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Nitrous oxides threaten diesel development

2nd October 1970, Page 34
2nd October 1970
Page 34
Page 34, 2nd October 1970 — Nitrous oxides threaten diesel development
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Which of the following most accurately describes the problem?

• "While diesel engines could be modified to reduce the emission of oxides of nitrogen (NO„) to conform to the value that will, it is anticipated, be required in California in 1973 and to the value that will probably be contained in Federal legislation in America by 1974/1975, we don't know how we shall meet the more severe requirement that will, in all probability, be stipulated in Federal regulations in 1980. It is reasonable to assume that legislation in Europe will follow the American pattern in due course. American manufacturers of diesel engines are viewing the prospect very seriously."

These comments were made by Mr C. C. J. French, a director of Ricardo and Co Ltd during a discussion at the symposium last week on "Critical factors in the application of diesel engines" at the University of Southampton. The symposium was arranged by the Combustion Engines Group and the Automobile Division of the Institution of Mechanical Engineers and the Diesel Engineers and Users Association. Earlier Prof S. G. Timoney, Mechanical Engineering Department, University College, Dublin, had posed the question: "What would be the effect on the production of carbon monoxide (CO) and NO by increasing the bmep of a conventional diesel from around 110 psi to 200 psi?"

Prof Timoney later told CM that his department would be conducting experiments with a highly turbocharged Rootes two-stroke diesel that provided automatic control of the compression ratio between 9 to 1 and 16 to 1 (CM January 24 1969) to ascertain the NO content of very high output diesels and the effect of changes in compression ratio. The maximum bmep of the Timoney /Rootes engine is around 250 psi.

Tribute was paid by Mr N. M. F. Vulliamy, assistant director of engineering of the Perkins Engine Group, to the paper by Mr. E. Holmer and Mr. B. J. Higgh of the Volvo company on "The turbocharged diesel as a road transport power unit" (CM, September 25) as "the best paper on diesel engines for a very long time" and similar tributes were paid by other delegates.

Elaborating on the relative pay-off potential of different outputs and weights of load-carrying vehicles, Mr Holiner said that 320 bhp provided the optimum pay-off of 63 per cent in the case of a 38-ton lorry, while 390 bhp gave an optimum pay-off of 85 per cent for a 44-ton vehicle. A 50-ton vehicle would provide the best pay-off (100 per cent) with a 430 bhp diesel.

Dealing, during the discussion on the paper, with the problems of operating a diesel on a low compression, Mr K. J. Bresser, chief research engineer or Rolls-Royce Ltd said that blue (as well as white) smoke could be produced that had a vile smell and was particularly objectionable in confined spaces. This resulted from fuel vaporized in the cylinders without burning being recondensed in the exhaust system. Increasing the swirl rate in the combustion space provided a limited gain.

Mr Bresser said that the authors had made out a good case for the variable compression ratio (VCR) engine. VCR would enable the high temperature required for light loads and idling to be obtained by raising the compression ratio. He complimented the authors on "breathing more life into the six-cylinder-in-line engine". The paper might upset some of the V8 people. It had been shown by "our friends in the North" [Mr Bresser was obviously referring to the Gardner company] that a long length was not necessarily an installation snag. In a later discussion on the turbocharger lag problem in applications of large diesels to generating electricity, Mr French said that it would be possible to "bring a turbocharger up to load" by employing compressed air stored in a reservoir. A paper on this subject was read by Mr F. Ratcliffe, station superintendent of the Central Electricity Board.

Before the start of the symposium, delegates were shown round the laboratories of the Institute of Sound and Vibration Research and were given information on particular noise problems. It was claimed that noise intensity varied as the fifth power of cylinder bore and the third power of engine speed (I = 135N3), and that variations between engines in current production in the same bore /speed category were minimal. The short-stroke/big-bore engine was noisier than a comparable long-stroke/small-bore engine because the load on the bearings was higher and it ran at a higher speed.

Experiments had been made with a cheap and simple form of sound insulation shield that comprised two thin steel sheets fastened together with widely spaced rivets. The relatively large areas between the rivets rubbed together when subjected to vibration and this improved the insulating properties of the shield, which could be applied to a complete engine in the form of a tunnel. If cooling air were blown through the tunnel better-than-normal cooling could be provided. Shields could be used to insulate particular components such as the exhaust manifold.

The author of a paper on "Improvements to conventional diesel engines to reduce noise", Mr M. F. Russell, section leader of CAV Ltd, claimed that noise intensity could be reduced by 5dBA without basic changes to the engine. By applying all noise-reduction measures, intensity could be reduced by 15dBA. These would include reducing combustion noise, improving structure attenuation by reducing the vibration of all external surfaces and by locating the engine in an acoustic enclosure.

In the conclusions of a paper on "Diesel engine as a source of cominercial vehicle noise" it was emphasized by the authors, Prof T. Priede, Mr P. E. Waters and Mr N. Lalor of the Institute of Sound and Vibration Research that the predominant source of noise was that radiated by engine surfaces and by the inlet and exhaust systems; fan and gearbox noises could however give a combined increase of some MA above that produced by the engine.

In the discussion on the two papers, Mr C. J. Walder, a director of the Ricardo company, pointed out that a long-stroke engine was more efficient than a short-stroke unit, and Mr Russell said that the noise of fuel-injection equipment was being reduced. P.B.


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