BLACK SMOKE
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FOLLOWING the series on smoke emission by W. C. Wilson, and the considerable interest aroused by his research into the problem from the p.s.v. side, a small group of goods engineers, including myself, found ourselves discussing the Wilson aper. However, this ended on a somewhat unsatisfactory note, with the question: Where does this leave us? ". The points raised by the group were many and varied, nd made it quite clear that some very real facts would emerge if each of the group vas to "let his hair down ".
First of all, we thank Mr. Wilson for most interesting series. He hit many ails on the head, just as he raised a ertain amount of ire when he threw own a very obvious gauntlet to those ngaged in the movement of goods traffic. 'herefore, although we fail to agree on zveral counts, as our two worlds are oles apart, we are grateful for the very kilful push into the deep end.
On the question of engines we must iffer from the p.s.v. man. Mr. Wilson ses a 9.8-litre power unit, and so do we, rid since he mentions &rating this ngine, it appears that his gross laden /eight will not exceed 12 tons. It also allows that he will have a pump setting f around 20-21 c.c. per 200 shots at 600 .p.m. In the goods world, this same 9-8 ngine will be found in both rigid eight/heeler and maximum-capacity articuated machines, and here the gross is 24 ans. Also, the eight-wheeler can be ■ perating a four-wheel drawbar trailer, rid the gross can be 32 tons.
The normal setting for the 24-ton-gross ngine is 26 c.c., but to operate the 32on-gross outfit, the setting at times caches 27 c.c., and this is nearing the moke line, as any of these engines will
■ egin to smoke, even in the pink of conbon, as the 27 c.c. mark is passed. The ).680 engine handles the job much better, au requires a 28 c.c. minimum setting .nd will make smoke at 30-5 c.c. But this .ngine is above its job and is rarely a ' smoker' unless unfit. ,
In the light of this, heavy smoke from : 9-8 engine powering a 12-ton-gross asseriger machine should be unheard of, it least with a reasonably fit engine. Chis. of course, now points the finger traight at the goods vehicle, and rightly .o, as all too often there is barely a nargin wide enough to cater for normal :ngine wear. So we can never enjoy the lerated engine; quite the reverse, in fact, is all too often the goods man is ,cratehing around for extra power, and as dr. Wilson very rightly states, unskilled lands and fuel stops are not the right answer. Again we cannot compare engine ife. The fabulous mileage obtained on i.s.v. operation is unheard of in the goods "mid. and the reason could be expressed n the following hypothetical ratio: If you :onsidered that the impact on a busngine piston equalled an 0-303 bullet at muzzle velocity, so could you think in terms of a fighter aircraft cannon shell in the case of the heavy goods piston. Therefore. 200,000 miles of effective life from a 9-8 engine on goods work is considered a fair target, with the smoke problem very near at all times.
Another comment recorded and quite fair, too, was the all-important one of spare vehicles, as rarely has the large p.s.v. operator all his vehicles fully occupied. The very nature of his business demands a reserve for special hours or duties, so he is better able to juggle things around for the benefit of a special exercise. In the goods world, there is never a spare truck, at least not readily available to the engineers, unless unfit. However, let us, the bad boys. now look at ourselves in a true light, which I am inclined to think was the intention of Mr. Wilson' anyway.
Under-powered Vehicles Experience with goods operation indicates that many vehicles are underpowered. Tests with various models show that the fit engine, at the correct load and correctly driven, will not emit excessive smoke: yet overloaded, or driven lazily, smoke can be produced from an otherwise fit machine. A good example is the Leyland 0.350 engine. This model has a smoke line at 17 c.c., yet it can be driven at that setting and not emit smoke if the revs are maintained and it is not allowed to " slog ".
From the groun came confirmation of this. Yes, the 0.350 is a smoker if out of tune or driven lazily. On delivery as new, it will be set at 14 c.c., yet this setting is too low for many tasks this stout engine is given, so settings of 15 to 16.5 c.c. are common, and quite a few operate near the 17 mark. At 14 c.c. it does not smoke, of course, but many operators are inclined to give the engine a " boost " for more power.
This comment was made by a member whose work is the overhaul of fuelinjection equipment, and as he is serving the general public be is in a good position to talk of fuel settings and smoke. Also, within reason, he will help the operator, and if a particular setting is asked for that is nearing the smoke line, he can only warn the customer: he could hardly refuse to uplift the pump on the grounds that the chart called for a lower figure. In fact, he may not necessarily be aware of the particular engine the pump is for, although this would be a rare occurrence. Many a customer will bring in a pump after a
smoke warning, knowing quite well that the pump is on the " high " side, and . will request a reduction just enough to lose the smoke, but not to lose the power. The result of such an adjustment will invariably bring with it a reduction in top end power, and the driver, who is a large factor in this, will notice the power loss at once. Yet the actual power still available to him is higher than when the engine was new.
All this is not an indication that the work of pump setting is a racket, and is carried out "any old how" to suit the whim of a customer, but it does mean that many medium-sized engines are barely able to cope with the work given them, unless given a fuel increase. It follows, therefore, that as and when engine tune begins to go off, so will excess smoke begin to creep in. Again, this is not a criticism of the medium oiler of any make, but it does mean that many operators are working this or that engine well above its intended capacity, and are not content with its original output.
