Effects of Biodiesel Blends on Emissions in Low Temperature Diesel Combustion

The simultaneous reduction of particulate matter (PM) and nitrous oxides (NOx) emissions form diesel exhaust is key to current research activities. Although various technologies have been introduced to reduce emissions from diesel engines, the in-cylinder reduction of PM and NOx due to improved combustion mechanisms will continue to be an important field in research and development of modern diesel engines. Furthermore increasing prices and question over the availability of diesel fuel derived from crude oil has introduced a growing interest. Hence it is most likely that future diesel engines will be operated on pure biodiesel and/or blends of biodiesel and crude oil-based diesel. In this study the performance of different biodiesel blends under low temperature combustion conditions (i.e., high exhaust gas recirculation and advanced fuel injection schemes) was investigated. Experiments were carried out using a multi-cylinder diesel engine with common rail technology and a low-pressure exhaust gas recirculation system.

The present results show that biodiesel blends generally produce lower PM emissions and higher NOx emissions compared to crude oil-based diesel fuel. Results also show that the injection timing shift is not the reason for the increase in NOx emissions when using biodiesel. Simultaneous reductions in NOx and PM emissions were achieved by using double injections with appropriate injection timings and fuel distributions.

Under low temperature combustion conditions, emissions for the 20% biodiesel blend and crude oil-based diesel are very similar. However, 100% biodiesel still shows an increase in NOx emissions while PM is reduced. Nonetheless, it is believed that NOx emissions will not be of great concern at low temperature combustion conditions for 20% biodiesel blends are used.