Last year the Aragon Hydrogen Foundation made a major breakthrough in technology of hydrogen and fuel cells. This advance was a washer (street cleaning sweeper powered with hydrogen or street hydrogen flusher). The pressure washer is designed for use in urban areas of cities.
This washer is designed under the LIFE + ZeroHytechpark Project. A project funded by the LIFE + European Commission.
The reason that this prototype was developed because the current energy model based on fossil fuels is unsustainable; high dependence on these fuels located in exclusive regions, high pollution and rising prices are clear examples. There is a real need of change, where mobility represents a significant portion because it is the major consumer of these fuels.
Nowadays, a new fleet of low or zero emission vehicles have been developed: hybrid and electric vehicles, either pure batteries or fuel cell powered.
The governments of various countries are encouraging the purchase of these vehicles; they are introducing them to public transport companies. In the EU, several mobility demonstration projects are promoting and testing the use of these vehicles. Within these projects are CUTE, CHIC, HyTransit, HyTech, High V.LO City, H2Moves Scandinavia. This shows the commitment that exists to reduce dependence on fossil fuels and the emission of CO2 to the atmosphere, in favor of sustainable transport fleet .
Furthermore not only it´s possible to use hydrogen technologies to substitute conventional transport, every council facility could be an opportunity to develop low emission and noise equipment.
Standard combustion engine street flusher are used to find on clean equipments of many councils. The main problems are the big amount of acoustic and emissions pollution produced by theirs motors. One solution is the use of electric flushers, but they have less autonomy and a very long battery recharging time. Using a hydrogen fuel cell, it is possible to increase autonomy and reduce the time to recharge electric vehicles. Moreover the silent function of fuel cell helps to use it without any disturbing.
The vehicle powertrain is based on a fuel cell. A fuel cell is an electrochemical device that converts chemical energy of a fuel directly into electricity through a chemical reaction with oxygen or another oxidizing agent.
Hydrogen is the most common fuel, but hydrocarbons can also be used such as natural gas and alcohols for example methanol. Fuel cells differ from batteries because they provide a continuous supply of electricity until the cessation of the fuel input.
A fuel cell consists of a stack of cells. Regardless of the type of fuel cell, each cell consists of three basic components: two porous electrodes (positive or cathode and negative or anode), separated by an electrolyte, which is a dielectric medium, which is a poor conductor of electricity but allows the passage of certain ions.
The use of the fuel cell as vehicle propulsion involves several advantages. The most important, as explained above, is the high efficiency. Furthermore, another advantage is that the electrical energy is converted directly by chemical processes which make it a silent system and since it do not have moving parts it reduces the need for maintenance. Other key advantage offered by the fuel cells is the environment; the use of hydrogen in fuel cells, when combined with the air, producing only water as the only byproduct.
Made the introduction we will explain what has been designing street hydrogen flushers developed by Aragon Hydrogen Foundation.
Prototype consists of a self-propelled tow that carries an onboard electric water pressure pump, a fuel cell and all the power train. The entire system is powered by a fuel cell running with hydrogen.
The first step was to carry out a simulation of the power train using the software Matlab / Simulink® to decide the optimal configuration.
Several cycles for the simulation have been used. One of these, the so called standard simulation cycles, consists of two parts, one the driving cycle to displace the tow and other the consumption of the water pump during the cleaning.
On this step several technical decision were made. One of the most important tasks was the power electronics devices design. On this project a free dc/dc converter design has been develop reducing the cost and weight of the prototype and providing a high efficiency energy conversion. The fuel cell output is coupled directly to the motors and pump controller avoiding the classic voltage stabilization dc/dc step and batteries or super-capacitors peak supply systems.
In vehicle applications fuel cells operate under load change conditions. Sudden load changes may result in improper water management and reactant starvation phenomena due to the slow response of the cell to load change, which results in performance loss and short lifetime.
Fast load-up rates has been avoided on this application, applying low response curves to the motor controller. A higher load-up rate provides a longer sustaining period of the aiming current as gas starvation takes place, but brings about an increase of the concentration over-potentials of cell voltages while no starvations appear.
Time of response is not a critical parameter requirement on this application, thus a slow load-up rate of 0.1A/ms has been taking in account.
Once the main equipment was defined, the electronics and p&i diagram were developed which is show in Fig 5.
The final configuration has been compared with standard batteries alternatives. Ragone curve, shown in Fig. 6, demonstrates the specific energy of fuel cells, batteries, ultra-capacitors, and conventional capacitors, versus their corresponding specific power levels. As depicted in this figure, batteries with high specific energy and low specific power are placed more towards top left of the figure while ultra-capacitors approach the opposite corner due to their high specific power and low specific energy.
There have been ongoing efforts by ESS (Electrical Storage System) manufacturers to bridge the gap between different storage devices by developing products featuring both high specific energy and high specific power.
The energy density of the ESS is one of the key characteristics on this development. The tow weight cannot exceed 750 kg at full load due to European regulations in order to be defined as light tow. This kind of tow has the advantage that its homologation process is much easier and does not pay taxes.
Once the power train elements were designed, the next step was to develop a specific tow for the application.
The fuel is stored on the front of the tow as a compressed gas on hydrogen cylinders at a pressure of 300bar. Fuel cell and the water pump are sited on the back part. . Fuel cell and the water pump are sited on the back part. A 350 L tank is placed to storage de necessary cleaning water to feed the water pump.
For more information on this project, please visit its website at the following link: http://zerohytechpark.eu/es