Combustion Modes in a Diesel-CNG Dual Fuel Engine 2011-01-1962
Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency.
One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine.
A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. Four load points are investigated and three different types of combustion are evaluated.
The study confirmed the desirable emission characteristics of HCCI and PPCI combustion and demonstrated the potential to control the combustion phasing by utilizing all degrees of freedom provided by a common rail injection system and two fuels.
