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IT is no exaggeration tq say that the same arrangement of engine cooling is provided by most manufacturers for vehicles intended to operate in the maximum possible temperature range, and this must leave a lot to be desired. An engine provided with sufficient radiator and waterjacket capacity, which, together with the assistance of a large cooling fan, is enabled to operate satisfactorily in the tropics, must necessarily be over-cooled in this country for at least the greater part of the year—and in some areas for the whole of the year.
In this country the greatest variation in ambient temperature from a warm summer day to an exceptionally cold winter one is likely to be in the nature of 70°F, and it will be of interest to consider whether the standard radiator covers this range adequately and whether cooling arrangements generally are sufficiently complex to take account of such variations; and still more important, what is the effect of those variations on the engine.
I cannot hope to be breaking new ground on the subject of engine temperature and its effect on efficient operation, as there has been a number of carefully prepared and detailed contributions on this subject in recent years. However, it could be said that I am applying the findings of these most helpful citizens to operation on a fleet basis.
First of all, why should we be concerned about coolant temperatures and to what extent? Once again it should be remembered that my own experience has been gained in a fleet of vehicles operated in the North of England, subject to considerable variation in the severity of demand, but with engines seldom highly stressed. In these conditions, except in high summer, it has been found most difficult to operate anywhere near the ideal temperature range. Spot checks carried out on a number of vehicles on days which could have been expected to produce both light and heavy traffic density showed that it was quite difficult to reach 160°F, and more frequently the range was between 135°F and 145°F.
More efficient at high temperatures
It is an accepted principle that a diesel engine will work more efficiently at what, judged by these standards, must be regarded as high temperatures; but our own investigations indicated that the accomplishment of this condition is far more complicated that might at first be supposed. For example, if high temperatures are to be maintained it is vitally important that lubricating oil should be good enough to stand up to those conditions, though the normal high grade oils which I believe are commonly used in most well-maintained fleets should be quite adequate.
The cooling systems of our own vehicles are certainly in the category of those which could be expected to operate satisfactorily in the tropics; in fact we have one delivery which was originally intended for South Africa. In addition to this, supplementary radiators for saloon heating have been fitted as original equipment on a number of machines, so in some ways we have exaggerated our own problem and this militates against a good comparison with standard vehicles, or possibly for the haulage operator whose power-to-weight ratio may be less advantageous. Nevertheless, the figures offered will, I believe, stimulate interest which will probably serve my purpose.
As to why temperature control is important, let the facts speak for themselves. During experiments, pressure were taken on two vehicles which had run approxi 40,000 miles. It was found that a temperature it from 80°F to 180°F brought an improved cylinde; pressure reading of 35-p.s.i. on one vehicle and 20-p the other, whilst cylinder pressures showed an a improvement of 45-p.s.i. on the first vehicle and 20-p the second.
The difference in reading on vehicles which cout been expected to be in precisely the same conditi( arouse curiosity, but I shall offer some observati this connection which should prove interesting. The of temperature on combustion condition, and inch the validity of smoke checks and the ability to rep readings, can be gauged from test results—one of w shown hereunder.
From the foregoing it will be seen how importat to obtain a reasonably high operating temperature if ; consumption figure is the aim, and just as important our point of view) is the effect of a cold engine I exhaust condition. It is not unreasonable to sugge; ensuring suitable engine temperature will do much t mote engine life; the private car industry has offt good deal of useful information recently on the relati. of oil-drain periods and the nature of conditions in the vehicles are operated. As I understand it, higher periods advocated for some vehicles are associate( an anticipation of relatively long journeys with few and reasonable temperatures. Where there is a incidence of stops and starts, such as those associate. the operation of delivery vehicles, it is suggested that orthodox drain periods will continue to be required.
