Janis Alnis' DIY Arduino Diesel Smoke Sampler Warns When Car Emissions Get a Little Smokey
A little optical engineering, and a cheap flashlight, provides a high-accuracy tool for emissions testing at home.
Optical researcher Janis Alnis, who is usually found working on high-accuracy atomic clocks, has turned his skills in an interesting direction: the creation of a do-it-yourself smoke meter for diesel vehicles.
"Upon yearly check-ups my car frequently exceeds the [emissions] limit value," Alnis explains. "Because I drive only in the city and soot deposits in [the] catalytic converter. A cure is to drive outside the city for at least an hour so that catalytic converter heats up to >+300°C and soot burns in the presences of palladium catalyst."
The problem, though: unless your vehicle is pumping out a particularly large amount of pollution, there's no way of knowing whether it needs a clean or not to pass the test — short of actually testing it, using a device like the AVL DiSmoke 280. With no DiSmoke 280 to hand, Alnis found a datasheet and set about creating his own.
"It has a lamp and photodetector on opposite ends of a 21.5cm (8.46") long tube," Alnis explains. "Why this length? It gives 1/2 of light absorption at [emission coefficient[ k = 3. More exactly, transmitted light has to be more than 53% to pass the exhaust cleanness requirement."
Building on previous air quality sensor projects, which operate in much the same way, Alnis set about creating his own engine emission meter. The sample tube is built from threaded water pipes with diamond-cut glass windows, while the light source is a cheap LED flashlight. A Photodetector at the other end includes a variable resistor for adjustment, and the resulting measurements feed into a project box with an Arduino and a 128×64 display for graphing and numerical readouts.
"[This] DIY absorption meter allows diagnosing diesel car exhaust smoke opacity to pass legal requirements and see improvements in exhaust particulate matter after driving 300 km on highway and adding additives to fuel," Alnis concludes. "The present project was to make a simple device quickly which works without fancy extras. One can make a Bluetooth operated sensor sending data directly to phone for plotting."
Full details, including schematics and source code, are available in Alnis' Instructables guide — though he warns the design lacks the heating element of commercial versions, meaning water condensation can be a problem on colder days.