Blowing for Economy
Page 38
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NY measure which reduces the exhaust temperature of an engine for a given power output is indicative of its potential for increasing the reliability of the unit in terms of improved valve and piston life. The favourable test results in respect of exhaust temperatures obtained with turbocharged engines may, therefore, be of outstanding importance.
The great majority of hauliers considers reliability and a long mileage interval between overhauls as the major factors in the efficient operation of their vehicles. The existing standard of dependability is high, mileages of more than 200,000 being regularly covered by many of the heavier lorries before reconditioning of the power unit becomes necessary.
They would mostly view the buying of a vehicle fitted with a smaller, but supercharged, engine with the same output as a rash gesture to the cause of progress, despite the promise of a reduced fuel consumption and the advantage of increased payload. Sustained endurance testing over many years would be necessary to convince them that supercharging applied to a standard engine to raise its power would not materially reduce its working life and increase maintenance costs.
Protagonists of supercharging point out that careful matching of the blower's characteristics to those of the engine, and the limitation of peak pressures, enable a higher low-speed torque to be obtained and the output tobe raised without overloading the unit thermally or mechanically. The reduction of exhaust temperatures by supercharging gives weight to this contention. It will fail, however, to convirice_the average haulier that he would not be risking his livelihood by employing supercharged engines.
Discussions with typical hauliers throughout the country have confirmed their distrust of high_ rated power units, but in favour of the supercharger is their readiness to meet the extra cost of a quantity-produced turbocharger if it could be applied to existing types of unit to reduce fuel consumption without necessarily raising the output.
Development work by blower manufacturers has been concentrated on increasing the power-toweight ratio of conventional types of oil engine. and this objective is the obvious target of longterm planning. The future of the blower may well depend, however, on the production of a unit, with or without an intercooler, designed specifically to improve consumption and thermal running conditions. To the typical haulier, successful application of such a unit would be of far greater practical interest than well-substantiated claims for a supercharger that raised the output.