Where rules and regulations hold the user to a strict load limit, standard settings are rarely altered, and any smoke Would not necessarily spring from intentional fuel increase, but rather from air shortage, or wear on the fuel rack mechanism. On the other hand, a tractor can be purchased ostensibly to work a payload of 10 tons, and find itself coupled to a heavy low loader, or similar, for a series of special jobs, and during that work can have a fuel setting increase to give extra power. Invariably that setting stays, the extra power obtained being more than welcome and certainly used to advantage, although now the smoke line can be very near indeed, and any lazy driving can produce smoke.
Upset Calibrations Further comment from the fuel member indicated that many pumps passing through his hands showed upset calibrations, and had obviously suffered crude adjustment of fuel stops. So much so, that certain sighting glasses were below the correct line, and others almost spilling over the top, and he stated that quite often smoke came from one cylinder only. owing to an excess delivery by that one element. Therefore, he offered the following warning: a set of pumps can be delivering perfectly level measured amounts of fuel, but these can be completely upset by inexperienced tampering or adjustment of the external fuel stops. If an increase is to be made, this should be carried out in the pump room only, as only on the Hartridge, Merlin or similar machine, can the amounts delivered be correctly measured. So attempts to increase power by fiddling
with the pump still on the vehicle can only lead to trouble.
From this member's comment, it is clear that the medium-sized oil engine is often the culprit where smoke is concerned, and this can hinge around three factors: excess fuel to increase power and often inexpertly obtained; overloading, with the engine being compelled to slog heavily; and lazy driving, banging on in high gears, particularly with worn. engines. Above the 9-litre size engine, and with the present gross laden weights, the smoke problem is less evident, and with 10and 11-litre engines, standard settings are adequate and smoke a rarity.
More "Punch" Needed A further point raised by the fuel member hinged around the heavy vehicle that is considered slow, by the now permitted road speeds. Here there are many requests for r.p.m. increase and, if this is not permissible, at least a little more " punch " to climb hills. Therefore, again, the only medium offering anything at all is increased fuel, via adjusted settings. Skilfully done, something can be gained, but only at extra fuel cost and the risk of smoke as engine condition deteriorates.
All members agreed that partly worn engines contribute heavily to the smoke problem, and piston rings that may seal the gap quite well for the blast of the firing stroke may not be so good on the next downward (induction) stroke, when they must seal equally well and -fill the swept area with clean air, and not a mixture of air and hot used engine oil.
Temperature came under discussion and mention was made of Mr. Wilson's experiments, but it was unanimously agreed that for goods operation it was necessary thatthe thermostat opened early and stayed open, and that a temperature of around the 200° F. mark was essential to good combustion. Comment was made on the M.o.T roadside smoke tests and there was some criticism. Many of the tests were taken on hill-top sites after a heavy climb, and it was agreed that with such a location there would be plenty of smoke to choose from.
It was confirmed by the fuel member that quite often he had tested pumps taken from vehicles after being stopped for excessive smoke, only to find that they were correct or near correct, and nowhere near the smoke line_ One pump was tested and found the maker's setting "spot on" and did not receive any readjustment, yet that vehicle had been given a G.V.9 for excessive smoke, and on being tested a second time by an M.o.T. examiner he could not find fault with it. Nevertheless, it had been caught emitting smoke at the top of a three-mile climb.
The answer to this came from another member, who pointed out that the top section of the hill in question was climbable in second gear flat out by this particular vehicle, and it was therefore understandable that a driver, having crawled most of two miles in low gear, would move into second gear at the earliest opportunity, and at three-quarters of the maximum r.p.m. on full throttle smoke would be noticed. A contributing factor could, of course, be an air shortage under the bonnet, after such a climb at less than walking speed.
The engine in question could not be made to smoke under normal road or town conditions, so it follows that a correctly set pump can provide more fuel than can be burned cleanly under certain road and handling situations. Smoke emission on level road conditions being another matter altogether, it was agreed beyond any argument that here indeed there was work to do and that responsibility rested upon the user, and a vehicle
emitting constant black smoke was in or of three conditions: Excessive ( unbalanced fuel delivery; engine wear 1 such a degree that' it was incapable t correct combustion; or so overloaded th: maximum revs could not be reached i the higher gears, with piston speed to slow for the maximum fuel delivery.
At this point one member was qui, blunt and suggested that the M.o.' people should add a portable weighbrid€ to their smoke-test equipment, and woul no doubt find many an answer on spot. As this is fair comment it shoul not be excluded. Here the reference to the lightor medium-sized oil engin,
Danger Not Proved
Equally blunt was the summing-uj and there is no reason to withold any c it. Briefly this was that black smoke, fc all its admitted nuisance value, is tic proved as yet to be as dangerous eve as the cigarette and would do little hart even to the would-be suicide; its rel trouble potential is without doubt cor cerned mainly with the visibility facto: and it is caused by a number of factot which are all curable. These are: Exce5 fuel delivered by the pump, intentiom or otherwise; air shortage due either t choked air cleaners or an engine, incar able by reasons of wear, of giving corm combustion; engines willing enough, bt too small to handle the unfair loads give them without extra fuel; these same ligl or medium engines being driven laza and slogging hard rather than bein allowed to romp along in the right gea with power then in reserve; and, final]) the operator who is greedy on all count and who will neither stick to the correc laden weight nor spend that 10s, pe 1,000 miles that would speed him safel past the smoke meter and give him a fi vehicle also.