Comparative Evaluation of EGR, Intake Water Injection and Fuel/Water Emulsion as NOx Reduction Techniques for Heavy Duty Diesel Engines

Despite the improvement in HD Diesel engine out emissions future emission legislation requires significant reduction of both NOx and particulate matter. To accomplish this task various solutions exist involving both internal and external measures. As widely recognized, it will be possibly required to employ both types of measures to meet future emission limits. Towards this direction, it is necessary to reduce NOx further using internal measures. Several solutions exist in that area, but the most feasible ones according to the present status of technical knowledge are EGR, water injection or fuel/water emulsions. These technologies aim to the reduction of both the gas temperature and oxygen concentration inside the combustion chamber that strongly affect NOx formation. However, there remain open points mainly concerning the effectiveness of water addition techniques and penalties related to bsfc and soot emissions. For this purpose, we have used a multi-zone simulation model in the present study to conduct a comparative evaluation between the aforementioned three NOx reduction methods. In the past the simulation has been used to examine by detail the effect of EGR, after modification it is used in the present work to examine the effect of intake water injection and fuel/water emulsion. The investigation has been conducted on a heavy duty diesel engine for various operating conditions. The evaluation of the three techniques is based on the reduction of NOx emissions by the same percentage compared to baseline values and to the comparison of the relative variation of bsfc and soot. Using the simulation the effect of the three NOx reduction techniques on engine performance and emissions is examined with special emphasis to the resulting fuel and soot penalties. The upper limit for NOx reduction was kept at 30% to avoid deterioration of engine power output when using fuel/water emulsions since the configuration of the injection system is maintained in the present analysis. From the simulation, information has been obtained concerning the effect of each technique on the combustion mechanism, the temperature history and the formation of both NOx and soot inside the combustion chamber.