Abstract
Traditional selective catalytic reduction aftertreatment technologies used to reduce NOx are very limited at exhaust temperatures below 175°C. Therefore, under these low engine load conditions, having effective in-cylinder control of NOx emissions is important. Previous work by the authors explored the effect of fuel physical properties on the ability to control NOx in-cylinder. That work was limited to one direct injection near top dead center. Modern diesel high-pressure fuel systems have the capability of five or more injections in one engine cycle. A higher-volatility diesel fuel and high amounts of exhaust gas recirculation to delay ignition could provide an opportunity for reduction in engine-out NOx through an increased level of fuel premixing. By appropriately timing multiple short injections, a more optimal distribution of fuel in-cylinder may be achieved, which could reduce NOx while maintaining an efficient combustion phasing. A computational fluid dynamics model previously validated against experimental data was used to explore several injection strategies with increased levels of fuel premixing to assess the potential trade-offs between NOx and CO/unburned hydrocarbon (UHC) emissions and thus reduce reliance on the aftertreatment system for NOx control. The results show that the devised injection strategies resulted in an increased level of fuel premixing. However, none of the attempted injection strategies resulted in significant NOx reductions, and all strategies showed a significant increase in CO and UHC emissions.
