BLACK SMOKE Th
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9:xperts Attack
THE 26th Conference of the National Society for Clean Air began at Harrogate on Wednesday and ends today. One complete session of the conference, during the afternoon of the opening day, was devoted to air pollution from road vehicles. Four papers on this subject were put forward for discussion. These were: "Administrative Control of Smoke from Road Vehicles," by D_ Lister, county health inspector of Northumberland; "Prevention of Air Pollution from Diesel-engined Road Vehicles," by G. J. Waring, Leyland Motors, Ltd.; "Some Factors Concerning Diesel Engine Exhaust Fumes," by J. K. Lock, the British Petroleum Co., Ltd., and "Methods of Removing Smoke from the Exhaust of Diesel Engines," by L. E. Reed and S. C. Wallin, the Department of Scientific and Industrial Research.
The Problem
"THE r pollution inspectors report
all vehicles emitting excessive smoke and the eight worst -vehicles are referred to the police the following morning. The police are then responsible for directing the vehicles to the municipal testing ground, where tests are made simulating loaded road conditions.
"If the examination, in which a smoke meter may be empli;?yed, confirms excessive smoke emission, the examining officer removes the clearance certificate, so that the vehicle cannot be used until the defect is remedied."
This description of the way in which legislation against exhaust smoke from oil-engined vehicles has been put into effect in Durban, South Africa, was given by Mr. D. Lister. He felt that a similar scheme might be a workable basis for combating the problem in this country.
Value of Threat
Tests, using an approved smoke meter, could be carried out by the police, by the official testing stations, or by Ministry of Transport examiners. It would, not be practicable to check regularly all the 300,000 or so oil-engined vehicles on our roads—or even the 25 per cent. of these which he considered might be guilty of emitting unreasonable smoke. But if the enforcement authority had the power to refer for testing under controlled conditions any vehicle seen to be smoking excessively, with subsequent penalty if this observation was confirmed, all operators would be encouraged to raise their standards—if only to avoid the loss of time by testing.
Under present British legislation, such action was not possible. .Regulation 79 of the Motor Vehicles (Construction and Use) Regulations, as amended in 1957, made the emission of smoke an absolute offence provided that it was likely to cause damage to property, or 'injury or danger to persons. The first alternative of damage and injury could not be used in practice against smoke from internalcombustion engines. Therefore, the only cases which could be prosecuted successfully were those where the amount of smoke was sufficient to obscure visibility to the prejudice of road safety.
D22 Thus it appeared that the police were now able to take action with confidence against, a vehicle emitting very heavy smoke, but could not deal with more moderate exhaust densities.
Theft was now a movement for further alterations to the Regulations so as to widen their scope. It was suggested that, as well as injury and danger, they should include terms such as "inconvenience, discomfort and annoyance." However, these possibilities did not have complete support from the police, who would have to prove the vague allegations. At present, the cases on which they took action were so flagrant that defence was rarely offered. Mr. Lister thought that if the law was amended to permit really effective action against exhaust smoke, it was likely that there would be opposition from hauliers.
As another example of the type of legislation which could be enforced, he quoted a road traffic law in force at present in the State of California, where air pollution was of particular importance. This stated that no motor vehicle should be operated in a manner resulting in the escape of excessive smoke, flame, gas, oil or fuel residue. " Excessive " smoke was determined by visual comparison with the Ringelmann chart (a scale of smoke density now used in Britain to determine the acceptability of industrial exhausts).
Mr. Lister thought that if moderate smoke (which in aggregate caused greater general pollution, as it was given out by more vehicles than the 1 per cent, or so which smoked heavily) was to be checked, it was necessary to use some definite method of measurement.
An instrument which made 'possible precise evaluation of smoke density was the Hartridge-BP Smokemeter, manufactured by Leslie Hartridge, Ltd. This device, by using a light source and a
photo-electric cell, compared the density of a column of smoke with a similar column of clean air. The result was presented on a micro-ammeter on the dial of which was a smoke-density scale reading from 0-100. to represent the percentage of light absorbed by the device. The meter had been approved by the Motor Industry Research Association for research work, and could give continuous readings of exhaust density from a vehicle in motion.
Another unit which could be used for tests on the road had been developed by Bosch. This meter drew exhaust gas through a paper filter disc. After the test, the darkened filter papers were compared' in a separate photo-electric unit, the result being given on a scale reading from 0-10. An advantage of the Bosch instrument was that the soiled filters provided a permanent record. However, it could sample only small quantities of exhaust gas and did not provide a continuous record of exhaust density.
During the preparation of his paper, Mr. Lister had undertaken a visual check of exhaust emission trorn ml-engined vehicles on a trunk road incline. The results of this are given in an accompanying table. He stressed that the classifications used in the table should be taken as approximations, because assessment of smoke densities against a moving background from often-obscured exhaust pipes did not lead to great precision.
Visible smoke represented 3,0-50 per cent, light-absorption, moderately heavy smoke up to 70 per cent. light-absorption, and heavy smoke anything over 70 per cent. This survey indicated that 1 per cent, of all vehicles seen was liable to prosecution, whilst public service vehicles seemed better than most lorries.
Palliatives
"moRE emphasis should be given to the prevention of smoke rather than to devising methods of removing it, once it has been formed." This conclusion resulted from tests of various devices for removing smoke from exhaust gas, which were described by Mr. L. E. Reed and Mr. S. C. Wallin.
