Fuel Cell

One of the most innovative parts of the eco-runner vehicle is the propulsive part which makes use of hydrogen as propellant/fuel. The basic principle behind the working of a fuel cell is the electrochemical energy conversion where energy is extracted from the gas and gets converted it into electricity. The fuel (on the anode side) and the oxidizer (on the cathode side) react in the presence of an electrolyte. Fuel cell can operate virtually continuously as long as the necessary flows are maintained.

Technically speaking, the hydrogen cell used in our car falls under the PEM (proton exchange membrane) category. It capitalizes on the basic simplicity of a fuel cell. The electrolyte, in this case, is a solid polymer in which protons are mobile. Onto each side is bonded a catalyzed porous electrode. These fuel cells have an advantage that it can start quickly since the polymer electrolytes can work at low temperatures. MEAs being thin mean compact fuel cells can be made from them. The voltage of a single fuel cell can be quite small, about 0.7- 1 V, when drawing useful current. Therefore, a collection of fuel cell in series is required to produce useful voltage (stack). The fuel cell stack used in our car consists of 36 cells connected in series. Bipolar plates are used to interconnect the cells as it serves two purposes: makes connection all over the surface of one cathode and the anode of the next cell and secondly, it serves as a means for feeding oxygen to the cathode and fuel gas to the anode. Cooling plays an important role in the efficient operation of the cell. The usual methods of cooling cells in the power range between 100 to 1000 W is to make extra channels in the bipolar plates through which cooling air can be blown. Two fan blowers are attached to the top face of the fuel cell stack to induce a forced convection over the FC stack. The Balance Of Plant (BOP) unit consists of compressors (to feed pressurized air to cathode), fan blowers (as part of cooling system), power conditioning units (DC–DC converter), electric motors to drive the compressors and blowers, fuel storage system (a 1 L tank containing highly pressurized hydrogen), control valves and pressure regulators to regulate the mass flow of the reactants and to maintain the pressure within fuel cell required for its optimum operation respectively.

In more general term, fuel cells have got their own advantages and disadvantages. It is efficient, simple, reliable, and silent in operation and above all the by-product of the fuel cell reaction is pure water, which makes it essentially “zero emission”. A PEM FC operates at low temperatures, uses ambient air as oxidizer and can reach relatively high efficiencies. Further more, a PEM cell allows a quick start-up and has a high energy-density compared to other types. On the other hand, the water and exhaust gas (like CO-gas) management is quite difficult and the used materials for the construction of the FC stack are expensive.

Based on the performance requirements, a fuel cell was ordered that could deliver 100W nominal and 300W maximum power, from the German Research Institute in Fuel Cells (ZBT, Duisburg). They delivered a custom-made FC system with a metal hydride tank to store the hydrogen. The advantage of this technique is that the hydrogen is stored under low pressure (max 15 Bar) in the hydride atom raster. This allows the storage of a great amount of hydrogen in very small volume. The volume of the tank used in the Eco-Runner H2 is about one liter and contains a maximum of 300 nominal liters of hydrogen (at 15 Bar). A big disadvantage of the technique is the weight of the metal hydride (the tank weighs 3kg) and the limited flow rate of the hydrogen gas. The release of the H2 gas out of the raster is an endothermic reaction; therefore if the flow rate is too high the tank will freeze and the flow gets blocked. An advantage from the safety point of view is that when the tank gets pierced, it will automatically freeze, which can remarkably improve the safety factor of the vehicle during a crash.

Some new challenges that are posed from the FC part are to make use of lighter frame for the support structure, lighter endplates of the fuel cell stack, make use of a carbon fibre tank for hydrogen storage along with light weight pressure reducer and try to reduce the power consumption of blower and compressor. We are also planning to introduce a fuel cell monitoring system along with either a battery or boost caps, to ensure that the current is drawn from the FC only at the most efficient point.