Multi-injection investigation of a high-volatility diesel in advanced compression ignition combustion for NO x control

Abstract

Traditional selective catalytic reduction aftertreatment technologies used to reduce $\mathrm{N}{\mathrm{O}}_x$ are very limited at exhaust temperatures below $175°\mathrm{C}$ . Therefore, under these low engine load conditions, having effective in-cylinder control of $\mathrm{N}{\mathrm{O}}_x$ emissions is important. Previous work by the authors explored the effect of fuel physical properties on the ability to control $\mathrm{N}{\mathrm{O}}_x$ 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 $\mathrm{N}{\mathrm{O}}_x$ 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 $\mathrm{N}{\mathrm{O}}_x$ 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 $\mathrm{N}{\mathrm{O}}_x$ and CO/unburned hydrocarbon (UHC) emissions and thus reduce reliance on the aftertreatment system for $\mathrm{N}{\mathrm{O}}_x$ 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 $\mathrm{N}{\mathrm{O}}_x$ reductions, and all strategies showed a significant increase in CO and UHC emissions.