The fuel cell powered vehicle is one of the most attractive candidates for the future due to its high efficiency and capability to use hydrogen as the fuel. However, its relatively poor dynamic response, high cost, and limited life time have impeded its widespread adoption. With the emergence of large supercapacitors (also know as ultracapacitors, UCs) with high power density and the shift to hybridization in the vehicle technology, fuel cell/supercapacitor hybrid fuel cell vehicles are gaining more attention. Fuel cells in conjunction with supercapacitors can create high power with fast dynamic response, which makes it well suitable for automotive applications. Simulation results show that hybridization of fuel cell vehicles with supercapacitors with load leveling control can significantly reduce the stress on fuel cells electrically and mechanically and benefit fuel economy of the vehicles. Compared to fuel cell vehicles without energy storages, fuel cell-supercapacitor hybridization achieved fuel economy increases of up to 28% on the FUDS cycle and up to 24% on the US06 cycle for mid-size passenger vehicles. In general, the maximum fuel economy improvements are greater using supercapacitors than batteries. The simulation results show that the power assist control strategy is better than load-level control for batteries because of the lower losses in the DC/DC converter and batteries, but load level control is better for supercapacitors. The best approach for hybridization of the fuel cell vehicles is to use supercapacitors with load leveled control as it greatly mitigates the stress on fuel cells and results in a near maximum improvement in fuel economy and fuel cell durability.
Proton Exchange Membrane fuel cell (PEMFC) technology for use in fuel cell vehicles and other applications has been intensively developed in recent decades. Besides the fuel cell stack, air and fuel control and thermal and water management are major challenges in the development of the fuel cell for vehicle applications. The air supply system can have a major impact on overall system efficiency. In this paper a fuel cell system model for optimizing system operating conditions was developed which includes the transient dynamics of the air system with varying back pressure. Compared to the conventional fixed back pressure operation, the optimal operation discussed in this paper can achieve higher system efficiency over the full load range. Finally, the model is applied as part of a dynamic forward-looking vehicle model of a load-following direct hydrogen fuel cell vehicle to explore the energy economy optimization potential of fuel cell vehicles.
Class 8 trucks using various powertrains and alternative fuel options have been analysed to determine their fuel economy, greenhouse gas emissions, and economic attractiveness at the present time (2013) and in the future.This was done by modelling the vehicles and simulating their operation on day, short haul, and long haul driving cycles. The economic attractive was determined by calculating the differential vehicle cost of each powertrain option and the corresponding breakeven alternative fuel price needed to recover the additional cost in a specified payback period with a fixed discount rate. The baseline vehicle was a diesel engine truck of the same weight and road load using $4/gallon diesel fuel. The use of some of the powertrains resulted in an energy saving and others resulted in higher energy consumption, but compared to the conventional Class 8 diesel trucks, conventional LNG-CI trucks, LNG-SI and LNG-CI hybrids, battery electric trucks, and fuel cell trucks can reduce CO 2 emission by 24-39% over the day drive cycle and 12-29% over the short haul and the long haul drive cycles.The breakeven fuel price was calculated for all the powertrain/fuel options. The economic results indicate that at "today's" differential vehicle costs, none of the alternative powertrains/fuels are economically attractive except for the LNG-CI engine in the long-haul application (VMT=150,000 miles) for which the DGE cost is $2.98/DGE and the LNG cost is $1.70/LNG gallon. If the differential costs of the alternative powertrains are reduced by ½, their economics is improved markedly. In the case of LNG-CI engine, the breakeven fuel costs are $3.42/GDE, $1.96/LNG gallon for the long haul applications (VMT= 150,000 miles) with payback periods of 2-3 years. This makes LNG cost competitive at 2013 prices of diesel fuel and LNG. The fuel cell powered truck is also nearly cost competitive at VMT= 150,000 miles, but this requires a fuel cell cost of less than $25/kW. Hybridizing is not attractive except for the conventional diesel vehicle operating on the day cycle (some stop and go operation) for which the breakeven diesel price is about $2/gallon at ½ today's differential vehicle costs. The regulated exhaust emissions from the LNG-CI engines will meet the same standards (EPA 2010) as the new diesel engines and use the same exhaust emission technology.
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