It would be too much to expect vehicle manufax to tailor vehicle cooling systems to the requireme individual customers, but so much can be done, ev the smallest operator with the minimum of workshop ities, that there is no reason why a sophisticated c system suitable for particular operating conditions at atmospheric conditions most usually experienced can; evolved. The measures which we have taken are in g those which can easily be applied on a fleet basis and tamed without difficulty. The cost of modificatiot certainly be more than repaid by better m.p.g., engine wear will unquestionably be reduced in direct to the length of time that cold running is avoided.
The first measure
The first and most obvious measure taken to se( quick rise in engine temperature is by the employmen thermostat, the operating temperature of which is in of standard. We ourselves employ components operate at 20° above standard. Though it mu admitted that manufacturers are not altogether happy this method of control, they are concerned (it ap with the sharp temperature gradients in coolant which can occur when this type of thermostat is employed.
It would seem, however, that this method of additional control is not likely to produce a startling variation, or one which should cause concern. For example, eight of my own vehicles checked on a day when the ambient temperature was 55'F showed four vehicles fitted with a 185" thermostat, the average of which was 169' in the coolant, while four fitted with the 165° standard unit showed 152' as an average. Our aim has been to operate in the 185-190° range and this has been found most difficult indeed.
Measures taken on standard vehicles (though I would emphasize that these are still in the experimental stage and will not be employed on a fleet basis until we are satisfied that every possible advantage and disadvantage has been well explored) have been the employment of twoblade fans instead of the standard four-blade fan, a shortening of blades, and their complete removal. In addition to this we have assembled radiators where a complete section of tubes in plain copper has been installed instead of those carrying the customary cooling fins, and if this proves successful we shall eventually blank off the appropriate section in the top and bottom plates.
Greatest step forward The greatest single step forward, however, in safe and trouble-free temperature control has been the employment of the Varivane automatic radiator blind. This is a neat and inconspicuous assembly, They are used with a blanking plate, the fitting of which has been our standard practice for the winter months of the year for a very long time. We have found it necessary to remove the plates in the warmer months and to consider supplementing them with an additional plate which could be attached during the coldest months of the year. We have also been concerned with the untidy appearance which ensues when drivers add all sorts of impromptu blanking methods.
The Varivane shutter appears to be the perfect answer. It has, I appreciate, already been advocated by a number of people concerned with various aspects of controlling engine temperature, so all that I shall need to say is that we examined this accessory critically in order to ensure that it was likely to be sufficiently robust to be fitted to service vehicles and maintained without difficulty or cost.
The first of the units fitted for test purposes were assembled to operate at the standard 165°F, they worked well enough and certainly produced a higher average temperature in the coolant than the remainder of the fleet, but it was still not high enough to suit our purpose. A second test carried out with a thermostat set to operate at 185F brought us much closer to the optimum temperature desired, and this will now form our standard equipment.
It would seem easy enough to remove cooling fans where their function is obviously marginal,. but it is necessary to give some consideration to freak conditions where a combination of an exceptionally warm day, a heavy run, and some degree of cylinder block fouling could lead to boil
ing, thus presenting a danger to personnel and possibly having an adverse effect on the engine itself. Fouling of cooling systems is yet another of the factors emphasized by the very long periods which engines can and do operate without being removed from the chassis for major repairs: the amount and nature of deposits will vary according to the water supply most generally used, but in some cases these can be of some consequence and lead to a reduction of cooling capacity, possibly at a point where it is most needed. In my own department radiator flushing, or perhaps I should be more ambitious and say cooling system scavenging, is now placed on the same basis as household spring cleaning. There are cleaning materials which, placed in the water, will have a mild cleansing effect. if used regularly they will probably prove quite adequate.
Then there are others rather more costly which clean systems very thoroughly, so much so that where cylinder block fouling is a problem, or cleaning of this kind is undertaken for the first time, this may be the form of material to be used. It can be particularly helpful with some forms of cooling tubes whose section, or changes of section, positively invite obstruction, and in these cases a thorough cleansing will probably save far more than the cost of labour needed to restore full flow conditions.
