You Can't Be Cool And Be Kind
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Experimental Application of Serck/Behr Hydrostatic Fan Drive Holds Promise of Increased Engine Life Because of Higher Operating Temperapres
by John F. Moon, A.M.I.R.T.E.
TO many operators the cooling system of a vehicle is an unavoidable evil that needs to be kept filled with water or anti-freeze, has to be drained for many engine repairs and has a fan belt with an unfortunate habit of breaking. Not a pretty picture, but as air-cooling seems to be unacceptable to British transport men, they're stuck with the radiator.
Yet the cooling system holds the key to increased engine life and power, and reduced fuel consumption, so really it deserves much more respect and attention than it usually gets. Even designers tend to err on the generous side when it comes to cooling systems, a larger and more inefficient system than theory suggests often being used.
Fortunately, some operators have become aware of the shortcomings of standard cooling systems, and—at their own expense—are trying out new equipment which they are confident will eventually lead to greater engine efficiency and reduced cooling-fan power losses.
How can the cooling system affect engine performance and life? In a nutshell, the answer is that most cooling systemsprovide too much cooling, with the result that
a38 .u.igines work at temperatures up to 50 per cent. lower :han is: desirable with, furthermore, a considerable lifference between the coolant temperatures at the top and lottom of the water passages.
By raising the coolant temperature under normal running
;conditions, greater combustion efficiency can be promoted, vith -consequent improvement to the fuel-consumption ate. Even more important, however, in the long run, is he reduction in bore-wear rate which takes place when he coolant surrounding. the bores is consistently over 150°F.
It has been proved that ideally the temperature in the immediate vicinity of the bores should be above the dew point of the exhaust -gases-say 194`.F. In this way condensation and acid formation within the bores can be eliminated, with subsequent reduction in bore, Wear. For this ideal state to be achieved, the temperature differential throughout the depth of the bore should be as small as possible—certainlv under 15c F.
.0n the face of it, it would appear fairly simple for vehicle• and engine designers to achieve these -cooling conditions but, unfortunately, modern production methods and the relatively high cost of hand-built units encourage most manufacturers to adopt one or two standard radiators for all their vehicles, with the result that engines operating in a British winter are considerably over-cooled, compared with the same type of engine and the • same radiator operating in the Australian bush. •
Admittedly there are exceptions to this rule, and concessions are also made with respect to fan size, shape and speed, but here again, the larger the fan the greater its power absorption. In any case, with the over-sized radiators so much in vogue at present, the cooling fan is needed for less than 20 per cent. of the total time that an engine is running.
Thus, having accepted that engines should operate at higher and more constant temperattires. the obvious answers are either to reduce the radiator size or provide 'some sort of fan drive which will automatically bring the • fan into operation only when the engine temperature rises 'above a predetermined optimum level. Marine and railWay engineers have accepted this for some time, so why not their automotive fellows?
One of the pioneering branches of British haulage, which seems to have subconsciously adopted the principle of trying anything once, is that connected with the oil companies. Compression-ignition engines, .articulated vehicles, pneumatic tyres, power-assisted steering,. exhaust brakes and air suspension. systems all owe much to the long-suffering oil-company transport engineers.
Oil-company Experiment It is not surprising, therefore, to find at least one of the oil-company fleetsnamely, that belonging to Shell-Mex and B.P., Ltd.--already experimenting on a fairly broad front with thermostatically controlled fan drives and automatic shutters. One of the pieces of equipment currently fitted to a Shell-Mex and B.P. Scammell is the Serck/Behr automatic fan-control system, made by Serck Radiators, Ltd., Warwick Road, Birmingham, II. Recently I was afforded the opportunity of obtaining temperature readings on this vehicle and comparing them with a standard tanker running in tandem with the one fitted with the special fan drive.
The comparative results obtained are indicated in the accompanying graphs and are discussed later on in this article, but first it would perhaps be as well to describe the SerckjBehr design. This equipment, which is of German origin, has already been used extensively on marine, railway locomotive and stationary industrial engines, but this Scammell application is the first time that the Serck system has been applied to a road vehicle in this country, and so far this is the only instance of its use in this way.
The patented ScrcklBehr system consists of four basic units, of which the temperature controller is the essential item. This controller is inserted into the engine cooling system so that water paSsing from the radiator goes through the controller body before entering the engine cooling passages. Thus, it is sensitive to the minimum, water temperatures in the system. Contained within the controller is a Vernatherm waxfilled sensing element, and this actuates a spring-loaded valve controlling a by-pass in the fan-drive hydraulic circuit. When the water temperature is lower than the figure at which the Vernatherm is set to operate, the by-pass valve is open, but any rise above this temperature gradually closes the valve, so permitting the fan to be driven at a speed proportional to temperature requirement.
