Maximizing the Effectiveness of Water Blended Fuel in Reducing Emissions by Varying Injection Timing or Using After-Treatment Device

Water-emulsified diesel fuel technology has been proven to reduce nitrogen oxides (NO_x) and particulate matter (PM) simultaneously at relatively low cost compared to other pollution-reducing strategies. While the mechanisms which result in these reductions have been postulated, the development of new analytical tools to measure in-cylinder soot formation using optically accessible engines can lead to a deeper understanding of combustion and the chemical and physical mechanisms when water is present during combustion. In this study, an optically accessible single cylinder engine was used to study how water brought into the combustion chamber via an emulsified fuel changes the combustion process and thereby reduces emissions. In-cylinder measurements of relative soot concentrations were used to determine the effect of water-emulsified fuel on soot formation. Results of this experiment show that the water not only physically changes the way combustion occurs, but more importantly, modifies the chemical kinetics of the combustion process. The physical changes (i.e. temperature) lead to lower NOx levels, analogous to what happens when timing is changed. The chemical kinetics changes, however, also lead to reduced particulates independent of the temperature change. This kinetic change is robust to timing adjustments, thereby breaking the correlation between NOx reduction and PM increase that typically occurs when engine adjustments are made to reduce emissions.

To further understand these process changes, emulsified fuels with varying water levels (0 to 20%) were evaluated in a multi-cylinder marine engine using three different timing of injections. This testing in an actual engine confirms that as the water level is increased the amount of NOx and PM are reduced without compromising engine performance. Furthermore, changing the timing of injection can be done in conjunction with using an emulsified fuel to further optimize the engine performance and decrease emissions. In addition to engine optimization, water emulsified fuel in combination with a DOC was tested and was shown to reduce particulate emissions greater than each technology separately and nearing the level typically offered with a diesel particulate trap.