THE DIESEL ENGINE: HAS IT A FUTURE FOR SPORTS CARS? —asks Capt. J. S. Moon in this controversial and informative review
IN one of his ever-interesting articles in a weekly contemporary, some three years ago, Cecil Clutton suggested that there might be a market for a type of car based somewhat on the . lines of the vintage sports car, with a large, comparatively slowrunning• engine fitted into a chassis of present-day design, and went on to describe such a car, with an engine following roughly the layout of the E-type “30/98′ Vauxhall. Frankly, perhaps because I am no great enthusiast for the vintage type of Sports car as such, Sam Clutton’s modernised vintage car would have no great appeal for me. I should feel disinclined to sacrifice the smooth, running and effortless performance of the modern multi-cylinder sports-tourer engine with
out some really tangible gain. •. If, however, the engine of Sam Clutton’s car is replaced by a modern four or more cylindered diesel of roughly the same cubic capacity, then the vintage enthusiast will get his large rather slow-running engine with the slight roughness which he finds so attractive but, at the same time, a car will result that will give an economy of running that is almost unbelievable to those unfamiliar with the present-da‘y commercial diesel engines. Due to its economy when running under partthrottle conditions, a diesel engine in la car will give almost double the mileage per gallon compared with a petrol engine doing the same job, and this on a fuel that for the same rate of taxation will always be a few pence per gallon cheaper than petrol. i Before examining in detail the type of engine that is likely to be suitable for use in a sporting car, it is worth running briefly through the history of the diesel as adapted to private-car use. (In parenthesis, I should say that, at present, I am, like large numbers of enthusiasts, divorced from my records, and that these historical notes are based solely on an exceedingly third-rate memory. Thus should mention of anyone’s pioneer efforts be omitted, or should the details be inaccurate, I hope to be corrected without too much ill-feeling.) As far as I know, the first private car to be fitted with a diesel engine was a 3-litre Bentley, into which Norris, Henty & Gardner, Ltd., the famous marine and commercial-vehicle engine manufac turers, fitted a 4LW Gardner engine for expc ri Lel it al purposes. The Gardner 4LVs. is a 4-cylinder of 4i-in: by 6-in. bore itral stroke (5,579 c.c. capacity. and 29 11.1). lt.A.C. rating). It develops swine_ 68 li.p. at 1,700 r.p,m., and weighs rather under 10 c NV . The car was fully described
in the motoring Press at the time, and performed quite creditably in the Monte Carlo Rally in 1932, although I believe that the brakes rather let it down in the final tests.
Shortly after this, a 2-litre Lagonda was actually converted to operate on the diesel cycle, presumably by the substitution of a new cylinder head. As to the success of this conversion I have no recollection, and, in fact, have grave doubts as to whether any success could be expected. Thba fiat diekei car. to cOMei before. the public eye with any prominence was the 0-litre A.E.C.-engined racing car which was driven at Brooklands and Montlhery. by Capt. George Eyston. This car is also worthy of note as being one of the first saloon racing cars, though towards the end of its active career the saloon _ body was removed and a single-seater open body substituted. [Actually the 1903. 114er Electric and, in particular, the Rerfault 45 and Peugeot saloon racing cars of about 1924 must not be forgotten.—En.] In this form it took Diesel-engined Class International records at speeds in excess of 120 m.p.h. .(Incidentally, at any rate until the early days of the war, this car, which was called
Black Magic,” stood in a corner of A.E.C.’s Southall works covered over with a dust sheet, though the engine assembly had been removed.) [A, was sold in 1944.—En.] The • 6-cylinder engine had a bore and stroke of 115 by 146 mm. (9,090 c.c. and 49.2.h.p. rating), developed upwards of 130 b.h.p., and weighed under 1,500 lb., thanks to the large amount of light alloy embodied in its construction, so giving a power/weight ratio directly comparable with that of the commercial-vehicle petrol engine wkfich it was designed to replace.
