Effect of n-Butanol Addition on Combustion and Emission Characteristics of HTL and Diesel Blends

HTL is a kind of biodiesel converted from wet biowaste via hydrothermal liquefaction (HTL), which has drawn increasing attention in recent years due to its wide range of raw materials (algae, swine manure, and food processing waste). However, from the previous experiments done in a constant volume chamber, it was observed that the presence of 20% of HTL in the blend produced as much soot as pure diesel at in chamber environment oxygen ratio of 21%, and even more soot at low oxygen ratios. It was also observed that n-butanol addition could reduce the soot emission of diesel significantly under all tested conditions. In this work, the spray and combustion characteristics of HTL and diesel blends with n-butanol added were investigated in a constant volume chamber. The in-chamber temperature and oxygen ranged from 800 to 1200 K and 21% to 13%, respectively, covering both conventional and low-temperature combustion (LTC) regimes. Time-resolved images of the spray and natural flame luminosity (an indicator of soot) were captured by a high-speed camera coupled with a copper vapor laser beam. The experiments revealed that n-butanol addition could reduce the soot emission of HTL and diesel blends under lower oxygen concentration conditions but would bring a longer ignition delay under low-temperature conditions. Under high oxygen conditions, the addition of butanol doesn't affect the ignition delay and heat release rate significantly but further enhanced the soot's emission of HTL and diesel blends.