Laser solution to damp spark plugs

Laser igniters are set to revolutionise transportation by replacing spark plugs that have powered internal combustion engines for more than 120 years.

These low cost igniters, made from ceramics, will now provide cleaner, more efficient and more economical vehicles, says study author Takunori Taira of Japan's National Institutes of Natural Sciences.

In the past, lasers strong enough to ignite an engine's air-fuel mixtures were too large to fit under an auto hood.

But the end of the spark plug could be in sight, after scientists designed a laser which can start combustion engines.

Researchers claim that the approach would increase efficiency of engines, and reduce their pollution.

Spark plugs, which have changed little since their invention 150 years ago, are designed to ignite the fuel-air mixture near the spark gap.

But lasers create a more efficient burn, as the beams can be split to ignite the fuel mixture from multiple points deep in the cylinder.

Spark plugs are also susceptible to wear and tear problems and erode easily as they age, and the point at which a plug will spark is also unpredictable.

The idea has only become practical because of the advent of smaller lasers. A team from Romania and Japan has demonstrated a system that can focus two or three laser beams into an engine’s cylinders at variable depths.

“In the past, lasers that could meet those requirements were limited to basic research because they were big, inefficient, and unstable,” said Takunori Taira of the National Institutes of Natural Sciences in Okazaki, Japan. The new lasers, which are the same shape and size as spark plugs, can also be housed in ceramic casings which survive better in the high temperatures of a combustion engine.

They would offer hotter and more precise ignition than spark plugs, which in turn would improve an engine’s fuel efficiency and lower emissions. “Timing — quick combustion — is very important,” Mr Taira said. “The more precise the timing, the more efficient the combustion and the better the fuel economy.”

The team is in discussions to develop the technology with Denso, an international car component manufacturer.

The research will be presented at the Conference on Lasers and Electro-Optics in Baltimore in the US next month.

Spark plugs work by sending small, high-voltage electrical sparks across a gap between two metal electrodes.

The spark ignites the air-fuel mixture in the engine's cylinder, producing a controlled explosion that forces the piston down to the bottom of the cylinder, generating the horsepower needed to move the vehicle.

Engines make NOx as a byproduct of combustion. If engines ran leaner - burnt more air and less fuel - they would produce significantly smaller NOx emissions. Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy.

Unfortunately, these high voltages erode spark plug electrodes so fast, the solution is not economical. Conversely, lasers, which ignite the air-fuel mixture with concentrated optical energy, have no electrodes and are not affected.

Equally important, Taira says, lasers inject their energy within nanoseconds, compared with milliseconds for spark plugs. "Timing - quick combustion - is very important. The more precise the timing, the more efficient the combustion and the better the fuel economy," he says.

Lasers promise less pollution and greater fuel efficiency, but making small, powerful lasers has, until now, proven hard.