The LETHE© (Low Emissions Turbo-Hybrid Engine) city car of the University of Roma 1: Final proposed configuration

• Design of a road prototype of Hybrid Series vehicle, with a small Gas Turbine set.
• In the LETHE (Low Emissions Turbo-Hybrid Engine) the GT (gas turbine set) serves solely as a battery pack recharger.
• Definition of the degree of hybridization (ratio of the installed battery pack power and the GT one).
• Vehicle hybridization and emissions evaluation in comparison to European directives.

A longstanding interest of the Authors' research group at University of Roma Sapienza (UDR1) is the design, development and fielding of a road prototype of a new concept of Hybrid Series vehicle, endowed with a small Gas Turbine set as a thermal engine. This solution offers several advantages with respect to traditional internal combustion engines and even to the existing generation of Hybrid propulsive systems: a reduced engine weight and size, lower emissions, substantially extended range, ease of maintenance, and more efficient braking energy recovery. In the LETHE© (Low Emissions Turbo-Hybrid Engine) the GT (gas turbine set) does not directly provide traction, but serves solely as a battery pack recharger. The vehicle is, in all respects, equivalent to a purely electric vehicle, except for the presence of an on-board recharger. Much care was placed in the design phase in the quest for an “optimal” design: first of all, an original method for identifying the most convenient degree of hybridization (ratio of the installed power of the battery pack to that of the GT) was defined and formalized, so that the resulting power balance between the two units satisfies the main design specifications and guarantees a practically acceptable operational life of the battery package while enabling the vehicle to complete a typical city mission (about 25–50 km) in a purely electric mode and without recharge. This paper presents a review of the previous conceptual and design results and describes in detail a possible road prototype configuration (weights, packaging of all units within the body of the vehicle, logic control unit, GT- and electric motor size and power, battery package characteristics). Some discussion is also devoted to the foreseeable impact of the deployment of a LETHE© fleet on the mid-range scenario of the Italian urban transportation system.