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In the environmentally conscious world we live in, auto manufacturers are under extreme pressure to reduce tailpipe emissions from cars and trucks. The manufacturers have responded by creating clean-burning engines and exhaust treatments that mainly produce CO2 and water vapor along with trace emissions of pollutants such as CO, THC, NOx, and CH4. The trace emissions are regulated by law, and testing must be performed to show that they are below a certain level for the vehicle to be classified as road legal. Modern engine and pollution control technology has moved so quickly toward zero pollutant emissions that the testing technology is no longer able to accurately measure the trace levels of pollutants. Negative emission values are often measured for some pollutants, as shown by results from eight laboratories independently testing the same SULEV automobile.

In order to achieve the emission levels required for Low Emission Vehicles (LEV) and Ultra Low Emission Vehicles (ULEV) it is necessary to obtain insight into emission reactions to the motor management systems during transient engine performance. The optimisation of transients in typical driving profiles, such as shifting, acceleration load reversal, necessitates suitable gas measurement equipment. A technique capable to resolve one combustion cycle consists in spectroscopic gas analysis by using tunable infrared diode lasers. This paper describes the available equipment and demonstrates that a diode laser system fulfils the specific demands for the analysis of transient operating characteristics of engine management systems.

Although conventional CVS (Constant Volume Sampling) equipment is well established, future requirements for measuring the emitted concentrations of regulated components from ULEV (Ultra Low Emission Vehicles) cars will require optimized dilution ratios. By means of a needle driven by a stepper motor the variable CFV (Critical Flow Venturi)-CVS will be able to adjust the CVS maintaining critical conditions to a predefined volume in less than one second. Using this new design and operating it with software-controlled predefined volume modes, it will be possible to optimize dilution ratios by at least a factor of three. In this case ULEV measurements could be performed by using conventional analyzers.