IIT Bombay researchers develop new technique to accurately measure soot

This will help designers build better combustion-based devices such as internal combustion engines in cars. 

Researchers from the Indian Institute of Technology (IIT) Bombay have developed a new data-processing technique to measure low amounts of soot accurately. This will help designers build better combustion-based devices such as internal combustion engines in cars. 

What is soot? 

Soot are tiny black particles that rise from a flame. Soot is formed when the fuel does not burn entirely. When fuel burns properly, a blue flame is seen, whereas the flame is yellow when the soot is formed during burning and it becomes hot. Soot can cause cancer and respiratory and cardiac disorders; it can also reduce the life of machine parts. 

In a recent study by a group of five researchers from IIT Bombay led by Neeraj Kumbhakarna, professor from the department of Mechanical Engineering, demonstrated a new technique to effectively reduce measurement errors when soot is present in low amounts. The study was published in the June issue of the Journal of Aerosol Science and jointly funded by the Industrial Research and Consultancy Centre, IIT Bombay, and the Indian Space Research Organisation (ISRO). 

The researchers analysed digital camera pictures of burning fuel to guess the temperature of the fuel and use the information to estimate the soot volume. The amount of soot can be measured using methods such as collecting and weighing the soot and studying a light beam shone on soot particles. The current study uses the last method. 

The researchers passed a beam of red laser light of a specific frequency, through a droplet of burning fuel and took images as it burned. The light falling on the camera also contains the light from the burning fuel. The researchers used a narrow band filter to let only the laser light pass and filter out the light emitted by the burning fuel. 

“When a flame having soot particles is shone with light, called background light, the particles absorb and scatter some of this light, so light reaching the camera is less bright,” said Anand Sankaranarayanan, a post-doctoral researcher from IIT Bombay and co-author of the study. 

The researchers used the relation between the initial brightness of the laser light, the brightness of the light falling on the camera and the soot volume to calculate the amount of soot. They then used a data-processing technique to compute the values of brightness from their images. Their challenge was to estimate the initial brightness of background light falling on soot particles since this is not directly captured in the images. 

The researchers predicted the brightness of background light at every moment instead of using an average. They observed the flickers in background light at areas present outside the flame of the burning fuel, where there is no soot. They used it to estimate the background light falling on the soot particles. “Using our new data processing technique, we got lower errors, especially when the amount of soot produced is low. Our technique does not require any additional equipment or extra expenditure, which is an added advantage,” said Sankaranarayanan. 

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