Diesel Smoke Causes and Cures
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MINISTRY ENGINEER TELLS OF PROGRESS AND METER PROSPECTS THE Ministry -of Transport is collating
evidence about specific problems and defects in diesel engines and equipment leading to black smoke emission, in an attempt to provide an overall picture which may be useful in taking preventive action, but the process is likely to be a lengthy one. This was revealed at Harrogate on Friday by Mr. H. D. Fawell, superintending engineer, mechanical engineering, Ministry of Transport. Mr. Fawell was presenting a paper, "Road Vehicle Pollution" to the annual conference of the National Society for Clean Air, as recorded briefly last week.
After commenting that an eye was being kept on the measures being taken, especially in the U.S.A., in reducing the output of toxic gases from petrol engines, Mr. Fawell said that concentration of attention at present on the diesel engine's emissions in this country was because of the unpleasant colour and smell of black diesel smoke, which caused public concern. He then examined some of the main causes of diesel smoke, among them: mistimed fuel injection because of timing-gear slackness; over-long fuel injection through a blocked nozzle, poorly fitted injector, badly-seating needle and so on; loss of engine compression through excessive wear, or sticking valves or incorrect clearances; a choked air filter; fouled air passages in a vacuum type of fuel-pump governor; incorrect setting of the maximum fuel stop on the pump: changes in the temperature and pressure of the atmospheric air; and possible variations in fuel oils.
Relating Smoke to Power Referring to the British Standard for diesel engines which is being drafted, Mr. Fawell said one of the factors being considered was the establishment of a smoke standard related to power output under specified test conditions. Without such a standard, purchasers could be unaware of how close a particular engine might be to the smoke limit when on full power. There were many operators who appreciated the significance of having an engine big enough for the job, but there were those who imagined they were saving money by sending a boy on a man's errand; a vehicle which was underpowered was constantly thrashed by the driver, and engine and fuel consumption suffered in consequence, to a degree offsetting the lower capital cost.
The speaker also commented that it would "not be unreasonable" to assume that the eventual plating scheme for goods vehicles in the U.K. would at least take power/weight into account, even if there was not a specific requirement.
Of fuel additives and devices such as afterburners, oxidizers and the like, suggested as a means of reducing diesel smoke emission, Mr. Fawell said that c2 many had been considered and some had been tested by Warren Spring Laboratory but so far these tests had not indicated that the improvements obtained were a worthwhile and practicable contribution and they were not comparable with the improvement that could be obtained by good design, proper use and good maintenance.
Saying that it was hoped to develop annual testjng of all goods vehicles, Mr. Fawell reported that the recruitment of vehicle examiners which he had mentioned last year was now complete and further recruitment now in progress would enable them to extend their activities. He said that the smoke checks carried out by the Ministry of Transport technical staff had been on a regular and increasing basis over the past three years.
Prohibitions The examiners graded smoke visually into heavy (meriting an immediate G.V.9), medium (resulting in a delayed prohibition notice) and light (which brought the operator a warning letter). The follow-up action which resulted from prohibition notices or letters was, he said, one of the most important aspects of smoke checks, bringing the examiners into direct contact with operators.
Mr. Fawell said that, to many operators, fuel injection equipment was still something of a mystery and, in consequence, fuel injection specialists were setting up all over the country; many, but not all, of these specialists were linked to the manufacturers of the equipment and had received intensive servicing training but, even so, it was perhaps a disadvantage that they were all too frequently divorced from the commercial vehicle garages and repairers used by operators and had no knowledge of the condition of the engine associated with the equipment they were servicing. Also, there was no direct control over them by manufacturers, and standards inevitably varied. Nevertheless, said Mr. Fawell, to any operator without the specialized equipment and training who was tempted to dabble with fuel injection equipment the only advice he could give was: "don't ".
The speaker stressed that the vehicle examiner could often play an allimportant role by helping the operator to understand where a smoke-producing fault really lay and advising him on its correction.
.Detailing the way in which smoke checks were carried out, Mr. Fawell listed several reasons why the use of smoke meters which involved the vehicle being driven on the road with a meter attached was undesirable, and he was also cautious about the results obtained by a "free acceleration" test, in which the vehicle is stationary while its engine is revved and a meter reading taken. There were, he said, difficulties in devising a test of this sort which truly indicated road performance, but it had practical advantages and the procedure could not be summarily dismissed. Ideally, the Ministry would like to have an instrument which did not have to be attached to the vehicle but could instead provide a spot reading when used by an observer at the roadside or in a following car— but there were many practical difficulties. Consideration was, however, being given to the possibility of using one or other of a number of modern techniques which could perhaps be applied and the Ministry was keenly interested in research to this end. If it were possible to provide practical means of measuring black smoke objectively in this way they would have made an important advance in their campaign against smoking vehicles.
Meanwhile, he said, the Ministry's most effective weapon against smoke was the trained body of examiners, whose judgment was seldom questioned. The ability • to prosecute offenders did not depend on the existence of a prescribed standard of smoke emission related to an acceptable method of test and measuring equipment, said Mr. Fawell, but court action would, be greatly facilitated thereby.
Smoke Toll During his paper, Mr. Fawell gave details of the number of prohibitions served by M.o.T. examiners following national and regional smoke checks over the past three years. Up to the end of September, 13,500 prohibitions had been served, of which 800 were immediate and the remainder delayed. In addition, more than 2,000 warning letters had been sent to offenders.
Mr. Fawell also gave details of police activities regarding smoke. He said that in 1961 the police prosecuted in over 1,500 cases and issued nearly 400 warnings in respect of smoking vehicles; in 1962 this rose to 3,000 prosecutions and over 500 warnings.
The Discussion In the discussion following Mr. Fawell's paper, Mr. G. H. Mitchell, R.H.A. committee secretary, pointed out that vehicle operators did not want engines that smoked but they had to use the vehicles provided by manufacturers, and he regretted that after a year's consultation the British Standards Institution had not reached a decision, on diesel engine performance, regarding smoke. (Mr. C. W. Oliver, chairman of the R.H.A. highways and vehicles committee, had intended to address the conference on these points, as suggested in The Commercial Motor last week, but was unable to attend at the last moment.) Dr. L. E. Reed, of the Warren Spring Laboratory, said that any Ministry test meter should take a reading of the smoke in the exhaust pipe and not once the smoke had been discharged into the air.
The operator always gets the blame for diesel smoke but even the best of them cannot cause less smoke than is inherent in the engine" said Dr. Reed. Reminding delegates that the conference had talked about diesel smoke for a number of years, yet the problem remained, he felt that sterner measures were now necessary and called for" resolute action" by the operator, the manufacturer and the Ministry.
M. D. Lister, Northumberland County Health Inspector, repealed a suggestion first made, he said, in 1957, that the exhaust outlet should be visible, by the mirror or other means. from the driver's seat.
Mr. P. Draper, an individual member of the .Society, stressed that properly designed and properly maintained diesel engines could not ,possibly smoke under any conditions of load, gradient or operation. Teealemit Stations: Tecalemit (Engineering) Ltd. has appointed the-following companies Is official automatic chassis lubrication fitting stations: Bale's Garage Ltd., The Square, Barnstaple : Nelson. Garages (Western) Ltd., William Street, Swansea: The Reliance Garage (Norwich) Ltd.., Heigham Street. Norwich and Wheatley and Whiteley, 99 Kirkstall Road, Leeds, 3.
Peking Exhibition: Aveling-Barford Ltd are showing a dunip truck and a motor grader at the British 'Industrial Exhibition at Peking. November 2-14.