of the gas exchange ducts to the cylinder wall and the removal of valves from the cylinder head. This makes placement of injectors and spark plugs closer to optimum. Indeed, variable compression would be much easier to adopt than in the conventional poppet-valve engine architecture.

4. Taxonomy of Terms Single-sleeve Valve: A means to control the gas exchange of an engine via a single movable liner element placed between the piston and the stationary cylinder walls, the motion of which is likely to be elliptical in nature. Energies 2021, 14, 616 20 of 21

Sleeve: A movable thin-walled liner between the piston and the cylinder block. Sleeve pocket: The space left between the head and the cylinder barrel when the sleeve moves downwards. Double sleeve A pair of sleeves, one nested (i.e., concentric) inside the other which control the gas exchange of an engine (exhaust outside of the inlet). The motion of these sleeves is likely to be linear in nature. Junk head: The type of cylinder head closure used on a sleeve valve engine, which in section looks like a Chinese “junk” sailing vessel. Cuff valve: The means to control the gas exchange of an engine via a movable short cylinder liner element, normally outside of the combustion space. 2 cycle engine: The term is inter-changeable with that of 2 stroke engine, where used it relates to the description used in the patent. RON Research octane Number. MON Motor octane Number.

Author Contributions: Conceptualization, R.H. Methodology, R.H. Investigation, R.H. Writing— original draft preparation, R.H. Writing—review and editing, J.T. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References 1. Galpin, J.; Colliou, T.; Laget, O.; Rabeau, F.; De Paola, G.; Rahir, P. Design of a Fuel-Efﬁcient Two-Stroke Diesel Engine for Medium Passenger Cars: Comparison between Standard and Reverse Uniﬂow Scavenging Architectures; SAE Technical Paper Series; SAE: London, UK, 2017. 2. Fedden, A.H.R. The Single Sleeve as a Valve Mechanism for the Aircraft Engine; SAE Technical Paper 380161; SAE: Warrendale, PA, USA, 1938. [CrossRef] 3. Knight, C.Y. Internal Combustion Engine. U.S. Patent No. 968,166, 4 April 1904. 4. Knight, C.Y. Internal Combustion Engine. U.S. Patent No. 1,090,991, 4 June 1906. 5. Knight, C.Y. Internal Combustion Engine. U.S. Patent No. 1,136,143, 10 October 1908. 6. Burt, P. Internal Combustion Engine. International Patent Application No. GB418,988x, 8 August 1909. 7. McCollum, J.H.K. Internal Combustion Engine. International Patent Application No. GB409,216, 29 May 1909. 8. Montagu, D.S.; Barrington, E.J.; Burgess-Wise, D. Daimler Coventry: The Full History of Britain’s Oldest Car Maker, 1st ed.; Patrick Stephens Ltd.: Somerset, UK, 1995; p. 114. 9. Hunt, W.H. Valve Mechanism for Two-Stroke Gas Engine. U.S. Patent No. 1,292,322, 13 December 1915. 10. Stokes, C.L. Internal Combustion Engine. U.S. Patent No. 1,308,560, 2 April 1916. 11. Bischof, B. 2 Cycle Internal Combustion Engine. U.S. Patent No. 2,022,841, 9 February 1931. 12. Kipfer, P.F. Two-Stroke Internal Combustion Engine. U.S. Patent No. 2,134,286, 20 May 1936. 13. Kammer, G.S. Two Stroke Cycle. U.S. Patent No. 2,197,107, 21 February 1939. 14. Scott, L.L. GM. Internal Combustion Engine. U.S. Patent No. 22,611,567, 13 July 1939. 15. Rowledge, A.J. Two Stroke Sleeve Drive of V Engines. International Patent Application No. GB524642A, 2 February 1939. 16. Ricardo, H. Two Stroke Sleeve Valve Engine. U.S. Patent No. 2,367,963, 11 June 1943. 17. Hiett, G.F.; Robson, J.V.B. A High-Power Two Cycle Sleeve Valve Engine for Aircraft. Aircraft. Eng. Burn. Publ. 1950, 22, 21–23. [CrossRef] 18. Nahum, A.; Foster-Pegg, R.W.; Birch, D. The Rolls-Royce Crecy; Rolls-Royce Heritage Trust: Derby, UK, 1994; ISBN 1-872922-05-8. 19. Halsing, K. GM. Sleeve Valve Engine. U.S. Patent No. 2,409,761, 24 February 1945. 20. Meulien, H.; Bertin, J. Valve Means for Two Stroke Cycle Internal Combustion Engines. U.S. Patent No. 2714879, 1 August 1951. 21. Sparmann, E.E.K. Two Cycle Engine Sleeve Valve Control of Scavenging. U.S. Patent No. 2,523,599, 26 November 1946. 22. Chen, Y.; Chen, C. Two Stroke Engine. U.S. Patent No. 6662764B2, 6 November 2003. 23. Beninca, J.; Jones, M. Compound Drive for the Sleeve Valve of an Engine. International Patent Application No. WO2010094078A1, 26 August 2010. 24. Cleeves, J.M. Single Piston Sleeve Valve with Optional Variable Compression Ratio Capability. U.S. Patent No. 9650951B2, 16 May 2017. 25. Ellis, P. Sleeve Valve Engine. U.S. Patent No. 2017/009617A1, 12 January 2017. 26. Pattakos, J. Rotary Sleeve Valve for Asymmetric Timing in Two Strokes. International Patent Application No. GB2563685A, 26 December 2018. 27. Turner, J. Sleeve Valve Engine. International Patent Application No. GB2432398, 18 November 2005. Energies 2021, 14, 616 21 of 21

28. Fedden, A.H.R. Bristol Aeroplane Company Improvements in or Relating to Internal Combustion Engines Having Sleeve Valves. International Patent Application No. GB425060A, 15 November 1935. 29. Mayer, A.J. Continental Engine. U.S. Patent No. 2016680, 8 October 1931. 30. Fedden, A.H.R. Bristol Aeroplane Company Cylinder Head for Internal Combustion Engine. U.S. Patent No. 1962987, 28 August 1931. 31. Niven, A.M. Continental; Cylinder Head. U.S. Patent No. 1820628, 25 August 1931. 32. Turner, J.W.; Monsma, J.P.L. An Investigation into the Port Timing of a Burt-McCollum Sleeve Valve and Its Interaction with a Simple Variable Compression Ratio Mechanism; SAE Technical Paper 2017-24-0168; SAE: Capri, Italy, 2017. 33. Turner, J.W.G.; Head, R.A.; Chang, J.; Engineer, N.; Wijetunge, R.; Blundell, D.W.; Burke, P. Two-Stroke Engine Options for Automotive Use: A Fundamental Comparison of Different Potential Scavenging Arrangements for Medium-Duty Truck Applications; SAE Technical Paper 2019-01-0071; SAE: San Antonio, TX, USA, 2019.