No go on NOX?
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WHY should California dominate diesel-engine design on a global scale? More precisely, why should legislation that is necessary to reduce the emission of nitrous oxides (NOX) in atmospheric conditions peculiar to one area of the globe be accepted by diesel-engine designers generally as the yardstick on which to base research and development work, when ndrmal emissions of NOX are probably less than a minor hazard to health in the atmospheric conditions that prevail in the rest of the world?
American standards of emission that will be applied over the years are those which are required by California. It may be impossible to produce diesels that comply with the standard or the cost could be prohibitive.
It is significant that Dr J. H. Weaving, research manager of the BLMC atmosphere pollution control research laboratories, stood out as the champion of rational thinking on the subject in the discussions on vehicle emissions at the FISITA conference in June.
Dr Weaving's plea for relaxation of emission standards and his suggestion that the money saved could well be spent on cancer research and allied medical projects served to emphasize the seriousness of the problem and at the same time to bring it into proper perspective. Unnecessary panic at this time — panic is not too strong a word judging by the tone of some of the comments heard — could cost the industry millions. Diesel-engine designers face a bleaker prospect than the designers of petrol engines who can more readily reduce NOX by derating the engine.
Dr Weaving was one of many speakers at the conference to object to the influence of California on pollution requirements, and it is significant that he briefly put the case for the two-stroke diesel when exhaust gas recirculation was being discussed as a means of reducing NOX emission. He asked why no one had had the courage "to make up their minds to produce a decent two-stroke diesel", and claimed that the two-stroke had a number of advantages over the four-stroke in terms of low NOX emission. Because exhaust scavenging was far from complete, the residual gas helped to reduce NOX and the low bmep of a two-stroke was also favourable to reducing pollution. A two-stroke that had a bmep of little more than 50 per cent of that of a four-stroke of the same capacity had a higher bhp output.
While the makers of two-strokes (and many users) will claim that "decent" units of this type have been produced for 25 years or .more, Dr Weaving's comment is one that cannot be dismissed lightly if NOX pollution by diesels is to be reduced to the Californian level or even to a more realistic level yet to be decided.
All-catalyst methods It is notable that a colleague of Dr Weaving, Mr C. D. Haynes, section head of BLMC pollution laboratory, was the co-author of a paper on emissions with Mr R. Lindsay, head of automotive fuels, Shell International, in which the use of allcatalyst methods was claimed to be the best type of control for reducing NOX to the level that would be required in America, in 1976. Be that as it may, the conference produced ample evidence that "internal" improvements in design (as distinct from adding a catalyst externally) could go a long way to solving pollution problems. And there is hope that the end product of the progress made will be a better diesel with a lower fuel consumption and possibly a longer life.
Mr G. Torazza of Fiat obviously ha unshakable confidence in the Fi variable-valve-lift system that he describe in his paper. And the fact that it is suitali for petrol engines as well as diesels coul foster acceptability on a bigger scale am therefore, reduce development and produ( costs. Ricardo technicians probably kno• as much about combustion control as an in the world today, and the fact that Mr I Downs, Ricardo's managing directoi congratulated Mr Torazza on th variable-lift concept was significant.
The very high-performance diesel engin of the future may well be turbocharged /intercooled low-compressio unit if its pollution level is acceptable an the starting problem can be overcome. Th use of a turbocharger can reduce dies( smoke emissions and increasing the bme by turbocharging a low-compression dies( could be preferable to employing a naturall aspirated engine having a highe compression ratio if anti-pollutio requirements dominate the scene in th coming years to the extent . that i anticipated by engine makers.
The mechanics of variable-valve-lif systems were the main theme of M Torazza's paper which made only a brit reference to the gains obtainable; thes included improved breathing and turbulenc throughout the engine's load/speed rangc increased low-speed torque and better rut consumption as well as a reduction emissions. But he did not explain th changes in combustion phenomena tha would be favourable to performance.
Comments• by the authors and speaker during the vehicle emissions sessions gay promise that research work would revea new concepts of combustion control. An unless the claims made in papers by U14 and Italian authors on the use of LPG a part of the fuel charge in diesels (up t( around 30 per cent on full throttle) can b regarded as an indication of the mos hopeful mdthod of increasing performano as well as reducing NOX and othe pollutants, the variable-valve-lift systen possibly gives the best promise of ar acceptable solution of emission problem that would also be favourable t( performance. It could well represent ; means of allying mechanical modificatior of conventional units to combustior research in a highly profitable way.