IF YOU believe that oil and water don鈥檛 mix, it鈥檚 time to meet Keith Johnson.
Recently retired as a professor of materials physics at MIT, Johnson has
succeeded where many have failed鈥攂y combining diesel fuel with tap water
to form a mixture that cuts pollution, maintains engine efficiency and works in
existing engines.
His fuel is as simple to make as instant coffee, yet it is stable for years.
If he can make it cheaply enough, it could improve the lives of millions of
people who live in cities packed with old, diesel-powered buses and cars. Their
clapped-out engines belch soot and nitrogen oxides (NOX) that damage
the environment and cause lung disease. Clean up vehicle exhausts, and these
cities should become cleaner and healthier places to live.
The reason that his fuel is so stable and green, says Johnson, is that he has
found a family of detergent-like surfactants that chemically bond molecules of
water to molecules of the diesel, nudging the water molecules into stable
20-molecule clusters resembling 鈥渂uckyballs鈥�. Johnson calculates that these
clusters pulsate with vibrations, an effect that endows them with remarkable
chemical properties. He has licensed his discovery to Quantum Energy
Technologies (QET), based in Cambridge, Massachusetts, which plans to make and
market his watery fuel worldwide.
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Johnson鈥檚 find is the culmination of research that started early this century
when car drivers noticed that adding a splash of water to their fuel often
boosted engine power. During the Second World War, researchers worked without
success to improve fuel performance and stretch supplies by doping petrol with
water. And in 1994, American physicist Rudolph Gunnerman made headlines by
claiming that his cream-coloured blend of water, naphtha and petrol cut
pollution and boosted fuel efficiency by more than 40 per cent. But Gunnerman鈥檚
fuel has yet to reach the market.
That honour has gone to the French oil company Elf Aquitaine which has begun
to market 鈥淎quazole鈥�, a milky-looking blend of diesel fuel, surfactants and
about 13 per cent water. After two years of tests, Elf claims that Aquazole
halves the amount of exhaust particulates and cuts NOX emissions by about 15
per cent.
Both Gunnerman鈥檚 fuel and Aquazole are emulsions in which the water is
dispersed in the fuel as small droplets. Water molecules are polar, possessing a
tiny electrical charge that leaves them ready to bond with other charged
molecules but unwilling to link to electrically neutral ones like those in
petrol or diesel fuel. To overcome this repulsion, chemists use surfactants with
polar groups at one end and non-polar groups at the other. These behave like
molecular peacekeepers, stabilising the mixture by locking the water inside
small surfactant bags called micelles.
The micelles in these fuels are micrometres across, so large that they
scatter light and the two fuels appear white. The size of the micelles also
makes them unstable. With time, the non-polar and polar components separate into
distinct layers and the mixture becomes useless. This, says Johnson, is a huge
problem for anyone attempting to manufacture fuels in this way: 鈥淓mulsions of
water and fuel have a history of separating over time.鈥�
According to Fr茅d茅ric Barnaud, who leads the Aquazole project
team, Elf鈥檚 fuel is stable for at least three months, 鈥渂ut it should last for
over six months鈥�, he says. However, diesel fuel is sometimes stored for long
periods before use and a short shelf-life could be a big problem. The more
stable the fuel, the better chance it has of becoming a commercial success. And
this is where Johnson鈥檚 mixture scores.
He has succeeded in creating a 鈥渕icroemulsion鈥� in which the water is
dispersed in droplets just nanometres across. These are too small to scatter
light so the mixture is clear. Unlike the larger droplets in Aquazole, the
surface tension in Johnson鈥檚 tiny water clusters makes them stable for long
periods. 鈥淎 microemulsion is a thermodynamically stable system,鈥� agrees Philip
Schulz, a chemist involved in the development of Aquazole at Elf. The water
molecules in Johnson鈥檚 clusters are also attached directly to molecules in the
diesel fuel via covalent bonds formed with the surfactant. These bonds further
stabilise the mix. Johnson鈥檚 tests seem to confirm this: samples of his fuel
have remained stable for up to three years, he says.
Tom Kearns, professor of diesel technology at Massasoit Community College in
Massachusetts, backs Johnson鈥檚 claim. Kearns began testing Johnson鈥檚 fuel more
than a year ago. 鈥淲hen I first heard about it, I thought it was ridiculous. I
laughed,鈥� Kearns admits. 鈥淏ut we have some of the fuel that鈥檚 been sitting on a
shelf for a year and it hasn鈥檛 separated.鈥�
Best of all, producing this microemulsion doesn鈥檛 require any fancy
processing鈥攋ust mix the ingredients and stir, says Johnson. He refuses to
reveal exactly which surfactants he uses, but claims that part of the secret to
making nanometre-sized drops lies in the way the water molecules arrange
themselves.
