Guessing on gas fuelling
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OPERATING costs of an lpg-fuelled lorry compared with a diesel, are approximately the same — but only when top price is paid for derv. These are the main findings of an experiment sponsored by NFC and Rolls-Royce with the co-operation of BP Oil Ltd.
A 16-ton Leyland Clydesdale has been operated by NFC subsidiary Scottish Road Services Ltd, on behalf of the Scottish Milk Marketing Board since February. It has been used daily, collecting milk and delivering it to a creamery.
The Rolls-Royce B81 gas engine , develops 121kW (162bhp) at 3,000rpm, which, for this application, is coupled to a Lynx gearbox while retaining the standard rear axle with a ratio of 7.428-to-1.
The installation was undertaken to NFC's central engineering specification by Midlands BRS at its Oxford workshop in close co-operation with Rolls-Royce.
As far as noise and emis sions are concerned, the results have been satisfactory. But NFC was very cagey when questioned on comparative costing: "A longer trial will be needed before the economics of its operation can be fully evaluated."
Fuel consumption of the lpg, at the moment is 56.5lit/100k m (5mpg), compared with the 31.41kt/100km (9mpg) of the equivalent diesel-engined machines on the same sort of operation.
Where the problem arises in relation to comparative costing is how much the company pays for derv. According to Walter Batstone, NFC's chief engineer: "We need 15 per cent improvement on the engine to equate cost for cost." If NFC paid 'normal' prices for its diesel, instead of taking advantage of bulk purchase discount, the comparative operating costs would work at at 9.3 pence per mile, for diesel, and 9.2 pence per mile for LPG.
But NFC does get a substantial discount because of the vast quantity of fuel it purchases: hence the need-fora 15 per cent improvement in mpg.
The lpg is contained in two tanks slung on the nearside of the chassis frame. Total capacity gives the Clydesdale a range of about 400km (250miles); any further increase in range will depend on log availability (log pumps are not exactly as common as diesel ones).