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Cut down the fuel bill

21st March 1975, Page 71
21st March 1975
Page 71
Page 71, 21st March 1975 — Cut down the fuel bill
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Which of the following most accurately describes the problem?

Some methods for curbing rising fuel bills really do work but not all are legal yet

4 the light of the present economic imate any method of cutting costs is elcome, especially in the category of iel consumption. Although the diesel vine is less heavily penalized than the univalent petrol unit, any saving, how'Cr small, is worth while especially hen large annual mileages are volved. In this article I have tried to ring some new trends to light as well as 'minding the operator of some more mi liar ones.

.cademic interest

Although it is obviously beyond the :ope of an individual operator, creasing the allowable maximum gvw 1 38 tons provides one simple way of itting down the total fuel bill. I chose le word "total" in this context very irefully for the individual truck mpg gure will obviously be worse at the gher weight.

Taking the results from the recent /14 test of a Volvo F88 to illustrate the Dint we can see the following. For 32 ins gvw the overall fuel consumption as 2.30 km/ I (6.5 mpg) for the total st route of 1,172 km (728 miles) with a tyload of 21.54 tonnes (21.2 tons). For tons gvw the fuel consumption -opped to 2.06 km/ I (5.8 mpg) for a nresponding increase in payload to tonnes (27.2 tons). With this extra tyload it would be possible to iminate one journey in five.

Five trips at 32 tons with this same olvo would shift 106 tons of payload hile four trips at 38 tons would move :.arly 109 tons. In terms of total fuel md, the truck would use 2,564 litres 64 gal) at 32 tons whereas, at 38 tons, ,en though the individual mpg figure as lower, the decrease in trips would it the fuel used down to 2,278 litres 01 gal).

One point which has been stressed /er and over again during the past ielve months is the effect of speed and -lying technique on fuel consumption. t 32 tons gvw, a truck needs about )8 kW (145 bhp) to cruise at 80 km/ h 0 mph), but at 96 km/ h (60 mph), .3 kW (205 bhp) is required. The imple" answer to this is the road-speed )vernor, but obviously drivers will not be keen on this idea.

Frontal area and its effect on the aerodynamic horsepower requirement is the latest gimmick related to fuel consumption. Although the basic performance parameters have remained unchanged with large boxvan-type vehicles cruising at the sixty mark on the motorway, only recently have serious attempts been made to improve a situation which previously, was accepted as unavoidable. Many companies are now fitting winddeflector devices to their vehicles although how much scientific thought has gone into some of them is open to question.

The attachment which has received most of the publicity to date is the Airshield. In conjunction with Golden Wonder Ltd, Conitnercial Motor carried out some independent trials at the high-speed circuit of the MIRA proving grounds with some interesting results.

One factor which arose from the test was the increase in vehicle maximum speed at full throttle with the device fitted. By maintaining the same speed with and without the air deflector, an improvement of around 10 per cent was noted with the A irshield in place, which is fine for the operator if he can persuade his driver to keep at the same speed (back to the roadspeed governor again). Otherwise any benefit in fuel saving will be lost, but the driver will get his outfit back to base a little earlier.

In these same tests we verified the importance of road speed and its relationship to fuel consumption. In its original state the Ford/York Freightmaster outfit returned 3.12 km/ 1 (8.3 mpg) at full throttle.

Cutting back to around the fifty mph mark brought this figure up to 3.97 km/1 (11.2 mpg), while cruising at a constant 65 km/ h (40 mph) gave us a fuel consumption of 4.96 km/1 (14.0 mpg). In terms of hard percentages, the cruising speed of 40 mph gave an improvement of almost 60 per cent in the amount of diesel consumed.

When we discussed these points with Leyland's Bob Fryars he said that such devices were all very well for constantly coupled units with a fixed cab height/ box van height relationship. In terms of increasing aerodynamic horsepower requirements the worst case was a badly sheeted load which could, in the worst case, just about double the drag. The message is plain to see. Don't let the sheets flap in the wind and try to keep the load in as even a"shape" as possible. With some loads this is obyiously impossible but every little helps.

I have already referred to the idea of a road-speed governor to curb the vehicles top speed but, apart from any adverse driver reaction, this could cause problems in some operations. Restricting the vehicle top speed to, say, 50 mph is all very well, but on long motorway gradients it is useful to allow the truck to "wind up" going down hill to avoid too many downchanges on the uphill

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