Tiny clusters
Researchers such as Richard Saykally at the University of California,
Berkeley, and David Clary at University College London have shown that water
gathers spontaneously into various structures, such as a ring of five molecules
held together with hydrogen bonds
(鈥淲acky water鈥�, 快猫短视频, 21 June 1997, p 40).
These rings join in a variety of shapes and Johnson says that
one of the most common is a 12-sided structure using just 20 water
molecules鈥攁 pentagonal dodecahedron.
In nature, these clusters exist only for a split second before they grow
larger or are destroyed by the jostling molecules around them. But Johnson has
hit upon a family of surfactants that gather round the 12-sided clusters and stabilise them
(see Diagram). 鈥淚n essence,鈥� he says, 鈥渨e鈥檙e nanostructuring
飞补迟别谤.鈥�
In Johnson鈥檚 estimation, these 12-sided water clusters have some remarkable
properties. First, electrons in the oxygen atom of each water molecule interact
with the electrons on nearby oxygen atoms. Together, they form what chemists
call 鈥渄elocalised pi orbitals鈥�, which stick out from the surface of the cluster
like bristles from a brush. This arrangement increases the reactivity of the
cluster since the electrons can bond with nearby molecules. Here again,
Johnson鈥檚 secret surfactants have an important role to play. They are rich in
oxygen and donate electrons to the water clusters, making them more reactive.
鈥淭he electron is not very strongly bound into the system, so it鈥檚 easier to
share it to form a bond,鈥� says Ken Jordan, a chemist at the University of
Pittsburgh.FIG-mg21775101.JPG
The cluster鈥檚 architecture also means the oxygen atoms are just 2.7 angstroms
apart鈥攕o close that the electrons on one oxygen atom can feel the charge
of the electrons on its neighbours. The charges repel, but as the oxygens are
gripped by strong bonds, they can鈥檛 move apart. Johnson suggests that the bonds
continually deform to minimise repulsion, twisting and stretching in an effort
to stabilise the cluster. This is known as the dynamic Jahn-Teller effect (鈥淭he
heat is on鈥�, 快猫短视频, 3 May 1997, p 26). These vibrations make
the water clusters more reactive, says Johnson, by lowering the energy barrier
for chemical reaction.
This, Johnson argues, is part of the reason why his fuel is so clean. He has
calculated that electrons on the clusters鈥� oxygen atoms react with molecules
such as anthracene in the diesel fuel that would normally turn into soot
particles as they burn. Instead, the electrons break these soot precursors apart
and the fragments turn into water, carbon monoxide and carbon dioxide.
Simultaneously, the water in the fuel cools the combustion process and slows the
formation of NOX. The result: in lab tests, QET has found that the fuel
reduces sooty particles in diesel exhaust by as much as 80 per cent and NOX
by more than 30 per cent. There鈥檚 also a slight improvement in engine
power, says Johnson.
Despite the evidence, Johnson鈥檚 theories don鈥檛 convince everyone. 鈥淭here鈥檚 no
way to tell if his fuel is using 20-molecule water clusters,鈥� argues Saykally, a
pioneer in the study of water clusters. 鈥淐hemical models aren鈥檛 reliable enough
to address this. Calculating the properties of something as big as a 20-molecule
cluster greatly exceeds quantum chemistry鈥檚 current state of the art.鈥� Chemist
Dudley Herschbach from Harvard University agrees: 鈥淜eith鈥檚 theory is plausible
but speculative.鈥�
Johnson is confident about his ideas because of computer models that he has
developed based on his earlier studies of metal clusters. He has simulated the
electrical behaviour of molecules in all sizes and shapes of water cluster,
substituting different oxygen isotopes into the model and charting the changes
in the vibrational frequencies of the cluster鈥檚 bonds. 鈥淚t鈥檚 only with clusters
of around 20 molecules in size that you begin to see vibrations in the range
matching those where the Jahn-Teller effect is active,鈥� he contends.
