Hi, my name is Niek Goselink, I am a second year master student at the faculty of Aerospace Engineering. More importantly, I am this year’s fuel cell engineer for the Eco-Runner Team Delft. It is my responsibility to operate the fuel cell in a save and efficient manner in the Eco-Runner 9. The fuel cell system is the heart of the car, as it produces the power which drives the car.
The basic operation of a fuel cell system is really simple, it is the reverse reaction of electrolysis. In an electrolysis reaction, water is being split in hydrogen and oxygen by passing an electric current through it. Reversing this reaction, thus combining hydrogen and oxygen, an electric current is produced. This is also the basic process which takes place in our fuel cell system. Both hydrogen from a small tank and oxygen in the air are added as an reactant to the fuel cell stack. To further understand the working principle of a fuel cell, firstly we have to take apart the fuel cell stack itself. The ‘stack’ is a series of cells, in which the reactions take place. Such a cell consists of two electrodes (anode and cathode) divided by an electrolyte. At the anode, the hydrogen is being split in two separate protons, , releasing electrons and thus energy. These protons are able to penetrate the electrolyte, in our case a proton exchange membrane, while the electrons follow an electric circuit to the cathode side. At the cathode, the protons which have penetrated through the electrolyte will react with the electrons and oxygen from the air into water. The flow of electrons through an external circuit from the anode to the cathode, produces an electric current and can be used to power a load, in our case an electric motor which drives the car.
As the sole emission from a fuel cell system is liquid water, a hydrogen fuel cell is therefore well known as a zero emission power supply system.
Fuel Cell system development
As Eco-Runner Team Delft we believe in the idea of hydrogen as an energy carrier and vital component in the energy transition. By building the most efficient hydrogen driven car, we hope to show the possibilities of hydrogen to the general public and create awareness about this topic. Although creating awareness on the possibilities of hydrogen is one of our prime drivers, we primarily focus our year on building an extremely efficient car. As mentioned before, the fuel cell is a vital component in this quest for high efficiency. The fuel cell is the first component in line which creates losses, irreversibilities in the transformation of chemical energy (enclosed in the hydrogen) into kinetic energy (acceleration of the car). The fuel cell has the possibility to make or break this efficiency goal. With an inefficient fuel cell, the subsequent components will not be able to recover these initial loses. It is therefore of the utmost importance to optimize the operation of the fuel cell as much as possible. In order to do so, there are a few areas one could focus on. First, is the transformation of chemical energy into electrical energy, a process which takes place in the stack. By optimizing the size and conditions (temperature, pressure and humidity) within the stack, this transformation can be made more efficient, thereby reducing loses. Next to this, is it also possible, to reduce the power requirements of the Balance of Plant (BOP). The BOP is the auxiliary system which keeps the fuel cell stack alive and kicking. This system delivers the required amounts of reactants (air and hydrogen) to the stack and consists of a range of pumps, valves and circulation circuits. The BOP is powered by the energy produced in the stack. If we would reduce the power required for pumping, more power can be delivered to the motor to drive the car. Luckily, both these areas are interrelated; the BOP regulates, among others, the cooling circuit and hydrogen recirculation, which affects the temperature and humidity. The aim is therefore, to adjust the operating conditions, while simultaneously reducing the power requirements of the components. As with every challenging engineering project, this will require making trade-offs in our system to reduce power requirements and increase chemical reaction rates. For optimizing and developing the BOP, we work together with Teesing, a company specialized in delivering high-grade tubing and connectors. This year, we opted to renew all of the tubing and connectors of the system and increase the tubing diameter. This would in turn reduce the backpressure created by the circulation circuits and thus lower the power requirements for pumping. Moreover we investigated the possibility of redesigning the cooling circuit. Last years’ cooling layout, included a heat exchanger with cooling fan, a so called active cooling system. As the fan, consumes significant amounts of power, we would like to get rid of it and design a more passive cooling system, which would use less mechanical cooling devices. Therefore, we have added a thermal mass to the system, which is separated from the fuel cell itself. The thermal mass was placed in the motor compartment in close proximity to the rear wheel. While driving, the turning of the wheel, will create a turbulent airflow, which will cool the thermal mass by convection. The cooling liquid is pumped through the fuel cell and afterwards through the thermal mass. The heat taken from the fuel cell by the cooling fluid will be released in the motor compartment, after which the liquid is routed back into the fuel cell stack. This new design required double shut-off quick connectors, to enable us to couple and de-couple the cooling circuit from the fuel cell system. This would reduce the installation time of the system, while also increase the cooling capacity which is especially important when the race is held on a hot and sunny day.
We are really grateful for the cooperation with Teesing, together we worked towards a really efficient fuel cell system in a really efficient hydrogen powered vehicle! With this system we believe we are able to bring the first place in the Shell Eco-marathon back to Delft.
|Figure 1: Top view of the Fuel cell system, showing the stack with cells|
|Figure 2: Overview of the new Fuel cell system, including the control board at the side|
|Figure 3: The new cooling lay-out. Seen from the front is the thermal mass, with the quick connectors connected in the back from and to the fuel cell system|