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Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with Diesel combustion. Presenter Fredrik K�nigsson, AVL Sweden

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with diesel combustion. 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. One feature of port-injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine. Increased diesel pilot proved efficient at reducing NOx emissions at low λ.

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.

Nozzle coking in diesel engines has received a lot of attention in recent years. High temperature in the nozzle tip is one of the key factors known to accelerate this process. In premixed CNG-diesel dual fuel, DDF, engines a large portion of the diesel fuel through the injector is removed compared to regular diesel operation. This can result in very high nozzle temperatures. Nozzle hole coking can therefore be expected to pose a significant challenge for DDF operation. In this paper an experimental study of nozzle coking has been performed on a DDF single cylinder engine. The objective was to investigate how the rate of injector nozzle hole coking during DDF operation compares to diesel operation. In addition to the nozzle tip temperature, the impact of other parameters on coking rate was also of interest. Start of injection, λ, diesel substitution ratio and common rail pressure were varied in two levels starting from a common baseline case, resulting in a total of 10 operating cases.