New device could allow drivers to monitor emissions
It could soon be possible to monitor your car's pollutant emissions as you are driving along, thanks to new research from the University of Manchester. Scientists from the university's School of Chemical Engineering and Analytical Science have created a device which uses lasers to measure levels of carbon dioxide (CO2), carbon monoxide (CO) and methane (CH4) from directly inside the exhaust. The work, which is published in the journal Applied Optics, was partly funded by the Fifth Framework Programme (FP5) ASSYST (Advanced Laser Sensor Systems for Leading Edge Manufacturing) project. Currently exhaust emissions are measured by drawing the fumes into a box where they are measured by a range of sensors. This system has a number of drawbacks, the researchers note. For example, it is slow to respond and the gases themselves often adhere to the tubing leading to the box. The system is also prone to interference. In contrast, the near-infrared diode laser offers faster results and less interference. What's more, the lasers and photodetectors which make up the device are readily available and work at room temperature. The scientists hooked up their device to a car engine mounted on a test bed with the aim of seeing how emissions varied under different conditions. The system allowed the researchers to see, for example, how the concentrations of the gases under study change as the engine is started; CO2 levels rise rapidly then level off after a few seconds, while CO levels peak when the engine is started before falling off again. Methane levels were also found to peak and then drop sharply when the engine is started. The scientists obtained similar information for other variables, for example what happens when the throttle (the amount of air and fuel going to the engine) is increased and decreased. 'This is the first instance of this type of near-IR diode laser sensor being used directly in the exhaust of a static internal combustion engine to measure emissions,' commented Dr Philip Martin, one of the authors of the paper. As well as testing their system on the test bed engine, the scientists have taken their equipment out into the real world and used it to measure the exhaust emissions in passing vehicles. 'Components handling the high sensitivity and robustness required to apply this approach in the real world are only now becoming available,' explained Dr Martin. 'We have already constructed a battery-powered roadside unit using the same technology, employing rugged and robust telecommunications components.' The success of these tests led the researchers to look into the possibility of an onboard system. 'Such advances make it feasible to have a flexible onboard vehicle engine diagnostics system for control purposes,' they write. 'The dependence of the emissions on the vehicle operating conditions is also useful for the analysis of remote vehicle emission measurements.' Currently the device has two lasers operating at different frequencies; one detects carbon dioxide and carbon monoxide levels, while the other detects methane. Now the scientists are keen to add more lasers to their device to measure other important pollutants such as nitrogen oxide, nitrogen dioxide and specific hydrocarbons.
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