The 6Dl locomotive is the first of the SM42 locomotive series which was modernised to the double-generator version. Based on the successful technical and functional solutions used previously in 6Dg and 18 D series locomotives, it was additionally adapted to supply electricity to the train set. The 6Dl locomotive is also the first locomotive modernised by NEWAG S.A. which was equipped with energy absorbing crash buffers.

The scope of the modernization includes constructing a completely new loco body mounted on the old locomotive underframe using the existing bogies and fuel tanks which have been overhauled and modernised. The loco was equipped with two C18 high-pressure diesel engines manufactured by CATERPILLAR of 563 kW power connected by a flexible coupling with synchronous generator sets. Each power-generating unit with an intake and exhaust system has been fitted on a common, specially designed frame supported on the locomotive underframe. The engine exhaust systems are fitted with DOC filters.

The mounted power generator sets can work in two configurations: the first uses the power generated by both engines for tractive purposes while the other allows to use the power generated by one set for tractive purposes with the power generated by the other set to be used as power supply for train cars.

The trainset is supplied with electric power thanks to a specially designed converter mounted on the locomotive platform in the container in front of the driver’s cab. The buffer beams have sockets compliant with UIC 522 card.

The starter powered from the supercondenser system ensures the engine’s proper start-up with a reduced number of battery cells and reduced load of the starting current on the cells.

Electric drives for diesel engine cooler fans were used for the first time in the 6Dl locomotive. The engines of the cooler fans and the engines of auxilliary equipment are powered by inverters.

Locomotives are fitted with a modern braking system using two screw compressors, an integrated pneumatic board and a spring-actuated parking brake.

The loco designers have also focused on the functional and aesthetic solutions. They designed a modern body with fronts made of plastic. The driver’s cab, located in the loco’s central part, has two ergonomic control panels for the driver. The cab interior walls are covered with pleasant-looking mat composite panels. The cab has air-conditioning, efficient heating, LED lighting, as well as amenities such as a hob plate, fridge, a washbasin with hot water etc.

Wide doors placed on front walls of the cab lead onto platforms. The lowered machine room ceiling and panoramic windscreens provide very good visibility and meet the contemporary requirements in design. Additionally, locomotives have been fitted with a digital monitoring system. Two cameras mounted at the front of the loco and two inside the driver’s cab enhance the field of vision of the track and facilitate shunting operations (couplers’ visibility). The view from the cameras is recorded.

6DI locomotives have permission to be operated by one driver.