Using a laser-based, soot-heating technique, a team led by researchers at Sandia National Laboratories’ Combustion Research Facility (CRF) has demonstrated the ability to measure ‘real world’ particulate emissions from a vehicle under actual driving conditions.
While on-board measurements of gaseous emissions are routine, real-time particulate measurements have been far more elusive, yet are essential for validating emissions guidelines for vehicle compliance in the US.
Pete Witze, an engineer in Sandia’s CRF engine combustion department, recently collaborated with Artium Technologies, Chevron Oronite, and the National Research Council (NRC) Canada to demonstrate the feasibility of obtaining on-board measurements of vehicle particulate emissions using laser-induced incandescence (LII) technology. LII is a non-intrusive diagnostic technology that can perform real-time measurements of particulate emissions produced by internal combustion engines.
Sandia, Artium Technologies and the NRC have worked together to develop the portable version of LII instrumentation that was successfully applied during this recent trial. Consequently, this new method may alter the way in which the automotive industry effectively gauges particulate emissions.
During the past decade, CRF and NRC researchers honed the LII technique, discovered in the 1970s, with the NRC securing an important temperature-measurement patent that is key to the current measurement capability.
The most notable result during the recent tests, said Witze, was obtained during the coasting descent.
‘Although the vehicle speed and engine rpm were reasonably steady for the period from 470 to 600 seconds, the particulate emissions suggest that fuel injection cycled on and off intermittently,’ said Witze. While the researchers believe the ideal fuelling strategy would be to turn off injection for the entire descent, the vehicle is equipped with a catalyst that needs to be kept at its operating temperature.
The average particulate emissions measured by LII during this period were 8.4 ppb, as compared to 10-11 ppb during steady state idle. This suggests that the engine control module has been programmed to minimise fuel consumption during a descent while maintaining idle-like particulate emission levels and an active catalyst. The ability to measure on-board particulate tailpipe emissions is of growing environmental interest because of the desire to validate current US Environmental Protection Agency (EPA) vehicle certification procedures.
These procedures, which have been the industry standard for more than 30 years, measure emissions using a chassis dynamometer and specify engine speed to be applied during testing. Because such tests do not replicate variables such as grade changes and weather encountered under actual driving conditions, the automotive industry expects dynamometer emissions testing to be supplemented with on-road measurements in the future.
In general, innovative new methods are needed to evaluate the effects of mobile source emissions – both from off- and on-road sources – on air quality, especially as the EPA and state agencies, such as the California Air Resources Board (CARB), update their mobile source emission models.
In conducting the tests, Artium’s commercially available LII instrument and ancillary equipment were placed in the trunk and on one side of the rear seat of a 2002 Volkswagen Jetta with automatic transmission and a turbocharged direct-injection (TDI) diesel engine. An on-board diagnostics (OBD) scan tool interface was used to access the vehicle and engine speeds for recording while the vehicle was driven on a test route in the Bay Area’s Livermore Valley in northern California.
These measurements were then time-matched with the LII measurements to obtain a synchronised data set correlating time-resolved particulate emissions with a variety of vehicle operating conditions that included city driving, motorway driving with entrance-acceleration and hill ascent, and coasting descent on a rural road.
Sandia’s Witze said another unique aspect of the LII measurement technique is that, unlike other systems, it does not require an operator in order to conduct the tests. For this and other reasons, he said engine manufacturers have proven to be ‘extremely interested’ in LII.
More information on Sandia’s particulate matter research and partnerships can be found by clicking here.