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Blow Your Own Trumpet

4th September 1959
Page 37
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Page 37, 4th September 1959 — Blow Your Own Trumpet
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contrast to the high esteem which turbocharged oil igines stand with certain ators, the majority view is the turbocharger is an liable gadget that would probably cause early engine re. Although the claims made for turbocharging ;enerally suspect, a substantial nucleus of enlightened ators would accept units aspirated in this way if exact information were obtainable on engine beariressures, turbocharger maintenance and replacement is important to the future of turbocharging in this try and to the promotion of exports that this nucleus Id be given appropriate information in full. If an le is offered naturally aspirated and in turbocharged L, the standard ratings can include a range of power uts which would normally be covered by a number igines having basically dissimilar main components. cost of a turbocharged engine in pounds per b.h.p. terefore, lower than that of its naturally aspirated terpart, and turbocharging greatly simplifies uction planning.

itish manufacturers of turbochargers have earned a reputation in technical circles at home and overseas, extensive research has shown that their units can be :ssfully applied to most standard engines to provide .ases in output up to, or exceeding, 50 per cent. It been demonstrated in the laboratory that the tant increase in cylinder pressure is small in properto the gain in power, because pressure charging ides improved combustion characteristics.

Accurate Matching Important power unit having a robust crankcase assembly and le bearing areas can, therefore, be turbocharged )ut risk of premature crankshaft failure or a high of bearing wear, so long as the engine and turboter are accurately matched in both performance and ical features. If this requirement is fulfilled, the >charged vehicle engine can be classified in the same ;ory as the turbocharged industrial unit, which has t highly favourable record over the past 25 years. many industrial applications the use of turbo;Mg has increased the life of the engine between r overhauls by a worthwhile margin, despite an ovement in power output of the order mentioned. This is partly explained by the availability of ample compressed air, which can be used to cool the exhaust valves during the overlap period and to assist in scavenging the cylinder of burned gases.

The development of turbochargers for vehicle engines has lagged behind industrial applications because it has been necessary to eliminate acceleration lag and to reduce the cost, weight and dimensions of the unit. The modern turbocharger for vehicles operates with negligible lag, its cost and weight are acceptable, and it can normally be accommodated without obstructing other components. Vehicles with turbocharged engines have completed more than 100,000 miles of arduous service. and detailed checks have indicated that wear rates and so on are comparable with those of the normally aspirated version.

Essential Information

A maker's claim that the turbocharger is accurately matched to the engine carries little weight with a critical operator unless stress details are given, in particular the increase of peak bearing pressures and its effect on the crankshaft load-speed factor. Of greater importance to the general operator are data and instructions on routine maintenance, periodic cleaning, the availability of replacement units and related costs, together with mileages that can be expected between replacements.

Operators should be given the opportunity of opting for economy by including in the range an engine which is turbocharged with the sole object of reducing fuel consumption, the peak power output being virtually unchanged. The experience of Continental operators has confirmed that the turbocharger can afford a valuable saving in consumption by virtue of the engine's improved efficiency.

Some operators may require practical demonstration that simple mechanical changes can readily be made to the system to enable a vehicle to complete its run in the event of turbocharger failure. This would not discredit a claim for long life made by the manufacturer.

To overseas operators in mountainous areas the selfcompensating characteristic of a turbocharged engine, giving automatic power correction for increases in altitude, is often its most valuable feature. This results from reduced air density, which allows the speed of the turbocharger rotor to increase proportionately, and it is essential that the operator should be given data showing the maximum altitude at which the unit can operate safely without overspeeding.

It is known that turbochargers are being developed to give charge ratios far in excess of 2 to I. for which specially modified engines will eventually be required Whilst this may show that the makers have mastered the lesser technical problems of low-pressure turbocharging. the full exploitation on a commercial basis of lower ratios should be given priority.


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