Dutch Operators Welcome Turbocharged Units
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By P. A. C. Brockington,
A.M.I.Mech.E. RE directors of Van Doorne's Automobielfabriek, N.V., Eindhoven, Holland, have no regrets they undertook the production of Les under Leyland licence. The re of a Dutch commercial vehicle
o withstand the rigours of sustained speeds for long distances, when it r regular use on the main internal highways, and ambitious con3rs' projects have created a demand wavy vehicles equipped with units can Tug" at low revolutions for rdefinite period.
both applications an exceptionally it crankcase assembly is an advan and in the case of the lugging re it is essential if crankshaft res are to be eliminated.
Favourable Results
e stiffness of the basic structure of D.A.F.-Leyland units may also, in account for the favourable results ned by turbocharging the D575V, litre engine, which corresponds to Leyland 0.350 unit and develops ).h.p. at 2,400 r.p.m, in its naturally ated form. Equipped with a B.S.A. icharger. the unit is known as the '5V engine, and its automotive ; is thereby increased to 148 b.h.p.
e same speed.
rbocharged units are included in standard range of engines, and nd exceeds supply. Over 100 5V units are in service, and it is ast that 50 per cent, of the engines iced will eventually be of the turboed type. Existing orders cover a of 400 turbocharged units of all , including industrial and marine es.
own as the D475V, a 4.75-litre unit recently introduced to eater for requiring an engine of lower r, and is an original D.A.F. project at an exactly similar type is not led in the Leyland range. Basic the engine is a 0575V unit orating a modified crankshaft • a shorter stroke, and its rating of :h.p. at 2.500 r.p.m. extends the ard range to three engines to cover outputs required for the heavier of vehicle.
ng fully tested in the research department, a petrol version of the D475V engine produces 135 bhp. at 3,500 r.p.m, This power unit will probably be added to the standard range early in the new year after prolonged endurance tests have been completed.
Although it is not expected that there will be a heavy demand for the petrol engine, it has been ordered by a number of operators for special types of service. More costly than conventional petrol engines of comparable power, the unit offers a long life and a relatively favourable fuel consumption.
Production planning is based on a total of 15-20 engines a day, and up-todate machine tools are employed throughout the factory. The crankcases are cast in Holland, and all machining is performed at the works, which includes honing the cylinder blocks before the liners are inserted. This process has been included in the production line to facilitate heat flow from the cylinders to the water jackets. Of the other main components, some are imported as finished parts, notably the nitrided crankshaft, whilst the majority requires machining or processing. The head of the quality-control department is directly responsible to the management and has absolute authority in condemning substandard parts.
All engines are fully tested under varying loads before dispatch, and work in the test house includes the experimental operation of units to establish their suitability for special types of service locally or in other countries.
The turbocharged DS575V unit with the greatest vehicle mileage to its credit was stripped by the operator after 100,000 miles for a detailed check of the working parts, and its condition was comparable to that of a normally aspirated counterpart after a similar mileage. Included in this operator's fleet are 15 vehicles equipped with D.A.F. turbocharged engines, and many of these are employed for runs from Venlo. in the south of Holland, across the Brenner Pass to Milan.
At its highest point the pass is over 6,000 ft., and the performance of the blower at this altitude is important in two ways. Because of the rarefied atmosphere, the blower operates at a higher speed, and, although this is favourable to performance, the r.p.m. is increased well above the rated speed.
It has been confirmed, however, that the speed increase can be readily accommodated by the blower and that the automatic power correction it provides does not involve risk of premature breakdown. A normally aspirated engine is derated 4 per cent. per 1,000 ft., which represents a loss in power of about 22 per cent. at 6,000 ft. in the view of one large operator with -whom I discussed turtiocharging in .Holland, a turbocharged engine is eminently suitable for trunking runs at sustained high speed, but may be unreliable because of premature bearing trouble if the vehicle is continually slopping or slowing down and then accelerating at full load.
This criticism is, however, refuted by D.A.F. technicians; a number of operators is employing tippers and heavier earthmoving machines equipped with turbocharged engines on arduous site work, and they report favourably on the performance of the power units. Turbocharging has not impaired reliability.
The turbocharger is a standard B.S.A. unit and gives a pressure ratio of 2 to I. Dynamometer tests of engines fitted with electronic recording instruments have been performed in the D.A.F. experimental department to enable pressurevolume diagrams to be prepared. These show that the increase in peak cylinder pressure is small compared with the improvement in output, a particular advantage of turbocharging being that a lower rate of pressure rise is obtained.
. A comparison between the specific fuel consumptions of the D575V and the DS575V units, obtained under test, shows that turbocharging improves the minimum consumption by about 3 per cent.
The short-throw crankshaft of the D475V engine reduces the stroke from 4.75 in. to 3.92 in., which gives a " square " stroke-bore ratio, the bore of 3.92 in. being unchanged. Comparing automotive ratings, the maximum torque of the engine is reduced from 257 ft.-lb. to 210 ft-lb. by the reduction in stroke. The unit has a gross (S.A.E.) rating of 100 b.h.p. at 2,500 r.p.m., whereas the gross rating of the D575V is 120 b.h.p. at 2,500 r.p.m.
Injection Pressure
Plungers of the injection pump are increased in diameter from 7.5 mm. to 8 mm., and injection pressure is 110-I R5 atmospheres, instead of 145-150 atmo
spheres. Twin micro fuel filters are employed in place of a single filter, and other modifications include the use of a flywheel suitable for a Rockford 12-in. clutch in place of the Borg and Beck 13-in, clutch fitted to the more powerful unit.
On all D.A.F. vehicles, the air cleaner is located outside the bonnet to reduce the temperature of aspirated air to a minimum, and its position is such that air currents around the filter pick up the minimum amount of dust.
Detailed instructions regarding power ratings are given to DA.F. representatives responsible for advising operators on engine performance factors and the effects of changes in ambient temperature, humidity and altitude. Both S.A.E. and D1.N.70020 ratings are normally quoted, and the latter is given as the automotive rating.
u22, The German D.1.N. rating shows the net output of the engine when driving all accessories, including a six-bladed fan. as specified for vehicle applications. Output is based on a barometric pressure of 29.92 in. of mercury and an air temperature of 68 degrees F.
Elimination of the fan in determining the one-hour and I2-hour ratings by the British standards method is regarded as an adjunct to accuracy. Tests in the laboratory show that the six-bladed fan of the D.A.F. engines absorbs around 4 b.h.p. on the test-bed and up to 8 b.h.p. when the engine is installed in a mock-up radiator-and-cab assembly with the same type of shroud. Experiments with pusher-type fans have proved that they are more efficient than conventional fans and absorb more power. When pushing the air, the standard six-bladed fan absorbs 14 b.h.p. and is sensitive to air obstruction by the bonnet.
In the opinion of the D.A.F. test staff. these variations show the desirability of basing automotive ratings on engine output without the fan, and of giving the power absorbed by the fan in the laboratory and in typical applications. This would remove one cause of misunderstanding amongst many causes in enumerating the factors that must he taken into account in assessing the practical value of the various engine ratings.