The Eco-Runner H2 is the second Eco-Runner built by Eco-Runner team Delft. When comparing the vehicle with it's predecessor some major changes can be seen. The shape changed drastically as well as the internal systems. More details about the Eco-Runner H2 are listed below.
The drive train is the part of the vehicle that transfers the electrical energy developed by the fuel cell to the wheels. In the Eco-Runner a gear system is used, since the back wheel has a different rotational speed at 30 km/h than the motors at their point of maximum efficiency. Therefore, a mechanical advantage is needed. In the coming year, we hope to further optimize this system.
When the chassis and the body work are joined the product is called a monocoque, a carrying skin. The monocoque is split in two parts. The lower part is responsible for carrying all the forces. Both parts are shaped aerodynamically to have a very small drag coefficient.
To ensure the efficiency of the whole system, the motor control system should meet all the requirements of the other subsystems. It gets power from the fuel cell and uses this power to drive the motor of the Eco-runner. It should also change the control strategy flexibly to meet different road conditions. Velocity and acceleration speed commands can be given by eco-runner pilot though the motor control system. The motor control system can be called the "operational center". It makes combinations among the energy system, mechanical system and electrical system and builds a bridge between pilot and the Eco-runner.
This year, the eco-runner has a whole new part. A little piece of electronics will record everything that happens to the vehicle. It will, for example, know its position by using GPS, it will know how hard the motors have to work, what the temperature of the fuel cell is, how fast the vehicle is driving and what the pilot ate yesterday (just kidding about the last one). All this information is very convenient to have because it can help a great deal with making a good strategy for the vehicle. This information will make our pilot a more fuel efficient driver, just like the fuel consumption indication in your car helps you to drive efficiently.
Strategy is very important for moving around efficiently. Everybody knows it's not very efficient to leave the traffic light with your car by applying full throttle on your gas pedal. The problem is, for a fuel cell this can be very different. A fuel cell works entirely different than the engine in your car. Maybe it is more efficient to apply full power at the start. Strategy is there to find out. It is important to know how to use electrical motors in an efficient way, or how to use a fuel cell efficiently. Therefore, much information in the form of graphs should be used to think up a good strategy. When you know how you should work efficiently with all different parts of the vehicle, strategy will determine how they should work together. The new strategies have to be applied in some way. We've decided to do this in a special way. We won't ask the pilot to apply so-and-so much throttle, but program a chip to do it for us. The chip will have a special program in it which will control the throttle of the Eco-Runner at all times. The pilot will just have to flip a switch, and off it goes. Different programs will be used to pass special parts of the track, like hills.
The aerodynamic shape will determine how air flows around the vehicle. Some calculations have shown even the slightest bug or edge can change the air flow over the vehicle. When the air flow is changed this way, it means the eco-runner will need much more hydrogen to drive the same distance. The top of the eco-runner is currently made out of PETG plastic. This plastic is hard to work with. Especially worrisome is the part where the top and the bottom parts connect. There is a sharp edge there right now. A whole new top will be made this year. It will be made out of glass- or carbon fiber, a very good material to use for this purpose. Hopefully it will be as smooth as possible and have a smooth connection to the bottom part. Then we will be very happy.
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.
Results May 2008 - 1467 km/l in Nogaro, France
July 2008 - 2282 km/l, 1st place of hydrogen category at Shell Eco-marathon in Rockingham, England