Typical black exhaust smoke contained 1.6 gm, per cu. metre of soot, which was equivalent to 2 per cent. of the fuel burned by the engine. Heavy smoke was accompanied by combustible gases which represented a further 7 per cent, of the fuel input. Thus, if smoke was dispersed in the exhaust pipe and not at source, fuel wastage was not prevented. As an example of the pollution which heavy smoke could cause, it was stated that a heavy vehicle operating for 40 hours a week and emitting black smoke for five minutes in each hour would give out 2 cu. ft. of soot (if separated and allowed to settle) in that time. Exhaust soot normally had a particle size from 0-1 micron. This was below the size range which could be effectively dealt with by cyclone-type filters, and therefore these devices had been discounted as a possible•line of research.
Probably the most effective method of removing smoke was to burn it, as the products of combustion were innocuous gases and there was no solid residue. This system was tested by passing the exhaust gas through a metal tube heated by two furnaces in series, whilst preheated air was introduced into the gas stream. It was found that a temperature of at least 800°C. was required to make the exhaust smoke unobjectionable. This was not practicable for use on vehicles as it required 27-kW. energy, which represented 11 per cent, of the fuel consumed by the test engine.
Trials were carried out also on catalytic smoke combustion. Using cobalt oxides as the catalyst, 85 per cent. of the smoke was removed, but it was found that only half of this was oxidized, the remainder being retained by the catalyst. All the other catalysts tried filtered out a certain amount of the smoke but none oxidized more than 40 per cent, of it.
Simple filtration with a number of types of filter media was tested. Pads of fibrous material removed a high percentage of the soot, but the material became clogged quickly and tended to disintegrate under the vibration. None of the filters tested proved satisfactory for application to vehicles.
Although scrubbers for removing pollution from oil engine exhausts had received considerable attention, they were thought to be more efficient in removing undesirable gases from the exhaust than in preventing smoke.
Prevention
ma oil engine manufactfirer aiming at 1' high efficiencies would produce 9I unit with an inherently dirty exhaust, said Mr. G. J. Waring. Although the prevention of smoke-emission limited engine output, the designer was interested in high b.m.e.p. (torque) and high h.h.p. which must essentially be coupled with good specific fuel consumption.
These three requirements could not be reconciled with excessive exhaust smoke. Apart from this, the manufacturer was morally obliged to produce an initially clean engine which would maintain this characteristic over a long working life.
The availability of devices such as the Hartridge-BP Smokemeter had made the engine designer's job more simple. However, the meter did not provide the complete answer, as it measured only density and ignored volume—the actual amount of smoke being an important factor in pollution. Thus, there was still need for visual observation.
The smoke limit of an engine was reached either when its speed range was raised too far, or when fuel input was stepped up to increase the torque produced. Generally speaking, a good power unit was one in which the limiting points of clean running were high up the speed and load ranges. The lower these came, the less satisfactory was the engine.
To extend the clean-running range as far as possible, some manufacturers permitted a certain acceptable amount of exhaust smoke at high speeds and outputs. What was acceptable had yet to be fully defined but Mr. Waring suggested that for a new engine exhaust gas. giving 25 per cent, light-absorption on the Hartridge meter should be the upper limit. In service, this could be •allowed to rise to 45 per cent. as the engine and its fuel injection equipment deteriorated. When the engine reached the higher figure it would be an indication that it required maintenance.
Once the engine left the manufacturer, there were three main factors which could affect the cleanliness of the exhaust. These were faults in the fuel injection equipment, a reduction in cylinder compression, or interference with induction (as could be caused by a choked air filter). Alone, or in combination, these faults would reduce combustion efficiency, to foul the exhaust.
All fuel injection equipment components were precision-manufactured. Thus they were seriously affected by dirt or sludge and could be protected only by very careful maintenance of the filtration system. Apart from failures in the injectors or fuel pump elements, such considerations as the fitting of the
injector in its bore or pump timing could adversely affect combustion.
All these problems could be overcome by efficient and regular servicing. It was less simple to prevent the abuses which some engines suffered at the hands of unwise operators or drivers. Deliberate over-fuelling by increasing the injection pump delivery was not unknown and this, like unauthorized alterations of the governor setting, caused the engine to emit smoke in greater quantities than was ever intended. Excess fuel devices for cold starting had also been tampered with on occasions to operate continuously or intermittently and give 25-100 per cent. over-fuelling.
Same Abuse
Writing of the same abuse in his paper, Mr. J. K. Locke stated that "much of the blame placed on the diesel engine as a contributor to air pollution has been caused by the comparatively few drivers who Misguidedly indulge in this bad practice." He confirmed the reasons for excessive smoke emission given by Mr. Waring, and emphasized that the extra power achieved by increasing the fuel input above the manufacturers' recommendation was achieved only at the expense of proportionally very much higher fuel consumption.
Tests had been carried out to determine the effect of fuel quality on exhaust density. Two heavy commercial vehicles employed for this work were assessed for smoke emission under full-torque acceleration, using three grades of gas oil and kerosene. Kerosene produced slightly less smoke than the gas oils, but overall there was little difference with any fuel. The lower smoke level with kerosene was partly due to its reduced specific gravity. Had the fuel pump been adjusted to deliver the same weight of fuel, the difference in exhaust density would have been less pronounced.
The variation in quality of the test fuels was much greater than that allowed by the current specification for diesel fuel in this country. It could be assumed, therefore, that variation in fuel quality in Britain had a negligible effect on exhaust cleanliness,