Power for the hydraulic system is provided by a geartype pump in the case of this vehicle application, although on large engines an axial-piston pump is usually employed. The fan-drive motor also is of the axial-piston type, and the fan assembly is mounted directly to the driven shaft of this pump.
The fourth main item in this experimental application is an hydraulic ram which controls shutters mounted ahead of the radiator block. This ram is in parallel with the motor, and its setting is such that it starts to open the shutters fractionally before the fan starts to revolve.
The simplicity of the system is apparent, therefore. The engine is driving the hydraulic pump the whole time, but when the coolant temperature is low the fluid circulates freely between the pump, the controller and the reservoir. Rise in water temperature initially opens the radiator shutters, following which the cooling fan starts to revolve, until, at a hydraulic pressure of about 500 p.s.i., the fanis turning at its maximum speed of 2,000 r.p.m. On larger installations pressures of up to 2,000 p.s.i. are common.
This maximum fan speed can, of Course, be varied to suit individual applications. Where it is possible to use a smaller radiator than that fitted as standard (with subsequent weight saving) a higher fan-speed setting could be given by using a higheroutput pump.
The vehicle to which this equipment had been fitted last year is a Scammell tractive unit which, when the tank semi-trailer is fully laden with industrial fuel oil, normally operates at a gross train weight of about 22f tons. The tractive unit is over five years' old, and the power unit is a Gardner .6LW overhauled—a coolrunning unit at the best of times, because of the large radiator thought to be necessary with this engine.
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Engine and radiator had remained in perfectly standard trim, other than in the fitting of the Serck/Behr equipment, and the obvious removal of the normal thermostat from the engine cooling system. The temperature controller had been set to give full fan speed at a water temperature of 175° F., the setting being such that the radiator shutters opened at 165° F. (and a hydraulic pressure of 40-50 p.s.i.), at which temperature the fan started to idle. Variation of these temperature settings can be accomplished quite simply, merely by using a different Vernatherm unit.
The vehicle against which the Serck-equipped tanker was run was almost identical, although a few months younger and having a more modern cab. The standard Gardner thermostat—which cracks open at I38°F.—had been replaced by a similar bellows-type unit cracking open at 150°F., this having been standard procedure for most Shell-Mex and B.P. Gardner-engined vehicles, until recently, although even higher settings are currently being employed, with wax-type .thermostats.
Both vehicles were waiting for these tests at the Shell-Mex and B.P. Langley Green installation, the morning of the test being wet, with an ambient temperature at the time of starting of 39.5°F. Both vehicles were unladen, with kerb weights of approximately 94 tons.
Thermostats had been inserted into the radiator inlet and outlet pipes, also the sump, whilst during the runs readings were taken also of the average cab temperatures and the temperatures at the cab-heater outlets.
Temperature readings were taken roughly at mile intervals in the case of both vehicles, and the results obtained are shown clearly in an accompanying graph from which it will be seen that, despite the fact that the standard vehicle had its radiator 77 per cent, blanked off, the highest water temperature recordqd at the radiator inlet was 154° F., against 170° F. for the Serck vehicle.
Reference to the curves makes it clear that at no time was the temperature differential between inlet and outlet greater than 10° F. in the case ol the Serck vehicle, and that the average running temperature was in the regior of 160° F. Quite a different picture was told by the readings taken witi the unmodified vehicle, the tempera. ture differential of which averagec 20° F., with general inlet and outle temperatures of 142° F. and 120° F respectively.
The initial rate of temperature rim from cold was about the same in ttu case of both vehicles, both Scammells not having been run for about 15 hours before the test began. This would be explained partly by the blanking on the standard vehicle and partly by the fact that its thermostat would not,have opened during the first few miles.
A possible difficulty with regard to running a Gardner engine at higher coolant temperatures than standard is that oil temperatures also might rise. If these became excessive, damage to the white-metal main and big-end bearings could result. It was interesting to note, therefore, that the oil in the sump of the unmodified engine tended to warm up slightly more quickly than that of the Serckequipped unit, and when arriving at the Shell-Mex and B.P. Worcester installation-28 miles from the starting point—the sump oil of the standard Scammell was at a temperature of 106°F., compared with 105°F. for the other vehicle. Thus, bearing failures can in no way be aggravated by the Serck system.
No Severe Ascents The route between Langley Green and Worcester was by way of the Halesowen By-pass, Hagley, Harvington, Ombersley and Worcester City, and was covered by both vehicles at an average speed of 24 m.p.h. There were no really severe hills to ascend on the way out to Worcester. Indeed, as the fall in temperature recorded for both vehicles at about the five mile mark suggests, a descent was made just before reaching the Halesowen By-pass.
