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The control of NOX emissions by exhaust gas recirculation (EGR) is of widespread application. However, despite dramatic improvements in all aspects of engine control, the subtle mixing processes that determine the cylinder-to-cylinder distribution of the recirculated gas often results in a mal-distribution that is still an issue for the engine designer and calibrator. In this paper we demonstrate the application of a relatively straightforward technique for the measurement of the absolute and relative dilution quantity in both steady state and transient operation. This was achieved by the use of oxygen sensors based on standard UEGO (universal exhaust gas oxygen) sensors but packaged so as to give good frequency response (∼ 10 ms time constant) and be completely insensitivity to the sample pressure and temperature. Measurements can be made at almost any location of interest, for example exhaust and inlet manifolds as well as EGR path(s), with virtually no flow disturbance.

Recent work has investigated the use of O₂ concentration in the intake manifold as a control variable for diesel engines. It has been recognized as a very good indicator of NOX emissions especially during transient operation, however, much of the work is concentrated on estimating the O₂ concentration as opposed to measuring it. This work investigates Universal Exhaust Gas Oxygen (UEGO) sensors and their potential to be used for such measurements. In previous work it was shown that these sensors can be operated in a controlled pressure environment such that their response time is of the order 10 ms. In this paper, it is shown how the key causes of variation (and therefore potential sources of error) in sensor output, namely, pressure and temperature are largely mitigated by operating the sensors in such an environment. Experiments were undertaken on a representative light-duty diesel engine using modified UEGO sensors in the intake and exhaust system.

NOX emissions are one of the major limiting factors of modern diesel engine technology; they heavily influence, directly or indirectly, both engine and after-treatment design, cost, complexity and reliability; they are also linked in an important trade-off with CO₂ emissions and therefore fuel consumption. It is paramount for OEMs (Original Equipment Manufacturers) to exploit more sophisticated techniques for modeling the formation of NOX to reduce costs and increase their ability to meet the legislative requirements for both CO₂ and NOX. Many existing simulation models predict NOX simply by interpolating steady state engine maps with limited ability to efficiently capture the effects of engine warm up, speed-load transients and air system dynamics. For conventional powertrains running on light cycles this might still be acceptable, but it becomes inadequate when applied to fast and deep transients across unconventional speed and load patterns.