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Selective diesel develop
Page 64
Page 65
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meet to GI level
British Leyland Motor Corporation has advised Commercial Motor that at some date in the future the truck and bus division of BLIVIC will concentrate diesel engine production on a relatively small number of basic models to cater for power outputs up to the lowest rating of the Leyland gas turbine. From the information given, it is apparent that four models will cover the horsepower range up to this output and that a number of models will be phased out in due course, The production of any model will be continued indefinitely, however, if justified by operator demand.
It is probable that the rating of the most powerful diesel will exceed that of the gas turbine with the lowest rating, possibly by a fairly wide margin. It is, therefore, likely that operators will have the choice of a diesel or turbine in the case of some of the larger vehicles in the range produced by the Corporation.
The dividing-line output at which the gas turbine will "take aver" is provisionally 350 bhp, but it is feasible that a turbine of lower output will be developed. A new basic diesel engine will be produced in due course to replace a number of units at the lower end of the horsepower range.
Three diesel engines in the existing truck and bus division range are currently the focal point of development work. These comprise the 400/401 (6.54-litre), the 500 (8.2-litre) and the V8 (12.154-litre) units which will cover outputs of 100 bhp up to at least 350 bhp in naturally-aspirated and turbocharged form. Lower outputs will be provided by the existing 200 series (3.77-litre), 300 series (5.1-litrel and 310 series (5.7-litre) units, pending the production of the new engine. Modification of these units will enhance their reliability and reduce their production costs, and turbocharging may well be applied to one or more of the units.
A major part of the output range will be jointly covered by the 500 and the V8. The decision to include both forms in the range was dictated by the need to cater for all types of installation and operational requirement. The current naturally-aspirated rating of the 500 of 170bhp (at 2,600 rpm) is the lowest rating of the unit that is commercially practical, while the lowest practical naturally-aspirated rating of the V8, based on cost and weight, is 220 bhp.
British. Leyland points out that the fixedhead feature of the 500 enables it to accept higher turbocharger pressures than other units produced by the Corporation or (probably) by any diesel manufacturer in this country or overseas. While the current maximum rating (BS AU 141) of the 500 in turbocharged form of 260 bhp at 2,600 rpm could not be increased without the use of intercooling, the inclusion of an aftercooler in the system (between the blower and the engine) will enable the output to be raised to 250 bhp. Up to this rating the cooling system of the vehicle will be used to provide the cooling medium,
Industrial versions
Industrial versions of the engine will be available for suitable applications having a higher output, which will be possible because ample cooling water is normally available from an outside source, in the case of a static installation, to feed the intercooler.
It will be recalled (CM August 30, 1968) that a 500 development engine has been operated at a sustained cylinder pressure of 2,240 p.s.i., the unit being equipped with a specially matched turbocharger and intercooler. According to Leyland technicians there is no distortion of the cylinder block or deterioration of the crankshaft or journal bearings at this high pressure.
Of special importance with regard to thermal distortion, the use of a fixed head has reduced the temperature difference round the periphery of the piston crown from 30 /40deg C to about 3deg C. which in turn reduces thermal distortion of the bore to a minimum. And the absence of holding-down bolts eliminates a source of mechanical strain that can augment distortion.
It is notable that the minimum specific fuel consumption of the 500 turbocharged 260 bhp unit is 0.335 lb/bhp/h. The 500 will be available in horizontal form for p.s.v. applications and, as mentioned in the CM article, a special economy version in turbocharged form develops 200 bhp at 2,000 rpm and has a minimum specific fuel consumption of 0.33 lb /bhp /11 which compares with a consumption of 0.36 lb/bhp /h of the naturally-aspirated unit. Operating at a lower speed reduces friction losses and this increases the overall efficiency of the unit.
