Experimental study on ignition and combustion characteristics of biodiesel-butanol blends at different injection pressures

In this work, the biodiesel derived from animal and vegetable oils was investigated, and it was mixed with 10%, 30% and 50% of n-butanol by volume. The objective of the investigation is to explore the ignition and combustion characteristics of biodiesel-butanol blends at different injection pressures. The experiment was performed in a constant volume combustion chamber. An injector with a single-hole nozzle was adapted to inject different fuels into the combustion chamber with a static environment. The ignition and combustion processes were captured by a high-speed camera with schlieren imaging technique and natural luminosity imaging technique, respectively. A few macroscopic ignition and combustion parameters were obtained and analyzed, such as ignition delay time, ignition distance, flame area and flame luminosity. Results show that the ignition delay times of all tested fuels increase with decreased injection pressure or increased n-butanol proportion. Increasing the injection pressure or n-butanol proportion could increase the ignition distance. The variation law of the flame area is analogous to that of spatially integrated natural luminosity. Increasing the n-butanol proportion or injection pressure decrease the combustion duration and the variation rate of flame area and spatially integrated natural luminosity. The time integrated natural luminosity decreases with increasing the injection pressure or n-butanol proportion. In addition, the flame has a larger fluctuation with adding a large proportion of n-butanol, which is not beneficial for ignition and combustion processes.