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. ■ INTRODUCTIONIncreasing environmental concern and stringent regulations about pollutant and green house gas emissions from internal combustion engines (ICE), along with dwindling reserves of economical petroleum-based fuels, clearly point to the need for significantly improved engine combustion processes. One way of achieving substantial fuel savings is through increased ICE efficiency, which currently transfers only 30−40% of the fuel energy into useful work. 1,2 Not surprisingly, most incremental advancements in ICE efficiency and emission mitigation have been focused on the engine itself (e.g., high-pressure fuel systems, multiple fuel injections per stroke, combustion chamber architecture, turbo charging, exhaust gas recirculation (EGR), and after-treatment). 2 While these changes have been helpful, there is significant opportunity for breakthroughs and improvements in the exploitation of fuel properties. Although compression ignition (CI, or diesel) engines are more powerful and approximately 30−35% more fuel efficient than similar-sized spark ignition (that is, gasoline) engines, 3 the conventiona...

Transition of diesel spray to a supercritical state under engine conditions

“…14,15 Recent studies also look at droplets injected into a supercritical environment. 16,17 Research more closely related to automotive fuels (gasoline and diesel) and ICE conditions is presented by Anitescu et al 18 The authors demonstrated a transition to a supercritical state for a diesel/gasoline mixture (''dieseline'') and also showed a change in fuel sprays (a widening of cone angles) when ambient conditions are increased to supercritical conditions. Until now, most work has used single-component liquids.…”

Simulation of supercritical fuel injection with condensation

“…Some potential benefits of injecting supercritical diesel fuels in engines have also been experimentally proved. Anitescu et al [13] found that the jet spreading angle was enlarged and the observable jet core length was reduced, which is direct evidence that fuel/air mixing was significantly enhanced when dieseline (a mixture of diesel and gasoline) was injected in a supercritical state. It was also argued that such distinctive behavior could further reduce the fuel impingement and wall film formation in direct injection engines [13].…”

“…Anitescu et al [13] found that the jet spreading angle was enlarged and the observable jet core length was reduced, which is direct evidence that fuel/air mixing was significantly enhanced when dieseline (a mixture of diesel and gasoline) was injected in a supercritical state. It was also argued that such distinctive behavior could further reduce the fuel impingement and wall film formation in direct injection engines [13]. This is especially beneficial to advanced low temperature combustion (LTC) strategies for which early fuel injection is generally a prerequisite to improve the homogeneity of the fuel air mixture.…”

Flash boiling spray of diesel fuel mixed with ethane and its effects on premixed diesel combustion

“…Following Senda, Wada et al [13][14] applied mixed fuels consisting of i-pentane (C 5 H 12 ) and n-tridecane (C 13 H 28 ) to a premixed charge compression ignition engine with very early injection. Anitescu et al visualized the flash boiling sprays of the blends of gasoline and diesel fuel, injected into ambient air [15]. However, there have been only a few studies addressing a flashing spray injected into engine-relevant conditions near top dead center.…”