Can a Bunsen Burner Make Diesel Cleaner?

In a bid to minimise the environmental impact of burning diesel, a combustion scientist at American owned Sandia National Laboratories has pioneered an innovative method inspired by the simple yet effective mechanics of the Bunsen burner.

Used in high school science classrooms around the world, Bunsen burners produce a single open gas flame. Charles Mueller has taken the iconic benchtop instrument and reimagined it as a miniature device that can be installed in diesel combustion chambers to encourage low emissions burning and minimise nitrogen oxides (NOx) and soot particle emissions.

Minimising the eco footprint of self-combustion

While gasoline engines use electric spark plugs to ignite fuel in the cylinder and push the piston, diesel engines don't need the initial spark. Instead, injectors spray fuel at high pressure into the cylinder, where droplets travel at up to 600 meters per second and split into bacterium-sized beads. They then collide with air to create "fuel-air charge" which is then squeezed by the plunging piston to generate extreme pressure and heat, resulting in self ignition.

While the diesel self-combustion process is more energy efficient, it also creates toxic NOx emissions. Regular diesel engines minimise NOx emissions using a technique called dilution, which reroutes low-oxygen combustion gases from the last engine cycle back into the air intake chamber. This technique lowers both the temperature and oxygen levels in the fuel-air mixture. While NOx emissions are reduced, the lower operational temperature means not all the diesel fuel is consumed. The result is a build-up of partially burned carbon, also known as soot.

“Breaking the trade-off between soot and nitrogen oxides is a research area of highest priority for diesel-engine development,” says Paul Miles, manager of the engine research program at Sandia.

Creating a clean, blue flame

Mueller and his team sought to overcome the issue of partially burned diesel by thoroughly premixing the fuel with air prior to ignition. When searching for a way to lower temperatures while still ensuring a thorough mix, the vertical tube and clean blue flame of the globally recognised Bunsen burner immediately came to mind.

“If you unscrew the tube and light the gas jet, you get a tall, sooty orange flame,” says Mueller. “But turn off the gas, screw the tube back on, relight the burner, and you get a nice, short blue flame.”

Mueller says that while the tall flame gets its orange colour from heated soot particles, adding the tube forces the burner to consume more fuel which creates the short blue flame. This effect is partially caused by slots at the bottom of the tube that direct air into the fuel stream. Mueller simulated this effect by equipping diesel engines with miniature Bunsen burner chimneys, with the technology now patented as ducted fuel injection (DFI).

From slashing emissions to developing eco-friendly propulsion technologies, science is at the forefront of new developments. For a glimpse of the latest cutting-edge innovations in the battery-powered vehicle market, don't miss 'Recent advances electrify the lubrication industry.'