Shortly after this, further diesel-engined records were made by George Eyston, driving his front-drive racing car fitted With an experimental Rolls-Royce diesel aero engine—not a Rolls-Royce creation —in place of the Rolls1Royce ” Kestrel ” which was its normal power unit. The large swept volume of this engine, however, rather excludes it for a practical road vehicle. R. J. Munday, of ” 80/98 ” Vauxhall and Munday-Special fame, then appears on the scene to take long-distance c.i. class records with one of the old 19-litre ” flatiron ” Thomas-Specials, fitted-with a Perkins engine, a make that had already been fitted with success to one or two private cars and light commercial vehicles, a purpose for which it was, and is, acimir
ably adapted on account of its comparatively small size and cubic capacity. My recollections of Munday’s ” Special ” are very hazy, but I think that the 2.7-litre engine was used, in which case the engine dimensions were 85.1 mm. bore by 120.6 mm. stroke (18.2 h.p. R.A.C. rating). I do recall, however, that a Zoller supercharger was used to boost the output and increase the speeds for the shorter runs. To adapt a blower to a diesel is even more simple than to do so to the conventional petrol engine, since pure air only has to be compressed.
Further experiments followed, of which I can recall a Tippen engine fitted to a ” 15/18 ” Lanchester saloon, and another chassis fitted with one of the earlier examples of a new, lighter Gardner engine known as the 4LK, of 95 by 185 mm. bore and stroke (3.8 litres capacity and 22.4 h.p. rating), developing 58 h.p. at 2,000 r.p.m. and weighing only 684 lb.
I think that it was in 1987 that the world’s first production diesel cars were exhibited at the Berlin Motor Exhibition, on the stands of Mercedes and Hanomag. Both of these German firms produced diesels of relatively small size—about 1}-2 litres swept volume and 14 h.p. R.A.C. rating—which were fitted as a standard alternative power unit to their cars. Shortly afterwards Citroen announced a small diesel unit of 75 by 100 mm. (1,770 c.c. and 13.9 h.p. R.A.C. rating), which was fitted to their small commercial vehicles and also used as the power unit in the 15-h.p. rear drive car. Incidentally, this engine was designed and developed in the British laboratories of H. R. Ricardo & Co. Finally, during 1939, after considerable experiment, arrangements were made by the Studebaker concessionaires in this country for the conversion, on a production scale, of Studebaker cars by fitting Perkins diesels. The particular model selected is the ” Panther,” which is a 6-cylinder of 88.9 by 127 mm. bore and stroke, which gives 4,729 c.c. capacity and 80.1 h.p. R.A.C. rating. It developg
85 h.p. at 2,600 r.p.m., which is the normal maximum governed speed, though higher engine speeds can be attained at the cost of reduced engine life. The weight, with flywheel and auxiliaries, is 712 lb., or 151 lb. per litre of capacity and 8.4 lb. per horse-power, a very low figure for an engine of this class: As a comparison, the Ford V8 with aluminium heads develops about 88 h.p. and weighs around 570 lb., which represents 158 lb. per litre and 6.5 lb. per h.p. The Studebaker Perkins was dealt with in fair detail by the weekly motoring Press at the time.
The Perkins engine is of fairly normal mechanical construction, and apart from the obvious external difference of the fuel injection equipment in place of electric ignition and carburetter, could quite easily be taken for an average type of petrol engine. The combined cylinder block and crankcase is an iron casting, with a pressed steel sump closing it at the bottom. The camshaft is carried high up on one side of the block so that only short push-rods are needed to operate the valves, which, as in all diesels, are in the cylinder head. The camshaft and the auxiliaries are driven by a Triplex roller chain at the front-end, enclosed in an aluminium timing case with a pressedsteel cover. The forged steel crankshaft is a much more massive affair than would be found in a petrol engine, and has a main bearing on each side of each throw— the usual practice in all but the smallest diesels. The main and big-end bearings are of copper-lead, a bearing metal that stands up to the heavier pressures of a diesel better than white metal. The single-piece cylinder head contains the combustion chambers, into which the air is compressed on the compression stroke, and in which the majority of the combustion of the fuel takes place. The sprayer, of C.A.V. make, injects into this chamber, which in the particular form used in the Perkins ” Panther ” is known as the ” Aeroflow ” combustion cell. The fuel injection pump is also of C.A.V. manufacture, and is equipped with the C.A.V.
pneumatic governor, which controls both the idling speed and the maximum speed of the engine. The specific fuel consumption of the ” Panther ” engine under the most economical running conditions— about 1,000-1,600 r.p.m. on full load— is as low as 0.40 lb. per b.h.p. hour, whereas it takes a good petrol engine to better 0.60 lb. per b.h.p. hour (and, of course, the economy of the diesel compared to the petrol engine is even more marked under part-load conditions).
