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The continuous increase in the price of diesel fuel, the longer availability of CNG and the potential to reduce CO2 enhances the attractiveness to replace diesel fuel by CNG, especially in the aspiring economic markets. One possibility of this is the portrayal of Dual Fuel operation, using a conventional diesel engine with minor modifications, which can be operated either in diesel or a Dual Fuel (gas/diesel) mode. In this combustion mode, it must be possible to obtain a diesel substitution rate up to a maximum of 90 % and 70% on average, as the actual work indicates. In order to illustrate the potential of such a concept, tests were carried out on a 4 cylinder, 7 litre commercial vehicle engine, which was equipped for external carburation using commercial CNG components, as well as a development control unit with software functionality designed in-house.

Liebherr Machines Bulle SA has chosen a technical solution for their 4 cylinder engines on the basis of cooled EGR and a closed DPF system including a fuel dosing unit to achieve Stage IIIB / Tier4i Emission Standards. Main portions of the development, especially the engine and after treatment calibration was performed together with Engineering Center Steyr. The calibration was done under consideration of best fuel consumption, optimized combustion acoustics, satisfying vehicle dynamics as well as fulfillment of legislative regulations, engine and vehicle boundaries. The usage of complex software functionality, a sophisticated calibration process as well as a high end 2000bar injection system was mandatory.