Investigations on the low temperature reforming combustion of n-butanol/n-heptane mixtures utilized on an optical engine

N-butanol is a highly potential carbon-neutral fuel because it can be obtained from the fermentation of woody stems, straw, agricultural waste, etc. Which contains cellulose biomass and lignin. Studying low-temperature reforming combustion of n-butanol can provide an important reference value for its application in compression ignition engines and provide a potential solution to the condition expansion and cold start problems at homogeneous charge compression ignition (HCCI). Therefore, this paper used n-heptane as the diesel characterization fuel on an optical engine, and studied the effects of different reforming temperatures (623 K, 523 K, 423 K) on the low-temperature reforming combustion of n-butanol/n-heptane mixtures (B30, B50, B70) through a homemade low-temperature fuel reforming system. This paper used flame self-luminous high-speed imaging technology to reveal the flame development process and combustion characteristics. The results show that low-temperature reforming delays the ignition delay of B30 and B50 but advances the ignition delay of B70. When the reforming temperature increases, the maximum pressure rise rate of B50 and B30 decreases, the flame development rate slows, and the flame self-luminescence brightness weakens. At the same time, the flame development mode gradually changes from being dominated by sequential spontaneous combustion to being dominated by flame propagation. For B70, as the reforming temperature increases, the maximum pressure rise rate increases first and then reduces, the flame development rate accelerates, and the combustion becomes more intense. In addition, the flame development mode gradually changes from flame propagation dominated to sequential spontaneous combustion dominated. In general, the more n-butanol is added to the mixtures, the slower the flame develops.