The larger and more powerful engines which are used in ‘buses and coaches do not generally have such a favourable power/weight ratio as that quoted above, as crankshaft speeds are generally restricted to 1,600-1,800 r.p.m. in order to improve the reliability and to obtain the required life between overhauls, which is expected to be, and is, several times as long as that of the average private car. Extensive use is made of the more expensive light alloys, such as electron, for unstressed parts such as crankcase bottom halves, timing cases, etc., and even for crankcases, though there has been a tendency to drop this material for this use, as it has been found that much better bearing life can be obtained by making crankcases in RR50 aluminium alloy or even in cast iron. Incidentally, the increase in weight of an iron crankcase which is designed to do the same job as an alloy one is very much less than one might think, due to the much thinner sections that can be used to give the same rigidity. In the latest L.P.T.B. ‘buses, an exhaust manifold fabricated from steel tube saves a considerable amount of weight compared with a cast-iron one.
Compared With the nasty looking lump of metal that one finds in most private-car engines these days, the larger diesel crankshaft is a thing of joy to the beholder, with its large main and big-end journals, which are usually bored out, and its machined finish all over. Bearings are either of copper-lead or white metal cast in thick steel shells, and lubrication is invariably forced, very often right up to the little-ends through rifledrilled con.-rods. Camshafts are either overhead, operating the valves by means of rockers, or else the valves are operated by push-rods and rockers from a camshaft which may be in the crankcase or, in quite a few engines, high up on the side of the cylinder block so that the pushrods are short in length. As engine speeds are fairly low the camshaft and all other auxiliaries can conveniently be driven by a single, long duplex or triplex roller chain, which threads a somewhat tortuous path over and under suitably-sized sprockets. Incidentally, not only the dynamo and the water pump, but the fan as well, are usually positively driven.
Diesels of this size can be designed so that starting by hand is possible, but this entails the slight extra complication of a decompressor device to enable the engine to be turned over the high compressions, and of a flywheel sufficiently heavy to spin the engine over one full compression when it has been swung by hand. This latter requirement, in my mind, makes for an engine that is very sluggish, and I am certain that for privatecar use the possibility of hand-starting should be completely forgotten. As an example of the type of performance that can be expected from this
class of engine the following figures for the 7.7.-litre A.E.C. are quoted. The six cylinders have a bore and stroke of 105 by 146 mm., and the weight of the complete assembly varies around 12 to 13 cwt., depending upon the particular build-up of the engine. Two different types of cylinder head are available, the first and original design having a combustion cell of the Ricardo ” Comet ” type, in which form the engine develops up to 115 h.p. with a clear exhaust, and up to 125 h.p. with a visible exhaust, and has a specific fuel consumption of about 0.44 lb. per h.p. hour. In its alternative form, the direct injection type, in which the injector sprays directly into the combustion Space over the piston, power output is rather lower (up to about 105 h.p. with clear exhaust), but the specific consumption is improved to about 0.40 lb. per h.p. hour. Cold starting is rather simplified, as the provision of heater plugs to assist this is not required. That, then, is the 4-stroke diesel as developed to the beginning of the present war. That there have been considerable developments during the war is undoubted, but unless these have been epoch-making in extent, it must be confessed that, so far, the 4-stroke diesel hardly seems sufficiently developed to warrant its use in the sports car of the future, even though it does begin to be an attractive proposition for the utility car whose owner does big annual mileages;
The supercharged 4-stroke is a possible sports-car power plant but, although considerable laboratory research has been completed, and one north country corporation has operated supercharged doubledeek ‘buses over considerable mileages with some success, I think that this is a possibility that must be borne in mind for the future, but must be put aside for the time being. There remains the 2-stroke diesel, which, for long remained at the back of the transport diesel engineer’s mind as the possible eventual form that these engines would take. However, apart from the German Junkers engine, which was manufactured under licence in other countries (by Napier in this country in its aero engine form), there was formerly no example of the 2-stroke in serious use for transport purposes. Very great inter est was aroused, therefore, when the General Motors Corporation announced in America, in 1939, the introduction of a range of supercharged 2-stroke engines for transport and industrial purposes. The power output of these engines, judged on a capacity basis, showeil considerable improvement over 4-stroke engines then in production, although, as the engines were designed and built cut i rt’l y of ferrous metals, as is Anwrira Ii practice, the improvement in poweriwcigl t ratio was not so striking. These advantage: are paid for in a slightly inferior
specine fuel eonsumrtion.–about 0.45 lb.