A note of warning is necessary, however, in regard to the material that can be disturbed in this way; water pumps and points in the cooling system where dislodged matter is apt to settle again will need to be the subject of special attention until all such material has been removed.
Servis Recorder experiments Experiments carried out with the aid of a Servis recorder, and a temperature sensing thermostat placed in the header tank of a vehicle operated on passenger services in a town centre where our maximum temperatures are likely to be experienced, have served to indicate that special attention to fan operation is needed. Three recordings were taken on the same vehicle with ambient temperatures within one degree on each of the three days recorded, these figures being registered at mid-day.
Indicated on the periphery of each disc by heavy lines are the periods for which water temperature is estimated' to have reached 190°F in water returned to the header tank. No. 1 shows our experience when an electrically-operated fan was employed, this having been arranged to cut in at 190'. It will be seen that there were relatively few periods (and those of short duration) when it was needed; this may well indicate that the fan was, in fact, exerting the necessary degree of control. No, 2 shows a day when the vehicle was operated without a fan, and it will be observed that for quite a long time water temperature was at 190° or even more—an undesirable state of affairs to which I shall make further reference. No. 3 shows what occurred when a two-blade fan driven by the engine in the ordinary way was employed, and it should be appreciated that this
replaces the standard four-blade fan. Only for a very brief period was the desired temperature obtained, and then obviously for a very short time indeed.
There are now alternative types of electrically operated fans available which can be arranged to operate automatically at specified temperatures. This type of equipment is already standardized on some vehicles and there would seem to be reason to believe that the practice would be extended, so perhaps the only question to be posed is to what extent conversion of existing vehicles can be justified, and this must be determined by operating conditions, by the type of unit employed, and the cost at which conversion can be effected.
Temperatures of at least 185° F
I believe that I shall have established the value of operating at temperatures of at least 185°F, and if this is accepted the means taken to achieve it must be of interest. A vehicle fitted with a Varivane automatic blind, and a standard radiator modified so that the rear bank carries no cooling fins, showed a temperature climb of 1.6°F for each five
1340 0, minutes of service operation; this woulc
4 ' have been on early morning operation whet
running is very light, and,, incidentally a 185°F-opening thermostat would havt been employed.
A similar test was taken on one of oul most recent deliveries which has the addi. tional radiator fitted for saloon heating, but in this case had been fitted with a specially tailored radiator modified to the needs ot this particular cooling system. In this instance a Varivane blind, but employing the electrically driven fan was used and the recorder showed in the same circumstances a temperature rise of 2.91°F per five minutes of.operation. The reduction in the time taken to reach the desired temperature must be considered to be a very worth-while advantage. The effect was that for the first vehicle it took 40 minutes to reach I35°F, and on the other 32 minutes to reach 166°. I need not elaborate on the significance of this position.
Contradictory opinions Contradictory opinions have been expressed by quite eminent engineers on the subject of the effect in power demand on fans operated behind a blank surface such as is represented by an automatic radiator blind in the closed position. There would probably be a considerable difference caused by the speed at which a fan is driven. One experiment that I witnessed was intended to show the disparity, if any, between the power demand of a fan driven in the open air at the speed which we would expect to incur on the engine with which I was concerned, and the same fan operated with enclosures to closely simulate the conditions represen ted by our own vehicles. No difference could, in fact, be detected.
Most of my remarks connected with temperature control appear to have been directed to producing conditions which, it must be admitted, are marginal between the ideal operating temperature and the creation of conditions which could be hazardous. Actually our own experiments have convinced us that 185°F, with perhaps 5' tolerance, is the most that should be aimed at.
In fact, I would add a warning by pointing out that two vehicles operated with the temperature control methods outlined, but no cooling fan, were found to have a condition in the injectors which could militate against their effective, long-period operation. This we are inclined to to attribute, though with a limited number of observations, to overheating in the cylinder head; it must be remembered that there will be a difference of 10° in the temperature experienced in the header tank to that in the cylinder heads. In addition to this, in some circumstances there will be a temperature surge when an engine is idling or switched off, and we have reason to believe that this marginal condition should be avoided.
