Development and application of a control scheme to reduce insufficient operation of an NG-diesel dual-fuel automobile

The thermal efficiency levels are generally maintained while the smoke emission levels are reduced significantly with natural-gas–diesel dual-fuel operation in comparison with those with diesel operation. Thus, the dual-fuel mode is a good choice for in-use vehicles to reduce the smoke emissions and the fuel cost. However, the higher hydrocarbon and carbon monoxide emissions compared with those for traditional diesel operation under low loads is a concern. In this paper, a control scheme is proposed to reduce insufficient operation in the natural-gas–diesel dual-fuel mode. Also, a control system, including a control unit and actuating devices, is developed to realize the scheme. The responses of the governor lever, the smoke emissions of the vehicle and the fuel consumption values are compared and analysed. The test results show that the response of the governor lever is sufficient for practical applications, as it is able to follow the pedal stroke instantaneously with good accuracy. The lugdown smoke emissions of the diesel mode do not conform to those given in the Chinese Standard GB 3847-2005, but those of the dual-fuel mode do. In the road tests, the substitution ratio of liquefied natural gas to diesel is 61.36%, and the fuel cost saving ratio is up to 21.71%. Overall, the scheme and the electronic control device work reliably and can be applied to both liquefied natural gas and compressed natural gas as gaseous fuels.

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