Compressed Natural Gas (CNG) has favorable characteristics as a vehicular fuel, in terms of fuel economy as well as emissions Using CNG as a fuel in a series hybrid vehicle has the potential of resulting in very high fuel economy (between 26 and 30 km/liter, 60 to 70 mpg) and very low emissions (substantially lower than Federal Tier II or CARB ULEV) This paper uses a vehicle evaluation code and an optimizer to find a set of vehicle parameters that result in optimum vehicle fuel economy
The vehicle evaluation code used in this analysis estimates vehicle power train performance, including engine efficiency and power, generator efficiency, energy storage device efficiency and state-of-charge, and motor and transmission efficiencies Eight vehicle parameters are selected as free variables for the optimization The optimum vehicle must also meet three performance requirements accelerate to 97 km/h in less than 10 s, climb an infinitely long hill with a 6% slope at 97 km/h with a 272 kg (600 lb) payload, and have a 610 km (380 mile) range in the combined urban/highway driving cycle
The optimizer used in this work was originally developed in the magnetic fusion energy program, and has been used to optimize complex systems, such as magnetic and inertial fusion devices, neutron sources, and rail guns The optimizer consists of two parts an optimization package for minimizing non-linear functions of many variables subject to several nonlinear equality and/or inequality constraints and a programmable shell that allows interactive configuration and execution of the optimizer
The results of the analysis indicate that the CNG senes hybrid vehicle has a high fuel economy and low emissions These results emphasize the advantages of CNG as a near-term alternative fuel for vehicles