Hydrocarbon based fuels have become a mainstay of day-to-day life, and for many access to cheap fuel allows them to afford to get to work. As humanity’s need for cheap energy increases, and available oil reserves diminish, it is becoming increasingly important to develop alternative fuel sources, as well as increase reliance on public transportation, such as busses for local travel.
As we begin to utilize public transportation more effectively, it’s important to research technology that will help improve both fuel economy, and reduce emissions. One method of reducing emissions, while increasing fuel economy is using a hydrogen fuel cell. Fuel cells use the chemical reaction of mixing hydrogen and oxygen to form water, and in the process electrical energy is formed. This energy is used to power a battery, which will then power an electric motor. There are many different types of fuel cells with varying ranges of power, efficiency, and price.
Most busses today run a turbo diesel engine. These engines are capable of generating the horsepower needed to move a bus, so why should we be looking to move away from them? Diesel engines are notorious for poor emissions, particularly in regards to particulate matter, and poor fuel economy. Diesel itself has a limited temperature range of operation, gelling when too cold. It is also better to allow large diesel engines like those found in busses and trucks to idle, rather than turning them off when stopped for short periods of time. Fuel cells offer none of these constrains wile providing several advantages.
While fuel cells are an excellent method of increasing the efficiency of a bus, hybridization is also beneficial for a bus running a fuel cell. Hybridization involves adding some form of hybrid system, such as regenerative breaking system to the bus to allow it to gain back power lost by stopping. For a bus, whose application requires they make frequent stops, a regenerative breaking system is ideal. Given the large surface area of a busses’ roof, solar cell hybridization is also an option.
There are several companies around the world that have designed busses to meet the demand for a fuel cell powered bus, while matching or improving the efficiency of the diesel engine. In 2007, Daimler AG released thirty six experimental hydrogen busses powered by Ballard Power Systems fuel cells, dubbed the ‘Citaro FuelCELL,’ in Hamburg. “Thanks to improved fuel cell components and hybridization with lithium-ion batteries, the Citaro FuelCELL-Hybrid consumes almost 50 percent less hydrogen compared to the preceding generation. The operating range of the fuel cell bus is around 250 kilometers.” Thor Industries, the largest bus manufacturer in the United States, is running a power train based on the UTC fuel power technology. This bus, known as the ‘Thunderpower’ is currently in service in California, where it sees ranges of operation of 175-200 miles. This propulsion is provided by a 75kW fuel cell.