As mentioned in an article on the V8 (CM May 24, 1968) the unit has "built-in design features" that provide for uprating by detailed refinements and by turbocharging. Because of the unit's relatively short stroke of 114mm compared with a bore of 130mm and its maximum rpm of 2,600. piston speed is a modest 1,951 ft /mm. which compares with a piston speed of 2,132 ft /min. of the 500. The V8 develops 247 bhp (BS AU 141). in stan dard UK form a 1312 litre export version gives 272 bhp at the same speed—and uprating to 350 bhp will represent a proportional increase over the standard rating of about 42 per cent, Liprating the 500 from the output of the naturally-aspirated engine (170 bhp) to 350 bhp is equivalent to an increase of approximately 106 per cent.
Range flexibility
The recent announcement of a turbocharged 401 producing 160 bhp substantiates the claimed range flexibility of the basic 400 series. In extensive development work on the 400 and 401 naturally-aspirated units, particular attention has been paid to improving the porting and to other means of increasing breathing capacity, and friction losses of the units have been minimized. In its current naturally-aspirated form the 401 develops 138 bhp (BS AU 141) at 2,600 rpm and operates at a piston speed of 2,060 rpm, the lower-rated400 (of the same bore and stroke) having an output of 125 bhp at the reduced rpm of 2,400, in this case the piston speed being only 1,900 ft/min. No information is available regarding the speed at which the lowest-rated, 100 bhp, version will develop its maximum output.
Reverting to the future of the 3.8-litre, 5.1-litre and 5.7-litre units, it is known that they have been subjected to a -value engineering" exercise to give an operational life to match operators' requirements. Of major importance,. however, the exercise involves measures that aim at affording "absolute reliabilityfor the planned life span of the units. It is pertinent that the lower-powered engines are also employed as farm-tractor power units.
While British Leyland's programme of engine development is based on the extensive use of turbochargers, other means of pressure-charging are being investigated, which might provide a comparatively simple method of increasing the weight of air in the cylinders over a wide speed range. A method of driving a turbocharger to give improved low-speed torque is also being considered for possible future application.
In the British Leyland view some form of pressure-charging is essential as a means of producing higher powers at an acceptable engine weight and cost. The performance and reliability of available turbochargers is considered satisfactory and it is noteworthy that the design of turbochargers is a "current concern" of the Corporation. Much valuable data is available from the gas turbine division.
Promoting research in the , field of diesel noise reduction is an active policy of the Corporation and BLMC has instituted a lectureship at the Institute of Sound and Vibration Research, Southampton University. The Corporation attaches great importance to noise research arid is working in close collaboration with the Institute on noise problems.
Up to 500bhp
While it is anticipated that the maximum power required for 38/42-ton g.v.w, vehicles of the future will not exceed about 400 bhp (equivalent to about 10 bhp /ton) and gasturbine development will be conditioned by this requirement, gas turbines will be available with ratings up to 500 bhp based on the same model.
The use of improved materials will enable the gas turbine to operate at a specific fuel consumption of not more than 0.40 lb /bhp /h down to 30 per cent load. And by 1975 "further major variations" will increase the number of options available. In prospect the gas turbine is preferred for higher-powered vehicles because its fuel-consumption /firstcost/operating-cost factor will be more favourable than that of an equivalent diesel and it will offer noise and driver-convenience advantages.
While value engineering has also been applied experimentally to the large diesels in the range to reduce their first cost and to adjust their life expectancy to operator requirements, it has enabled improvements to be incorporated in a number of units at a lower cost without penalties. In a particular case an experimental -denatured" engine was designed to reduce manufacturing costs by 20 per cent and was a "better engine in every way".
Over the years there has been little significant change in the quality of the materials available, British Leyland points out, but advances in the preparation, manipulation and finish of materials have aided progress to a considerable extent. The need to reduce servicing to a minimum is an inherent ingredient of the design philosophy of the Corporation. The development of the fixed-head engine was in accord with this philosophy.
All BLMC diesel engine specifications give a BS AU 141 (gross) rating which includes a smoke requirement. This was also included in a test-code developed some years ago by Dr. A. Fogg, deputy managing director and director of engineering of the Corporation. Dr. Fogg emphasizes that users of British Leyland engines who "default on smokeare operators who neglect maintenance. BS AU 141 is identical to the original Leyland test-code.