Dazo Water Fuel Technology

2. PROPERTIES OF HYDROGEN

Hydrogen is the most abundant element in our universe. In addition to being a component of all living things hydrogen and oxygen together make up water, which covers 70 percent of the earth. In its pure form, a hydrogen molecule is composed of two hydrogen atoms (H2) and is a gas at normal temperatures and pressures. It is the lightest gas (even lighter than helium) with only 7 percent of the density of air. If you get it cold enough (–423 °F), gaseous hydrogen will liquefy, and it can be transported and stored in this form.

There is virtually no “free” hydrogen on earth; all of it is combined with other elements (mostly oxygen or carbon) in other substances. Every molecule of water contains two hydrogen atoms and one oxygen atom. Hydrocarbon fuels such as coal, gasoline, diesel, and natural gas also contain hydrogen. In the case of gasoline and diesel fuel, there are approximately two hydrogen atoms for every carbon atom, while natural gas contains four hydrogen atoms for every carbon atom.
In order to directly use hydrogen as a fuel (whether in a fuel cell or in an internal combustion engine), it must be separated from these other elements. The hydrogen fuel used in vehicles is either derived from water (by electrolysis) or from a gaseous or liquid hydrocarbon fuel (by reforming). After being separated it must be stored—first at the fuel station and then on the vehicle. Some fuel stations include liquid hydrogen storage, but on the vehicle, hydrogen is usually stored as a gas at high pressure. It is also possible to store a liquid fuel (gasoline, diesel, and methanol) onboard a vehicle and then use an onboard reformer to separate the hydrogen just before it is used in the fuel cell engine. While this requires additional equipment on the vehicle, it removes the need for high-pressure gas storage.

This chapter provides an overview of the properties of both gaseous and liquid hydrogen that are necessary to understand how hydrogen differs from more familiar motor fuels, such as gasoline and diesel fuel, and what is required to handle and use it safely. While there are risks, hydrogen can be as safe, or safer, than diesel and other fuels when vehicles and fuel stations are designed and operated properly. All fuels require particular design and handling practices based on their properties, and all present certain hazards when mishandled. Understanding the properties of hydrogen is necessary to understanding what is required to use it safely.
Building on the discussion of hydrogen properties, this chapter also provides an overview of the general principles that govern safe design and use of hydrogen fuel. These principles inform the design and operating guidelines presented in chapters 3 through 5.