computer simulation techniques have been used to evaluate the effect of powertrain choice on the fuel utilization (fuel consumption per tonne-km of payload) of heavy articulated vehicles. powertrain parameters which were investigated included engine capacity and aspiration, engine torque-speed characteristics and final drive ratio. fuel utilization was shown to improve as engine capacity was reduced. an improvement of 2.5 per cent per litre reduction of engine capacity was obtained for vehicles of 32-40 tonne gross weight. in practice most of the fuel consumption benefits associated with the choice of an optimum size engine can be obtained by modifying the characteristics of high capacity turbocharged engines in combination with a change in final drive ratio so that the engine will operate at lower speed and higher torque whilst producing the same power output as a smaller capacity turbocharged engine. most heavy duty diesel engines, which are part of optimised powertrains of articulated vehicles, operate at average engine efficiencies within 10 per cent of the best peak engine efficiency available in 1978 products. the scope for further improvement is therefore limited.(a)

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