In offering the pros and cons it should be observed that
1 have related our own experience and offered information gained in connection with it, so 1 would lay down no hardand-fast rules; indeed, it would be presumptuous to do so with the limited information gleaned from our own special type of operation.
Anti-freeze employed
For many years now my undertaking has employed antifreeze in all vehicles throughout the winter period. More than half the vehicles are parked in the open and at one time it was the practice to start them up frequently enough to prevent freezing on every night where there was a danger of this occurring. The effects on cylinder wear, and oil deterioration, can well be imagined. Anti-freeze has since become a much more popular safeguard, and we are no longer the odd man out in this connection.
We use a good quality anti-freeze and have found this a worth-while investment; the only time that we purchased a cheaper commodity, the eventual cost was greater. The bill for anti-freeze is, however, of some consequence and the need for regular topping up is undesirable for though it is simple enough to do, it is not quite so easy to ensure 100 per cent compliance.
We have now found a way of pressurizing cooling systems at relatively low cost. A temperature gauge inserted as part of the experiment is no longer used, for it was found that because of its exposed condition low readings were given: as already pointed out, we now rely on the return to the header tank. The pressurized system needs a special radiator cap, this being the most costly item. The overflow pipe is connected to the end of a rectangular tank through the medium of a relief valve which has to be obtained from the manufacturers; the tank is, of course, vented on the top to atmosphere and this simple system works well and needs no maintenance.
Though the capacity of the tank is one gallon, it seldom receives more than three pints and there is a big difference between this quantity and the amount which is usually displaced through the overflow pipe and lost. We shall, we understand, tend to get a greater displacement' when the anti-freeze is reintroduced. The other factor counting for the disparity is that with this form of system less aeration takes place. The shape of the rather utilitarian tank has a history for our first experiments were made by using an empty paint tin. When we were encouraged to make more permanent installations there seemed nothing against the shape and our panel beater found it possible to make sufficiently robust canisters at low cost.
Variation in pressure Readers of earlier articles in this series may recollect that our own research work found us with a variation in pressure on two engines which could have been expected to be precisely the same. The problem posed has continued to exercise our curiosity and to prompt further inquiries aimed at resolving the riddle of why one engine will perform much more satisfactorily than another, the reasons for the variation in effective engine life between similar units operated in the same conditions, and also why cylinders in an engine can show very different rates of wear.
Reference was made to the inference that manufacturers could, if it were deemed a practical proposition, offer much better standards of combustion, which would in turn be reflected in improved exhaust condition. Even the highest standards of engine construction on a mass production basis must call for variations, and consideration of the handbooks issued by all engine manufacturers will indicate that totting up all the potential pluses and setting against them all the potential minuses in dimension will create the possibility of disparities between engines and cylinders in a particular engine which are of some consequence.
One usually feels rather comfortingly that the pluses and minuses will tend to cancel themselves out; but this does not accord with the facts. As a stimulating exercise I posed to certain friends, for whose technical ability I have a very high regard, the question of how much variation they would expect to find in piston height on a large capacity diesel, and in general their response coincided with my own impression prior to more detailed consideration of this point; that is to say, relatively little.
The variations are not merely hypothetical; they do occur, they are of consequence, and they can have a direct bearing on the variationsin condition to which I have referred. For example, a check made on an engine which had the cylinder heads lifted for the first time showed a variation in piston height of 0.013 in.
It may be argued that engines which are already offering an adequate output and run extremely high mileages with a minimum of attention cannot have much wrong with them. When it is appreciated, however, that variations which can be found quite frequently can lead to a variation in compression ratio of some 13 per cent, and that the effect on the all important cylinder-head turbulence is of real consequence, the situation may be considered to justify a measure of personal research work.