per h.p. hour. Since the date of it introduction, many thousands of G.M. diesel engine, have been made, and have given very valuable and reliable service in varying &tragical ions, including tanks,
commercial vehicles, agricultural and industrial tractors earth-moving machinery, boats and launches, etc. As the C.M. does pave the way towards a practical sports-car diesel, and as the
engine as it stands contains certain features that would give rise to considerable enthusiasm if incorporated in a sports car, let us study its specification in a certain amount of detail.
The engine is a vertical in-line type, made in 8-, 4and 6-cylinder forms, which are identical except for the number of cylinders, and the she of the Roots blower which is mounted on the side of the block. The blower delivers air to the air box which surrounds the cylinders, and which communicates with the interior of the cylinders through numbers of holes which are drilled through the liners about half-way down. These holes, or ports, are uncovered by the piston on its down stroke, when air flows in from the air box, until the ports are again covered on the up stroke. The continued upward motion of the piston compresses the air until, at the end of the up-stroke, it is hot enough to ignite the fuel, which is sprayed in through the injector in the cylinder head. The resultant expansion provides the power stroke which drives the piston down, until, when rather more than half-way down, two poppet exhaust valves in the cylinder head open and the gases are allowed to escape. Shortly after, the air ports are uncovered and air from the air box is forced into the cylinder, so scavenging the cylinder of the remaining burnt gases. Certain of the fresh air escapes through the exhaust valves, which remain open until just after the inlet ports are closed, so that the valves themselves are to some extent cooled. The combined cylinder block and crankcase is a very rigid casting in iron, which also contains the air box, which is a space surrounding the water jackets round the cylinders, except for the passage about half-way down the cylinder where the air box communicates directly with the dry cylinder liners, in which are drilled the air ports referred to above. The crankshaft is carried in thin-shelled, copper-lead main bearings in this block, there being one main bearing between each pair of cylinders ; all the bearings are of the same dimensions. The drop-forged, steel connecting rods, which have steel
shelled, copper-lead big-end bearings, are rifle-drilled throughout their length, and at their upper end have a jet through which oil is sprayed on to the underside of the piston head for cooling purposes. The pistons are malleable iron castings, tin-plated on the skirts, which carry six rings, four compression and two skirt scraper, which latter cope with the oil from the spray jet. The combustion space takes the form of a shallow saucershaped depression in the piston head. The camshaft is carried in an open trough at the top of the cylinder block and operates tappets which are carried in the detachable cylinder head. An identical trough on the other side of the block carries a shaft known as the balanceweight shaft, which has, like the camshaft, eccentric weights at the ends. These balance weights are required, because with an in-line 2-stroke engine with equal firing intervals, there are no pairs of pistons moving in the same phase. This means that the engine is out of primary balance by a couple which tends to rock it about a transverse axis at engine speed frequency. The eccentric balance weights on the camshaft and balance-weight shaft (which revolve at engine speed in opposite directions) set up another couple tending to rock the engine about the same axis but in the opposite direction to that set up by the pistons, so that the two cancel out. Two shafts with balance weights revolving in opposite direction are necessary or a couple about a vertical axis would be set up. The two exhaust valves per cylinder are operated by two cams per cylinder, through separate push-rods and rockers. The exhaust valves are quite sizeable (11V-in. diameter) and operate at a speed that in a 4-stroke engine would be equivalent to over 4,000 r.p.m., so that special attention is paid to valve gear design. Instead of the usual ball-joint, the push-rods are connected to the rocker by a fork end and clevis pin. The ball lower end of the push-rod is held in the spherical seating in the tappet by a Ushaped collar on which bears a spring surrounding the push-rod and held down by a hollow plug in the upper end of the
tappet guide. This spring thus keeps the roller-ended tappet in contact with camshaft and also helps to return the pushrod and rocker while the valve is closing.
