An experimental investigation into the use of exhaust gas recirculation for diesel engine NOx control

Air pollution generated by the world's transportation sector has come under intense scrutiny as public awareness of the detrimental impacts to health, vegetation, materials, and the atmosphere associated with this pollution has increased. The frequent generation of the "brown haze" that plagues many of the metropolitan centres around the world has become of the utmost concern. Nitrogen oxide emissions (NOx) from the transportation sector are primarily responsible for the generation of this "smog", for which the diesel powered vehicles have been identified as one of the prime contributors. Although the most beneficial NOx control strategy for diesel powered vehicles will most likely be a combination of several technologies, one approach that has had considerable success in gasoline powered engines, is the use of exhaust gas recirculation (EGR). This control strategy is based upon chemically and thermodynamically altering the composition of the intake working fluid by recycling a portion of the exhaust gas back to the engine intake. As diesel powered engines have, until recently, been able to comply with the NOx emission regulations, this technology has had limited use in these engines. Therefore, the focus of this research investigation was to further enhance the understanding of the underlying mechanisms that dictate the influence of EGR on engine performance and NOx emissions such that this control technology can be successfully implemented into diesel powered engines.; To delineate the effects associated with the application of EGR an experimental investigation was performed using a synthetic atmosphere diesel engine test facility. Experimental testing of the engine was successfully undertaken using a wide variety of intake working fluids including atmospheric air, synthetic EGR, and other non-conventional atmospheres designed to highlight the individual effects associated with the recirculation of exhaust gas to the intake charge.; Based on an analysis of the experimental results, the impact of EGR on diesel engine performance and NOx emissions was quantified and the mechanisms responsible for the effectiveness of this control technology were established. Upon identification of these controlling mechanisms more suitable variables for the control of the recirculated exhaust gases, relative to present EGR control strategies, were proposed.; Many intriguing and sometimes unexpected findings were obtained throughout this research investigation. It was confirmed that the application of EGR precipitated significant reductions in diesel engine NOx emissions. It was also found that the dominance of temperature on the formation and control of NOx has been overstated and that the oxygen availability, time and the presence of nitrogen were also of importance. Furthermore, it was discovered that the dilution of the intake oxygen concentration by the recirculation of exhaust gas into the incoming air charge was the dominant parameter that controlled the influence of EGR on in-cylinder NOx generation. (Abstract shortened by UMI.)...