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Q Could turbo-charging be applied to a petrol engine to improve fuel consumption? And has such an application been made?
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AEquipping a low compression petrol engine with a turbo-charger might improve fuel consumption by virtue of the resultant increase in low-speed torque, which would augment the pulling power of the unit and thus reduce the amount of gear changing required. In the case of a high compression engine, however, application of a turbocharger would necessitate lowering of the compression ratio, to avoid a detonation on full throttle and this would be unfavourable to fuel consumption.
A well-known maker of sports car petrol engines has been experimenting with turbo-charging for some years but no test data has been published. In 1962 an Oldsmobile car engine with a compression ratio of 10.5 to 1 was fitted with a turbo-charger. To avoid detonation without reducing the compression ratio, a mixture of alcohol and distilled water was injected into the air-stream when opening of the throttle increased the manifold pressure beyond a critical limit. The turbo-charger was virtually ineffective at lower throttle openings but gave a 30 per cent torque increase on full throttle.
Obviously, this represents a complicated and costly way of overcoming the detonation difficulty. Even if it could be obviated by running the engine on a fuel of higher octane. the overall running cost would be substantially increased.