The camshaft and the balance-weight shaft are geared together, and one of these two mating gears (which have helical teeth) is driven by one idler from the flywheel end of the crankshaft.
The fuel-injection equipment operates on the same principle as the Bosch-type equipment fitted to most British engines, but instead of having an injector in the cylinder head with a separate injection pump unit mounted as an engine auxiliary, the injector and the pump element are combined in a single unit for each cylinder, which is mounted vertically in the cylinder head between the two valves, with the pump element plunger operated from a third cam on the camshaft through a roller tappet and push-rod and rocker in the same way as the valves. There are advantages in this from the point of view of engine servicing, and also from the elimination of pipelines between the pump and injector. In the G.M., advantage is taken of the fact that there is a copious supply of fuel which has not been metered out, to lead a proportion through passages round the injector nozzle and so keep it cool. The metering of each injector (by which the power output is varied) is controlled by a rack rod on each injector, which engages with a control shaft which runs the length of the cylinder head and is operated by the accelerator, through a small centrifugal governor.
The blower is of the Roots type, with aluminium-alloy rotors, which are of interest because they have three lobes instead of the two to which we are more accustomed, and because the lobes are helical in form so as to avoid pulsations in the air box. The blower runs at 1.94 times engine speed and gives a pressure of about 8 lb. per sq. in. at full speed. It is driven by, a gear meshing with the camshaft or the balance-weight shaft gear and from the other ends of its two shafts are driven the governor, the water pump, and the small vane pump which circulates the fuel-oil through the injectors under slight pressure.
The cooling system and the lubrication system are fairly straightforward and depend to some extent on the particular application. In some applications, the latter is of the dry-sump variety. The oil pump is mounted below No. 1 main bearing cap and is driven by spur gears from the crank.
A very interesting point is that the majority of the parts are designed to be reversible, so that a right or a left-handed engine can be built up with very few differing parts. Thus, both ends of the crankcase are the same, so that it just has to be turned round to put the blower and air-intake filters on one side or the other. Again, the cylinder head is reversible, so that by turning the head round and transposing the camshaft and the balance-weight shaft, the exhaust can be on the same or the opposite side to the blower. By assembling the idler gear in the camshaft/balance-weight shaft drivetrain on one hub or an alternative, the direction of rotation is varied.
Now for a few figures. Bore and stroke are 4f in. by 5 in. (108 by 127 mm.), giving a capacity of 3,486 c.c., 4,648 c.c.
