Assessment of the Greenhouse Gas Emission Reduction Potential of Ultra-Clean Hybrid-Electric Vehicles

The study focused on the emission reduction and fuel economy benefits of the application of hybrid/electric powertrain technology to tight-duty vehicles (mid-size and compact passenger cars). The approach taken was to calculate the exhaust emissions (gm/mi) energy use (Wh/mi and mpg) for a wide range of vehicle designs (steel and light-weight materials), engines, energy storage devices, control strategies, and driving cycles using two vehicle simulation programs (SIMPLEV and AVTE). The full fuel cycle total emissions were then calculated for each of the hybrid designs using an EXCEL macro, which used as inputs the vehicle simulation results and upstream emissions to account for the vehicle evaporative and refueling emissions and the production and distribution of the fuel and electricity used by the vehicles. The total emissions calculations included the effects of the vehicle use-pattern. The key conclusions drawn from the results of the study were the following: (1) light-duty vehicles using an engine-powered hybrid driveline can have up to double the fuel economy and thus one-half the total CO2 emissions of conventional ICE vehicles of the same weight and road load, (2) Vehicles using a load-leveled fuel cell fueled with compressed hydrogen can have about one-third the total CO2 emissions of a conventional vehicle using gasoline, (3) the calculated total emissions of mid-size, battery-powered vehicles in the LA Basin are close to or less than the CARB EZEV standards, (4) hybrid vehicles with an all-electric range of 50 miles more have total emissions close to those of an electric vehicle for a use-pattern of 10,000 miles per year, (5) regulated emissions and CAFE standards for light-duty vehicles should be set terms of total full fuel cycle emissions for NMOG, CO, NOx, and CO2 rather than exhaust emissions and mpg as is current practice, and (6) the marketing of advanced hybrid vehicles, including fuel ceil powered vehicles, will be driven by CAFE or other vehicle efficiency standards and not regulated emission standards, because the ultra-clean emission standards can also be met using advanced engine technologies in conventional engine drivelines with catalytic exhaust after-treatment without large retooling investments by the auto industry.