Archives for : March2005

Fuel Cells

Fuel cells are largely envisaged as the most likely successor to the internal combusion engine (ICE) and are at advanced stages of development for use in motor vehicles. Fuel cells are not restricted solely to transport and can be used for power generation in a range of contexts. It is however, transport that is believed to hold some of the greatest possibilities for the technology.

Mercedes-Benz A-Class NeCAR Fuel Cell Vehicle

 

Background and History

The fuel cell was invented by Welshman Sir William Grove in 1839. It was his ‘gas voltaic battery’ that laid out the principles for modern fuel cells. Grove new that passing a current through water caused the separation of water into hydrogen and oxygen and hypothesised that the reaction could be reversed – thus creating an electric current. From his experiments, he created the first fuel cell. The term ‘fuel cell’ only came later in 1889 with Charles Langer and Ludwig Mond’s attempts to produce a working device.

In the 1960s, NASA used fuel cell technology to create electricity for spacecraft. Further development took place in the ’70s but it wasn’t until the 1980s that testing began in the automotive industry. In the mid ’90s, automotive prototypes were finally coming closer to practical use but the size of componentry was still a serious problem. Now, the size of fuel cell components has become manageable and testing is in advance stages.

Ballard Fuel Cell Timeline

The Principles of Fuel Cells

In the most basic sense, a fuel cell works in a similar way to a battery, changing chemicals from one form to another, generating an electric current as a by-product. The key difference is that whilst batteries hold energy to be released, fuel cells can generate energy only whilst they are supplied with fuel and air. The fuel used is typically hydrogen but can take other forms.

Unlike the combustion engine, a fuel cell has no moving parts making it far more efficient. Power is output as electric current which is passed to electric motors which in turn drive the vehicle. A combustion engine can actually only ever transfer a fraction of its input energy into motion; with substantial losses due to converting heat into mechanical energy. Toyota have stated that their conventional petrol engine offers a ‘tank-to-wheel’ ratio of 16% compared to their fuel cell vehicle which offers 48%.

In terms of vehicle design, fuel cells can now be packaged within relatively standard proportions.

The following components must be incorporated:

  • Fuel cell stack
  • Battery
  • Electric motor(s) – depending upon your choice of drive configuration
  • Hydrogen tank
  • Electronic contol unit.

The Main Types of Fuel Cell

Proton Exchange Membrane (PEM)
PEM fuel cells are relatively small with a good power generation ratio for their size. These systems use a solid polymer membrane as the electrolyte and operate at low temperatures. The solid electrolyte means simpler production and longer life whilst low operating temperatures allow faster start-up and power increase responses.

Proton exchange membrane fuel cells are the choice for automotive applications due to the favourable performance they offer in a small package. All current automotive fuel cells use the PEM system.

More details on the PEM Fuel Cell
Others..

Alkaline
Alkaline systems need pure oxygen and hydrogen to work which makes them less versatile than other types of fuel cell.

Phosphoric Acid
Common for use in industrial power generation, they are typically used in static applications. With their high operating temperature, corrosive electrolyte and complex system, they are not appropriate for automotive roles.

Molten Carbonate
These systems are highly complex and use a molten electrolyte. This means the system operates at very high temperatures; this allows the process to take place without a fuel processor but it is only used in wholesale energy production applications.

Solid Oxide
These systems run at extremely high temperatures and can operate with far less pure fuels than other systems; their overall operation is relatively simple. Planned use as very large static power stations.

Powertrain

This section looks at the principles and design concerns associated with the most common form of automotive propulsion – the internal combustion engine as well as some of the less well know variants and alternatives.

The Internal Combustion Engine

 

The Wankel / Rotary Engine

The rotary engine was conceived by Felix Wankel in Germany in 1926 with the first functional prototype not actually running until 1957 – this was largely due to the Second World War and the fragmented post-war Germany.

Electric Motors

Electric motors were one of the earliest means of propelling autocars.