Wobbly molecules
He also points to a team at the University of Lyon that used Raman techniques
to measure the vibrational properties of water. He claims their findings are
consistent with his theory. 鈥淣ature is never kind enough to give you just one
size of cluster,鈥� he says, 鈥渂ut in our fuel, evidence tells us that the
20-molecule cluster is the predominant form.鈥�
Jefferson Tester, director of MIT鈥檚 Energy Laboratory agrees that Johnson is
onto something. 鈥淜eith鈥檚 claims are logical,鈥� he says. 鈥淗is ideas are also
compatible with what we see in our lab when we test mixtures of water and fuel.
And the increased reactivity is an indication that the Jahn-Teller effect could
be at work here.鈥�
Jordan may not be convinced, but he is intrigued. 鈥淚t certainly doesn鈥檛 sound
impossible,鈥� he says, citing cage-like structures of water molecules called
hydrates that exist in nature: 鈥淥ne couldn鈥檛 have predicted those shapes in
补诲惫补苍肠别.鈥�
Whatever the truth, the ultimate test for Johnson鈥檚 fuel lies out on
the street. And so far, things look promising: in June last year, a team from
West Virginia University tested the fuel in a bus under simulated urban driving
conditions. The results were encouraging, with reductions in pollution levels
approaching those seen in the lab. And Johnson鈥檚 water fuel has certainly
pleased Douglas Wheaton, responsible for alternative fuels at the Massachusetts
Port Authority. For about a year, a Massport bus has used QET鈥檚 diesel blend as
it shuttles passengers around Boston鈥檚 airport. 鈥淲e鈥檙e a large airport crammed
into a corner of East Boston,鈥� Wheaton says. 鈥淯sing Johnson鈥檚 fuel to reduce
pollution is one way to mitigate our impact on the community.鈥�
Although Massport hasn鈥檛 measured the amount of pollution produced by
Johnson鈥檚 fuel, Wheaton is convinced: 鈥淚t is obviously significantly cleaner
than regular diesel exhaust,鈥� he says. Others are interested too. Three private
bus companies in Costa Rica are conducting long-term tests of Johnson鈥檚 water
fuel and QET is in talks with several companies worldwide.
When the fuel is ready for sale鈥攚ithin six months, Johnson
says鈥擬assport will be a customer as long as the cost is comparable to
regular diesel fuel. And that means no more than a 5 per cent price difference.
Right now, Johnson鈥檚 fuel can鈥檛 meet that target, but QET expects its price to
fall as production is scaled up.
Reducing the cost of the fuel while maintaining its environmentally friendly
performance is a trade-off. The surfactant is the most expensive component of
the fuel but Johnson can reduce pollution levels even more by adding as much as
21 per cent water. But add more water and Johnson must mix in extra surfactant
to keep the fuel stable鈥攁nd the costs rise.
So he is looking for ways to eliminate surfactants altogether. One answer is
to subject water to 鈥渟upercritical鈥� temperatures and pressures鈥攁bout 374
掳C and 220 atmospheres. Supercritical water is somewhere between a liquid
and a vapour, and Johnson believes that its primary form is 20-molecule
clusters. Under these conditions, the molecules of diesel fuel and the water
molecules in the clusters bond directly, without the need for surfactants.
In lab tests, the supercritical fuel reduces pollutants even more effectively
than the surfactant-aided blend鈥攔emoving about 90 per cent of particulates
and halving NOX emission, says Johnson. This makes it cleaner than
natural gas. QET is negotiating with a US electricity company to test the fuel
in a power station. QET is also designing engine modifications to enable a
vehicle to create the blend on board.
But this combustible cocktail is just the beginning. Johnson has set out on a
scientific voyage of discovery to explore and exploit the other strange
properties of these water clusters. He is already awash with other applications
and is looking into the role his clusters might play in biomedical products. He
can鈥檛 reveal anything about these yet鈥攃ommercial interests are at
stake鈥攂ut he has even bigger ideas on his mind. He points to data gathered
recently by NASA鈥檚 new submillimetre-wave astronomy satellite (SWAS) that
suggest clouds of freezing matter in deep space throb with vibrations resembling
those of 20-molecule water clusters. Johnson speculates the clusters might pack
the voids between distant stars and galaxies: 鈥淭hese should be stable in the low
temperatures and vacuum of space,鈥� he suggests.
His modest office is also stacked with papers implying that water clusters
may even play a key role in protein folding and in determining the structure of
living cells. Perhaps his watery fuel is just the tip of an iceberg? 鈥淭he more
we can learn about the molecular behaviour of water,鈥� he says, 鈥渢he more we鈥檒l
learn about life itself.鈥