A hill in the vicinity of Hartlebury (17 miles) was climbed in top gear, the ascent taking three minutes, and it was on this section that both inlet and outlet temperatures of the Serck vehicle rose to 170°F., at which point the radiator shutters might just have started to open, although it was impossible to observe this from the cab.
On the same hill the coolant temperatures of the standard model were falling, although it is not recorded whether the driver of that Scammell had engaged a lower gear to ascend the gradient—the temperature drops suggest that probably he had.
A load of 3,000 gal. of fuel oil was taken on by both vehicles at the Worcester installation and the return journey towards Birmingham was recommenced 3+ hours later in the case of the standard vehicle and 31 hours later in the case of the experimental model, the difference being to allow the first vehicle to discharge at the customer's premises while the second vehicle was en route so that neither vehicle would have to wait to pump out. In case it should be thought that it really took over three hours to load two vehicles, it should be pointed out that lunch and discussions took place in the intervening period.
Higher Water Temperatures The laden runs followed the same route as far as Halesowen, and the second part of the graph shows that approximately the same temperature differences were Dbtained as when running unladen, except that slightly higher figures were obtained with the Serck-modified Scammell. Gradients caused the fan to operate at close )n full speed on two occasions, this having been registered 3y observing readings of the hydraulic pressure in the fanirive circuit.
This second set of curves again shows how relatively :onstant the inlet and outlet temperatures were compared with those of the unmodified vehicle, the drop in the water emperatures of the standard vehicle when descending the -lartlebury Hill being quite obvious. In both cases traffic sold ups in Worcester within a mile of the installation ;aused fairly rapid temperature build ups, and the peaks it the tail end of the graph were caused by the ascent of ucklow Hill. Third gear was used by both vehicles during this sixminute climb, which was followed immediately afterwards by a descent of the same hill before entering the premises of W. Somers, Ltd., where both vehicles were discharged.
Temperature readings were taken during the discharging operations also, and these figures are graphically recorded here. While the standard vehicle was discharging the ambient temperature was 46`.F., and it can be seen that both water temperatures fell during this operation.
Lower Ambient Temperature
The Serck-fitted Scammell, which started pumping half an hour after the other tanker, did so in an ambient temperature of 41.5F„ despite which the water temperatures rose and averaged 50°F. higher than those of the standard job, the shutters remaining closed and the fan at no time revolving.
Heater-outlet temperatures were consistently at least 20°F. higher in the case of the Serck-equipped vehicle than they were with the standard vehicle during all stages of the test, but because the cab of the modified Scammell was an older design than the other vehicle's and therefore draughts of hurricane intensity came around the doors and through the floorboards, the interiortemperatures were not greatly different. At the end of each run the Serck Scarnmell's cab temperature was 68°F. compared with 64°F. for the other vehicle.
No fuel-consumption figures were -taken during these runs, but figures were taken by Shell-Mex and B.P. officials during six months' operations with both vehicles, which are almost invariably engaged on similar. duties. These show that the vehicle with the Serck drive had averaged 10.25 m.p.g. compared with 9.9 m.p.g. for the standard model.
Thus, although the real object of the exercise is to determine the percentage increase in bore and piston-ring life—and it is too early yet to say what this will be a helpful saving in fuel costs of 4 per cent. has been realized already.
This 4 per cent. alone is worth having (many bus operators would give their back teeth for half that amount), and when it is considered that a relatively slow vehicle, operating in heavy traffic and spending a considerable time pumping, can achieve this, it is not hard to appreciate that long-distance goods and passenger vehicles could show an even greater saving.
Higher Heater Temperatures
Another advantage applying particularly to passenger vehicles is that the higher water temperatures signify higher saloon-heater temperatures, and long-distance coaches could have considerably higher temperature settings to further, this aim, it being generally accepted that most vehicles engaged on motorway operation run too cool.
Yet another advantage of this . hydrostatic fan-drive layout is that the relative positions of engine and radiator are completely flexible, giving considerable design latitude as to the location of these components.
Serck Radiators. Ltd., are the first to admit that this experimental installation has not been cheap to carry out, but then what experimental installations are? Future conversions could be made using smaller hydraulic components, thus reducing the initial cost.
Once the cost bogy has been overcome it will not be hard to envisage conscientious operators taking a lot more notice of this sort of equipment, particularly if the hopes of increased engine life are fulfilled. The days of the power-consuming fan and the icicle-bound engine are numbered, and it is in everybody's interests that this should be so