Hydrogen-fuelled fuel cell technology (as used by Honda FCX Concept)

Hydrogen-fuelled internal combustion engine (as used by BMW Hydrogen 7)

Concept

Honda’s V-Flow FC Stack combines hydrogen fuel with oxygen to create electricity via a chemical reaction. This powers an electric motor, that delivers drive to the car’s wheels

Hydrogen fuel is burned in an internal combustion engine, which creates power to drive the car. It’s a tried and tested technology that’s been around for 100 years. We know it works

Fuel

Uses only hydrogen as fuel

The BMW H7 can switch between petrol and hydrogen fuel – but that means it is impossible to optimise the engine for petrol or hydrogen, so therefore the engine is never working at its optimum. Also it can run solely on petrol – meaning the user can run the car on petrol the entire time (with CO₂ levels of up to 327g/km)

Reliability

Relies on a chemical reaction, not moving parts – but technology is new and further testing needs to be carried out

Continues to use moving parts, but technology is proven

Emissions

A true zero harmful emissions vehicle (only water vapour is emitted from the exhaust)

Zero CO₂ emissions, but emits nitrogen oxides (NOx) – albeit low levels) – created by the hydrogen and air mix burned in the engine

Storage

Hydrogen stored as a compressed gas (at 35 MPa in a 171 litre tank)

Hydrogen stored in liquid form stored at -253 Celsius

Storage qualities

The drawback of compressed gas is that energy is used in the compressing of the gas, and in-car storage tanks have to be fairly large in order to carry sufficient amounts of hydrogen

Liquid hydrogen is highly energy intensive as it has to be cooled down to -253 Celsius and therefore it has some storage problems. For example, if left for a period of time without using the car (currently estimated to be 9-14 days), ‘boil off’ takes place, meaning the liquid hydrogen warms up, is vaporised and escapes from the tank. As well as draining the fuel, this also means the car cannot be stored in a contained area for any length of time

Efficiency

When employed as part of a car’s powertrain, fuel cell technology is incredibly efficient at using energy. The V-Flow FC Stack in the Honda FCX Concept is 60 per cent efficient at using the energy value of its hydrogen fuel. To put that into perspective, a petrol-fuelled hybrid is 28 per cent efficient, while a petrol internal combustion engine is just 18 per cent efficient at using the fuel (all when measured on the LA4 cycle)

Not nearly as efficient as a fuel cell, but we do not have the exact data to provide an exact comparison. It is likely that a hydrogen internal combustion engine is half as efficient as a fuel cell, but that cannot be proven at this time

Range

Due to their excellent efficiency, fuel cells generally have a longer range. Honda’s FCX Concept has a range of 354 Miles with a full tank. With only half of the amount of hydrogen that can be carried by the BMW Hydrogen 7, the FCX can travel 250 miles

The range of the BMW’s hydrogen tank is 125 miles

Technology

Totally new way of powering a vehicle with innovative technology – the ultimate alternative fuel solution

An evolution of the combustion engine

Design

Could revolutionise the car design industry: fuel cell cars do not have to accommodate a sizeable and heavy combustion engine, and the associated cooling components. Plus, the FC Stack can be housed anywhere in the vehicle, allowing for a better centre of gravity and improved weight distribution

Based on existing car design

Infrastructure

Requires development of a new hydrogen refuelling infrastructure

Circumvents the problems of lack of infrastructure (as the internal combustion engine can run on petrol – but of course environmental benefits are lost)

Safety

Honda’s FCX cars are in commercial use in America and Japan, which means they have to go through the same stringent crash and safety tests as any other vehicle. As well as protecting occupants from front, side and rear impact, the FCX also features special impact-absorbing framework around the fuel cell system and high-pressure hydrogen tanks, to shield them during a collision

Should still meet current safety/crash test regulations, as hydrogen is stored within tanks in existing car design

Timing

FCX to be launched as production vehicle in US and Japan during 2008

There are cars in limited production, with fleets of test cars being used to raise awareness