1. Petrol is vapourised by waste heat recycled from the electric fuel cell and then burned inside ADL’s partial oxidisation/multi-fuel reactor. Sulphur is removed here. Hydrogen and carbon monoxide are formed as by-products. Most of the carbon monoxide is turned into hydrogen and carbon dioxide
2. Hydrogen-rich gas passes through the clean-up vessel where most remaining carbon monoxide is burnt off by preferential oxidisation – which leaves hydrogen molecules intact
3. Hydrogen gas combines with air to form electricity with near-zero emissions. Water and heat are by-products
An electric car that has a petrol tank but no battery could appear on the roads as soon as 2000.
The Anglo-American developers of the technology, which makes electricity from petrol, say emissions are almost zero while performance, notably acceleration, is as good as that of a normal petrol-engined car.
Fuel cells compete with hybrid internal combustion/battery technology as the ideal power source in electric vehicles. But fuel cells are more challenging as they need hydrogen to make electricity.
Engineers at Arthur D Little in Cambridge, Massachusetts have now found a way to make a constant stream of hydrogen gas from petrol. Meanwhile Cambridge Consultants, ADL’s UK subsidiary, has developed a control system to match.
The project has $15m of funding from the US Department of Energy, and is part of the Partnership for a New Generation of Vehicles – a programme which aims to develop technology for a passenger car able to travel 80 miles on a single gallon of petrol.
The ADL team has made what amounts to a miniature chemical plant the size of a normal car engine. This multi-fuel processor, or reformer, sits inside the vehicle continuously processing petrol (or any other hydrocarbon fuel) to deliver hydrogen gas to the fuel cells which then generate electricity to drive the wheels. The target is for a 50kW electric vehicle system which is enough to power a medium-sized car.
The research has overcome a stumbling block to the uptake of fuel cells in cars – a ready fuel supply.
The partial oxidisation (POX) method is not new, but it has taken ADL five years to hone this complex chemistry. The business of removing hydrogen from carbon-rich petrol is tricky. That explains the preference for simpler, hydrogen-rich fuels such as methanol used by Daimler-Benz as fuel for its cell, or Ford’s choice of compressed hydrogen.
Extracting hydrogen from petrol inside a car is innovative. `We have turned gasoline into electricity for the first time,’ says Bill Mitchell, ADL programme manager. Recently engineers showed the system’s flexibility by switching between ethanol and petrol `on the fly’ without loss of electrical output. Energy efficiency is good given the size-to-efficiency limitation of all fuel cells. In ADL’s system, around 40% of petrol converts to electricity, compared with 20% output efficiency for the typical IC engine.
Using POX chemistry, ADL’s fuel processor produces a hydrogen-rich gas. The trick is to remove by-products, such as sulphur and carbon monoxide, that in volumes above 50ppm `poison’ the fuel cell. Most of the residual carbon monoxide is removed down to 10ppm by burning, or preferential oxidisation, in a second vessel developed by ADL with rocket research laboratory Los Alamos. Here the challenge is to prevent hydrogen from burning.
In terms of efficient conversion of petrol to hydrogen, Mitchell says there is still work to be done. Now 80% of petrol is converted to hydrogen. But emissions of nitrous oxide, sulphur dioxide and particulates fall within government guidelines, failing to register on ADL test equipment calibrated down to 1ppm.
Frank Escombe, managing partner at EscoVale, the UK-based international fuel cell consultancy, sees a future for POX in the portable power market too.