Dieseline for Supercritical Injection and Combustion in Compression-Ignition Engines: Volatility, Phase Transitions, Spray/Jet Structure, and Thermal Stability

Abstract

To optimize the injection–combustion process of increasingly diversified fuels, thermophysical and chemical properties of new blends are required over a wide range of compositions, pressures, and temperatures, including supercritical fluid states. Among the important thermophysical properties, the vapor–liquid equilibrium, as represented by the fluid volatility, is critical. In this study, the volatility of automotive gasoline–diesel fuel (dieseline) blends was determined by the advanced distillation curve method. Distillation curves were constructed for blends of 10, 30, 50, 70, and 90% (v/v) and compared to those of automotive gasoline with octane number 97 and diesel fuel no. 2. The results showed that dieseline volatility is close to that of gasoline at the start of distillation and leans toward that of diesel fuel at the end of the process. A GC-MS analysis of distilled fuel fractions showed that the more labile components of dieseline thermally decomposed at the end of the distillation process. Experiments on thermal stability of dieseline in a batch reactor showed no significant thermal decomposition at 400 °C for 1 h. This reactivity-inhibition of the thermally labile compounds was attributed to the lighter, less reactive fuel components, which, contrary to the case of distillation, were not removed from the system during the batch-heating process. Other experiments showed that this fuel behavior facilitated phase transition from liquid to SC states, with the more chemically stable gasoline acting as an anticoking agent for heated diesel fuel. Compared to unheated fuel, the mixing of heated dieseline with the air upon injection has been improved substantially. This information is essential for efficient fuel systems and combustion chamber designs to optimize supercritical fuel utilization in diesel engines, decrease fuel consumption, and practically eliminate harmful emissions without any after treatment.