Optimizing conventional combustion and implementing low-temperature combustion of biodiesel in a common-rail high-speed direct-injection engine

Biodiesel and different biodiesel-diesel blends were run in a production compression ignition engine to determine optimized engine control module (ECM) settings for each fuel. Focus was placed on a combination of exhaust gas recirculation (EGR) ratio and start of injection (SOI) timing, as these parameters are easily modified and have significant effects on engine emissions. Tests were run at low to moderate engine load at different engine speeds. It was found that with the ECM???s default settings, higher blends of biodiesel tended to result in higher NOx emissions and lower soot emissions, in line with previous studies. It was also found that increasing the EGR ratio to account for the different stoichiometric air-fuel ratio of biodiesel was effective in bringing NOx emissions to similar or lower levels compared with those of petroleum diesel. At low load conditions, improved fuel economy could also be achieved by advancing the start of injection relative to the ECM default timing. Pure soybean biodiesel was also run with high rates of EGR and modified injection schemes in order to achieve simultaneous reduction of NOx and soot emissions consistent with low temperature combustion. At low load conditions, increasing the EGR ratio to high levels was sufficient to achieve very low NOx and soot emissions. As engine load increased, high levels of EGR brought NOx emissions to very low levels, but soot emissions increased substantially. The amount of EGR was increased to the point of combustion deterioration without seeing a reduction in soot emissions. Thus, the engine???s default injection strategy needed to be modified in order to achieve low temperature combustion. Strategies found effective were a reduced amount of pre-injection, later injection timing, and a combination of the two. With these strategies, low temperature combustion was achieved through a moderate range of engine load. To see the effect of engine speed, cases were run at different speeds with a constant load. Modifications to the injection strategy were found to be beneficial at different engine speeds