Not All Hydrogen Cars Are The Same

Honda FCX

Honda FCX Concept

Honda’s FCX Concept will be on display at the Tokyo Motor Show this week, and in order to inform, educate and dispel some of the myths associated with hydrogen fuel, we’ve put together the following fact sheet, which compares just two ways in which hydrogen can be employed.

Hydrogen will fuel the next generation of global vehicles. It’s a fact accepted by the entire industry. And given that it’s the most commonly-occurring element in the universe, supply is not an issue.

A future of cars powered by hydrogen is an exciting prospect to consider. Not only can hydrogen help cars to emit zero CO2 emissions, but the development of technology to use the fuel promises to change the ways cars are designed, built and run forever.

However, there are different ways of using hydrogen as a fuel for a car. For example, it can be burned within an internal combustion engine or it can be used in a fuel cell to produce electricity to power a motor.

But while the initial fuel is the same, the way that the fuel is used, the technologies employed to use the fuel – and not least the benefits and disadvantages of the ways in which it’s used – are totally different.

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
Published 22 October 2007 Melanie Carter

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