and 6,972 c.c. in three, four and sixcylinder forms respectively. The power output depends upon the valve timing, and may be what is known as reduced output, standard, medium or high output. High output engines are generally used solely for marine purposes, as in this application the high torque available cannot be used at very low speeds, when it can do harm. In standard output form, the ” six ” produces some 168 h.p. at 2,000 r.p.m., and in medium output form some 190 h.p. at 2,100 r.p.m. Unfortunately, I have not got the high output figures. These figures represent 23.4 and 27.3 h.p. per litre, respectively, and 76 and 85 lb. per sq. in. rn.e.p. (It should lie remembered, incidentally, that these are equivalent to m.e.p.s of double these figures in a. 4-stroke engine.) In its present form the engine is heavy, weighing 1,597 lb. as a ” six ” (229 lb. per litre and 8.4 lb. per h.p. in medium output form), but by using light-alloy in place of the iron timing cases, blower casing, water pump casing, etc., the weight could probably be cut down to some 1,200 lb. without a severe increase in cost. This would give a power/weight ratio of 6.3 lb. per h.p., with the possibility of further reduction in weight by using a light-alloy block, and an increase in power by using high output settings, which, I think, would be permissible in a sports car, which is assumed to be driven with a certain amount of intelligence. If the engine were re-designed for privatecar work, when it would operate under a much lower power factor than in its present applications, the dimensions of many parts could be reduced, and by using light-alloy reciprocating parts and a flexible engine mounting, it might be feasible to eliminate the balance-weights and balance-weight shaft. By these means I think that a 2-stroke diesel having the same, if not better, power/ weight ratio as that of the vintage sports car, is now quite a practical proposition. To bear this out I can quote some rather limited particulars of a 2-stroke diesel which bears a name familiar to motoring enthusiasts, that of Alfa-Romeo. The following particulars are quoted from a somewhat brief description which I came across some two years ago. As to whether this engine was ever produced in any numbers, and whether it attains G.M. standards of reliability (which are very high), I do not know. The AlfaRomeo is a Vee 6-cylinder, having a bore and stroke of 05 by 130 mm. (5,522 c.c.). The two cylinder blocks and crankcase are combined in a single light-alloy casting. A Roots blower provides the necessary boost for the air intake,, and the exhaust arrangement is, as in the G.M., by two valves per cylinder. These are operated by one overhead camshaft per block. Incidentally, the valve springs are of the hairpir type, this being the only example I know of their use in an in-line engine, although they are very frequently used in Motor-cycle engines, of course. The fuel injection of the Alfa-Romeo is of Bosch pattern, and like the British-made C.A.V. equipment, has normal injectors in the cylinder heads and an injection pump between the blocks. I do not remember the angle between the cylinder blocks, but suspect that it is 60, to give equal firing intervals with crank throws at 120. If this is so, then the engine is probably nearly enough balanced, by means of counterbalance weights on the cranks, to render any other balancing device unnecessary. (If the Vee angle were 900 the engine could be perfectly balanced by this means.) The power output-240 h.p. at 1,800 r.p.m., which is 43.4 h.p. per litre with an m.e.p. of 156 lb. per sq. in. The weight-1,188 lb., or 216 lb. per litre or 4.95 lb. per h.p. What about a rather smaller and lighter edition of that in a vintage-type sports car ? Yes, I think so [Capt. Moon has in mind the diesel engine applied to cars of sports type and used normally. Nevertheless, it is not without interest to recall the excellent showing made by c.i.-engined cars in the field of record-breaking. In 1934 Eyston had achieved over 1201 m.p.h. with the A.E.C. and, before the A.I.A.C.R. decided to recognise c.i.-engine records, a Wankesha diesel car clocked 129.56 m.p.h. and a Cummins diesel car 137.19 m.p.h. over a mile at Daytona. By 1939 the highest speed officially recorded by a diesel-engined car was 159.1 m.p.h. by Eyston’s “Flying Spray,” set up over the flying kilo. at the Salt Beds. The diesel Hour Record stood to Eyston’s A.E.C. at 105.6 m.p.h., set up at Montlhery, and, with Denly, he held the 12-Hour record at 99.03 m.p.h. and the 24 flours at 97.05 m.p.h. No class divisions were recognised for c.i.-engined records—something for the R.A.C. to agitate for postwar—but a Hanomag with a diesel engine of only 2-litres capacity held the s.s. kilo. and mile and f.s. 5 kilo. and 5-mile records at speeds of from 54 to 96.9 m.p.h., while a 1,767-c.c. diesel Yacco-Special had lapped Montlhery at between 68 and 70 m.p.h. for 4,000 kilo. up to eight days. Admittedly, the larger-engined recordholders had not attempted these records, but the speeds are excellent. Munday’s 21-litre Munday-Special held the British c.i.-engine flying kilo. record at 94.7 m.p.h. and five other British c.i. records at over 88 m.p.h. for distances of 50 kilo. to 100 miles. So diesel engines of all sizes have proved that they can pull out the speed. They score on economy, too, Eyston’s car using about 4s. worth of fuel per 100 miles at over 100 m.p.h., and some 7s. worth of fuel per 100 miles in open form on the 24-Hour run, at just under 100 m.p.h.—En.]