In classic railcars, the drive units are usually installed beneath the floor. This arrangement means that by comparison with separate drive modules, there is no additional loss of passenger space. A major disadvantage, however, is that this engineering design entails the use of steps to enter the compartments because an end-to-end low floor section cannot be realised.
The specification of the French manufacturer Alstom to MAN as the supplier of the engine for the power pack was to enable the realisation of this end-to-end low-floor section in its railway vehicle Regiolis. What is special about this installation is that the four or six drive systems, each comprising a diesel engine with flanged-on generator, cooling system and controls, are arranged on the roof of the vehicle.
The requirement formulated in the operator's specifications is for an engine as compact and light as possible. EU Stage 3b, in force since 2012, had to be fulfilled without the use of a second operating fluid at the same or even lower levels of fuel consumption than engines in predecessor or comparable projects. In addition, besides the issue of noise avoidance, protection against fire is of central importance, not least due to the planned installation area on the roof. Acceptance of the engines in accordance with UIC 623 is required.
The Regiolis from Alstom will be operated from 2013 on by SNCF in France as a suburban train on routes with heavy traffic and short distances between stops. The adaptation of an engine whose origins were in road transport for use as a railway engine means fulfilling a different set of requirements: the load spectrum of a railway engine differs significantly to that of a truck engine, besides which there can be rapid and frequent alternations between the operating points. In addition, different laws with regard to exhaust emissions apply.