The importance of this position has been appreciated in some quarters, probably for quite a long time. For example, in the extremely well-equipped and well-organized workshops of the United Automobile Services Co. Ltd. at Darlington. measures are taken during engine reconditioning to ensure that potential differences in compression ratio are reduced to the minimum.
'Quality control'
Somewhat limited, and certainly cautious, publicity has been given by Leyland Motors to the imposition on its products of what is, I believe, known by them as "quality control ". I have been privileged by virtue of my interest in the work we have done on exhaust smoke limitation to have a talk with Mr. Ian Black, and his assistant Mr. Hoghton. I use the word privileged because of the difficulty I experienced in insinuating myself into their presence. The Leyland company and the quality control team, though most determined to associate production-line methods with the quality of precision in power units and so on previously probably found only in limited high-class car production, are most cautious in forecasting the outcome of this high standard drive.
The deliberate, careful, and typically Scots verbal economic handling of the facts by Mr. Black is impressive, for it becomes borne in upon the listener that he will only be satisfied with improvements that can be permanently incorporated into the vast production of the Leyland company.
My own inquiries were naturally directed only to the work done on engines, and though I would not presume to steal the thunder of those responsible for producing the results hoped for, and those whose task it is to satisfy an instinctively dubious and critical public of operators and engineers, an outline of the important facts will serve to stimulate interest in what we shall be told by the company in due course.
The principal problem is, of course, to ensure that the heights of piston crowns in relation to the upper face of the cylinder block arc as uniform as possible. These have always been held to what was considered to be the closest practicable tolerance; but, in spite of the fine limits to which these components are manufactured, the height of any piston will be affected by an accumulation of tolerances in the crankshaft to piston build-up, resulting in variations of individual cylinder power output. I believe that our own experience will indicate that it is worthy of consideration.
In the system of control which is already being applied to engine production, these variations are to be reduced to a maximum on the 0.600 engine of 0-006 in. This is being done by grading pistons into various sizes with a tolerance range of 0-010 in.; pistons will be marked on the crown leading to easy identification and thus facilitating preservation of the desired balance during servicing. Experiments have gone on, and will no doubt be continued, under the direction of the quality control team into the balancing to extremely fine limits of injectors and fuelpump elements. It would be inexpedient for me to make more than a general reference to this for though everything possible will be done in this connection, Mr. Black does not expect to achieve startling results, and once again I believe that the emphasis must be on standards which can be reduced by labour which is not highly specialized.
The effect upon a production basis is to offer an improvement in fuel consumption of approximately 31 per cent. In addition to this, it has been found that peak performance tends to be achieved more quickly. There can be no doubt that combustion conditions are critical; with our own very limited facilities we have been able to establish this, and I hope that I have been able to bring this out in my articles by showing the effect of temperature on fuel consumption and exhaust condition. To achieve a balance of this kind
and to reproduce very closely similar conditions in cadcylinder will, I believe, be a step forward of some conse. quence and will certainly help to control exhaust condition
Efforts made by engineers to improve fuel consumption etc., by maintaining high engine temperatures may be founc to create a problem, the effects of which may not be at firsi realised. This is that the existence of high under-bonnei temperatures can exert an adverse effect on air intake. I believe I shall not need to elaborate upon this, and alsc on the functioning of the fuel injection equipment itself, so we are in the paradoxical position of needing the engine to be hot, but everything surrounding it to be cold.
A good deal can be done in this direction. Much has already been written on the subject of cold air intake, and I have emphasized the need to have some air directed over the outside of the engine even if this is by automatic control and only brought into operation when the engine is really hot, for the fan it not only drawing air through the radiator for cooling purposes but also promotes air circulation under the bonnet.
Air filtration is worthy of consideration, though it poses problems not easy of solution. The modern engine, though compact, is expected to be parked in the smallest possible space so as to give the utmost possible room for carrying capacity. This makes it difficult to install adequate airfiltration equipment and lighter components can require an abnormal amount of maintenance. This is surely a field for manufacturers to explore so that we may have air filtration incorporated which will require the absolute minimum of attention.